Regarding the issue of reversing a screw pump
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Question: As a positive-displacement pump, when shutting down a screw pump, what is the correct procedure – to close the pump’s outlet or inlet? I am looking for the operating procedures for shutting down a screw-type lubricating oil pump
The pump inlet should be closed. It’s the exact opposite of starting the pump.
Just stop the operating pump and start the backup pump
Search for 【Operating procedures for screw pumps】 on Baidu by yourself, or look for it in forums.
Basic operating procedures Basic operating procedures 1. Filter operation； Y-type filters, basket filters, operation of A and Y-type filters: 1) Check and confirm that there are filters inside the Y-type filter and that nothing is blocking them. 2) Open the inlet valve of the Y-type filter, and open the outlet valve of the Y-type filter. B. Operation of the basket filter 1) Check and ensure that there is a filter element inside the basket filter, and that it is not clogged with dirt. 2) Open the inlet valve of the basket filter, slowly open the top exhaust valve of the basket filter; once all the air has been released, close the exhaust valve, and then slowly open the outlet valve of the basket filter. 2. Pump operation ； Shielded pumps, centrifugal pumps, screw pumps. A. Operation of centrifugal pumps: 1) Starting the pump: First, open the inlet valve of the pump, close the outlet valve, turn on the shaft seal water for the centrifugal pump, start the centrifugal pump, and then slowly open its outlet valve. 2) Shutdown of the pump: First, slowly close the pump’s outlet valve, shut down the motor of the centrifugal pump, turn off the shaft seal water for the centrifugal pump, and then close the pump’s inlet valve. 3) Pump switching: Open the inlet valve of the standby pump, turn on the shaft seal water for the standby pump, and start the standby pump. Once the pressure at the pump’s outlet reaches normal levels, slowly open the outlet valve of the standby pump while simultaneously closing the outlet valve of the pump in use, to ensure that the pressure at the outlet of the standby pump remains within normal ranges. Stop the motor of the switch pump, turn off the shaft seal water for the switch pump, and close the inlet valve of the switch pump. B. Operation of the screw pump 1) Starting the pump: First, open the outlet and inlet valves of the pump, then start the pump. 2) Shutdown of the pump: First stop the pump, then close its inlet and outlet valves. 3) Pump switching: (Two people are required to operate this process.) Person A opens the inlet valve of the standby pump, and while Person B starts the motor of the standby pump, Person A quickly shuts down the motor of the pump being switched off, as well as its inlet valve. C. Operation of canned pumps
1) Starting the pump: Open the pump’s inlet valve, close the outlet valve, then start the pump. Gradually open the outlet valve. Once the pressure stabilizes, check whether the pump’s pointer is within the green zone on the dial. At the same time, verify that the pump’s return pipe is unobstructed. If it is observed that the pump’s pointer is no longer in the green area, close the outlet valve and shut down the pump. 2) Shutting down the pump: Slowly close the pump’s outlet valve, stop the pump, and then close the pump’s inlet valve. D. Operation of the water ring vacuum pump: 1) Starting the pump: First, open the liquid outlet valve of the gas-liquid separator, then open the inlet valve of the water ring vacuum pump. Next, open the DM water valve of the water ring vacuum pump and adjust it to the set value, after which start the water ring vacuum pump. 3. Operation of heat exchangers: Plate heat exchangers, shell and tube heat exchangers. A. Operation of plate heat exchangers: 1) Starting up the heat exchanger: First, open the outlet discharge valve of the heat exchanger, then slowly open the inlet valve (note: the inlet valve does not need to be opened fully). Once fluid begins to flow out through the discharge valve, close it and open the outlet valve, opening the inlet valve fully. B. Operation of the shell-and-tube heat exchanger 1) Commissioning of the heat exchanger: First, open the outlet discharge valve of the heat exchanger, then slowly open the inlet valve (note: the inlet valve does not need to be opened fully). Once the gas has been discharged through the discharge valve, close it and open the outlet valve, opening the inlet valve fully. (First, introduce the cold medium; then, introduce the hot medium.) 2) Shutting down the heat exchanger: First, close the inlet valve for the hot medium, and then close the inlet valve for the cold medium. 4. Operation of the pressure gauge: 1. Close the isolation valve of the pressure gauge before putting it into use. 2. Open the isolation valve of the pressure gauge after the pump has started. 3. Slowly open the exhaust valve of the pressure gauge. 4. Close the exhaust valve only after material has flowed out of it. 5. Operation of the rotor flowmeter ； Commissioning of the rotameter: First, fully open the outlet valve of the rotameter, then slowly open the inlet valve of the meter ； Deactivation of the rotameter: First, close the inlet valve of the rotameter, then close the outlet valve of the rotameter. 6. Operation of steam pipes ； 1. First, open the inlet and outlet valves of the steam trap on the steam pipeline. 2. Slowly open the steam inlet valve on the steam pipeline; it is essential to do this slowly in order to prevent water hammer from occurring.
1) Starting the pump: Open the pump’s inlet valve, close the outlet valve, then start the pump. Gradually open the outlet valve. Once the pressure stabilizes, check whether the pump’s pointer is within the green zone on the dial. At the same time, verify that the pump’s return pipe is unobstructed. If it is observed that the pump’s pointer is no longer in the green area, close the outlet valve and shut down the pump. 2) Shutting down the pump: Slowly close the pump’s outlet valve, stop the pump, and then close the pump’s inlet valve. D. Operation of the water ring vacuum pump: 1) Starting the pump: First, open the liquid outlet valve of the gas-liquid separator, then open the inlet valve of the water ring vacuum pump. Next, open the DM water valve of the water ring vacuum pump and adjust it to the set value, after which start the water ring vacuum pump. 3. Operation of heat exchangers: Plate heat exchangers, shell and tube heat exchangers. A. Operation of plate heat exchangers: 1) Starting up the heat exchanger: First, open the outlet discharge valve of the heat exchanger, then slowly open the inlet valve (note: the inlet valve does not need to be opened fully). Once fluid begins to flow out through the discharge valve, close it and open the outlet valve, opening the inlet valve fully. B. Operation of the shell-and-tube heat exchanger 1) Commissioning of the heat exchanger: First, open the outlet discharge valve of the heat exchanger, then slowly open the inlet valve (note: the inlet valve does not need to be opened fully). Once the gas has been discharged through the discharge valve, close it and open the outlet valve, opening the inlet valve fully. (First, introduce the cold medium; then, introduce the hot medium.) 2) Shutting down the heat exchanger: First, close the inlet valve for the hot medium, and then close the inlet valve for the cold medium. 4. Operation of the pressure gauge: 1. Close the isolation valve of the pressure gauge before putting it into use. 2. Open the isolation valve of the pressure gauge after the pump has started. 3. Slowly open the exhaust valve of the pressure gauge. 4. Close the exhaust valve only after material has flowed out of it. 5. Operation of the rotor flowmeter ； Commissioning of the rotameter: First, fully open the outlet valve of the rotameter, then slowly open the inlet valve of the meter ； Deactivation of the rotameter: First, close the inlet valve of the rotameter, then close the outlet valve of the rotameter. 6. Operation of steam pipes ； 1. First, open the inlet and outlet valves of the steam trap on the steam pipeline. 2. Slowly open the steam inlet valve on the steam pipeline; it is essential to do this slowly in order to prevent water hammer from occurring.
The volumetric pump cannot have its outlet closed, as this can easily cause damage to it! Adjust the flow rate using the inlet/outlet connection line or the inlet valve!
Operating Procedures for Screw Pumps I. Before starting: 1. Check whether the process is correct. 2. Is the area around the pump clean, with no items that could interfere with its operation? 3. Check whether the screws of the coupling guard, footings, and other components are tight, and look for any signs of looseness. 4. The bearing oil reservoir must contain sufficient lubricating oil; the oil level should be kept within the specified range, and the quality of the oil should be good. 5. Select an appropriate pressure gauge based on the pump’s purpose and operating conditions. 6. Pumps equipped with bearing shell cooling water and shaft seal water should maintain unobstructed water flow. 7. Check whether the voltage is within the specified range, and verify that the motor’s wiring and grounding are in good condition. 8. Rotate the coupling by hand to check for any foreign objects inside the pump that might cause knocking noises or jamming, and eliminate such issues. II. Pump startup and operation: 1. Fill the pump chamber with the liquid material; dry friction is strictly prohibited. 2. After opening the inlet and outlet valves of the screw pump (the valves must be fully open to prevent overloading or cavitation), start the motor. 3. If there is a bypass valve, start the pump with both the suction and discharge valves as well as the bypass valve fully open, in order to minimize the load during startup. Once the prime mover reaches its rated speed, gradually close the bypass valve. 4. During operation, check whether the shaft seal is in good condition; a droplet-like leakage is acceptable. A slight amount of leakage from the shaft seal is permitted – if the leakage rate is no more than 1 drop per 20–30 seconds, it is considered normal. Check whether the pump’s discharge volume is normal, as well as any vibrations or noises; if any abnormalities are detected, stop the pump immediately and address them. III. Shutting down the pump: Before stopping the vehicle, it is necessary to first stop the operation of the motor, then close the inlet valve, and subsequently close the outlet valve (to prevent dry running and avoid damaging the working surfaces). IV. Precautions during operation 1. Before starting, the inlet valve and outlet valve should generally be fully opened. After opening the outlet valve, the pump should be started as soon as possible. It is strictly prohibited to start the pump without opening the outlet valve (if the outlet valve is closed, it is necessary to ensure that all inlet and outlet connecting valves are fully open). 2. If the flow rate required by the process is low, the outlet valve can be left partially open or closed; at the same time, the valve connecting the inlet and outlet should be fully opened. Once the pump is running properly, the outlet valve can be gradually opened according to the process requirements, while the connecting valve should be slowly closed until normal operating conditions are achieved. 3. It is strictly prohibited to operate for extended periods without priming the pump. 4. Stop the pump immediately in the following situations: severe leakage, abnormal vibration, unusual odors, sparks, smoke, impacts, or persistently high current levels. 5. During operation of the screw pump, the bearing temperature must not exceed the ambient temperature by 35°C, with the maximum temperature not exceeding 80°C. 6. Flow rate and pressure remain stable; current does not exceed the rated value. 7. Sealing leakage must not exceed the following limits: 7.1 For mechanical seals: no more than 5 drops per minute for heavy oils, and no more than 10 drops per minute for light oils. 7.2, Packing seal: For heavy oil, no more than 10 drops/min; for light oil, no more than 20 drops/min. V. Common Problems and Solutions Serial Number Common Problem Symptoms Cause of the Fault Solution 1 Insufficient flow rate after the pump starts Air leakage in the pump body or suction pipeline Seal the leaks, remove the air from within the pump, and refill it. Clogged inlet pipeline or filter, or valve opening too small: Increase the opening of the outlet valve, clear the inlet pipeline, or remove and inspect the inlet filter. Excessive clearance in the screws: Replace them. Improper functioning of the check valve: Repair or replace the check valve. 2. Unstable operation or too low output pressure: Misalignment of the coupling: Realign it. Foreign objects inside the pump casing: Open the pump body to inspect and clean it. High suction resistance: Worn or damaged bearings: Check whether the inlet pipeline and filter are clogged or if the valve openings are too small, and clean them accordingly; replace the bearings. Worn or misaligned synchronizing gears: Adjust, repair, or replace them. Loose anchor bolts: Tighten them. 3. Sudden increase in outlet pressure: Damaged pressure gauge: Replace the outlet pressure gauge. Clogged outlet pipeline or faulty outlet valve: Clear the outlet pipeline or fix the outlet valve. 4. Leakage at the shaft seal: Improper installation or damage to the mechanical seal: Reassemble or replace it. Worn shaft journal: Repair it. VI. Routine Maintenance 1. Regular inspections 1.1. Check for leaks at the shaft seal and all mating sealing surfaces ； 1.2 Check whether the cooling system is unobstructed, and whether the pressure and temperature are within reasonable ranges ； 1.3. Check the smoothness of operation; see if there is any vibration ； 1.4 Check whether the base bolts are loose ； 1.5. When parking for an extended period, drain all materials from the system; when the temperature is low, check for freeze and condensation prevention. 2. Regular inspections 2.1. Check the oil level of the lubricating oil or grease in the bearing housing on a weekly basis ； 2.2 Check the vibration level on a monthly basis to assess bearing wear. 3. Regular oil changes
3.1. Perform regular oil changes according to the recommended intervals. Within the first month of operation, replace the lubricating oil after 100 hours of use; thereafter, change the oil every 500 hours. 3.2 When changing the oil, visually inspect the interior of the tank for any deposits or residues, and decide whether cleaning is necessary; if not, new oil can be added directly. 4. Routine inspection after 8,000 hours of operation 4.1. Check the condition of the bearings and other wear-prone components; replace them if necessary ； Clean the filter and deposits inside the pump. 5. Maintenance Precautions 5.1 When the screw pump is to be stored for an extended period or taken out of use, anti-rust measures should be taken ； The method involves applying rust preventive grease to unpainted metal surfaces, including shaft surfaces and the interior cavity of the stuffing box ； 5.2 Lubrication (Proper lubrication is a prerequisite for the long-term reliable operation of the pump): A. The areas that require lubrication include the bearings of the pump and the universal joints of the drive shaft ； B. Lubricant: Lithium-based grease; for pumps that transport food-grade media, food-grade grease is used at the ball joints of the drive shafts ； C. The bearings of the pump should be removed and cleaned regularly, depending on the operating environment and conditions, and re-lubed with grease. The filling amount should be 1/3 to 1/2 of the space within the bearing and its housing ； D. The timing for replacing the grease in the universal joint of the drive shaft depends on the temperature and pressure of the conveyed medium; also, check whether the sealing sleeve and O-ring seals are damaged ； 5.3, Shaft seal A: For screw pumps equipped with packing seals, it is necessary to regularly check for leaks and tighten the packing cover in a timely manner; it is appropriate for a slight amount of fluid to leak out (tightening it too much can cause the packing to overheat and get stuck) ； B. When replacing worn packing rings, they should all be replaced ； C. For pumps equipped with mechanical seals, any signs of leakage must be promptly checked. Aged O-rings, as well as rotating and stationary rings with damaged surfaces, should be replaced in a timely manner. D. For pumps used to transport high-viscosity, easily sedimentable or solidifiable, and corrosive media, the mechanical seal should be thoroughly cleaned prior to long-term inactivity, and grease should be applied to the friction surfaces of the rotating and stationary rings. 5.4 During the operation of screw pumps, components such as the \"stator\" and \"universal joint\" are those that tend to get damaged easily. After replacing the stator, users should first lubricate the interior of the stator with a lubricant; this will **increase the stator’s lifespan**. 5.5 When using a screw pump during cold winter seasons, after shutting it down, it is necessary to unscrew the drain plug at the bottom of the pump body to drain all the medium. Prevent frost cracking. 5.6 When the screw pump is to be out of service for a long period, it must be completely disassembled, dried thoroughly, and the rotating parts and joints should be lubricated with grease before reassembling and storing it properly. 5.7 Generally, the pump is completely disassembled for major maintenance every 3,000 hours, with damaged parts replaced. Pumps that have undergone major repairs generally need to undergo necessary tests to ensure that their key performance parameters meet the original technical specifications. 6. During routine maintenance or when replacing the stator and rotor: 1.1. Disassemble the pump: A. Unscrew the nuts of the four tension bolts and remove the pressing chamber ； B. Pull out the stator while rotating it ； C. Remove the suction chamber ； D. Open the universal joint seal sleeve and remove the pin or universal joint ； 1.2 Thoroughly clean the removed components and replace worn parts in a timely manner. The stator should be removed every 1,000 to 1,500 hours to check for wear on the stator and rotor, and to refill the universal coupling and bearings with oil. 7. Major repairs: 7.1. Disassemble the pump ； 7.2 Remove the lower coupling or pulley ； 7.3. Open the stop tab of the round nut stop washer, and unscrew the round nut ； 7.4. Remove the input shaft along with the seal box, and then disassemble it further. VII. Precautions for using mechanical seals: 1. Mechanical seals are leak-proof; if a leak is detected, it should be checked and resolved promptly. 2. Dry running without a medium is prohibited; double-end external mechanical seal pumps must not operate without cooling water flow to prevent damage to the sealing friction pairs. 3. When the pump is used to transport corrosive media, it should be thoroughly cleaned before it is shut down for an extended period of time. First, the plug on the sealed casing should be removed, and a flushing fluid should be injected through this hole to prevent the accumulation of substances that could render the spring ineffective. After that, the pump should be cleaned using clean water or clean oil in a circulation process throughout the entire system. 4. Pay attention to keeping the surfaces of the friction pair clean to prevent damage; this is especially important when the materials of the rotating and stationary rings are silicon carbide, as silicon carbide is very brittle. Special care must be taken during installation and removal. If the surfaces of the friction pair are damaged, they should be replaced promptly. 5. Both the rotating ring and the stationary ring have an annular seal ring, which ensures sealing of the stationary ring against the seal box and of the rotating ring against the shaft. If it ages, it should be replaced in a timely manner. 6. If there is an anti-rotation pin at the bottom of the stationary ring, be sure to install it; otherwise the stationary ring may rotate along with the moving ring. 7. Mechanical seal; depending on the user’s requirements, other types of mechanical seals or double-face seals can also be used.
3.1. Perform regular oil changes according to the recommended intervals. Within the first month of operation, replace the lubricating oil after 100 hours of use; thereafter, change the oil every 500 hours. 3.2 When changing the oil, visually inspect the interior of the tank for any deposits or residues, and decide whether cleaning is necessary; if not, new oil can be added directly. 4. Routine inspection after 8,000 hours of operation 4.1. Check the condition of the bearings and other wear-prone components; replace them if necessary ； Clean the filter and deposits inside the pump. 5. Maintenance Precautions 5.1 When the screw pump is to be stored for an extended period or taken out of use, anti-rust measures should be taken ； The method involves applying rust preventive grease to unpainted metal surfaces, including shaft surfaces and the interior cavity of the stuffing box ； 5.2 Lubrication (Proper lubrication is a prerequisite for the long-term reliable operation of the pump): A. The areas that require lubrication include the bearings of the pump and the universal joints of the drive shaft ； B. Lubricant: Lithium-based grease; for pumps that transport food-grade media, food-grade grease is used at the ball joints of the drive shafts ； C. The bearings of the pump should be removed and cleaned regularly, depending on the operating environment and conditions, and re-lubed with grease. The filling amount should be 1/3 to 1/2 of the space within the bearing and its housing ； D. The timing for replacing the grease in the universal joint of the drive shaft depends on the temperature and pressure of the conveyed medium; also, check whether the sealing sleeve and O-ring seals are damaged ； 5.3, Shaft seal A: For screw pumps equipped with packing seals, it is necessary to regularly check for leaks and tighten the packing cover in a timely manner; it is appropriate for a slight amount of fluid to leak out (tightening it too much can cause the packing to overheat and get stuck) ； B. When replacing worn packing rings, they should all be replaced ； C. For pumps equipped with mechanical seals, any signs of leakage must be promptly checked. Aged O-rings, as well as rotating and stationary rings with damaged surfaces, should be replaced in a timely manner. D. For pumps used to transport high-viscosity, easily sedimentable or solidifiable, and corrosive media, the mechanical seal should be thoroughly cleaned prior to long-term inactivity, and grease should be applied to the friction surfaces of the rotating and stationary rings. 5.4 During the operation of screw pumps, components such as the \"stator\" and \"universal joint\" are those that tend to get damaged easily. After replacing the stator, users should first lubricate the interior of the stator with a lubricant; this will **increase the stator’s lifespan**. 5.5 When using a screw pump during cold winter seasons, after shutting it down, it is necessary to unscrew the drain plug at the bottom of the pump body to drain all the medium. Prevent frost cracking. 5.6 When the screw pump is to be out of service for a long period, it must be completely disassembled, dried thoroughly, and the rotating parts and joints should be lubricated with grease before reassembling and storing it properly. 5.7 Generally, the pump is completely disassembled for major maintenance every 3,000 hours, with damaged parts replaced. Pumps that have undergone major repairs generally need to undergo necessary tests to ensure that their key performance parameters meet the original technical specifications. 6. During routine maintenance or when replacing the stator and rotor: 1.1. Disassemble the pump: A. Unscrew the nuts of the four tension bolts and remove the pressing chamber ； B. Pull out the stator while rotating it ； C. Remove the suction chamber ； D. Open the universal joint seal sleeve and remove the pin or universal joint ； 1.2 Thoroughly clean the removed components and replace worn parts in a timely manner. The stator should be removed every 1,000 to 1,500 hours to check for wear on the stator and rotor, and to refill the universal coupling and bearings with oil. 7. Major repairs: 7.1. Disassemble the pump ； 7.2 Remove the lower coupling or pulley ； 7.3. Open the stop tab of the round nut stop washer, and unscrew the round nut ； 7.4. Remove the input shaft along with the seal box, and then disassemble it further. VII. Precautions for using mechanical seals: 1. Mechanical seals are leak-proof; if a leak is detected, it should be checked and resolved promptly. 2. Dry running without a medium is prohibited; double-end external mechanical seal pumps must not operate without cooling water flow to prevent damage to the sealing friction pairs. 3. When the pump is used to transport corrosive media, it should be thoroughly cleaned before it is shut down for an extended period of time. First, the plug on the sealed casing should be removed, and a flushing fluid should be injected through this hole to prevent the accumulation of substances that could render the spring ineffective. After that, the pump should be cleaned using clean water or clean oil in a circulation process throughout the entire system. 4. Pay attention to keeping the surfaces of the friction pair clean to prevent damage; this is especially important when the materials of the rotating and stationary rings are silicon carbide, as silicon carbide is very brittle. Special care must be taken during installation and removal. If the surfaces of the friction pair are damaged, they should be replaced promptly. 5. Both the rotating ring and the stationary ring have an annular seal ring, which ensures sealing of the stationary ring against the seal box and of the rotating ring against the shaft. If it ages, it should be replaced in a timely manner. 6. If there is an anti-rotation pin at the bottom of the stationary ring, be sure to install it; otherwise the stationary ring may rotate along with the moving ring. 7. Mechanical seal; depending on the user’s requirements, other types of mechanical seals or double-face seals can also be used.