The Purpose For The Brake System On A Fluid Drive
by Turbo Research Inc.
There is only one purpose for having a brake on the output shaft of a fluid drive; to aid in the operation of the boiler feed pump by stopping the boiler feed pump shaft and to keep it from rotating when the pump is out of service.
There are certain boiler feed pumps which are designed and built in ways that will cause them to gall and consequently to seize if they rotate for more than a few seconds or a few minutes at low speed with no or low flow through them. Typically, these pumps have stainless steel components that can rub together. They are often the higher performance, higher pressure pumps, but this is not always the case.
There usually is sufficient experience with each boiler feed pump over the years to know if that pump has or has not seized when it was at low speed during those times when a) the pump was out of service and simultaneously, b) the brake is imperative.
For those boiler feed pumps which have not seized when they were operated at low speed for several hours, or for which the manufacturer indicates that no problem will arise by operating at low speed with low/no flow, the brake is not required, and there is no value in using it.