Revolutions per minute (rpm) vs. Flow: Static Eyeballs vs. Variable Orifice Returns. Figure courtesy Eco-Blu Pool Components LLC

By Sean Walsh & Zach Schulz

When looking at rpm versus flow (see Figure 3), research shows as the flow/speed (rpm) of the system increases, the less efficient a smaller pool return becomes at providing a given flow. The smaller the orifice, the greater the restriction and the harder the pump needs to work.
On the other hand, a variable orifice return will self-adjust, allowing the system to operate more efficiently (use less energy) when obtaining a given flow rate at a lower speed (rpm).

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Revolutions per minute (rpm) vs. Pressure: Static Eyeballs vs. Variable Orifice Returns. Figure courtesy Eco-Blu Pool Components LLC

By Sean Walsh & Zach Schulz

In terms of rpm versus pressure, research shows as the pump speed/flow rate increases, so does the pressure on the system. This increase in pressure can result in the reduction in the life expectancy of the filtration system. The added pressure, and restriction it creates, is directly related to the size of the pool return. The smaller it is, the greater the restriction as flow increases. Further, this restriction also demands higher speeds (rpm) from the pump for a given flow when compared to a larger pool return.
Typically, a pump will operate at low-flow/low-speed (rpm) for the majority of its life. However, when there is a need for the system to increase its flow/speed (rpm) (e.g. during a heating cycle), and a variable orifice pool return is installed, it will open, based on the flow rate, and reduce unwanted restriction on the system. This also allows for greater flow at lower pump speeds. Further, overall stress on the system is reduced and less equipment failures are likely to occur.

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By Sean Walsh & Zach Schulz

One way of skirting around issues related to pool components not being designed around the low-flow or variable-flow concept and/or over agitation is to set the pump to operate at a low-flow rate (to save money) and install smaller orifice returns, in correlation to the flow rate, to enhance pump performance (i.e. agitation/circulation). However, as stated earlier, certain components require higher flow rates to operate properly (e.g. heaters, chlorine generators, etc.). Therefore, in this scenario, one could keep the flow low, but when this equipment needs to be operated, the flow needs to be increased, which will then lead to over agitation as well as increased back pressure and energy usage.

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By Sean Walsh & Zach Schulz

One challenge that has made it difficult for some business owners and service providers to offer their clients newer pump technology is the simple fact most swimming pool components were not designed around this low-flow or variable-flow concept.
In fact, most system components on the market today were created for single-speed pumps, which blast large volumes of water at a constant high-flow rate for short operation cycles, rather than using a low-flow rate for much longer operational periods. Therefore, when a pool owner switches from an inefficient pump to a variable- or two-speed pump, compromises have to be made to the overall pool system.

Read the full article: Circulation