Pump Theory

Lesson 3 discusses the aspects involved with Pump Theory and Operation.

Shown above a Waterous Co. Single Stage Pump With The Chain Drive gear box and Mechanical Seals. However, let us give just a very Brief overview of what we mean by pump theory as it relates to our use of them in the Wildland Fire Service.

Pump Theory can take on several different versions of the same definition yet it all boils down to the fact that we use an impeller to impart(introduce), a form of mechanical energy to a fluid of a certain density, whereby we can perform some task with that fluid or simply transport the fluid to another location. Part of this theory is that we use 3 separate but interrelated aspects to make this happen. 1. We must have a fluid that is non compressible. 2. We must have a way to introduce an energy to the fluid so we can accelerate this same fluid and 3. We have to have a way of harnessing this energy we just created.

Waterous Co. Single Stage Pump Cutaway. Here Opens in new tab.

In the Fire service the only non flammable fluid we have to fight fire with that is cost effective and offers the best density is WATER. So with this water, energy is given to it by introduction of the impeller. The impeller has a certain diameter, and rotates at a certain speed, when the water enters the eye of the impeller its velocity is low, but as the water travels along the impeller vane towards the periphery, its velocity is greatly accelerated.

At this point we have now given the water, having density of mass, an acceleration and now it carries with it a force.

We are able to use the waters density against itself to shove water straight up hills or even inside fire suppression pipes in high rise buildings using this principle, or over vast distances.

So we have our first part, the water. Then the second part, is the impeller acting through a motor with a rotational speed gives the water its energy. Three, we harness this energy by the pump housing, hose etc. and can transmit it over long distances or up hills through our hose. A point of fact about hydraulics is this: Pumps are only able to build pressure for use after attempting to move water through a confined structure through a restriction. This means your restriction (nozzle) is at the end of a hose (confined structure) and provided by the pump that is able to increase flow by having a dual flange impeller. A dual flange impeller will NOT allow the water to slip past or over the vane causing a loss in flow, such as commonly found in trash pumps.