Centrifugal Pump Components and Priming Procedures

Main Components of a Centrifugal Pump

The Impeller

The impeller consists of a number of fins with curves designed to provide a smooth flow between the sheets.

Pump Body

The body (or casing) is the part that contains the impeller and where the fluid collects. It transforms the kinetic energy gained by the fluid through the impeller into useful pressure energy. The pump body is designed with an entrance and an exit for the fluid.

The Axis or Shaft

The axis is the element that transmits the torque produced by the engine to the impeller. It is robust and possesses a perfect finish.

Bearings

The bearings consist of a ring made of suitable material, such as bronze, which is as friction-resistant as possible. They dampen the effects of wear and reduce friction.

The Gland

The gland is responsible for the stuffing pressure against the pump body to prevent leakage of fluid through the center of the pump. It functions like a flange with two holes, through which it is fastened with screws while the center shaft rotates the pump.

Tow or Packing

The tow is a rope in round or square form and is manufactured in different materials and braid types. There are two main types:

• Soft stuffing: Fits better to the contour of the shaft.
• Hard stuffing: Its placement is more difficult as it is more rigid.

The Priming Process

Priming is the process in which gas accumulated in the body of the pump and the suction pipe is removed. The inner parts of the pump, whose lubrication depends on the liquid being pumped, can seize up if the body is not completely filled with liquid before starting operation. A centrifugal pump start is perfect when the pump body, impeller, and suction pipe are full of the liquid to be pumped. Depending on the suction type (positive or negative), the initiation process is different.

Positive Suction Priming

• a) Open all suction valves to let the liquid enter the tubing and the body, then close the discharge valves.
• b) Loosen the drain plug located on the discharge flange to dispose of all air content.
• c) When the fluid flows as a continuous stream (with no air bubbles), the pump is primed.

Negative Suction Priming

To fix this, ejectors are used, producing a vacuum superior to that which reigns within the pump. The process is performed as follows:

• a) Open the suction valve and close the discharge valve.
• b) Implement the ejector and remove all air from the pump and suction line.
• c) When the ejector exit pipe ejects the liquid in a continuous manner, the pump is primed and ready for operation.
• d) The ejector is allowed to operate until the pump is running and has reached operating speed.

Testing the Priming

To test the priming, start the pump operation after opening the tap and drain. If an uninterrupted water jet leaves, the process has been correct; otherwise, the process must be repeated.