The pump to select?
The pump to select? How to determine the pump to select? The correct pump. (exit at any time by scrolling to end of this document) A centrifugal pump performance curve is simply a tool which enables anyone to literally see how a pump will perform in terms of HEAD and FLOW. Every pump will be capable of developing a specific PRESSURE (PSI or BAR measurement translated into feet or meters head) at a specific FLOW (normally represented in gallons per minute or liters per minute) A note on establishing flow. If you do not know the flow you require it is relatively simple to determine if you just take it one step at a time and add all the outlets together. For industrial applications, for washing, heating or cooling the equipment will have a flow and pressure on the design plate. Flow in a system can be established by understanding the requirements. In our example we will use a house which has two bathrooms, a dishwasher, a washing machine, an electric geyser in the roof and a guest toilet with hand basin. Also a sink in the kitchen and an outside shower for the pool area. So we have the following outlets :- Bathroom hand basin taps 4 Bath taps 4 Shower taps 6 Toilet cistern 3 Guest basin tap 2 Sink in kitchen 2 Washing machine 1 Dishwasher 1 TOTAL 23 If we assume each tap will be required to deliver 2 gallons per minute (GPM) at 44 PSI or 3 bar, then we simply need to determine how many outlets we would expect to operate at any one time. It is unlikely that all toilets, all showers, all baths etc will be on at the same time. A good method is to take a third of the total outlets as your flow need for any single moment in time. In our example that represents 23 divided by 3 or 7.6 make it 8 outlets. This means a flow requirement of 8 X 2 = 16 GPM or 60 liters per minute. A note on the concept of PUMP HEAD. Think about the highest point of your body, the top of your HEAD. It is the same idea with pump language, Head refers to the measurement in feet or meters from the center line of the pump (the pump shaft center line) to the highest point to which the unit is expected to deliver fluid) The above definition of head is limited to what is known as the Static head. in other words, this is the measurement of the vertical height which should never change, it is static. Lets say you are needing to deliver water from a tank at the bottom of your garden, to the geyser at the top of your roof. The garden has a steep bank from the house to the lower area where the tank is located. The house is a double story. If one measures the height from the base of the tank […]