What Pressure Should My Pool Filter Be?
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When you ask the question "what pressure should my pool filter be?" it is impossible to answer this in a meaningful way except to say that your filter pressure should be less than 30 PSI. 30 PSI is the maximum operating pressure for almost all brands, makes and models of swimming pool equipment. You should never operate a pool system in excess of 30 PSI so certainly yours should be less than this number. However, aside from this safety tip about maximum operating pressure there is a very specific reason why I can not give you any more information about what your filter pressure should be.
The reason why I (or anybody else) can not tell you what your filter pressure should be is because your pool is entirely unique. There are no two pools built exactly alike. The number of pipes you have, the size of the pipes, the size and type of pump, filter, and peripheral equipment you have, the length of the pipe runs, the height of the pump relative to the pool water level...all of these things would change the pressure that your filter is (and should be) so without knowing about your exact pool then nobody can tell you what your filter pressure should be. So let's look more closely at what I can tell you about what your filter pressure should be:
Every swimming pool is unique so your exact ideal filter pressure is unknown. What is known is that 0 to 30 PSI is your instrumentation scale for pool pressure, and lower is better than higher in terms of system efficiency. High pressure indicates a higher resistance to flow in the system. A lower pressure indicates less resistance to flow which translates to efficiency in terms of fewer losses to friction and turbulence in the pipes, and less obstacles to restrict flow within the system. The better you design a plumbing system in terms of larger pipe sizes, fewer fittings and twists / turns in the pipes the more efficient the system will be and the lower the normal operating filter pressure.
Clean operating filter pressure - Every swimming pool is unique. You need to learn what your "clean operational pressure" is for your system. This means cleaning the filter media and then operating the pump in the normal way that you do (if you have multiple speeds it would be the maximum speed that you operate the pool). With the filter recently cleaned we now know the clean operational pressure of your unique pool system. It will be somewhere from 0 to 30 PSI, with lowering being optimal. Now you are able to know when your filter is starting to get dirty. On average you would clean your filter again when the pressure of your system rises 7 to 10 PSI above your clean operational pressure (but never over 30 PSI). You do not have to wait that long. This represents the longest you should wait but if you want to clean your filter sooner you can and it will only serve to help improve your system flow efficiency.
Beware of broken filter gauges - Pool filter gauges are not long lasting devices. They are cheap and last a little while befor ultimately failing for one reason or another. It is common to need to replace pool filter gauges often. If you suspect your filter gauge is not reading accurately then this is commonly tested by turning off the pool system and then removing the gauge from the filter. It should reset to zero when you remove it from the system. If it reads any other number than zero then it is defective and garbage. Replace with a new one using a thread sealant like teflon tape. Be warned to not bottom out the gauge when threading it back in. Perhaps hand tight plus 1/4 turn with a wrench. The flange receiver is plastic and it is very easy to crack pool equipment overtightening threaded connections. The pressure gauge is brass on the threads and can definitely crack the filter if you tighten it too much.
So while there is no specific numerical PSI that your pool filter should be at least now you know the safe operating range of 0 to 30 PSI and that all pool systems are different and that is why nobody can tell you what your pressure should be. Only that lower is better than higher, and that you should learn the clean operational pressure of your specific system so that you can know when your filter is dirty and needing to be cleaned.
Resistance to flow is measured as head in pools, specifically feet of head, like 30 or 60 for example. 30 to 60 feet of head resistance are real world numbers for what an average inground pool might be in terms of TDH, or total dynamic head if you were to measure it on your pool system. This information is useful to know as you can look up the pump brand and model (performance curve) and compare flow rate versus TDH. If you know that your pool is 60 feet TDH then you can also know the exact flow rate the pump is able to generate under that exact condition. This is how you design pool systems and ensure that a pump is sized suitably to a pool system. If you have a pool filter pressure that is too high it could be from a lot of resistance to flow in the pipes, but it also could be from a pool pump (motor) which is too powerful for your specific pool system. This is unfortunately fairly common, especially with the aftermarket pumps that sometimes get installed. People tend to shop with a bigger must be better approach to pool pumps and that is definitely not the right approach!
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