HOW
TO MAXIMIZE THE LIFE
OF YOUR SEALLESS PUMP
OF YOUR SEALLESS PUMP
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to Maximize the Life of Your Sealless Pump? Here are 10 ways to achieve longer life in a mag-drive or sealless pump 1) Before the pump can be started or even “bumped” to check rotation, make sure it is at least partially filled. Most sealless pumps use silicon carbide bearings, which have very little wear after many years provided they are used on clean fluids. These bearings require that the pumped liquid be used to both cool and lubricate the surfaces. If the pump has no liquid or very little liquid, the bearings will heat rapidly causing loss of the lubricating film and the bearing surfaces will crack and seize together. 2) Whether the pump is in an existing or new operation, it is important to keep particles and debris from blocking the internal clearances. In new services, a temporary line strainer with a fine mesh screen should be installed and later taken out of service if the fluid has no chance of debris. Occasionally, even clean services will have particulate as a result of tank or process equipment degradation. Standard mechanically sealed pumps can pass some larger solids without affecting its operation. A sealless pump with its many advantages cannot tolerate the blockage of its internals by large solids. The amount of solids that can be passed and their sizes vary between manufacturers. When in doubt, install a strainer with maximum surface are on the pump suction. Minimum 8:1 open area to pipe ratio. 3) Control the flow from your pump on the discharge side only. The suction to the pump should be as open as possible taking into consideration how much liquid is above the pump along with restrictions such as piping losses and fluid temperature. Controlling the pump form the suction valve can induce erratic performance, cavitation, and overheating. 4) When you start a sealless pump, it is best to have the discharge valve three quarters closed if possible. When a pump is started with the discharge wide open into an empty pipe, it will run to its maximum capacity until the pipe is filled and some back pressure is produced. This condition is referred to as “running out on the curve”. This can overload the motor and cause magnet decoupling, which produces instant temperature rise due to eddy current losses. Internal bearing circulation can be reduced and stresses caused by running at less than “Best Efficiency Point” (BEP) can cause early failure. If the pump will always start with the valve open and an empty pipe there are protective options available. 5) Make sure the pump suction and discharge are not stressed from unsupported piping. This can wreak havoc with internal clearances. 6) If you are pumping at higher temperatures, try to bring the pump temperature up gradually a few degrees per minute. Sudden temperature shocks can produce stress cracks in bearing surfaces and various metals and plastics expand and contract at different rates. 7) Monitor your pump through the use of Motor Load Monitors, pressure gauges, vibration, temperature and flow meters. If your sealless pump is metallic construction, the use of thermo probe sensors can be handy because of the higher than normal temperature rise due to eddy current losses. Motor load monitors, pressure gauges, and flow meters can show where the pump is running on its curve and signal or shut down the motor if the pump is in an upset condition. 8) Make sure that the gaskets, o-rings, and seals are compatible with the fluid you are pumping. Some pumps have several internal o-rings, which must be compatible with all the fluids the pump will contact. A swollen, degraded, leaking gasket can defeat the purpose of a sealless pump. Check a good elastomer guide. 9) If the pump is a frame mounted design with an oil lubricated bearing drive and flexible coupling, make sure the pump coupling and motor have been aligned after installation and again after a start-up period. Check the motor rotation only after filling the pump. 10) If your fluid is close to its vapor pressure or boiling point before it is pumped, many sealless pumps will add a considerable temperature rise to the fluid. As the internal fluid is heated and circulated from the high-pressure side of the impeller back to the low-pressure side, it picks up heat from eddy current losses across the metallic containment shell. If this heat exceeds the fluid’s vapor pressure, the liquid will flash causing loss of bearing lubrication. |
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