If you a looking to select the best water pump for your rainwater tank then you will see specifications like rated and maximum head and flow rates. What do they mean? What should you look for? Will the pump be adequate for your needs? The focus of this article will explore the question of rated and maximum “flow” in water pressure pumps.
Understanding Flow Rates
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).
Generally, a higher volume of water (l/min) that can be pushed through pipes by a pump, the more taps that can be serviced throughout your property and home. Yet, flow rates are also influenced by distance to the access points, pipework and elevation. This is where “maximum” and “rated” flow rates are helpful to understanding whether a water pump is adequate for your needs.
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.