Mike the Poolman

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What is my swimming pool filter gauge pressure supposed to be?

July 10, 2022

Here’s one of the most common questions I’m asked: “Mike, what is my pool filter gauge pressure supposed to be?”

This is a loaded question when you realize that all pools are different from each other. Depending on how the pool was built- the size of pipe used, the total distance of pipe, how many elbows are underground, and the size of the pump each play an important part in determining what pressure your pool filter operates at. In the pool industry, we refer to this as a pool’s “Water Hydraulics”.

Twenty years ago this question was easier to answer: Determine your filter pressure (PSI) when the filter is clean and that’s your benchmark. If your filter pressure is 5 when the filter is clean then your PSI gauge should operate around 5 PSI. If your pressure is 10 with a clean filter then your benchmark is 10- there is no absolute number. Your system pressure is what it is based on your pools water hydraulics.  As the filter collects particles and gets dirty, the resistance throughout the system increases and a properly working PSI reflects this accordingly by going up in pressure.

That was twenty years ago… when all we had were single speed pumps. With the introduction of variable speed pumps to the swimming pool industry, EVERYTHING changed. Because these pumps run at different speeds (aka flow rates), the flow through the system changes and the PSI on the filter changes as the flow changes. Think about your blood pressure. Is it the same when you’re taking a walk as when you’re running? Nope. As your pump (your heart ❤️) works harder to pump blood through your body, it changes the hydraulics in your system (measured as Blood Pressure). When the speed/ flow rate of your pool pump increases ( to make the pool sweep work or to send water to the solar panels on the roof) the resistance through your pool filter changes and is measured as PSI on that funky little gauge.

So, determining what your PSI should be on your swimming pool filter can be done, but you need to measure it under the same parameters each time. When you go to the doctor and measure your blood pressure do they have you do jumping jacks before they put the cuff on you? Of course not. They try and keep you relaxed so the readings they take are approximately under the same parameters each time you visit the doctor. If you have a variable speed pump, do the same thing: check your PSI under the same parameters each time.

One more thing: after all that, do you know what I recommend to my customers? Rather than waiting for a 5 pound PSI increase on your gauge before you clean your filter (like many people prescribe), I suggest keeping it simple. Clean your filter at least every six months and most of you will be just fine. If you wait for a 5 pound increase it might take 2 years to see it on your $15 gauge (which by the way, is unfortunately as reliable as a $15 part…) and then your filters are so impacted with dirt that they need to be replaced. If you stay on a six-month schedule your filters will last longer than waiting for that 5 PSI increase (the exception is if you have a lot of foliage in your backyard).

I hope this helps. Take care,
Mike the Poolman

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