Reducing Boiler Feed Pump Oversizing

Is it possible to reduce feed pump capacity with the oversized existing pump? If so, how? (AP_BOE_2010_P_1)

Yes, it is possible to reduce feed pump capacity with an oversized existing pump. There are several methods that can be used to achieve this, each with its own advantages and disadvantages.

**Impeller trimming:** This method involves removing a small amount of material from the impeller, which reduces its diameter and flow rate. Impeller trimming is a relatively inexpensive and straightforward way to reduce pump capacity, but it can also reduce pump efficiency.
[Image of Impeller trimming]

**Variable speed drive:** A variable speed drive (VSD) is an electronic device that allows you to control the speed of the pump motor. By reducing the pump speed, you can reduce the flow rate. VSDs are more expensive than impeller trimming, but they are more efficient and can also be used to control pump pressure.

**Throttling valve:** A throttling valve is a valve that is installed in the pump discharge line. By partially closing the valve, you can reduce the flow rate. Throttling valves are inexpensive, but they are also inefficient and can cause cavitation damage to the pump.

**Bypass valve:** A bypass valve is a valve that diverts a portion of the pump flow back to the suction side of the pump. This reduces the flow rate that is delivered to the system. Bypass valves are more expensive than throttling valves, but they are also more efficient.

The best method for reducing feed pump capacity with an oversized existing pump will depend on the specific application. In general, impeller trimming is a good option for small reductions in flow rate, while VSDs are a better option for larger reductions in flow rate. Throttling valves and bypass valves are typically only used as a last resort, as they are less efficient than other methods.