Types of valve selection for beer production lines and their advantages and disadvantages
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Brewing equipment 1. Butterfly valve: It has the following advantages and disadvantages during the production process: *Advantages: 1. It is easy and quick to open and close, requires little effort, presents low fluid resistance, and can be operated frequently. 2. Simple structure, small size, and light weight. 3. It can transport mud, with minimal liquid accumulation at the pipe outlet. 4. Good sealing can be achieved at low pressures. 5. Good adjustment performance. *Disadvantages are: 1. The range of operating pressure and working temperature is limited. 2. The sealing performance is poor. *Classification of butterfly valves: Butterfly valves can be classified by their structural design into offset plate type, vertical plate type, inclined plate type, and lever type. Based on the sealing type, they can be divided into the semi-sealed type and the hard-sealed type. Soft-sealed types generally use rubber rings for sealing, while hard-sealed types usually use metal rings for sealing. Based on the type of connection, it can be divided into flange connection and clamp connection ； Based on the transmission method, they can be classified into manual, gear-driven, pneumatic, hydraulic, and electric types. *Installation and maintenance of butterfly valves: 1. During installation, the valve disc should be in the closed position. 2. The operating position should be determined based on the rotation angle of the butterfly valve disc. 3. For butterfly valves equipped with a bypass valve, the bypass valve should be opened first before turning on the valve. 4. It should be installed in accordance with the manufacturer’s installation instructions; for butterfly valves with heavy weights, a solid foundation should be provided. 2. Ball valves have the following advantages and disadvantages during the production process: *Advantages: 1. Low fluid resistance, with a resistance coefficient equal to that of a pipe section of the same length. 2. Simple structure, small size, and light weight. 3. Tight and reliable; currently, plastic is widely used as the material for the sealing surfaces of ball valves, providing good sealing performance, and they are also extensively used in vacuum systems. 4. It is easy to operate and opens/closes quickly – only 90° of rotation is needed to go from fully open to fully closed, facilitating remote control. 5. It is easy to maintain; the ball valve has a simple structure, and the sealing rings are usually movable, making it convenient to remove and replace them. 6. When fully open or fully closed, the sealing surfaces of the ball and the valve seat are isolated from the medium; thus, as the medium passes through, it does not cause erosion of the valve’s sealing surfaces. 7. It has a wide range of applications, with diameters ranging from a few millimeters to several meters, and it can be used in conditions ranging from high vacuum to high pressure. *The disadvantages are: 1. Since the main material used for the seat seal ring in ball valves is polytetrafluoroethylene, it is inert to almost all chemicals. It also boasts a low friction coefficient, stable performance, resistance to aging, a wide temperature range of operation, and excellent sealing properties. However, the physical properties of polytetrafluoroethylene, including its high coefficient of expansion, sensitivity to cold flow, and poor thermal conductivity, require that the design of the valve seat seal take these properties into account. Therefore, when the sealing material hardens, its sealing performance is compromised. Furthermore, polytetrafluoroethylene has a low temperature resistance and can only be used at temperatures below 180°C. Above this temperature, the sealing material will age. When considering long-term use, it is generally not used at 120°C. 2. Its regulating performance is somewhat inferior to that of globe valves, especially pneumatic valves (or electric valves). *Classification of ball valves: Floating ball ball valve. In this type of ball valve, the ball is floating; under the pressure of the medium, the ball can move to a certain extent and press against the sealing surface at the outlet end, thereby ensuring sealing at that outlet. The floating ball valve has a simple structure and good sealing performance, but the load exerted by the working medium on the ball is transferred entirely to the outlet seal ring; therefore, it is necessary to consider whether the material of the seal ring can withstand the working load from the medium acting on the ball. This structure is widely used in medium and low pressure ball valves. Fixed ball valve: The ball of this type of ball valve is fixed and does not move under pressure. Fixed ball valves are equipped with floating seat valves; under the pressure of the medium, the seat moves, causing the sealing ring to press tightly against the ball in order to ensure a seal. Bearings are usually installed on the upper and lower axes of the sphere, resulting in low operating torque; it is suitable for high-pressure and large-diameter valves. To reduce the operating torque of ball valves and improve the reliability of sealing, oil-sealed ball valves have emerged in recent years. These valves inject a special lubricant between the sealing surfaces to create an oil film, which not only enhances the sealing performance but also reduces the operating torque; they are thus more suitable for high-pressure, large-diameter ball valves. Elastic ball valve: The ball of this valve is elastic. Both the sphere and the valve seat seal ring are made of metal materials, resulting in a high sealing pressure. The pressure of the medium itself is not sufficient to achieve proper sealing, so an external force must be applied. This type of valve is suitable for high-temperature and high-pressure media. An elastic sphere obtains its elasticity by having an elastic groove at the lower end of the inner wall of the sphere. When the channel is closed, the wedge-shaped end of the valve stem is used to expand the ball and press it against the valve seat to achieve sealing. Before rotating the sphere, release the wedge head; the sphere then returns to its original shape, creating a small gap between the sphere and the valve seat, which reduces friction on the sealing surfaces as well as the operating torque. Ball valves can be classified into straight-through, three-way, and right-angle types according to the position of their passages. The latter two types of ball valves are used to distribute the medium and change its flow direction. *Installation and Maintenance of Ball Valves Installation 1. Remove the protective covers on both sides of the flange, and clean the valve while it is fully open. 2. Before installation, the entire unit should be tested using the specified signals (electrical or pneumatic) (to prevent vibrations caused by transportation from affecting its performance); it can only be installed after passing the test (wiring shall be carried out in accordance with the circuit diagram of the electric actuator). 3. Before preparing for connection to the pipeline, it is necessary to flush and remove any residual impurities from the pipeline (such substances may damage the valve seat and ball). 4. During installation, do not use the actuator part of the valve as a lifting point to avoid damaging the actuator and its accessories. 5. Valves of this type should be installed horizontally or vertically in the pipeline. 6. The pipes near the installation point must not sag or be subjected to external forces; pipe supports or braces can be used to prevent the pipelines from deviating. 7. After connecting to the pipeline, cross-secure the flange connection bolts with the specified torque. To ensure a long service life and a maintenance-free period, the following factors are important: normal operating conditions, maintaining an appropriate temperature/pressure ratio, and having reliable data regarding corrosion. ● Even when the ball valve is closed, there is still pressurized fluid inside the valve body. ● Before carrying out any repairs, release the pressure in the pipelines and keep the valve in the open position. ● Before repairs, disconnect the power or gas supply. ● Before repairs, separate the actuator from its support. The packing area should be tightened further; if there is slight leakage at the packing area, tighten the valve stem nut further, but be careful not to over-tighten it – usually tightening it by 1/4 turn to 1 full turn will stop the leakage. Replace the valve seat and seals. Disassemble the valve to bring it into a semi-open position, and flush out any hazardous substances that may be present inside or outside the valve body. Close the ball valve, remove the connection bolts and nuts from both flanges, and then completely remove the valve from the pipeline. Remove the drive device-actuator, connection bracket, lock washer, valve stem nut, butterfly spring, gland, wear-resistant plate, and valve stem packing in sequence; then remove the bolts and nuts that connect the valve cover to the valve body, separate the valve cover from the valve body, and take out the valve cover gasket. Ensure that the valve ball is in the “closed” position, which makes it easier to remove it from the valve body, after which the valve seat can be taken out. Gently push the valve stem downward through the hole in the valve body until it is completely removed. Then take out the O-ring as well as the packing at the bottom of the valve stem. Note: Please proceed with care to avoid scratching the surface of the valve stem or the sealing areas in the valve body’s packing box. For reassembly, clean and inspect the parts that have been removed. It is highly recommended to replace seals such as the valve seat and valve cover gaskets with those from a spare parts kit, and assemble everything in the reverse order of disassembly. Lock the flange connection bolts crosswise using the specified torque. Use the specified torque to tighten the valve stem nut. After installing the actuator, send the appropriate signal which causes the valve stem to rotate, thereby moving the valve core to the open or closed position. If possible, please conduct pressure sealing tests and performance tests on the valve in accordance with relevant standards before reinstalling it in the pipeline.
Points to consider when selecting a thermal relay 1. Type selection. Under normal circumstances, a two-phase thermal relay can be used, but when the balance of the three-phase voltages is poor, the operating environment is harsh, or the motor is unattended, a three-phase thermal relay is preferable. For motors connected in a delta configuration, thermal relays equipped with phase loss protection should be used. 2. Selection of the rated current for the thermal relay. The rated current of the thermal relay should be greater than the rated current of the motor. Then, select the model of the thermal relay based on this rated current. 3. Selection and setting of the rated current of the heating element. The rated current of the heating element should be slightly greater than the rated current of the motor. When the motor’s starting current is 6 times its rated current and the starting time does not exceed 5 seconds, the setting current of the thermal element is adjusted to be equal to the motor’s rated current ； When the motor takes a long time to start, drives impactful loads, or stopping is not permitted, the setting current of the thermal element is adjusted to 1.1–1.15 times the motor’s rated current. Reposting is welcome; the information comes from Viku Electronic Market Network (www.dzsc.com)
It’s been three years since I graduated and started working in the field of automation; my main task is to manage control systems for food production lines, which are used in the beer, milk, and tea industries. However, lately I’ve felt that the knowledge I possess is not deep enough, and sometimes I don’t know how to approach new challenges. I hope everyone can help me – let’s discuss any issues together and keep learning. Thank you! With the arrival of the Year of the Ox, I wish everyone success in their work and happiness in their families.
Section 1: Common Control Electrical Appliances. Electrical devices used to control and protect motors and manufacturing machinery are called control electrical appliances. There are many types of control appliances, which can be divided into manual and automatic categories based on their mode of operation. The operation of manual electrical devices is controlled manually by staff, such as knife switches, combination switches, buttons, etc. The operation of automatic electrical devices is carried out automatically in response to commands, signals, or changes in certain physical quantities; examples include various relays, contactors, limit switches, etc. 1.1 Manually operated electrical devices 1 Switches – Also known as knife switches, these are generally used in low-voltage circuits where operations are not frequent. They are used to turn the power on and off, or to isolate a circuit from the power supply. Sometimes they are also used to control the direct start and stop of small-capacity motors. A knife switch consists of a blade (moving contact), a static socket (static contact), a handle, and an insulating base plate, among other components. There are many types of knife switches. Classified by the number of poles (blades) into single-pole, double-pole, and triple-pole ； Classified by structure into flat-type and rack-type ； Based on the operation method, they are classified into direct handle operation type, lever operation mechanism type, and electric operation mechanism type ； Based on the conversion direction, it is divided into single-shot and double-shot types, etc. Circuit breakers are generally used in series with fuses, so that the fuse will blow and automatically cut off the circuit in the event of a short circuit or overload. The rated voltage of knife switches is usually 250V and 500V, with a rated current of less than 1500A. When installing a knife switch, the power cable should be connected to the stationary contacts, while the load cable should be connected to the terminal linked to the blade. For knife switches equipped with fuses, the load wire should be connected to the other end of the fuse located on the lower side of the knife, to ensure that neither the knife nor the fuse remains charged after the knife switch cuts off the power supply. When installed vertically, pulling the handle upward connects the power supply, while pulling it downward disconnects it; it must not be installed in reverse, as this could cause the switch to fall loosely and inadvertently connect the power supply. The selection of a knife switch takes into account factors such as the rated voltage of the circuit, the continuous operating current, and the dynamic and thermal stability resulting from short-circuit currents. The rated current of the knife switch should be greater than the maximum load current it controls. When used for the direct start and stop of three-phase asynchronous motors of 3 kW or less, the rated current of the knife switch must be more than 3 times the rated current of the motor. 2 Combination switch: A combination switch, also known as a changeover switch, is a rotary knife-type switch that is primarily used to connect or disconnect circuits, switch power sources, control the start/stop, forward/reverse rotation of small squirrel-cage three-phase asynchronous motors, or operate local lighting systems. A combination switch consists of several moving contacts and stationary contacts, which are mounted within multiple layers of insulating elements. The stationary contacts are fixed on insulating pads, while the moving contacts are attached to a rotating shaft; they change their position to establish or break the circuit as the shaft rotates. 3 Button (switch): The button is primarily used for remotely operating relays and contactors to turn control circuits on or off, thereby controlling the operation of motors or other electrical devices. The contacts of a button come in two types: normally closed contacts (break contacts) and normally open contacts (make contacts). A normally closed contact is a contact that is closed when the button is not pressed and opens when it is pressed. A normally open contact is a contact that is open when the button is not pressed and closed when it is pressed. When the button is pressed, the normally closed contact opens first, and then the normally open contact closes ； Once released, the contact is returned to its original position by the return spring. The number and type of contact pairs within the button can be combined as needed, with at least one pair of normally closed or normally open contacts. (It’s something I created based on my own references and notes; please offer lots of guidance.) To be continued
1.2 Automatic Electrical Devices 1 Fuses: Fuses are primarily used for short-circuit or overload protection, and they are connected in series within the circuit that needs to be protected. When operating normally, the circuit functions like a wire, serving as a path for current flow ； When the circuit is short-circuited or overloaded, the fuse blows, thereby protecting other electrical devices in the circuit. The method for selecting the fuse rating current is as follows: (1) For fuses in light fixture circuits: the fuse rating current should be ≥ the sum of the operating currents of all lights in that circuit. (2) Fuse for a single motor: The rated current of the fuse should be ≥ the motor’s starting current ÷ 2.5. If the motor starts frequently, then the rated current of the fuse should be ≥ the motor’s starting current ÷ (1.6–2). (3) Fuse for several motors working together: The rated current of the fuse is equal to (1.5–2.5) × the rated current of the motor with the highest capacity, plus the sum of the rated currents of the remaining motors. 2 Circuit Breakers A circuit breaker, also known as an automatic air switch or automatic switch, is characterized by its automatic protection function; it can automatically cut off the circuit in the event of faults such as short circuits, overloads, or low voltage, thereby providing protection. A circuit breaker mainly consists of three parts: a contact system, an operating mechanism, and protective components. The main contacts are closed by an operating mechanism (manual or electric). The tripping mechanism of a switch is a set of linkage devices, including overcurrent trip devices and undervoltage trip devices, all of which are electromagnets. Once the main contact is closed, it is locked by the locking hook. Under normal conditions, the armature of the overcurrent release is released. In the event of a severe overload or short-circuit fault, the coil generates a strong electromagnetic force due to the high current flowing through it, which pulls the armature downward and pushes aside the locking hook, thereby breaking the main contacts and providing overcurrent protection. The operation of a under-voltage release is the opposite: under normal conditions it holds the armature in place, keeping the main contacts closed; when the voltage drops significantly or the power is cut off, it releases the armature, causing the main contacts to open and thus providing under-voltage protection. When the power supply voltage is normal, it must be re-connected to operate. General selection of air circuit breakers: (1) The rated current and rated voltage should be greater than or equal to the normal operating voltage and current of the circuits and equipment. (2) The current of the thermal trip device is equal to the rated current of the load it controls. (3) The rated voltage of the under-voltage release is equal to the rated voltage of the circuit. Selection of circuit breakers for motor protection (1) Long delay, with the current setting equal to the motor’s rated current. (2) The rated current of the overcurrent release shall be ≥ 1.5–1.7 times the motor starting current
3 Travel switch: A travel switch, also known as a position switch, is primarily used to convert mechanical displacement into electrical signals, thereby enabling electrical control of mechanical movement. When the moving parts of the machine strike the contact rod, the rod moves downward, causing the normally closed contacts to open while the normally open contacts close ； Once the moving part moves away, the contact rod returns to its original position under the action of the return spring, and all contacts return to their normal state.
4 Contactor: When the coil is energized, an electromagnetic attraction is generated that pulls the armature downward, causing the normally open contacts to close while the normally closed contacts open. When the coil is de-energized, the electromagnetic attraction disappears, and the spring causes the contacts to return to their original position. Depending on their purpose, the contacts of an AC contactor are divided into main contacts and auxiliary contacts. Main contacts are generally larger in size and have lower contact resistance; they are used to connect or disconnect large currents and are typically installed in the main circuit ； Auxiliary contacts are generally small, have high contact resistance, and are used to connect or disconnect lower currents; they are often connected to control circuits (also known as auxiliary circuits). Sometimes, in order to switch larger currents on and off, arc extinguishing devices are installed on the main contacts to extinguish the arc generated when the main contacts are separated, thereby preventing the contacts from being damaged. The contactor is one of the most important control devices in electric drive systems. The starting current when the load is turned on was taken into account during the design of its contacts; therefore, when selecting a contactor, it should primarily be determined based on the rated current of the load. For a Y112M-4 three-phase asynchronous motor with a rated power of 4 kW and a rated current of 8.8 A, an AC contactor with main contacts rated for 10 A will suffice. In addition to the current, the rated voltage of the contactor must also be at least equal to the rated voltage of the main circuit. 5 Relays A relay is an automatic control device that turns on and off low-current control circuits in response to specific input signals, thereby enabling remote control and protection. There are many types: (1) Based on the nature of the input signal: voltage relays, current relays, time relays, temperature relays, speed relays, pressure relays, etc. (2) Classified by working principle: electromagnetic relays, inductive relays, electric relays, thermal relays, electronic relays, etc. (3) Classified by output form: contact-type and contactless. (4) Classified by purpose: for control and for protection. (1) Electromagnetic relays have a structure and working principle similar to those of contactors, and are composed of an electromagnetic mechanism and a contact system. The relay responds to changes in various input signals ； The contactor operates only under the influence of a certain voltage signal. Relays are used to switch control circuits and protection circuits with low currents ； Contactors are used to control high-current circuits. Relays do not have arc-quenching devices, nor do they have primary and secondary contacts. ① A relay whose contact operation is related to the current magnitude in its coil is called a current relay. Used for current protection and control in power systems. When in use, the coil of the current relay is connected in series with the load. Relays are classified into AC and DC current relays based on coil current. Based on the magnitude of the attracting current, relays are divided into overcurrent and low (under)current relays. In DC circuits, a decrease or disappearance of the load current often leads to serious consequences; there are no significant overcurrent fluctuations, which is why low-current relays generally exist only in DC version. ③ An intermediate relay is a relay that serves functions such as signal transmission, amplification, inversion, and branching in control circuits. Intermediate relays are typically used to transmit signals and control multiple circuits simultaneously; they can also be used to directly control small-capacity motors or other electrical actuators. The structure and working principle of the intermediate relay are basically the same as those of an AC contactor. The main difference from an AC contactor is that it has more contacts, but these contacts have a lower capacity and can only carry small currents. When selecting an intermediate relay, the main considerations are voltage level and the number of contacts. It is a type of voltage relay, primarily used to increase the number of contacts and enable logical control. (2) Thermal relay: An electrical device that can change its operating time depending on the degree of overload is a thermal relay. Thermal relays are designed based on the principle of the thermal effect of electric current as well as the principle of thermal expansion of heating elements. Working principle of bimetallic strip: The lower layer of metal has a higher coefficient of expansion, while the upper layer has a lower coefficient of expansion. When the current in the main circuit exceeds the allowable value and heats the bimetallic strip, its free end bends upward and protrudes beyond the latch plate; the latch plate, under the pull of the spring, breaks the normally closed contacts. The contacts are connected to the control circuit of the motor; when the control circuit is disconnected, the coil of the contactor loses power, thereby breaking the main circuit of the motor. Thermal relays cannot provide instantaneous overload protection in a circuit, let alone short-circuit protection. Selection of thermal relays: (1) In principle, the rated current of the thermal relay should be selected based on the rated current of the motor. For motors with poor overload capacity, it is usually 60% to 80% of the motor’s rated current. For motors with a long starting time, it should be adjusted to 1.1–1.15 times the motor’s rated current. (2) In situations where the motor is not started frequently, it is necessary to ensure that the thermal relay does not malfunction during the motor’s starting process. Generally, when the motor’s starting current is 6 times its rated current, the starting time does not exceed 6 seconds, and continuous starting occurs rarely, the rating current of the motor is used as the basis for selection. (3) When the motor operates repeatedly and for short periods of time, it is important to determine the allowable operating frequency of the thermal relay. Thermal relays are not suitable for protecting motors that operate reversibly and experience frequent on-off cycles. For motors that operate at high frequencies, thermal relays may sometimes not even be usable