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The liquid ring vacuum pump is a variety of rotary positive-displacement pump that primarily uses liquid as the element in compressing gas. Compression is done by the ring of liquid produced by the eccentricity between the rotating bladed impeller and the pump's casing.
Electricity ensues from the near-complete filling, then becomes partially empty, every time the rotor chamber completes a revolution. The emptying and filling part generate a piston action in each set of impeller blades or rotor.
The components of the pump is designed in a way to receive gas when the chamber empties the liquid, and expels the gas when compression is done. Sealing chambers between the discharge ports and inlet are made to fully close the rotor areas and separate the discharge flow and inlet.
At the Start:
Proper installation of a liquid ring vacuum pump is vital for its optimal operation and maintenance. The guidelines here can be applied to almost all forms of liquid ring vacuum pumps, but the user should still refer to recommendations as provided by the manufacturer. Care should always be practiced when unpacking to prevent damage and misalignment during assembly. For motor units and pumps mounted on base plates, the unit should be elevated by the base. Hooks and slings should not be attached to the motor or pump since it can increase the chance of misalignment. The pump should not be operated without a sealing liquid, nor without being properly installed.
The components are normally shielded by a water-soluble preservative. This should be flushed out of the unit if any liquid other than water is used in a closed-loop scheme. Pumps that are made of non-ferrous materials such as stainless steel can be shipped without preservatives. Lastly, the unit has to be installed or stored to prevent any liquid within from freezing.
The Setup :
Liquid ring vacuum pumps are smooth-operating, slow-speed rotating machines. It is vital to make sure the base plate or the pump's frame is firmly anchored and installed levelly. 50 hp and above pumps work best in concrete pads, while smaller units can be mounted in existing skids and floors. All flanged or screwed joints in the piping should be checked for leaks and free of stain before start-up.
Pumps that are directly supplied with motors are test-run and aligned in the factory before shipping. During shipment or installation though, unforeseen circumstances or happenstance may affect the pump, so it might be good practice to check the alignment of the coupling before operation.
The guidelines given by the coupling manufacturer should be rigidly followed as a requirement, and carefully examined to exceed where possible.
Pumps that use v-belt drives need to be checked twice that the sheaves are properly aligned and installed before tensioning the drive. The v-belts are to be put in the grooves and over the sheaves without stretching them over the grooves' sides.
When the belts are properly in the grooves, the centers are made to pick up the slack, placing the belts taut. When the pumps operate, the slack part would have a minimal bow. Re-tension the belts as necessary after a few days' operation. Slipping or a squealing sound during startup means that there is insufficient tension. Overtension can diminish bearing life. If the unit is unused for a long time, the tension should be removed from the belts.
Extreme heat at 140 F or higher can shorten a belt's life and over-cure the rubber. The belt should not be switched from one groove or mixed when on the sheaves, and a replacement should only be done by a matching set. The sheaves should remain grease and oil-free, and belt dressing must never be applied.
Seal Liquid Piping :
The liquid ring vacuum pump operates on the principle of dependence in a supply of continuous clean seal liquid like water or anything similar. The liquid goes in the pump through a casing's connection and comes out of the pump with the gas.
Three simple seal liquid piping arrangements can be utilized for pump vacuum applications: closed loop, partial recovery, and once through. All of them have 4 elements:
-A way of breaking up the liquid-gas exhaust mixture
-A way of stopping flow when the pump is closed down
-A device to regulate the flow of liquid when needed
-An inlet for the seal liquid (from a tank or water main)
No Recovery, Once-Through :
This design allows seal liquid to be taken from a main and flows to the pump. The liquid waste is separated and exits through a drain. There is no recovery or recirculation, and there is no concern for contamination or conservation of the seal liquid.
The automatic solenoid valve makes sure the seal liquid flows in sync with the operation of motor pump (i.e, the valve closes to stop the seal liquid when the motor stops operating). A manual valve that shuts off seal liquid should be handled with care in case of flash cautions to close the valve before the motor stops, and to unlock the valve before turning on the motor.
Partial Recovery :
The seal liquid gets in and exits through the pump like the once-through arrangement, and afterwards, a small portion of seal liquid recirculates from the separator chamber to the pump, and the rest is drained.
New seal liquid is put in adequate amounts to keep the optimal temperature, allowing the pump to perform greatly. This system is used when the seal-liquid conservation is imperative (up to 50% fresh water consumption reduction if needed, and if other liquids are utilized, the consumption can be below 50%, depending on temperature and fluid vapor pressure).
Close Loop :
This system provides total recirculation of condensation and heat of compression using seal liquid, then it is rerouted back into the pump. For extended operation with high-suction pressures, where the system experiences severe pressure drop losses, use of a circulating pump may be required.
With arrangements of total or partial recovery, the seal liquid inside the separator-recirculator chamber needs to be at the pump shaft's centerline, or near it. Arrangements can also be made for low-level makeup or high-level overflow in total recovery systems. The level controls stop operation when the casing is filled with water, due to the motor being overloaded and could potentially damage the pump.
Liquid ring vacuum pumps should never be started with full seal liquid casing in any piping arrangement. Extra provisions are made to expel liquid from the pumps should they become flooded. These safety provisions are different depending on the manufacturer.
Draining of the pump may not be needed if the seal liquid is simultaneously turned off, and if an automatic valve is installed for this procedure.
A lot of liquid ring vacuum pumps have gland arrangement, or a regular packing for shaft sealings that are installed with lantern rings and given a gland connection to cool liquid. A liquid-cooling source is required, and must operate at 5 psig beyond the operating pressure. A stock supply for the gland cooling and seal liquid is regularly used.
A supply of flush liquid and cooling is needed if mechanical seals are used. It is advisable for a clean and separate source of seal liquid for the seals to be used. A monitoring device that detect leaks in the seal is needed for double mechanical seals.
Piping :
To start, the discharge flanges and suction are indicated with arrows in the casing. These should be the same size as with pump connections.
The discharge line should be as low in elevation in relation to the pump leading to the separator. A discharge leg can be utilized on top of the discharge flange if needed. A high elevation can cause back pressure that overloads the motor and affects the capacity of the pump.
The seal liquid piping must be of same size as with the pump's connection. If using a recirculated seal system that don't utilize a recirculation pump, a larger pipe is installed to compensate for pressure drop.
Peel off the seal from the pump's openings before connecting. Scrutinize closely for any foreign objects such as nuts, rags, dirt, bolts and welding slag before attaching to the pump.
During the pipe work connection, see if the flanges fit without strain, and check if the flange holes are perfectly aligned. The included gaskets must not show in the interior bore of the pump flange or the pipe. They must fit without relaying strain to the pump casing. You may fit in a protective mesh at the suction inlet of the pump during the first few weeks.
Electrical Connections :
Regular inductions motors are appropriate for operating liquid ring pumps. The beginning loads are easy, and across-the-line type of operation is recommended. A motor controller that has a protection for over-current of fuse or heater is recommended. The current rating in full-load, as marked in the motor, should be followed when selecting the protection rating. A disconnect switch may also be installed in between the power supply and motor controller.
The pump should be operated by hand when electrical work is finished. Loosen the gland rings as necessary for the shaft to operate easily. The direction of turning is indicated by the arrow direction on the pump. Prime it, turn the seal liquid on, turn the motor on and off to see the rotation, then shut off the seal liquid. If you see an incorrect direction, reverse two of the motor leads and try it again. A single-phase, 115V supply can be installed for control circuit. Solenoid valves, level controllers, alarms and vacuum pressure switches are to be supplied with 115V only in accordance to electrical safety code requirements.
Accessories :
Liquid ring vacuum pumps are created with many accessories, some from the manufacturer or by others. An application's unique requirements, type of control and mode of operation will dictate the need for certain items. Some of the most commonly used items are covered below:
Isolation valves disconnect the pump from the system if shut down for prolonged periods or when in maintenance. Gate or full-port ball valves minimize drops in pressure that are 3 inches or above. Inlet check valves halt seal liquid and gas from going back when the pump stops operation. Double-flexible, swing-check seal or equal-type valves are installed horizontally. Inlet vacuum relief valves prevent cavitation when the pump's suction pressure falls below the vacuum relief valve's setting. It will process gas or bleed in-atmospheric air. Most of these valves are atmospheric-pressure based and will need to be periodically calibrated. Flexible connectors connect slight misalignments in process and pumps. Inlet vacuum valves control the vacuum level by bleeding gas or atmospheric air. Pneumatically-operated diaphragms on globe valves are needed for a greater degree of control.
Inlet vacuum gases mark the pressure at the inlet of the vacuum pump. Seal liquid valves manually stop the flow of the seal liquid to the pump. Strainers keep out solid particles entering the seal liquid. Compound pressure gases indicate pressure at the connection inlet of a particular seal liquid heading to the pump. Discharge separator tanks break apart the gas and seal liquid emerging from the pump. They can be floor-mounted or on a base plate along with the pump, or carried by the discharge piping as used by once-through systems. Solenoid valves automatically start and stop the seal liquid's flow straight to the pump. Circulating pumps are utilized in total recovery systems to recirculate the seal liquid. They are needed when the pumps operate on an extended period with excessive pressure drops or high suction pressures due to piping and valves, or heat exchangers. Heat exhangers relieve heat from the recycled seal liquid. Atmospheric air ejectors give suction pressures that are lower than what liquid ring pumps can do when running alone. The ejectors are added and provide inlet pressures that can go as low as 3 torr in pumps. They are similar to steam ejectors, as gas or atmospheric air from discharges is utilized as motive force in compressing gas from system design pressure similar to an inlet pressure of a liquid ring pump. A motive shut-off air valve can be installed to enhance pumping capacity. A bypass can work as well to achieve capacity above 30 torr.
Troubleshoot Liquid Ring Vacuum Pumps :
Troubleshooting is also a necessary part of a liquid ring vacuum pump's maintenance and operation. Only those who are fully qualified and carrying proper equipment is authorized for testing. Good practice dictates that the equipment be closely inspected when arriving in-site. Installation should be error-free, and all the flow switches and valves should be correctly placed as per installation diagram. Verify correct pump rotation and that the system is primed before operation. All of these preliminary checks will make troubleshooting much easier. Malfunction can be due to conditions or utility reasons, equipment failure, or both. A breakdown caused by external factors may be identified by following these steps:
Step one is to compare the design conditions, the cooling water temperature and gas composition to your existing condition.
Any change in design may be due to gas composition that affects the vacuum system. An example is when an increase in load will raise the seal liquid temperature and affect the vacuum system. Changing the gas composition from condensable or non-condensable may affect the seal liquid and vacuum. Check and see if there is no excess air leakage. It can be determined by a drop test via Institute Standards Heat Exchange for Jet Vacuum Systems. Back pressure is per design conditions. Extreme back pressure will elevate brake horsepower, and may affect the vacuum's capacity pump.
If the malfunction is not from external influences, continue to troubleshoot as follows:
Check the temperature of the seal liquid- it should be as designed. A reduced seal can be caused by a semi-closed valve in the recirculation line or a plugged strainer. See if the pump's performance or heat exchanger is fouled up. All of these can have a direct effect on how well the vacuum system performs. Use a tachometer to measure pump speed and compare with design specs. If V-belt driven, inspect the tension for any slippage. Test the pump via Institute Standards Heat Exchange for Jet Vacuum Systems, then put it side-by side with the manufacturer's design curve. An adjusting of internal clearances may be needed to keep abreast of the performance curve.
Regular maintenance is still required even if the desired vacuum is attained. Inspect the following parts:
If packing is included with the vacuum pump, dripping is normal. Excessive leakage may be due to incorrect adjustment. The packing should then be realigned, and the dripping inspected for proper cooling. Pumps with mechanical seals are not supposed to leak. Make certain the seals are rinsed with clean liquid of compatible material.
Inspect the pump for high bearing temperatures, as the normal should only be 140 F. This could be caused by excessive piping stress, a contaminated lubricant, misaligned couplings, or overgreasing.
Inspect the pump for vibration and excessive noise. This can be due to high discharge pressure, bearing failure, coupling misalignment, a water-filled casing, improperly anchored pump, or lack of air flow directed to the pump.
Inspect the amperage of the motor. A high amperage can be caused by excessive seal liquid flow, motor malfunction, or a high discharge pressure
At the Start:
The components are normally shielded by a water-soluble preservative. This should be flushed out of the unit if any liquid other than water is used in a closed-loop scheme. Pumps that are made of non-ferrous materials such as stainless steel can be shipped without preservatives. Lastly, the unit has to be installed or stored to prevent any liquid within from freezing.
The Setup :
Liquid ring vacuum pumps are smooth-operating, slow-speed rotating machines. It is vital to make sure the base plate or the pump's frame is firmly anchored and installed levelly. 50 hp and above pumps work best in concrete pads, while smaller units can be mounted in existing skids and floors. All flanged or screwed joints in the piping should be checked for leaks and free of stain before start-up.
Pumps that are directly supplied with motors are test-run and aligned in the factory before shipping. During shipment or installation though, unforeseen circumstances or happenstance may affect the pump, so it might be good practice to check the alignment of the coupling before operation.
The guidelines given by the coupling manufacturer should be rigidly followed as a requirement, and carefully examined to exceed where possible.
Pumps that use v-belt drives need to be checked twice that the sheaves are properly aligned and installed before tensioning the drive. The v-belts are to be put in the grooves and over the sheaves without stretching them over the grooves' sides.
When the belts are properly in the grooves, the centers are made to pick up the slack, placing the belts taut. When the pumps operate, the slack part would have a minimal bow. Re-tension the belts as necessary after a few days' operation. Slipping or a squealing sound during startup means that there is insufficient tension. Overtension can diminish bearing life. If the unit is unused for a long time, the tension should be removed from the belts.
Extreme heat at 140 F or higher can shorten a belt's life and over-cure the rubber. The belt should not be switched from one groove or mixed when on the sheaves, and a replacement should only be done by a matching set. The sheaves should remain grease and oil-free, and belt dressing must never be applied.
Seal Liquid Piping :
The liquid ring vacuum pump operates on the principle of dependence in a supply of continuous clean seal liquid like water or anything similar. The liquid goes in the pump through a casing's connection and comes out of the pump with the gas.
Three simple seal liquid piping arrangements can be utilized for pump vacuum applications: closed loop, partial recovery, and once through. All of them have 4 elements:
-A way of breaking up the liquid-gas exhaust mixture
-A way of stopping flow when the pump is closed down
-A device to regulate the flow of liquid when needed
-An inlet for the seal liquid (from a tank or water main)
No Recovery, Once-Through :
This design allows seal liquid to be taken from a main and flows to the pump. The liquid waste is separated and exits through a drain. There is no recovery or recirculation, and there is no concern for contamination or conservation of the seal liquid.
The automatic solenoid valve makes sure the seal liquid flows in sync with the operation of motor pump (i.e, the valve closes to stop the seal liquid when the motor stops operating). A manual valve that shuts off seal liquid should be handled with care in case of flash cautions to close the valve before the motor stops, and to unlock the valve before turning on the motor.
Partial Recovery :
The seal liquid gets in and exits through the pump like the once-through arrangement, and afterwards, a small portion of seal liquid recirculates from the separator chamber to the pump, and the rest is drained.
New seal liquid is put in adequate amounts to keep the optimal temperature, allowing the pump to perform greatly. This system is used when the seal-liquid conservation is imperative (up to 50% fresh water consumption reduction if needed, and if other liquids are utilized, the consumption can be below 50%, depending on temperature and fluid vapor pressure).
Close Loop :
This system provides total recirculation of condensation and heat of compression using seal liquid, then it is rerouted back into the pump. For extended operation with high-suction pressures, where the system experiences severe pressure drop losses, use of a circulating pump may be required.
With arrangements of total or partial recovery, the seal liquid inside the separator-recirculator chamber needs to be at the pump shaft's centerline, or near it. Arrangements can also be made for low-level makeup or high-level overflow in total recovery systems. The level controls stop operation when the casing is filled with water, due to the motor being overloaded and could potentially damage the pump.
Liquid ring vacuum pumps should never be started with full seal liquid casing in any piping arrangement. Extra provisions are made to expel liquid from the pumps should they become flooded. These safety provisions are different depending on the manufacturer.
Draining of the pump may not be needed if the seal liquid is simultaneously turned off, and if an automatic valve is installed for this procedure.
A lot of liquid ring vacuum pumps have gland arrangement, or a regular packing for shaft sealings that are installed with lantern rings and given a gland connection to cool liquid. A liquid-cooling source is required, and must operate at 5 psig beyond the operating pressure. A stock supply for the gland cooling and seal liquid is regularly used.
A supply of flush liquid and cooling is needed if mechanical seals are used. It is advisable for a clean and separate source of seal liquid for the seals to be used. A monitoring device that detect leaks in the seal is needed for double mechanical seals.
Piping :
To start, the discharge flanges and suction are indicated with arrows in the casing. These should be the same size as with pump connections.
The discharge line should be as low in elevation in relation to the pump leading to the separator. A discharge leg can be utilized on top of the discharge flange if needed. A high elevation can cause back pressure that overloads the motor and affects the capacity of the pump.
The seal liquid piping must be of same size as with the pump's connection. If using a recirculated seal system that don't utilize a recirculation pump, a larger pipe is installed to compensate for pressure drop.
Peel off the seal from the pump's openings before connecting. Scrutinize closely for any foreign objects such as nuts, rags, dirt, bolts and welding slag before attaching to the pump.
During the pipe work connection, see if the flanges fit without strain, and check if the flange holes are perfectly aligned. The included gaskets must not show in the interior bore of the pump flange or the pipe. They must fit without relaying strain to the pump casing. You may fit in a protective mesh at the suction inlet of the pump during the first few weeks.
Electrical Connections :
Regular inductions motors are appropriate for operating liquid ring pumps. The beginning loads are easy, and across-the-line type of operation is recommended. A motor controller that has a protection for over-current of fuse or heater is recommended. The current rating in full-load, as marked in the motor, should be followed when selecting the protection rating. A disconnect switch may also be installed in between the power supply and motor controller.
The pump should be operated by hand when electrical work is finished. Loosen the gland rings as necessary for the shaft to operate easily. The direction of turning is indicated by the arrow direction on the pump. Prime it, turn the seal liquid on, turn the motor on and off to see the rotation, then shut off the seal liquid. If you see an incorrect direction, reverse two of the motor leads and try it again. A single-phase, 115V supply can be installed for control circuit. Solenoid valves, level controllers, alarms and vacuum pressure switches are to be supplied with 115V only in accordance to electrical safety code requirements.
Accessories :
Liquid ring vacuum pumps are created with many accessories, some from the manufacturer or by others. An application's unique requirements, type of control and mode of operation will dictate the need for certain items. Some of the most commonly used items are covered below:
Isolation valves disconnect the pump from the system if shut down for prolonged periods or when in maintenance. Gate or full-port ball valves minimize drops in pressure that are 3 inches or above. Inlet check valves halt seal liquid and gas from going back when the pump stops operation. Double-flexible, swing-check seal or equal-type valves are installed horizontally. Inlet vacuum relief valves prevent cavitation when the pump's suction pressure falls below the vacuum relief valve's setting. It will process gas or bleed in-atmospheric air. Most of these valves are atmospheric-pressure based and will need to be periodically calibrated. Flexible connectors connect slight misalignments in process and pumps. Inlet vacuum valves control the vacuum level by bleeding gas or atmospheric air. Pneumatically-operated diaphragms on globe valves are needed for a greater degree of control.
Inlet vacuum gases mark the pressure at the inlet of the vacuum pump. Seal liquid valves manually stop the flow of the seal liquid to the pump. Strainers keep out solid particles entering the seal liquid. Compound pressure gases indicate pressure at the connection inlet of a particular seal liquid heading to the pump. Discharge separator tanks break apart the gas and seal liquid emerging from the pump. They can be floor-mounted or on a base plate along with the pump, or carried by the discharge piping as used by once-through systems. Solenoid valves automatically start and stop the seal liquid's flow straight to the pump. Circulating pumps are utilized in total recovery systems to recirculate the seal liquid. They are needed when the pumps operate on an extended period with excessive pressure drops or high suction pressures due to piping and valves, or heat exchangers. Heat exhangers relieve heat from the recycled seal liquid. Atmospheric air ejectors give suction pressures that are lower than what liquid ring pumps can do when running alone. The ejectors are added and provide inlet pressures that can go as low as 3 torr in pumps. They are similar to steam ejectors, as gas or atmospheric air from discharges is utilized as motive force in compressing gas from system design pressure similar to an inlet pressure of a liquid ring pump. A motive shut-off air valve can be installed to enhance pumping capacity. A bypass can work as well to achieve capacity above 30 torr.
Troubleshoot Liquid Ring Vacuum Pumps :
Troubleshooting is also a necessary part of a liquid ring vacuum pump's maintenance and operation. Only those who are fully qualified and carrying proper equipment is authorized for testing. Good practice dictates that the equipment be closely inspected when arriving in-site. Installation should be error-free, and all the flow switches and valves should be correctly placed as per installation diagram. Verify correct pump rotation and that the system is primed before operation. All of these preliminary checks will make troubleshooting much easier. Malfunction can be due to conditions or utility reasons, equipment failure, or both. A breakdown caused by external factors may be identified by following these steps:
Step one is to compare the design conditions, the cooling water temperature and gas composition to your existing condition.
Any change in design may be due to gas composition that affects the vacuum system. An example is when an increase in load will raise the seal liquid temperature and affect the vacuum system. Changing the gas composition from condensable or non-condensable may affect the seal liquid and vacuum. Check and see if there is no excess air leakage. It can be determined by a drop test via Institute Standards Heat Exchange for Jet Vacuum Systems. Back pressure is per design conditions. Extreme back pressure will elevate brake horsepower, and may affect the vacuum's capacity pump.
If the malfunction is not from external influences, continue to troubleshoot as follows:
Check the temperature of the seal liquid- it should be as designed. A reduced seal can be caused by a semi-closed valve in the recirculation line or a plugged strainer. See if the pump's performance or heat exchanger is fouled up. All of these can have a direct effect on how well the vacuum system performs. Use a tachometer to measure pump speed and compare with design specs. If V-belt driven, inspect the tension for any slippage. Test the pump via Institute Standards Heat Exchange for Jet Vacuum Systems, then put it side-by side with the manufacturer's design curve. An adjusting of internal clearances may be needed to keep abreast of the performance curve.
Regular maintenance is still required even if the desired vacuum is attained. Inspect the following parts:
If packing is included with the vacuum pump, dripping is normal. Excessive leakage may be due to incorrect adjustment. The packing should then be realigned, and the dripping inspected for proper cooling. Pumps with mechanical seals are not supposed to leak. Make certain the seals are rinsed with clean liquid of compatible material.
Inspect the pump for high bearing temperatures, as the normal should only be 140 F. This could be caused by excessive piping stress, a contaminated lubricant, misaligned couplings, or overgreasing.
Inspect the pump for vibration and excessive noise. This can be due to high discharge pressure, bearing failure, coupling misalignment, a water-filled casing, improperly anchored pump, or lack of air flow directed to the pump.
Inspect the amperage of the motor. A high amperage can be caused by excessive seal liquid flow, motor malfunction, or a high discharge pressure
