Hydraulic components

II. DR-type pilot-operated pressure reducing valve 1. Structure and working principle: When the valve is not in use, it is in the open position, allowing oil to flow from port B to port A through the main spool (1). While generating pressure in chamber A, the DR10 model causes the pressure oil to act on the upper end of the main spool (1) and the cone valve (6) of the pilot valve, via the dampers (2) and (3) as well as the control channels (4) and (13). When the pressure in chamber A exceeds the set pressure of the spring, the cone valve (6) opens. At this point, the oil in the upper chamber of the main spool flows through the damper (3) to the spring chamber (7), thereby creating a pressure difference across the main spool. Under the effect of this pressure difference, the main spool moves, reducing the opening size in order to maintain a constant pressure in chamber A. The control oil is returned to the tank from the outside via channel (8) or (9). If a structure with a check valve is chosen, oil can flow from chamber A to chamber B. The DR20 and DR30 models operate on the same principle as the DR10 valve; the only difference is that the control oil is introduced from channel (4), and a flow regulator (12) is installed within the pilot valve to maintain a constant flow rate of the control oil. When the flow rate Q=0, the overload valve (10) can prevent the pressure in chamber A from rising, thus ensuring that the valve is not damaged. The ZDR…D direct-acting pressure relief valve is a tandem valve. It is a three-way valve, that is, a valve with a secondary circuit unloading device. It is mainly used to reduce the pressure in certain systems. This valve mainly consists of a valve body (1), a control spool (2), two pressure springs (3), a pressure adjustment device (4), and an optional check valve. Adjust the secondary pressure using the regulating device (4). The valve is in the normally open state, which means that oil can flow freely from channel P to P1 (DP type), or from A to A1 (DA type). The pressure oil in chamber P1 flows through the control channel (5) to the left end of the spool, pressing the spool against the spring. When the pressure in chamber P1 (i.e., the load) exceeds the set value of the adjusting spring (3), the valve spool (2) moves within the adjusting area to maintain a constant pressure in chamber P1. The control oil is introduced from chamber P1 through channel (5). If the pressure in chamber P1 continues to rise due to an external load, this causes the valve spool to compress the spring, allowing pressurized oil to flow through the hole (6) on the valve spool into chamber T (for unloading), thereby preventing further increase in pressure and achieving overload protection. The leaked oil is discharged to the fuel tank through the spring chamber (7). “For “DA”, a check valve can be selected, allowing oil to flow back from chamber A1. A pressure gauge is installed at the connection port (8) to measure the secondary pressure value. The ZDR…D type pressure reducing valve is a stacked plate-type pressure reducing valve. It is a three-way valve, that is, a valve equipped with a secondary circuit protection device. This valve is primarily used to reduce the pressure in the system. This valve is mainly composed of a valve body (1), a control spool (2), two pressure springs (3), a pressure adjustment device (4), and an optional check valve. The rotary pressure regulating device (4) can adjust the secondary pressure. When at rest, the valve is in the open position; that is, oil can flow freely from channel P to channel P1 (DP type), from A to A1 (DA type), and from B to B1 (DB type). The pressure oil in chamber P1 flows through channel (5) to the left side of the valve spool, thereby applying additional pressure on the spring of the valve. When the pressure in chamber P1 (i.e., the load) exceeds the setting value of the adjusting spring (3), the valve spool (2) moves within the adjusting range to maintain a constant pressure in chamber P1. The control oil is introduced from chamber P1 through channel (5). As the pressure in chamber P1 continues to rise due to external loads, it pushes the valve spool against the compression spring, allowing pressure oil to flow through the hole (7) in the valve spool into chamber T; as a result, the pressure there no longer rises, thereby achieving overload protection. The leaked oil is discharged to the oil tank through the spring chamber (8). “DA” and DB type pressure relief valves can be equipped with check valves, allowing oil to flow from A1 to A and from B1 to B. The secondary pressure value can be measured at the pressure gauge connection port (9). 2. Common faults of pressure relief valves and their troubleshooting. Common faults of pressure relief valves include failure in pressure regulation, radial seizure of the valve core, an increase in the pressure at the outlet after the operating pressure has been set, noise, pressure fluctuations, and oscillations. (1) Pressure regulation failure: Pressure regulation failure is characterized by the following symptoms: When the pressure regulation knob is turned, the pressure at the oil outlet does not increase. One of the reasons is the blockage of the damping holes in the main spool, as well as the blockage of dampers (2) and (3). As a result, the oil from the oil outlet cannot flow into the upper chamber of the main valve or the front chamber of the pilot valve; furthermore, the pressure at the oil outlet cannot be transmitted to the cone valve, which prevents the pilot valve from regulating the pressure at the main valve’s oil outlet. Furthermore, when the damping holes become blocked, the upper chamber of the main valve loses the effect of oil pressure P3, causing the main valve to function as a direct-acting spool valve with very weak spring force. As a result, the pressure relief port of the main valve closes at low pressures at the outlet, preventing any pressure from building up at the outlet. Furthermore, when the pressure-reduction port of the main valve is closed, factors such as the main valve spool getting stuck, the cone valve not being installed in the valve seat hole, and the external control port not being sealed also contribute to the inability for the pressure at the oil outlet to increase. When the pressure at the oil outlet fails to reach the specified value, this can be attributed to reasons such as an incorrect selection of the pressure-regulating spring, permanent deformation or insufficient compression stroke, or excessive wear of the cone valve. When the pressure regulating handwheel is adjusted, both the outlet pressure and the inlet pressure increase or decrease simultaneously. The reasons for this include blockage of the damping holes in the cone valve seat, blockage of the damper (3), blockage of the oil drain port, and leakage in the check valve. The damping orifice of the cone valve seat becomes blocked; once the damper (3) is clogged, the pressure at the oil outlet cannot be transmitted to the cone valve either, causing the pilot valve to lose its ability to regulate the pressure at the main valve’s oil outlet. Furthermore, when the damping orifice becomes blocked, no pilot flow passes through the damper (3) of the main spool, causing the oil pressures in the upper and lower chambers of the main valve to be equal. Under the force of the main valve spring, the main spool moves to its lowest position, resulting in the largest flow area at the pressure relief port; therefore, the pressure at this oil port changes in accordance with the pressure at the oil inlet. If the oil drain port becomes blocked, in principle, it is equivalent to the damping orifice of the cone valve seat being blocked, which in turn causes the damper (3) to become blocked. At this time, although the pressure at the oil outlet can act on the cone valve, there is still no pilot flow passing through the damper of the main spool; moreover, the flow area of the pressure reduction port is also at its maximum. Therefore, the pressure at the oil outlet changes in accordance with the changes in the pressure at the oil inlet. When the check valve part of the one-way reducing valve leaks severely, the inlet pressure will pass through the leakage point to the outlet, causing the outlet pressure to change in accordance with the changes in the inlet pressure. Furthermore, when the pressure relief port of the main valve is in the fully open position, the jamming of the main valve spool is also the reason why the pressure at the oil outlet changes along with the pressure at the oil inlet. When adjusting the pressure regulating handwheel, the pressure at the oil outlet does not decrease. The main reason is due to the jamming of the main spool. The reasons why the outlet pressure does not reach the minimum set pressure are mainly due to an overly tight fit between the \"O\"-ring in the pilot valve and the valve cover, etc. (II) Radial jamming of the valve core: Due to the weak spring force of the main valve in pressure reducing valves and check pressure reducing valves, the main valve core is prone to radial jamming under high pressure. This leads to a decline in the valve’s performance, causes excessive wear of the components, shortens the valve’s service life, and may even render the valve non-functional; therefore, this phenomenon must be eliminated. (III) The pressure at the oil outlet increases on its own after the working pressure is set. In some pressure-reduction control circuits, such as those used to control electro-hydraulic directional valves or externally controlled sequence valves, once the electro-hydraulic directional valve or externally controlled sequence valve changes direction or starts operating, the flow rate at the output port of the pressure reducing valve becomes zero; however, the pressure still needs to remain at the value that was set initially. Under such conditions, the pressure at the oil outlet of the pressure relief valve tends to increase, which is caused by excessive leakage from the main valve. Under such operating conditions, since the flow rate at the outlet of the pressure reducing valve becomes zero, the only flow that passes through the pressure reducing port is the pilot flow. As the pilot flow is very small, generally less than 2 liters per minute, the pressure reducing port of the main valve remains essentially in a fully closed position, with the pilot flow exiting through triangular grooves or inclined surfaces. If the main spool is too loosely fitted or severely worn, the leakage rate of the main valve increases. According to the continuity theorem for flow, this amount of leakage must also flow out through the damping orifice of the main valve; the flow rate through that damping orifice is thus composed of the original pilot flow rate and this amount of leakage. Since the area of the damping hole and the oil pressure P3 in the upper chamber of the main valve remain unchanged (P3 is determined by the pre-compression amount of the pressure-regulating spring), increasing the flow rate through the damping hole necessarily leads to an increase in the oil pressure P2 in the lower chamber of the main valve. Therefore, once the outlet pressure of the pressure reducing valve is set, if the outlet flow rate is zero, the outlet pressure will increase due to overly loose fitting or excessive wear of the main valve spool. (IV) Noise, pressure fluctuations, and vibration: Since the pressure reducing valve is a pilot-operated two-stage valve, its pilot section is shared with that of the relief valve; therefore, the causes of noise and pressure fluctuations are essentially the same as those of the relief valve. When a pressure relief valve is used at an excessive flow rate, oscillation of the main valve can occur, causing the pressure at the outlet to keep rising and then dropping again—rising and then dropping—this is due to the increased fluid force resulting from an infinite flow rate. When the flow rate is too high, the weak spring of the main valve is unable to counteract the increase in hydraulic force caused by such a high flow rate. As a result, the main valve spool closes the pressure reduction port under the action of this hydraulic force; consequently, the pressure and flow rate at the oil outlet become zero, and the hydraulic force also becomes zero. Then, under the force of the main valve spring, the main valve spool opens the pressure reduction port again, causing the pressure and flow rate at the oil outlet to increase, which in turn increases the hydraulic force and leads to the closure of the pressure reduction port, once more resulting in zero pressure and flow rate at the oil outlet. This causes oscillation of the main spool, resulting in continuous changes in the pressure at the oil outlet; therefore, when using a pressure reducing valve, it should not exceed the recommended nominal flow rate.

III. DZ-type Pilot Sequence Valve 1. Structure and Working Principle The DZ-type pilot sequence valve is suitable for hydraulic systems that require sequential operation controlled by pressure. The DZ type valve consists of a pilot valve, a main valve with an insert-type main spool, and an optional check valve. Depending on the conditions of oil supply and discharge, different types are formed (see graphic symbols). In the backpressure valve DZ…–30/210, the pressure oil in chamber A acts on the control piston (3) of the pilot valve (4) via channel (2) and through the damper (1); at the same time, the pressure oil also acts on the upper chamber of the main spool (6) via the damper (5). When the pressure in chamber A rises above the set value of spring (7), the control piston moves in the direction of spring (7). At this point, the oil in the upper chamber of the main spool (6) flows through the damper (8), control edge 14, and channel (9) to chamber B, creating a pressure difference on the main spool (6) that causes it to open, thereby connecting chamber A and chamber B. This opening pressure can be maintained constant under the action of the spring (7). The leaking oil on the control piston flows to chamber B through the internal channel (10). If oil is to be returned from chamber B to chamber A, a design with a built-in check valve can be selected. The back pressure valve DZ…—30/210X… operates on the same principle as the DZ…—30/210 model, with the difference lying in the way the control oil is supplied. For the DZ…—30/210X… type valves, the control oil is supplied from the outside through channel (2). The operating principle of the sequence valve DZ…—30/210Y is the same as that of the DZ…—30/210 model; the only difference lies in the way in which the leaking oil at the control piston is discharged. For the DZ…—30/210Y type valve, the leakage oil from the control piston must be returned to the tank through channel (10) or (11), without any back pressure. The control oil is discharged to chamber B through channel (9). In the unloading valve DZ…—30/210XY, the pressure oil in chamber X acts on the control piston (3) of the pilot valve (4) via channel (2) and the damper (1); simultaneously, the pressure oil in chamber A acts on the upper chamber of the main spool (6) through the damper (5). When the pressure in chamber X increases and exceeds the value set by spring (7), it causes the control piston (3) to move in the direction of spring (7). As a result of this movement, the oil in the upper chamber of the main spool flows through the damper (8) and hole (15) to the spring chamber (12) of the pilot valve (4). This allows the pressure oil to flow from chamber A to chamber B with almost no pressure loss, thereby achieving the purpose of unloading. The oil in the spring chamber (12) is discharged to the oil tank through channel (10) or (11) without back pressure. To allow pressure oil to flow from B to A, a design with a check valve can be used to achieve this. 2. Common faults of sequence valves and their troubleshooting. The main fault of sequence valves and one-way sequence valves is the failure to function in a sequential manner. There are two scenarios here: one is when the pressure in the oil inlet chamber and the oil outlet chamber rises or falls simultaneously ； Another possibility is that there is no flow in the oil outlet chamber. One of the reasons for the first situation is the blockage of the damper (5) inside the valve spool, which prevents the leaking oil from the control piston from entering the pressure-regulating spring chamber and returning to the oil tank. Over time, the pressure in the oil inlet chamber enters the flash chamber through leaks in the oil, acting on the lower surface of the valve spool. Since the area of the lower surface of the valve spool is much larger than that of the control piston, the hydraulic force causes the valve spool to move the valve to its fully open position, turning it into a normally open valve. As a result, the pressures in both the oil inlet chamber and the oil outlet chamber rise or fall simultaneously. Additionally, the sticking of the valve core when the valve is in the fully open position can also cause the aforementioned phenomenon. The same is true for a clogged damper (1). The reason for the second situation is that the oil drain port is installed in an internal return format, causing the oil pressure in the pressure-regulating spring chamber to be equal to the oil pressure in the oil outlet chamber. Since the upper area of the spool is larger than its lower area, the spool closes the valve port under the action of hydraulic pressure, turning the sequence valve into a normally closed valve; as a result, there is no flow in the oil outlet chamber. Additionally, a clogged damper (8) or a stuck spool when the valve is in the fully closed position can also cause the aforementioned phenomenon. (No flow in the oil outlet chamber) When the damper (1) on the end cover becomes clogged, the control oil cannot enter the control piston chamber; under the force of the pressure-regulating spring, the valve core closes the valve opening, and as a result, there is also no flow in the oil outlet chamber. IV. DA/DAW type pilot-controlled unloading valve 1. Working principle: The DA/DAW type valve is a pilot-controlled unloading valve whose function is to supply oil to the accumulator. In a hydraulic system equipped with both high-pressure and low-pressure pumps, it enables the low-pressure pump to be unloaded. This valve is mainly composed of a pilot valve, a main valve with a main spool, and a check valve. The check valves with a diameter of 10 are located inside the main valve body, while those with diameters of 25 and 32 are found in the connection plate beneath the main valve. When the DA-type valve switches from P→A to P→T, the fluid output by the pump flows from the check valve (1) to chamber A (P→A), and at the same time flows to piston (4) through channel (3) ； It flows through the damper (5) to the upper chamber of the main valve (6), and acts on the cone valve (8) via the damper (7). Once the system pressure reaches the unloading pressure set by the pilot valve (2), the cone valve (8) is immediately opened. When the control oil passes through the dampers (5) and (7) and flows from the Y port to the T chamber, a pressure drop is generated across the main valve (6) due to the dampers (5) and (7). At this point, the main valve (6) opens, and the pressure oil flows from chamber P to chamber T (P→T). When the main valve is opened and activated (P→T), the pressure in chamber A acts on the plunger (4) and the check valve, causing the cone valve (8) to open while the check valve closes. This completes the switch from P→A to P→T. When switching from P→T to P→A, since the area of the plunger (4) is 17% larger than the effective area of the cone valve (8), the force acting on the piston is also 17% greater than the force acting on the cone valve. If the pressure in the accumulator is below its corresponding switching pressure difference, the spring (9) closes the cone valve (8). In this way, pressure is generated in the upper chamber of the main valve (6), causing the main valve spool (6) to close, thereby shutting off P→T. In this way, the fluid output by the pump passes back into the hydraulic system through the check valve. DAW-type valve: This valve has the same performance as the DA-type valve, except that it is equipped with a solenoid valve on the pilot valve (2), which allows for switching from A to T or from T to A at any pressure set by the pilot valve. 2. Common faults and troubleshooting of DA/DAW type pilot-controlled load relief valves: (I) Failure of the load relief valve to relieve load. Due to the blockage of the damper (7), the oil in the upper chamber of the valve spool cannot be discharged; as a result, when the pilot valve is open, the pressures in the upper and lower chambers of the main valve are equal, and since the upper area is larger than the lower area, the main valve cannot open, and no oil is released for load relief via P→T ； The main valve cannot be unloaded either if it gets stuck in the closed position ； If the plunger (4) gets stuck and prevents the pilot valve from opening, unloading is also not possible. (II) Unloading under non-unloaded conditions: Since the damper (5) blocks the upper chamber of the valve spool, there is no hydraulic pressure in that chamber; moreover, the spring force of the main valve is weak, so the main valve spool opens under a very small force, resulting in unloading ； When the main valve is stuck in the open position, it also releases load, yet the control force does not reach the set value of the pilot valve. If the pilot valve piston gets stuck and the pilot valve remains in the open position, loading is also released. (III) Failures of the DAW-type solenoid valve also cause the aforementioned two types of failures. (IV) External leaks in various areas occur due to the damage of the individual “O”-ring seals. V. Common faults of pressure relays and their troubleshooting Common faults of pressure relays include reduced sensitivity and damaged microswitches. The former is caused by radial clamping of the valve core and push rod, or an excessive free travel of the microswitch. When the spool or push rod experiences radial jamming, the friction force increases. This resistance acts in the opposite direction to the movement of the spool and push rod; on one hand, it helps the oil pressure to overcome the spring force, resulting in a decrease in oil pressure and thus a reduction in the sensitivity of the pressure relay. In use, deformation of the microswitch bracket or loosening of the zero-adjustable part can increase the minimum travel distance of the microswitch, which was originally adjusted or ensured after assembly, thereby reducing its sensitivity. If the leakage from the pressure relay is not directed back to the oil tank, the high back pressure at the oil leakage port can also reduce its sensitivity. In a differential pressure relay, when the microswitch section and the oil release chamber are in opposite positions, pressure forces its way through the rubber diaphragm into the microswitch section, thereby damaging it. Furthermore, since the pressure-regulating spring chamber is connected to the oil release chamber, and there is no sealing device at the adjustment screw, external leakage will occur at the adjustment screw when the oil release pressure is too high. Therefore, the oil drain chamber must be directly connected back to the fuel tank. Furthermore, there is no sealing device at the electrical connector either; oil leaks to the microswitch, reducing its sensitivity, and leaks out from there as well. A pressure relay is a small electro-hydraulic control component that converts oil pressure signals into electrical signals. When the oil pressure reaches the set pressure of the pressure relay, an electrical signal is generated to control the operation of electrical components such as electromagnets, electromagnetic clutches, and relays. This allows the oil circuit to be unloaded, the pressure to be reduced, direction to be changed, and the actuator to carry out sequential actions; or it can shut down the motor, thereby stopping the operation of the system and providing safety protection.

VI. Common faults of pressure gauge switches and their troubleshooting (1) Inaccurate pressure measurement: Pressure gauge switches usually have damping holes; when dirt in the oil blocks part of these holes, the pointer of the pressure gauge will fluctuate violently, affecting the accuracy of the measured values. When the damping adjustment at the valve port of the KF-type pressure gauge switch is too high, it can also cause the pointer of the pressure gauge to move slowly and sluggishly, resulting in inaccurate pressure readings. When in use, attention should be paid to the cleanliness of the oil, and the damping level should be adjusted appropriately. (II) Increased internal and external leakage: After long-term use, the KF-type pressure gauge switch fails to close properly due to excessive wear of the valve openings, resulting in increased internal leakage. This causes the pointer of the pressure gauge to change as the pressure in the oil inlet chamber changes ； In K-type pressure gauge switches, excessive wear of the sealing surfaces leads to an increased gap, which in turn raises the amount of internal leakage and causes the pressures at various measurement points to intermix. In such cases, the worn-out parts should be replaced. Oil is leaking at the adjustment handle of the pressure gauge switch due to a damaged \"O\"-ring. VII. Check valves, fluid-controlled check valves, SV/SL type fluid-controlled check valves, stacked fluid-controlled check valves 1. Structure and working principle A check valve is also known as a non-return valve or reverse-flow preventing valve. Used in hydraulic systems to prevent the reverse flow of oil. Check valves come in straight-through and right-angled types. As shown in Figures 15 and 16. Both SV and SL type hydraulic check valves are seat-type valves that are activated by hydraulic pressure and can prevent backflow. This type of valve is used to isolate local pressure circuits, serving as protection against load drop in the event of a pipe rupture, as well as preventing load creep. This hydraulic check valve mainly consists of a valve body (1), a main valve (2), a pilot valve (3), a compression spring (4), and a control piston (5). SV type valve (without oil drain port) – The leaked oil returns internally; flow is always possible from port A to port B. In the opposite direction, the pilot valve (3) and the main valve (2) are held in place on their valve seats by the compression spring (4) and system pressure. If pressure oil is supplied to port X, the control piston (5) is pushed to the right. This first opens the pilot valve (3), and then opens the main valve (2). Thus, the oil first passes through the pilot valve and then through the main valve. To ensure reliable operation using the control piston (5), a certain minimum control pressure is required, as shown in Figure 18. SL-type valve (with oil drain port) – external return of leaked oil. In principle, this valve has the same function as the SV type. The difference lies in the addition of an oil drain port Y, which allows the annular area of control piston (5) to be isolated from port A. The oil pressure coming from port A acts only on area A4 of the control piston (5), thereby effectively reducing the control pressure required under these conditions, as shown in Figure 19. The Z2S type stacked hydraulic check valve is shown in Figures 20, 21, 22, and 23. The Z2S type check valve is a stacked hydraulic check valve. It can be used to close one or two working oil ports, offering a long leak-free operation time and good stability. The fluid can flow freely from A to A1 or from B to B1, but the flow in the reverse direction is blocked. If oil flows through the valve, for example from A to A1, the pressurized oil acts on the spool (1), causing it to move to the right and pushing the steel ball (2) away from the valve seat. When the check valve (3) is opened by control oil, oil can flow from B1 to B. The pressure is relieved in chamber B1, and all check valves (3) open. To ensure that the two main check valves can close reliably when the directional control valve is in the neutral position, ports A and B of the valve are connected to the oil return circuit. 2. Main faults of check valves The most common fault that can occur in check valves is leakage, which happens when oil enters from the P2 chamber in the opposite direction, and the cone-shaped valve element (or steel ball) is unable to seal the oil properly. This leakage phenomenon is more likely to occur when the pressure of the reverse-flowing oil is relatively low. At this point, it is necessary to check whether the contact between the cone surface of the valve core (or the steel ball) and the valve seat is tight ； Check whether the valve seat hole and the spool hole meet the required coaxiality requirements, or whether the valve seat is distorted when pressed into the valve body hole. If the requirements are not met, it is necessary to re-lube the conical surface of the valve core (or the steel ball) with the valve seat, or remove the valve seat and reinstall it until it makes tight contact with the conical surface of the valve core (or the steel ball). Additionally, damage may occur during the sealing assembly or disassembly of the valve seat or valve sleeve of the check valve with the valve body, resulting in internal leakage. If the check valve does not open and close smoothly, indicating that there is sticking in the valve core, it is necessary to check the geometric precision of the machining of the valve body hole and the valve core, as well as whether the clearance between them meets the required standards. This phenomenon can occur in check valves with a very low opening pressure, or in cases where such check valves with low opening pressure are used with their valve element axis installed horizontally ； Additionally, it should also be checked whether the spring is broken or excessively bent, causing jamming. It should be noted here that neither the straight-through check valve nor the right-angled check valve allows the cone surface of the valve core to be installed facing upward.

VIII. Electromagnetic and electro-hydraulic directional control valves 1. Structure and working principle: The 4WE5 type electromagnetic directional control valve uses wet-type AC or DC electromagnets. This valve controls the different operating positions of the valve core through an electromagnet. When the electromagnet is de-energized, the valve spool remains in the middle or end position due to spring pressure (except for pulse valves). When the electromagnet is powered, the valve core is pushed to the operating position; when the power is cut off, it returns to its initial state. At this time, pushing the fault check button with the hand can move the valve spool. Since the interior of the wet electromagnet is connected to the oil return chamber, the armature can move within the oil, which reduces wear and provides cushioning; it also improves heat dissipation and thus extends the service life. AC electromagnets feature a short operating time, a simple electrical control circuit, and no need for special contact protection. DC electromagnets have soft switching characteristics, a high operating frequency, are insensitive to overload or low voltage, and offer reliable performance. The WE type directional control valve is a spool-type directional control valve controlled by an electromagnet, and it is primarily used to control the on/off status and flow direction of liquids. Its structure mainly consists of a valve body (1), an electromagnet (2), a slide valve (3), and a return spring (4), etc. It is held in the middle position or initial position by a return spring when not powered (except for pulse valves). The thrust of the electromagnet acts on the spool valve (3) through the push rod (5), pushing it from its resting position to its operating position (final position), thereby changing the direction of the fluid flow from P→A and B→T to P→B and A→T. When the electromagnet is de-energized, the spool valve (3) is pushed back to its original resting position by the return spring (4). When the electromagnet is powered off, use the fault check button to move the slide valve. WEH type directional control valve (Figure 28) The WEH type directional control valve is a valve in which a solenoid valve serves as a pilot to control the spool. Used to control the on/off and flow direction of the liquid flow. The directional control valve consists of a main valve body (1), a main spool (2), one or two return springs (3), and a pilot valve equipped with one or two electromagnets. The main spool (2) is held in the intermediate position by spring force or hydraulic pressure. The pilot valve can use a wet-type DC (or AC) electromagnet (5), with the control oil from the pilot valve being used to shift the main spool (2). When the electromagnet is not powered, pressing the fault check button can move the pilot spool. Internal or external control can be used to regulate the input and output of oil. Three-way four-position directional control valve with spring centering (type 4WEH25…50/…): The main spool (2) is held in the middle position by two springs (3); the chambers of these springs are connected to the pilot valve T chamber (without back pressure). The control oil is introduced from channel (7) to the supply pilot valve (4); when the pilot valve changes direction, the control oil acts on one of the two ends of the main spool (2), pushing it to change direction and thereby enabling the various oil ports to be connected according to the function of the slide valve. When the electromagnet is de-energized, the pilot spool returns to its initial position (except for pulse valves); the control oil chamber (6) is connected to the oil tank through the pilot valve T chamber, and under the force of the spring, the main spool returns to its middle position. The control oil inside the spring is discharged through the pilot valve T chamber or the external outlet Y. The pressure-centering three-way four-port directional control valve (type 4WEH25H…50/…) in this design relies on pressure oil acting on the two end surfaces of the main spool (2), with a positioning sleeve inside the valve body keeping the main spool in the middle position. If one end of the main spool is unloaded, the main valve reverses direction, connecting the corresponding oil port ； The control oil at this unloading end is discharged through channel Y via a pilot valve. Two-position four-way directional control valves come in 4 different structures: 1. 4WEH…/… type: Both the pilot valve and the main valve have a return spring (which keeps the main spool in its initial position when the electromagnet is de-energized). 2. 4WEH…H/…/… type: The pilot valve has a return spring, which is used to keep the pilot spool in its initial position. 3. 4WEH…H…/0… type: The pilot valve has two electromagnets. There are no return springs in either the pilot valve or the main valve; in this case, the main spool is shifted by the combined action of the electromagnet and the pressure oil. Therefore, there is always one electromagnet in operation. 4.4 WEH…H/…/0F… type: The pilot valve has two electromagnets that allow the valve spool to be held in a certain working position (pulsating valve). There is no positioner on the main valve; it moves to the corresponding operating position under the action of pressure oil. In the structures of types 2.3. and 4 mentioned above, the main spool can operate properly only under the action of control oil. Model H.4WEH25…50/…6A…: In this configuration, the control oil is supplied and discharged from the outside. Control is not introduced from the exhaust port X, and is discharged through the exhaust port Y. ⑩ Plug M6 GB78-76-8.8, type H.4WEH25…50/…6A…E…: In this configuration, the control oil is introduced from chamber P of the main valve and returned to the tank via channel Y, without passing through chamber T of the main valve. The Y port on the connection plate needs to be blocked off. ⑩ Plug M6 GB78-76-8.8, type S3, model H.4WEH25…50/…6A…ET…: The control oil for this valve is of the internal supply and internal discharge type. The oil is controlled to be introduced from chamber P and returned to the tank via chamber T of the main valve. At this time, the X and Y ports on the connection plate should be blocked. Model H.4WEH25…50/…6A…T…: The control oil for this valve is introduced from an external control oil circuit, and then returned to the tank via the main valve T. The Y port on the connection plate should be blocked. ⑩ Plug M6 GB78-76-8.8 S3 reversing time regulator: An additive reversing time regulator can be installed between the pilot valve and the main valve. It is a parallel single-direction throttle valve (11). Adjust the oil supply speed to both ends of the main spool according to the requirements for the switching time. Turning the adjustment bolt (14) clockwise increases the commutation time, while turning it counterclockwise reduces the commutation time. To change from inlet throttling to outlet throttling, simply remove the pilot valve (14); the baffle (15) does not need to be moved. Rotate the direction change time regulator (11) 180° around its long axis and then reinstall the pilot valve. 2. Main faults of electromagnetic directional control valves and their troubleshooting (I) The electromagnet is powered, but the valve spool does not change direction ； Or the electromagnet loses power, and the valve spool does not return to its original position ； 1. Check whether the power supply voltage of the electromagnet meets the requirements for use; if the voltage is too low, the electromagnet will not have sufficient thrust to enable the valve spool to shift properly. 2. The valve core is stuck. If all the performance specifications of the electromagnetic directional control valve are met, but the aforementioned faults occur during use, the main thing to check is whether the operating conditions exceed the specified limits. Such as work pressure, flow rate, oil temperature, and the filtration precision of the oil. Check again whether the return spring is broken or stuck. For solenoid directional control valves with plate-type connections, it is necessary to check the unevenness of the surface of the mounting baseplate, as well as to ensure that the mounting screws are not tightened too much, which could cause deformation of the valve body. Furthermore, the burrs and flash generated during the grinding of the valve spool, if not completely removed and trapped in the radial balance grooves, can be flushed out by the oil flow over time and end up in the radial gaps, causing the valve spool to get stuck. In such cases, it is necessary to disassemble the component and clean it thoroughly. 3. The axis of the electromagnetic directional control valve must be installed horizontally. If installed vertically, the weight of components such as the valve core and armature will cause abnormal switching or resetting. 4. Electromagnetic directional control valves with dedicated oil drain ports, where these ports are not connected to the oil tank, or where the back pressure in the oil drain line is too high, can cause the valve spool to become stuck and prevent proper operation. (II) Burnout of the electromagnet 1. Overheating of the coil occurs when the supply voltage is higher than the specified operating voltage for the electromagnet. 2. The extension length of the push rod is too long, resulting in an improper match with the stroke of the electromagnet; as a result, the electromagnet’s armature cannot be attracted, which causes excessive current flow and overheating of the coil. This situation is more likely to occur when the user replaces the electromagnet by themselves after the first one burns out for other reasons. Due to the large variation in the distance from the attraction surface between the armature of the electromagnet and the core to the surface where the valve body is mounted, the extension length of the push rod that was originally used with the old electromagnet may not be entirely suitable for the replaced electromagnet. If the installation distance of the replaced electromagnet is shorter than the original one, then after the valve is assembled, an overly long push rod may prevent the armature from engaging, resulting in noise, vibration, or even damage. If the installation distance of the replacement electromagnet is longer than that of the original one, after the valve is assembled, the push rod appears shorter; as a result, during operation the switching stroke of the valve spool is smaller than the specified value, and the opening degree of the valve decreases. This leads to increased pressure loss, the oil tends to heat up, and it may even affect the speed of movement of the actuator. Therefore, when the user replaces the electromagnet by themselves, they must carefully measure whether the extension length of the push rod is suitable in combination with the electromagnet; replacement must not be carried out arbitrarily. The above reasons for the burnout of electromagnets mainly occur in AC-type electromagnets; DC electromagnets generally do not burn out due to faults. 3. The commutation frequency is too high, causing the coil to overheat. (III) Oil leakage at the push rod of the directional control valve in dry-type solenoid valves: 1. Generally, the oil chambers on both ends of a solenoid valve are oil discharge chambers or return oil chambers; it is necessary to check whether the pressure in these chambers is too high. If the oil drain or return pipes of multiple solenoid valves in the system are connected in series, resulting in excessive back pressure, they should be connected to the tank individually. 2. The dynamic seal “O”-ring at the push rod is severely worn and should be replaced. (IV) Oil seepage at the joint surface between the plate-type electromagnetic directional control valve and the base plate: 1. The base plate should be ground to achieve a surface finish of 0.8; the tolerance for unevenness should be 100:0.01, and there should be no protrusions. 2. The mounting screws are too loose. 3. The screw material does not meet the requirements; its strength is insufficient. Currently, the mounting screws for many plate-type connected solenoid directional control valves are made of alloy steel screws. If the original screw breaks or is lost, replacing it with a regular carbon steel screw will cause tensile deformation due to the oil pressure, leading to leakage at the joint surface. 4. The “O”-ring on the bottom surface of the electromagnetic directional control valve has aged and deteriorated, losing its sealing function; it should be replaced. (5) The engagement and release of the wet-type electromagnet are too slow: There is a sealing screw at the rear end of the electromagnet, and air remains in the rear chamber during initial installation. When oil enters the armature chamber, if the air in the rear chamber cannot be released, it will be compressed, creating damping that slows down the movement. Upon first use, the sealing screw should be tightened to release air; once the oil has filled the space, the seal should be tightened again. (VI) After long-term use, the operating mechanism experiences a reduction in movement speed: the push rod becomes shorter due to wear from repeated impacts, or the contact point between the armature and the push rod wears out, resulting in an insufficient stroke for the valve core to change direction. This leads to a smaller opening in the oil chamber, thereby reducing the flow rate. The push rod or electromagnet should be replaced. (7) The actual flow direction of the oil does not match the direction indicated by the graphic symbol: This is a problem that is likely to occur during use. The relevant departments in our country have formulated and issued standards for the graphic symbols of hydraulic components. However, due to the special structure of many products, the actual flow paths do not correspond to these standard graphic symbols. Figure 34 shows the hydraulic graphic symbol for a two-position four-way solenoid-operated spring-return type electromagnetic directional control valve; the spool type is I1 (type C), the solenoid symbol is located on the right, and the flow path in the initial position is P→ ； B→O(T) ； When the electromagnet is energized and attracted, it is P→B ； A→O(T). But in reality, for this type of electromagnetic directional control valve, according to the design drawings, the electromagnet is installed on the left side. There are also two types of passage configurations depending on the structure of the valve core ； One is as shown in the figure, while the other is exactly the opposite: at the initial position, there is communication between P and B, and communication between A and O (T), as shown in Figure 35. Therefore, when designing or installing the oil circuit system for solenoid valves, one should not rely solely on standard hydraulic graphic symbols, but rather make decisions based on the actual flow paths of the product. If an error has already occurred, for three-position valves, the issue can be resolved by swapping the electrical wiring. For two-way valves, the issue can be resolved by installing the electromagnet and related components in reverse order; if this does not work, the position of the piping must be changed, or a bypass plate can be used as a solution. In short, we should understand that standard hydraulic graphic symbols merely represent a code for a certain type of valve, and do not indicate the structure of that specific valve. The design and installation of the system should be carried out based on the product samples provided by each manufacturer. This situation is exactly the same for electro-hydraulic directional control valves, hydraulic directional control valves, and manual directional control valves. Since the diameter of such valves is generally large and the pipes are thick, it is very difficult to make changes in case of errors; therefore, special attention must be paid during design and installation. For the inlet and outlet oil chambers of an electromagnetic directional control valve, they can be interchanged as long as both are high-pressure chambers; the resulting flow path configuration will depend on the specific changes made. However, the oil return chamber and the high-pressure chamber cannot be swapped. In solenoid valves equipped with a dedicated oil drainage chamber structure, if the back pressure in the oil return chamber is lower than the allowable back pressure in the drainage chamber, the oil return chambers can be connected in series to lead the oil back to the tank. Otherwise, they should all be connected back to the fuel tank separately.

IX. Z2FS Type Stackable One-Way Throttle Valve 1. Structure and Working Principle: The Z2FS type stackable one-way throttle valve is a stackable plate valve; it can be combined with solenoid valves and direct-acting pressure reducing valves of the same diameter. This valve is used for throttling the main spindle oil circuit and the control oil circuit. When the valve throttles in one direction, oil returns directly through a check valve in the other direction. As shown in the diagram, when the pressurized oil in chamber A flows to the throttling position (1), it also passes through hole (2) and reaches the back side (3) of the spool (4), thereby creating a fixed throttle opening. The adjustment screw can be used to widen or narrow the throttle opening. By selecting different installation locations, inlet or outlet throttling can be achieved. Main oil circuit throttling: When this valve is installed between a directional valve of the same diameter and the base plate, it can change the speed of the cylinder (or hydraulic motor) being controlled. Control of oil circuit throttling: By installing this valve between the pilot solenoid valve and the main valve of the electro-hydraulic directional control valve, it is possible to change the speed at which the main valve spool shifts direction (i.e., to adjust the switching time). The Z2FS type stacked one-way throttle valve regulates the flow rate in the oil circuit by changing the cross-sectional area of the throttle opening, thereby achieving flow control. In reverse, the oil flow returns directly through the check valve. For paths 6 and 10, selecting different installation positions allows for inlet throttling or outlet throttling. For diameters of 16 and 22, different models are available to achieve inlet throttling or outlet throttling. Two oil circuits to the working oil chamber can be connected simultaneously. 2. Common faults of throttle valves and their troubleshooting The common faults of throttle valves and one-way throttle valves include failed flow regulation, unstable flow rates, and increased internal leakage. (1) Failure of flow regulation: The phenomenon of failure in flow regulation refers to the situation where the flow rate in the oil outlet chamber does not change even after adjusting the control knob (this phenomenon does not occur with simple throttle valves). The main cause of malfunction in flow regulation is radial jamming of the valve spool; when the spool gets radially jammed in the fully closed position, no flow occurs in the oil outlet chamber even after adjusting the control knob ； The valve spool gets stuck radially in the fully open position or after the throttle opening has been adjusted, and adjusting the adjustment handwheel does not change the flow rate in the oil outlet chamber. After radial sticking of the valve core occurs, it should be cleaned to remove dirt. When the inlet and outlet chambers of the one-way throttle valve are reversed (functioning as a one-way valve after reversal), adjusting the adjustment knob does not change the flow rate through the valve. (II) Unstable flow: Once the throttle valve and one-way throttle valve have their throttle openings adjusted and secured, unstable flow can occur at times, especially at the minimum stable flow rate. The main reasons for unstable flow rate are a loose locking device, blockage in the throttle section, rising oil temperature, and changes in load pressure. After the throttle orifice is adjusted and locked, mechanical vibrations or other factors can cause the locking mechanism to loosen, altering the flow area of the throttle orifice and thus leading to changes in flow rate. Impurities in the oil accumulate and adhere to the edges of the throttle orifice, reducing the flow area and resulting in a decrease in flow rate. When the pressure oil flushes away the impurities, the throttle opening returns to its original flow area, and the flow rate also returns to its previous value, which thus causes instability in the flow rate. When the temperature of the oil flowing through the throttle valve changes, its viscosity changes as well, which in turn causes instability in the flow rate ； When the load changes, the pressure changes as well, which alters the pressure difference between the oil on the upstream and downstream sides of the throttle valve, and this in turn causes flow instability. Measures to prevent unstable flow include, in addition to methods to prevent clogging of the throttle valve, improving control of oil temperature, tightening the locking devices, and keeping the load pressure as constant as possible or minimizing any changes in it. (III) Increased internal leakage: When the throttle opening of a throttle valve or check valve is closed, leakage will inevitably occur at the gaps used for sealing; therefore, throttle valves or check throttle valves cannot be used as stop valves. When the sealing surface is excessively worn, it causes an increase in leakage, and sometimes it also affects the minimum stable flow rate; in such cases, the valve core should be replaced. X. Common faults and troubleshooting of the stroke throttle valve. The main common faults of the stroke throttle valve and the one-way stroke throttle valve include failed flow regulation, unstable flow rates, increased internal and external leakage, and excessive backforce on the valve spool. The stroke throttle valve and the one-way stroke throttle valve are other structural forms of throttle valves; therefore, the causes of problems such as failed flow regulation, unstable flow rates, and increased internal and external leakage are essentially the same as those for regular throttle valves, and the methods for resolving these issues are also similar. Excessive backforce on the spool of the travel throttle valve and the one-way travel throttle valve refers to the backforce exerted by the spool on the travel stop being greater than the value designed. Reasons for this excessive backforce include radial jamming of the spool and blockage of the oil drain port. When the oil drain port becomes blocked, the oil that leaks from the gap between the valve core and the valve body cannot flow back to the tank. Over time, the pressure of the oil at the drain port equals the pressure of the oil in the inlet chamber; as a result, the hydraulic force acting on the area at the bottom of the valve core increases. This increases the force required for the stopper to push the valve core, and in severe cases, the stopper may not be able to move the valve core, leading to system failures. Therefore, when using a travel throttle valve and a one-way travel throttle valve, the oil drain port must be connected back to the oil tank. XI. 2FRM Type Throttle Valve 1. Structure and Working Principle The 2FRM type throttle valve is a two-way flow control valve. This valve is composed of a pressure reducing valve and a throttle valve connected in series; once the oil flow enters the speed control system, it is first depressurized by the pressure reducing valve and then throttled by the throttle valve. Since the pressure reducing valve provides pressure compensation for the throttle valve, the flow rate of the speed control valve remains stable regardless of changes in load. Additionally, the throttling window is designed with a thin edge, resulting in little variation in flow rate due to temperature changes. When the speed control valve is connected in parallel with a check valve, the oil flow can flow back in the opposite direction. The Z4S type rectifying plate is installed below the speed control valve, enabling stable flow in both directions through the speed control valve. 2. Common faults of speed control valves and their troubleshooting (I) Failure in flow regulation: This refers to a situation where adjustments to the throttling mechanism do not result in any change in the flow rate in the output chamber. The main causes for this are radial sticking of the valve element and failures within the throttling mechanism. When the pressure relief valve spool or throttle spool is in the fully closed position, radial sticking will result in no flow in the oil outlet chamber; whereas when it is in the fully open position (or when the throttle opening is properly adjusted), radial sticking will not cause any change in the flow rate in the oil outlet chamber controlled by the throttle mechanism. Furthermore, when the throttle control mechanism fails, it prevents the control screw from moving axially, resulting in no change in the flow rate in the oil outlet chamber as well. In the event of a stuck valve core or a malfunction in the throttling control mechanism, it should be cleaned and repaired. (II) Unstable flow: When the throttle opening of the pressure-reducing throttle type speed control valve is adjusted and locked in place, unstable flow can occur at times, especially at the minimum stable flow rate. The main reasons are a loose locking device, blockage in the throttle section, increased oil temperature, an excessively low minimum pressure difference between the inlet and outlet chambers, and reversed connections between the inlet and outlet chambers. When oil flows in the reverse direction through the QF type speed control valve, the pressure reducing valve does not provide any pressure compensation for the throttle valve, causing the speed control valve to function as a throttle valve. Therefore, when the oil pressure in the inlet and outlet chambers changes, the flow rate passing through them changes as well, resulting in unstable flow. Therefore, when in use, pay attention to the positions of the oil inlet and outlet chambers to avoid reversing them. (III) Increased internal leakage: When the throttle opening of a pressure-reducing throttle-type speed control valve is closed, sealing is achieved through gaps; as a result, some leakage is inevitable, and therefore it cannot be used as a stop valve. When the sealing surfaces (such as those of the pressure relief valve spool, throttle valve spool, and check valve spool) are excessively worn, it leads to an increase in internal leakage, resulting in unstable flow rates; this particularly affects the minimum stable flow rate. XII. Diversion – Common Faults and Troubleshooting of Diverting-Collecting Valves (I) Precautions for Use 1. Proper selection of valve specifications It can be seen from the curves showing the relationship between flow rate and speed synchronization accuracy, as well as those showing flow rate and pressure loss and reverse pressure loss, that the flow rate has a significant impact on the speed synchronization accuracy, as well as on the pressure loss and reverse pressure loss of diverting-collecting valves. Therefore, in practical use, it is important to select the appropriate valve specifications based on the requirements for speed synchronization accuracy, pressure loss, and reverse pressure loss. Once the actual flow rate of use in the system is determined, the selection of the specifications for the diverter–collector valve can be guided by the following principles ； When high speed synchronization accuracy is required, a valve with a nominal flow rate that is lower than or close to the actual flow rate of the system can be selected ； When a low pressure loss or reverse pressure loss is required, it is possible to choose a valve with a flow rate reduction that is close to the actual flow rate used in the system. 2. Choose the installation location correctly: When installing the diverter–collector valve, it is necessary to keep the axis of the valve core horizontal; it must not be installed with the axis vertical, as this will affect the synchronization accuracy due to the weight of the valve core. 3. Prevent oil leakage between chambers A and B due to different load pressures. Since the throttle holes inside the distribution–collection valve are connected to each other, when the actuator needs to stop during its movement, a hydraulic check valve should be installed in this synchronization circuit in order to prevent oil from leaking from one actuator to another as a result of differing load pressures, as shown in Figure 40. 4. Not suitable for systems with frequent movements: In dynamic conditions, the diverter–collector valve loses its ability to synchronize the speed of the actuating elements, making it even more difficult to achieve positional synchronization; therefore, it is not suitable for systems with frequent changes in load pressure or those that require frequent direction changes. 5. Avoid synchronization errors caused by other factors: As much as possible, no additional control elements should be connected between the diversion/port and the collection port of the diverter–collector valve, as well as between this valve and the actuating element, in order to prevent an increase in the synchronization error of the circuit due to differences in the leakage rates of these control elements or other reasons. 6. Influence of series and parallel connections on synchronization accuracy: In synchronization systems, the distribution and collection valves can be connected in series, in parallel, or in a combination of both ways, to suit various synchronization requirements. The greater the number of valves connected in series, the larger the speed synchronization error. In parallel connection, the speed synchronization error of the system is generally the average of the speed synchronization errors of each shunt-collector valve in the parallel configuration. (II) Common faults during operation and their troubleshooting: The main common faults of the distribution-collecting valve include synchronization failure, large synchronization errors, and abnormal movement at the end position of the actuating elements. 1. Synchronization failure: Synchronization failure refers to the situation where several actuating elements do not move at the same time. The main cause of synchronous failure is the radial jamming of the valve spool or reversing piston. To reduce the impact of leakage on the accuracy of speed synchronization, shunt-collecting valves typically have small clearance gaps between the valve spool and the valve body, as well as between the reversing piston and the valve spool. As a result, when the system oil is contaminated or the oil temperature is too high, the valve spool or the reversing piston may become radially stuck. Therefore, attention should be paid to the cleanliness of the oil and its temperature when using it. When it is found that the valve spool or reversing piston is stuck radially, it should be cleaned promptly to ensure the flexible movement of the valve spool or reversing piston. 2. Large synchronization error: The main reasons for large speed synchronization errors are axial clamping of the valve core, too low flow rate, and too small pressure difference between the inlet and outlet oil chambers. Once the valve spool is radially clamped, the moving resistance increases; as a result, a greater hydraulic pressure difference between chambers a and b is required to push the valve spool in order to achieve automatic compensation. This in turn leads to a larger difference in hydraulic pressure differences across the fixed throttle orifices on the left and right sides. From the orifice flow formula, it can be seen that the greater the difference in flow rate through chambers A and B, the larger the speed synchronization error will be. The causes and solutions for axial jamming of the valve spool are the same as those for synchronization failure. When the flow rate through the shunt-collecting valve is too low, or when the pressure difference between the oil inlet and outlet chambers is too low, it results in a decrease in the pressure difference of the oil on either side of the fixed throttle orifices. From the perspective of the impact of the pressure difference between the oil on both sides of the fixed throttle orifice on the speed synchronization accuracy, a smaller pressure difference results in poorer synchronization accuracy; therefore, too low a flow rate through the split-and-reunite valve, or too low a pressure difference between the inlet and outlet oil chambers, can both lead to an increase in speed synchronization errors. The operating flow rate of the diversion–collection valve should generally be no less than 25% of the nominal flow rate, and the pressure difference between the inlet and outlet oil chambers should be no less than 8–10 kgf/cm2. 3. Abnormal movement at the end position of the actuator: In a synchronization system that uses shunt-and-collect valves as synchronization elements, it sometimes happens that one actuator reaches its end position while another stops moving; this is caused by the blockage of the small orifice Ф on the valve spool. If the small orifice on the right side becomes blocked, when the actuator on the left side reaches its end position, the oil pressure in chamber a increases, causing the valve spool to move to the right side and resulting in the throttle orifice on the right side closing. At this point, the throttle hole on the right side closes, and the constant-flow hole becomes blocked as well; as a result, there is no flow into chamber B, causing the actuator on the right side to stop moving. When abnormal movement at the end point of the actuator is detected, it should be cleaned promptly to keep the constant-flow orifice unobstructed. In the manufacturing of shunt-collecting valves, in order to ensure that the structural dimensions of the left and right sections are equal, at the current level of technology, the assembly of the components on the left and right sides is generally carried out using a matching approach. Therefore, after cleaning and maintenance, each component must be assembled back in its original position; otherwise, it will affect the synchronization accuracy.