Boiler Feed Pumps: A Complete Guide

What are boiler feed pumps?

Pumps are mechanical machines devised for supplying water and slurries from one location to another. They can be driven by electricity, manual operation, wind energy, and convert these to the hydraulic form of energy.

They are usually classified into two types – Centrifugal Pumps and Positive Displacement Pumps.

Boiler Feed Pumps are mostly centrifugal pumps used in boiler systems for pumping feed water into the boiler. The water supply may be freshwater or the condensate water from the boiler system returned into the boiler. They are used to increase the water pressure high enough to be fed into the boiler drum. The continuous feedwater supply is crucial to boilers as it helps in maintaining the temperature of the boilers to prevent damage due to overheating.

Boiler feedwater pumps can be of any type from centrifugal pumps to positive displacement pumps depending upon the requirements based on boiler capacity and its usage and are driven either by steam or motor. Small size boilers are generally equipped with positive displacement pumps or stacked in-line centrifugal pumps. Large capacity boilers are generally operated with in-lined centrifugal pumps.

What are the parts of Boiler Feed Pumps?

The boiler feed pumps have the following parts-

Casing

The casing is a cover that surrounds the pump impeller and supports the entire pump assembly. It also assists in pressure generation inside the pump and acts as a seal to prevent leakages. The casing type which is used in feedwater pumps is called the diffuser casing.

Impeller

The impeller is a part of a pump that rotates inside the casing. It receives its energy from the shaft and adds to the fluid.

Shaft

The shaft inside a pump works to transfer mechanical energy from a motor of the turbine to the impeller blades.

Shaft sleeve

The shaft sleeve is a hollow cylindrical tube covering the shaft to prevent it from corrosion or other damages.

Mechanical Seal

Mechanical seal is an additional sealing arrangement that allows the shaft to pass through the wet area without allowing the water to pass through it.

How do the Boiler Feed Pumps work?

The function of a boiler feedwater pump is to supply feed water from the hot-well to the boiler drum. The pump takes water from the hot-well utilizing strainers and injects into the boiler drum through an orifice plate or a feed check valve.

The water axially flowing through the pump exerts a radial pressure along with the pump casing while crossing the impeller blades arranged along its path. This increases its pressure, which is proportional to the number of impeller blades along its path. The multi-stage feed pumps have two or more impellers in series to create substantial pressure. The overall pressure also depends upon the size of impellers. The high-pressure water after reaching its pressure value higher than the boiler inside pressure is then fed into the boiler.