Monthly Archives: October 2015

Choosing the Right Fire Pump

There are a large variety of fire pumps available in the market today, fabricated by several different manufacturers. Many in the industry are interested mainly in the hydraulic performance of the pump in question – specifically the gallons per minute (US GPM) and the pressure boost (US PSI) of the pump. If a pump can be found to deliver a specific GPM and PSI, and it is listed by a trusted 3rd party agency, then the evaluation often ends there. Rarely is the “type” of fire pump considered. In this article we will discuss the various types of UL/FM fire pumps available in the market today, in an effort to point out the advantages and disadvantages of each. We will focus on centrifugal fire pumps that carry either a UL or FM label, and are used specifically for stationary fire protection.

Horizontal Split Case

Horizontal Split Case (HSC) pumps are given their name due to the “split”” design of the casing, where the casing cover can be lifted off of the pump to expose the internal components. These components include the impeller, bearings, pump shaft, and so on. HSC pumps have two bearings, located on either side of the impeller, which are useful to withstand the large amount of vibration and thrust forces often caused by water turbulence in the suction piping. The pump casings are often designed to handle higher working pressures, and are often heavier. The durability of the HSC design allows the pump to be used for very large water flows – often in excess of 5000 GPM. It should be noted that an HSC pump is not always mounted horizontally, it is possible to have the same durability design features and have the pump designed to be mounted vertically.

Horizontal Split CaseThe HSC pump is often connected to either an appropriate driver by a coupling or driveshaft. When mounted horizontally, this can take up more floor space. It is because of a concern for floor space, that you do not see as many HSC pumps for flows below 1000 GPM as in prior years.

The impeller of an HSC pump is dependent on even water flow entering the eye (or inlet) of the impeller. There are two entry points of water into an impeller of an HSC pump, which is where the term “double suction” is used. If water enters the impeller unevenly, hydraulic imbalance can occur and cause stress to the pump shaft or bearings. The need for smooth, laminar flow in the suction piping of an HSC pump is precisely why the NFPA 20 has strict rules regarding the length of straight piping required on the suction side of an HSC pump (see NFPA 20 2013 4.14.6.3.1, and 4.14.3.1). As a general rule, the larger the volume of water to be pumped, the more important it is to have smooth laminar flow of water into the pump casing. Continue reading