industrial plants like yours use many different types of pumps one of the most common types of pumps that plants depend on is a centrifugal pump centrifugal pumps use centrifugal force to move process liquids one basic requirement that affects the operation of all centrifugal pumps large or small is that they must be primed in other words the pump casing and suction line must be completely filled with liquid before the pump is started if a centrifugal pump isn't primed it won't operate properly now some centrifugal pumps stay filled with liquid when they're shut down these pumps are often called self priming pumps sometimes they have components such as check valves that maintain the prime after the pump is shut down in other cases the system is built so that liquid does not drain out of the pump after it is shut down so with some pumps you may not have to prime the pump but this isn't always the case in some cases it may be necessary to prime the pump manually a common way to prime a centrifugal pump is to open the pump suction valve and the vent valve opening these valves allows liquid to fill the pump and air to escape in order for this to work however either the level of liquid to be pumped must be higher than the casing of the pump or the suction pressure must be great enough to force the liquid into the pump if the pump is handling a hazardous liquid the casing vent should be piped to equipment that will prevent the escape of hazardous liquids if the liquid level is below the pump casing or the suction pressure is too low a variety of devices can be used to prime the pump in some applications a vacuum system is used to draw air out of the pump by drawing air out this system Prime's the pump once the pump casing is full of liquid the vent valve is shut and then the pump driver is started centrifugal pumps can be started up and shut down in a number of ways the procedures that are used often depend on the type of centrifugal pump you're working with the type of driver that's used why the pump is being shut down or started up and company operating procedures we're going to look at some basic steps that can be followed to start up and shut down most centrifugal pumps but keep in mind that you'll always need to follow the specific procedures used by your company you should also be aware of the effect that starting or stopping the pump will have on the process this is the pump we'll be using it's a single stage centrifugal pump and it's part of a system that supplies cooling water to a facility the pump is driven by an electric motor water flow into and out of the pump is controlled by isolation valves the pump shaft is sealed with a mechanical seal one of the first steps in the startup procedure is to check the pump suction pressure in this case that's done by checking the level in the system expansion tank and making sure that the pressure in the expansion tank is correct on this pump the expansion tank ensures that there is sufficient suction head for the pump also the pump and it's driver should be checked for obvious signs of damage on some pumps auxiliary equipment may have to be checked before startup for example the lubrication systems must be checked also sealing liquid to a mechanical seal may need to be lined up to the seal once the preliminary checks are done the next step is to line up the valves in the cooling water system this step is based on the pump startup procedures which specify the valves to open or closed and the proper order on this pump the suction isolation valve is opened opening this valve provides a path for liquid to enter the pump the operator then starts the pump and checks it to make sure that it's operating properly these checks often include checking the pump suction pressure and discharge pressure checking the bearings for excessive vibration or overheating listening for unusual noises and checking the pump for signs of leaks venting the air from the pump while the suction valve is open will fill the pump with liquid this step is often referred to as priming the pump the discharge valve on this pump remains open when the pump is shut down so it's already in the proper position to run the pump on other pumps however the discharge valve may be shut when the pump is shut down in these cases the procedures may say to leave the discharge valve shut to partially open the valve before the driver is started or to fully open the valve before the driver is started in our procedure the discharge valve remains open when the pump is shut down so there is a flow path for the cooling water into and out of the pump at this point the control room should be informed that the pump is ready to be started the operator then starts the pump and checks it to make sure that it's operating properly these checks often include checking the pump suction pressure and discharge pressure checking the bearings for excessive vibration or overheating listening for unusual noises and checking the pump for signs of leaks on some pumps additional checks may have to be made to be sure that the pump is operating properly for example it might be necessary to check the amount of current that the motor is drawing okay that's a basic centrifugal pump start up now let's look at a centrifugal pump shutdown when the pump is no longer needed the operator receives permission and shuts off the pumps driver the running pumps discharge pressure should be checked to see if it's normal if there's no drop-off in pressure the pump switch is successful once the pump is stopped its suction isolation valve is closed in this example that's all that's required to complete the pump shut down on some pumps the suction and discharge valves are both when the pump is shutdown this will completely isolate the pump from the system as an operator you may be responsible for the proper operation of many pumps to ensure that they're operating properly you need to know what to look for to identify potential problems we're going to look at three components associated with centrifugal pumps and at some of the indications of problems associated with these components let's start by looking at packing and mechanical seals on most pumps the point where the pump shaft leaves the casing is a place where leakage can occur to prevent process liquid from being lost or contaminated either packing or a mechanical seal is often used to seal this area when packing is used operators should check to make sure that there is a small amount of leak off to lubricate and cool the packing if there's too little leak off the packing can dry out and burn if the packing dries out the pump should be shut down so that the packing can be replaced on the other hand if there's too much leak off the efficiency of the pump may be affected to control the leak off the packing must be tightened this should be done by tightening the nuts on the packing gland one flat at a time tightening the gland nuts one flat at a time ensures that the gland does not become cocked also this method ensures that the packing is tightened slowly and helps to prevent over tightening the correct amount of leak off may be different for each pump in a process or for each pump in a plant you should be aware of the leak off requirements for the pumps you're responsible for now if the pump has a mechanical seal you should check to make sure that there is no detectable leak off leak off from a mechanical seal is an indication that the seal has been damaged and should be replaced if you find a seal that is leaking you should report it according to your company's procedures there are other checks that you may have to make on a pump that has a mechanical seal for example if the seal is supplied with an external lubricating liquid the lubrication system should be checked for proper operation these checks may include verifying that the lubricating liquid is being supplied to the seal at the proper flow rate and pressure if the lubricating liquid is not supplied correctly the seal may fail prematurely if the lubricating system flow rate or pressure is not correct there may be a problem in this situation you should check the pump that supplies the lubricating system and make sure that the valves in the system are positioned correctly in addition to checking a pumps packing or mechanical seal it's also important to check the bearings on the centrifugal pumps and their drivers one of the easiest ways to check a bearing is to touch the bearing housing this way you can check the bearing for both overheating and excessive vibration if you feel excessive vibration it may be an indication of a problem with the pump problems such as bent shafts broken impellers and bad bearings can cause excessive amounts of vibration the cause of excessive vibration can often be determined using vibration analysis equipment devices such as thermometers temperature recorders and thermocouples can be used to obtain accurate indications of bearing temperatures that can be compared to previous values to see if there is a problem for example if the temperature of a bearing is higher than normal it may be an indication that the bearing is not being properly lubricated or that it is worn out how the lubrication of a pumps bearings is checked depends on how the bearings are lubricated some pump bearings are lubricated with Greece through fittings like this these bearings should be greased periodically in accordance with the plant's lubrication program some bearings are supplied by a grease cup when you check these bearings the lubrication program may require you to tighten the grease cup so that additional grease is provided to the bearing not all bearings use grease as a lubricant many pump bearings are lubricated with oil on some pumps an oil reservoir is part of the bearing housing and there's a sight glass that you can use to determine the oil level on other pumps an oiler is used to supply oil to the bearings when an oiler is used the level in the Oilers bottle should be checked if the oil level is too low the reservoir or the bottle should be refilled under the heavier loads the bearings in these pumps require a forced feed system to ensure proper lubrication a force-feed system may contain its own pump reservoir heater cooler and filters the pump should be checked to make sure it is producing the correct pressure the oil level in the reservoir should also be checked this can be done using a level indicator or through a sight glass if the level is too low the forced feed system may not adequately lubricate the bearings and they could be damaged in this case oil should be added to the reservoir in accordance with company procedures also the cause of the low level should be investigated and reported to supervisory personnel if the 4-speed system contains a cooler or heater it should be checked for proper operation otherwise the pumps bearings could be damaged if the temperature of the oil is too low there may be too much cooling water flow or the system's heaters may not be operating properly on the other hand if the temperature is too high there may be too little cooling water flow or there may be a problem in the cooler or in the cooling water system in either situation the temperature of the oil leaving the cooler must be adjusted so that the pumps bearings can be properly lubricated the oils temperature is often controlled by adjusting the amount of cooling flow many 4-speed systems also contain filters or strainers that are used to remove solid particles from the oil these particles could enter a bearing and cause damage during normal operation there is a drop in pressure as the oil passes through a strainer or filter this drop in pressure is often referred to as a differential pressure or Delta P as a filter or a strainer collects particles the pressure drop across it will increase if the pressure drop becomes excessive there may not be enough oil flow through the forced feed system and the pups bearings will be damaged to prevent this the strainer or filter element must be cleaned or replaced filters and strainers can also be found upstream or downstream of many centrifugal pumps where they're used to remove solid particles from the process liquid as particles buildup in a filter or stranor it restricts the flow of processed liquid and the difference in pressure across the filter or strainer will increase if a filter or a strainer is located upstream of the pump excessive particle build-up could cause the pressure at the suction of the pump to decrease if the pressure becomes too low the pump could cavitate and be damaged if a filter or a strainer is located downstream of the pump excessive amounts of solid particles will decrease the flow of fluid to downstream equipment to determine if the debris in a filter or a strainer is affecting flow through the process the readings on pressure gauges upstream and downstream of the filter or strainer can be compared to each other if the difference in pressures goes above a predetermined limit the filter or strainer must be cleaned or replaced if a centrifugal pump is not completely filled with liquid that is if it's not primed it doesn't have the ability to pump liquid one way that a centrifugal pump can lose its prime is for air to enter the pump casing causing the pump to become air bound there are several ways that air can become trapped inside a pump casing for example during startups the casing and suction piping may have to be vented if a sufficient amount of air remains trapped the pump will not operate properly another way that air can get into the casing is through a leak the suction of a centrifugal pump is normally at a low pressure and this low pressure could draw air into the pump through leaks or the packing on some pumps the packing is exposed to the same low pressure that exists at the pump suction on these pumps the packing is often supplied with liquid from the discharge of the pump this liquid cools and helps seal the packing if the flow of liquid to the packing is not adequate air could be drawn in through the packing air can also get into a pump after maintenance for example if piping has been worked on air in the pipes could make its way to a pump if the air becomes trapped inside the pump the prime could be lost there are several ways to tell if a pump is air bound one way is to listen to it a pump that's partially filled with air may produce a rattling noise similar to the noise a pump makes when it's cavitating however the noise caused by air binding may be only intermittently there are other noises that may be associated with air being drawn into a pump for example if the pump has leaks on the suction side you may be able to hear air being drawn into the pump in some cases it may be possible to see the flow path for the air being drawn into a pump with some pumps a vortex may form as liquid is pumped from the sump if the vortex is drawn into the pump suction it provides a path into the pump when the pump is partially filled with air the discharge pressure may vary greatly also on a pump that has an electric motor as a driver the amount of current drawn by the motor may vary greatly on the other hand when a pump is nearly filled with air the discharge pressure may drop to zero and the pump noise may become a very quiet hum in this situation when an electric motor is used as the driver the amount of current drawn by the motor will drop significantly a problem that's similar to air binding in a pump is vapor binding with vapor binding many of the same symptoms may be noticed however the causes of vapor binding are slightly different from the causes of air binding vapor binding occurs when a pump loses its prime because vapor has become trapped in the pump the vapor often forms in other parts of the process and is carried along or entrained in the process liquid until it becomes trapped in the pump formation of vapor in a process is affected by the liquids temperature and pressure process changes that increase the liquids temperature or decrease its pressure may cause vapor bubbles to form and become trapped inside a pump one condition that causes vapor to become trapped in a pump is suction pressure that's too low the pressure decrease in the pump suction can cause vapor bubbles to form when this happens the vapor could separate from the liquid and become trapped in the pump as more vapor collects the pump becomes vapor bound and may not be able to pump any liquid if the liquid temperature is too high the same basic process happens the high temperature causes vapor bubbles to form when this happens vapor may collect inside the pump and the pump could become vapor bound venting an air bound or vapor bound pump can restore the pump to nor operation however this may be only a temporary fix if there are leaks in the suction piping if the liquids temperature is too high or if the suction pressure is too low some other corrective action must be taken some of the fixes are easier to figure out than others and can be accomplished immediately for example if a pump has a packing leak that is drawing in air then adjusting the packing may stop the problem on the other hand if the pump is vapor bound and it's due to low suction pressure or high liquid temperature then the way the process is operated may have to be changed or the problem may be an indication that a component in the system is not operating properly and the component might have to be repaired or replaced