Purchasing pumps: Single-stage or two-stage?
There are several questions you need to answer before making your selection
There has always been a big controversy about what type of pump to choose when you are writing specs for a new piece of apparatus.
If price is a concern when buying your new pumper, then the choice and size of the pump is another area you need to investigate. First of all, do you need a 2000gpm single-stage or two-stage pump? Will a 1500 gpm or 1250 pump suffice?
The questions you need to ask yourself go on. What do you need to accomplish? Do you need to pump a lot of volume or pressure? Or, in the case of a two-stage pump, both? Deciding on what type of firefighting operation you normally encounter and if you also have other engines in your district that you use as strictly supply pumpers is another concern.
A single-stage pump has one dual suction impeller that takes water in both sides and provides water discharge to all discharge gates.
A two-stage pump has two impellers operating side by side, which gives, depending what part of the country you're from, the pump operator, MPO or engineer a choice by the use of a transfer valve.
This transfer valve has a volume or pressure position. Obviously a two stage pump can reach higher pressure than a single stage pump. This might be advantageous in operating at a high rise building or for extremely long stretches, for example.
The newer single stage pumps coupled with today's higher horsepower diesel engines are significantly more efficient and provide better performance than pumps from 20 to 30 years past.
Again it comes down to having the right tool for the right job. You and your apparatus committee ultimately have to decide what is the right choice for your department and the type of operation that you are trying to perform.
If you go on the websites of Hale, Waterous and Darley, you can get some useful info on the various types of pumps and their operation and efficiencies.
Another consideration when designing your new pumper is whether you are planning on installing a foam system based on Class A or B Foam, or a complete CAFS.
CAFS will add a considerable cost to the apparatus. If you are planning this option, make sure that your members understand everything about CAFS and how to use it at a fire scene or you might be wasting your time and money having a system installed if you don't plan on using the system on a fairly regular basis.
In any case, proper planning is the key to any apparatus purchase. Install what you feel your department really needs and investigate a great deal before you settle on your options.
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