How to Reduce High Pressure in Your Pool System

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There are several high water pressure scenarios that come up and for one reason or another have no apparent solution. You just replaced a failing motor or pump and your pressure jumped up from 10 to 20. Or your pressure crept up from 10 to 20 due to a dirty filter. You sprayed the debris off you filter cartridge like you did 50 times before but this time the pressure remained high. Or every time you turn the pump off, the back pressure is so high that it blows the cover off the skimmer or pushes the vacuum hose out of the suction port. This guide discusses these scenarios and possible solutions to correcting them.

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Step 1

Why do I have high pressure? A pool system’s pressure is generally measured at the filter’s pressure gauge; the usual range is 10 - 25 pounds per square inch (PSI.) When you installed your filter, or after a thorough cleaning, make a note of the “clean filter” PSI. This rating will be used as a benchmark for pressure tests down the line.

High pressure is generated by three conditions: 
  1. The pump is pushing a higher water flowrate than the filter can handle efficiently.   is trying to move a larger flow of water (GPM) than it can handle; 
  2. A blockage after the filter is causing a bottleneck, creating backpressure inside the filter.    is a blockage (BLK) in the system after the pump - from the pump's discharge port. 
  3. A suction air leak before or at the pump is causing an air pocket inside the filter, which in turn creates the dreaded backpressure.
  4. Excessive plumbing creates backpressure as the water’s momentum gets slowed by every turn or rise in elevation it makes.

Step 2

Clean your Filter. The most common cause of high pressure in a pool is a dirty filter. Take cartridges as an exmaple, as the material sives dirt from your pool water, the cartridge fabric more and more clogged. The clogging means the the water has fewer and smaller perforations in the filter media to squeeze through. This creates a traffic jam of water, that presents itself at spiking PSI reading on the pressure gauge. Cleaning methods for each filter type:

  • Cartridge - spray down cartridge for standard cleaning. For extra dirty cartridges, we suggest using Filter Clean.
  • DE - Backwash thoroughly, open filter to hose down grids and remove any linger DE powder and debris in base of filter. The Filter Clean chemical can also be used to fresh up old grids.
  • Sand - Backwash thoroughly. If the filter sand is older than 5 years or shows signs of clumping or channeling, replace sand.

Step 3

Check your filter media - If your filter’s pressure is spiking after changing your filter media you may have fallen into one of these traps:

  • Sand - too much sand slows filtration of the water through the tank, creating backpressure
  • Cartridge - Replaced your cartridge with the incorrect size. Though a cartridge may be the same overall dimensions as your original cartridge, the square footage may be significantly less. Less surface area, makes for less flow, then to high pressure.
  • DE - Installing the wrong grid size. Or applying too much DE powder when recharging the grids.

Step 4

Clogged Breathing Tube - Most filters have a breather tube to automatically purge air trapped at the top of the filter. This tube generally run from just under the top dome to the bottom of the tank. The breather tubes of some of the DE filters are integrated in the top manifold assembly and exit out through the discharge line. Air pressure in the top of the filter tank will build up if these breather tubes become clogged.

Step 5

Oversized Pump - If your high-pressure reading has come directly after switching out your whole pool pump or pump impeller and motor assembly then you may have incorrectly sized the equipment. A pump’s flow rate is determined by its’ horsepower (HP,) whether it is a high or medium head style and the feet of head rating of PVC plumbing. If you jump up a HP, switch to a High head style from a medium head without accounting for feet of head differences then your pump’s flow rate could make a leap by 10 or more GPM. 
If your filter was already maxing out on the smaller pump, all that extra water has nowhere to go, and the rise in backpressure begins.
Correcting an oversized pump:
  • Replace impeller with a lower HP version to lower the GPM output. This is by far the cheapest option, but make sure you refer to your pump’s schematics to determine if the diffuser needs replacing as well.
  • Replace whole pool pump with the correct match
  • If the new pump is a dual or variable speed, run only on the lower speeds.

Step 6

Closed Diverter Valves - If you have any diverter valves after the pump and filter, make sure they are completely open for max water flow. A partially closed diverter valve will throttle water flow, creating a flow bottleneck

Step 7

Enlarge Return Jets - One manufacturer has suggested replacing the return jets with ones with larger exit holes. This won't be as effective a change as something like changing your pump's impeller, but it should help.

Step 8

The key to eliminating high pressure in your pool filter system is reviewing potential flow restrictors or blockages in your system. 

Clean Your Filter - If you have diverter valves after the pump, you may have inadvertently closed off a section of your return lines. This action will restrict the total return flow and cause back pressure in your system. Open up these return lines.

Comments

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Anonymous  Posted: 6/26/2014 

What is the best way to clean out breather tube?
Thanks!

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InyoPools Product Specialist  Posted: 6/24/2014 

new_pool_owner - I would have concluded that your pump was too large for your filter and system in general, but if your system was operating at 10 psi before you had closed off the valves, the size of the pump should not be an issue. If you've check everything else in this guide, I am at a loss on how to correct your problem. I would suggest calling Hayward at 866-772-2100. Their tech staff should have some suggestions.
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 Posted: 6/23/2014 

We have a sand filter, with a hawward multi-port valve. After emptying the pre-pump filter basket, we closed the valves that lead to the pump and the pool. The pool is on higher ground than the actual pump, so this causes more pressure to begin with. After cleaning out the basket, and replacing the lid; the pump was turned back on to 'filter' and the pressure was high. We quickly turned off the pump because we realized the valves were still closed. With the pump off, the pressure is still too high. We set the filter to backwash, and then rinse, then back to filter. The pressure is still high. If the valve for incoming (into the filter) pipe, about half way-- then the pressure goes back down to about 10. But if it's wide open, then it's high at 20. We fear that we've broken something! Help!
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InyoPools Product Specialist  Posted: 4/29/2014 

Luis - If your filter pressure is going from 10 to 35 in 30 minutes, I would say that the algae is clogging it up. Try reducing the algae with an algaecide. See our guide on "How to Clean a Green Swimming Pool (Algae)".
 Reply

 Posted: 4/28/2014 

Hi, I'm very frustrated to the point that I have been thinking about selling my house. Last year we changed the de filter including the multiport valve. Something wasn't running right. The pump wasn't priming. We had to replace it the motor. Since last summer the water hasn't been clean. Now de filter pressure goes very high. Without any de the pressure is about 8 With the de is about 10 The bad thing is that after 30 mins the pressure goes up to35. Could it be the algae?
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