This page provides a short tutorial on what is flow rate of your pump and how to calculate it.
A pump’s job is not to deliver pressure; rather, it is to deliver a rate of flow, pumping a certain amount of liquid over a given amount of time from a tank or reservoir to the outlet. Flow rates are often referred to in gallons per minute or GPM. There are some smaller pumps that rate flow at gallons per hour or even gallons per day, outputting extremely small amounts of fluid over a given time.

If you are trying to calculate and need to convert GPM to GPH or GPH to GPM, divide the GPH by 60 or multiply the GPM by 60 (because there are 60 minutes in an hour).

GPM x 60 = GPH GALLONS PER HOUR

GPH/60 = GPM GALLONS PER MINUTE

When talking about how pumps work, or looking over pump specifications, you will come across maximum and rated “flow”. While flow rate from a tap or shower head is influenced by piping, water saving heads and aerators, the pump needs to be able to generate water flow, the output of which is represented in litres per minute (l/min).
In practical applications, such pump water to where it is needed around your property or in your home, the maximum flow won’t be achieved. To understand what type of flow rate you can expect after water is pressured through pipework with rises and bends, then the “normal” or “rated flow” becomes the significant value to consider. It is also important to understand that some pumps come with controller systems that detect flow rates, boosting pressure as necessary to provide a consistent water pressure.

Maximum Flow Rate
The “maximum flow” represents the number of litres that a water pump can pressure immediately from itself without any need to travel up and through pipework. That is, how much water volume can be pushed directly out from the pump.

In practical applications, such pump water to where it is needed around your property or in your home, the maximum flow won’t be achieved. To understand what type of flow rate you can expect after water is pressured through pipework with rises and bends, then the “normal” or “rated flow” becomes the significant value to consider.

It is also important to understand that some pumps come with controller systems that detect flow rates, boosting pressure as necessary to provide a consistent water pressure.

Rated and Normal Flow Rate
Simply understood, “rated flow” is the operating condition that the pump is designed for. Another term you might hear is “normal flow”. The normal flow rate is often less than the rated flow, and represents the conditions the pump is expected to operate at most of the time.

Pumps that list both, you should pay more attention to the normal flow. The pump might support such without doing much more than simply changing the impeller size. Consult the pump manufacturer if concerned about the operational flow rates you should expect. You don’t want to end up with a pump that doesn’t do the job.

To make your task easier, pump manufacturers often provide a line graph to displaying the expected maximum flow rates based according to head distance (how high water needs to be pushed up to reach your desired access point/s). Selecting the right pump often requires some understanding of where your pump will be located and the network of pipes it will be attached to.

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