by Mark Garcia May 6, 2015
The pool filter pressure gauge is an under-appreciated and sometimes neglected device. But it serves a very important function, letting you know the pressure inside of your filter tank, which translates to how well the entire filter system is operating.
What many people don't know is that every filter system operates at a different pressure. Your filter may be clean and normal at 9-10 psi, but your neighbor's filter gauge could run higher, and be clean at 15-16 psi. Some systems with very low resistance can run very low pressures, barely registering, while other filter systems can run quite high, pushing 30 psi when the filter becomes dirty.
Today's post is to discuss how to use your pressure gauge to help diagnose circulation or filtration problems, how to know if your pressure gauge is trustworthy and we'll also talk a little bit about the air bleeder assembly, which most filter pressure gauges are screwed into.
Common question, but each pool filter system has it's own "pressure personality", and there isn't a singular pressure range that's correct for all pool filters. If anything could be considered "normal", it would be about 10 psi. Most filter systems are designed to operate in the 5-15 or 10-20 psi range. The way to find out your particular correct pool filter pressure is to clean or backwash the filter thoroughly and empty the pump and skimmer baskets. Start up the filter, and when it reaches full head, note the pressure gauge reading. That is your clean, or starting, pressure. It should never drop lower than that (see below), and when it rises 5-10 psi above that starting pressure reading, it's time to clean the filter again. The pool filter pressure should be steady within this range. When it's outside this range, either very low or very high, then you'll know something's wrong. Some gauges allow you to set the clean and dirty range, or you can write it on the filter tank with a marker.
When the pressure is lower than normal, this usually indicates a flow problem before the pump. Something is blocking or restricting water flow into the pool pump. It's never a problem after the pool pump, because after the impeller, the pool water is under pressure, and obstructions result in higher than normal pressure. It bears repeating: when pool pressure gauge reading is low, look for the problem at the pump or before the pump. These are some common causes of low filter pressure:
When the filter pressure is higher than normal, this also indicates a flow problem. But here it's after the pump, not before. High pressure usually indicates a dirty pool filter, time to backwash or pull out the filter cartridge for cleaning. Be careful with high filter pressure, as filter tanks can rupture with deadly force. Always keep your hand on the switch and your eye on the pressure gauge when starting a pool filter - if you see the pressure spike - to 30, 40, 50... shut off the pump immediately and look for one of these problems below.
A pool pressure gauge that never goes higher (or lower) is suspect. Is it working - does it go to zero when you shut off the pump? Is it properly sized; 0-60 psi is the standard pool filter pressure gauge. I have seen some filter systems that operate on clean pools that have a very small range, and they can run for months and only gain a couple of psi on the pressure gauge. These filters are generally oversized with smaller pumps, which is a good way to go, in my opinion.
Give it a flick with your fingernail to see if the needle bounces. Shut off the pump and the gauge should go to zero. If the gauge stays at zero when you turn the pump on, the air bleeder assembly under the gauge is probably clogged with pollen and fine debris. Remove the gauge and the assembly and ream out the works. If the pressure gauge needle stays in place when you shut off the pump, the dial is likely bent. Gauges can also become faulty and rust where the pin holds the needle and the face/dial can become warped, especially on the plastic gauges. If your filter pressure gauge is broken, it's a simple part to replace. Just be sure to use Teflon tape on the threads before screwing it into place.
The air relief valve, aka the bleeder valve, allows you to bleed trapped air from the pool filter. In practice, it's meant to be opened after you start the pool pump, because air can become trapped in the top of your filter tank, which results in less effective filtering. When water begins to spray out of the air relief, just close up the knob. If your filter air bleeder is leaking water, see below.
It's probably not the gauge that's stripped, but for sand filters with top mounted valves, the gauge screws into plastic threads in the multiport valve housing or body. If the pressure gauge is cross threaded, this can damage the threads. A 1/4" NPT tap can be used to gently re-cut the threads again, and also using extra Teflon tape around the pressure gauge threads. If that fails, you can tap it out larger, to 5/16", and then use a threaded brass insert of the right size. If that fails, you will need to replace the valve body (or the entire valve), if the leak is excessive.
Rarely do pressure gauges leak water, but they can. A 1/4" pump plug can be used in place of the gauge temporarily until you buy a new pressure gauge. Usually the leak of a pressure gauge is actually the air relief assembly leaking water, and not the gauge. A leaking air relief valve can often be repaired with Teflon tape, or by replacing a small o-ring on the knob, or by installing a new air relief valve. The old Pac-Fab air bleeder fits many filters. For others, like Hayward filters, visit our parts department to order the correct air bleeder parts for your pool filter.
Pool filter pressure gauges are typically a 0-60 psi gauge, with a 1/4" NPT threaded attachment. The threads can be on the bottom of the gauge (used on top of DE, cartridge and side mount sand filters), or the threads can be on the back of the gauge (backmount) for use on sand filters with the valve on top. A 0-30 psi gauge can also be used for pool filters. Jandy has a 1/8" pressure gauge that is used on their pool cleaner Energy Filters, but this won't fit pool filters without a reducer bushing. Digital pressure gauges are available, but they are costly. In fact, digital gauges can be 10-25 times the cost of traditional analog pressure gauges. Oil-filled pressure gauges with a stainless steel body are more durable than regular gauges with plastic or powder coated steel cases, but they're not necessary.
Thanks for Reading!