Enting of a centrifugal pump


Here is the proper way to vent a centrifugal pump after it has been installed, or the system has been opened. I am assuming the pump is empty of liquid and both the suction and discharge valves are shut.

  • Open the suction valve. The pump fills part way.
  • Close the suction valve.
  • Open the discharge valve part way. Once the pressure equalizes the air will rise in the discharge piping.
  • Open the suction valve.
  • Start the pump.

Vertical pump installations present a special venting problem because the stuffing box lantern ring connection is below the mechanical seal faces. Cartridge seals often have a vent or flush connection close to the seal faces that can be connected to the suction side of the pump for venting.

If you do not have a cartridge seal you may want to install a drilled and tapped plate between the face of the stuffing box and the stationary part of the mechanical seal. A vent line can be connected from the plate connection to the pump suction.

Dual seals can present venting problems when used in a vertical pump. Check to see that your design has some sort of a sensible venting method for the area between the dual seals.

Self priming pumps need a vent or bleed line installed between the pump discharge flange and the discharge check valve, back to the suction source.

Without this vent the pump will not be able to deliver enough pressure to open the check valve. There will be some loss through this line when the pump is operating, but the alternative is to have someone open and close the valve every time you start the pump or install some type of an automatic valve that will open and close at the correct time