Priming for Reciprocating Pumps

mratheesh05-

Although reciprocating and diaphragm pumps are theoretically self priming they are not practical to operate in that manner. Without fluid in them they will take much longer to prime and this dry operation is what kills them, friction from operating dry, etc. The way you pipe them in is what resolves this problem. Always use check valves on the suction as near to the liquid level as possible. This prevents the fluid from returning to the suction container. Use a check valve on the discharge of the pump if flow rates permit it. This will supplement the suction discharge and keep the discharge lines from flowing back through the pump. Again, the thing that kills recip pumps is running dry. The fluids being pumped are used to lubricate the cylinder and the piston.

If the diaphragm pump you are referring to is a double diaphragm air powered one such as a Wilden, Aro or a Sandpiper it is not necessary to use check valves although it is best to do so. The bottom and tops of the diaphragm cavities have check valves in them. This is what makes them operate. As the diaphragm moves outward and increases the volume of the chamber the bottom check valve opens and lifts fluids into the chamber. When the diaphragm reverses and reduces the volume of the chamber the bottom check valve is forced closed and the upper (the discharge end) check valve is forced open permitting the fluid to advance through the discharge. When two of these chambers are put side by side with the pneumatic cylinder which moves the diaphragms is located between them the inherent pulsations are reduced in magnitude and increased by double the effective strokes of the pump. This is a good thing. The check valves installed on the piping to and from the pump prevents the loss of liquid due to failure of the internal ball check valves. This type of pump only has 4 wetted parts, the diaphragm, the two balls used as check valves and the chamber. Again, keep it wet.

Both pump types should be piped so that there is no loss of prime. Any small opening in them such as a crack or loose fitting could wreck the whole system. Keep the prime.

Good Luck, Old Salt