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.
THE ISSUE - System pressure is generally measured at the filter pressure gauge. Most systems operate at around 10 psi or a little higher. Any reading over around 20 is considered high and operating at that level for a period of time puts a strain on your system's pump and filter. High pressure is generated by three conditions: 1- the system is trying to move a larger flow of water (GPM) than it can handle; 2- there is a blockage (BLK) in the system after the pump - from the pump's discharge port. 3- There is a suction air leak [AIR] before or at the pump that cause air to build up in the top of the filter tank creating back pressure. In general pressure leaks after the pump, do not cause pressure build ups.
CLOGGED FILTER [BLK] - This is the most common problem leading to high pressure. Over time the creases of the pleats in the cartridge filter get embedded with fine debris, oils and chemicals. This embedded material will not come out with a simple spraying when you clean out the larger debris. We sell a cleaning product called "Cartridge Cleaner" which many people have found will eliminate this embedded material. One filter manufacture has suggested putting DE material into the creases of the pleats to help clean this embedded gunk out of the cartridge filter. Mix a 1# coffee can of DE in 5 gallons of pool water and pour the mixture into your skimmer. With the pump on, this action will coat the inner pleats of the filter.
SUCTION AIR LEAK - This is the second most frequent cause of high pressure and back pressure. If you have a large suction leak, the pump will probably lose prime before pressure will build up. But is you have a small suction leak, air will be sucked into the system and build up in the top of the filter tank. Over time, sometimes hours, the back pressure will build up to the point. that it signficantly reduces the water flow through the filter and out to the pool. When the pump is turn off, this back pressure will surge back through the pump and skimmer. Some pool owners have seen a 2 foot water column shooting up though their skimmer cover from this back pressure. Look for leaks in any connections that you have recently changed.
CLOGGED BREATHER TUBE [BLK] - 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.
OVERSIZED PUMP [GPM] - If you miscalculated your pump requirements, you may have a larger pump than your system can handle. Your pump is trying to push more water though your pipes and filter than they can handle so your system pressure goes up. This is also a common problem when people replace their pumps motor without regard for THP (Total Horse Power). Your motor's actual HP or total HP is the product of HP and Service Factor (SF). If you had a motor with a HP rating of 1.0 and a SF rating of 1.0, your motor's THP is 1.0. If you replace this with a motor with a HP of 1.0 and a SF of 1.5, you are replacing it with a much larger motor of 1.5 THP. If your pool was designed for a 1 THP motor, it may not be able to handle one with 1.5 HP. If the pipes and filter cannot handle the greater water flow, pressure will build up after the pump. When the pump is shut off this pressure (back pressure) will surge back through the pump, through the suction pipes and back into the pool. At this point you may want to replace your motor or a simpler (cheaper) solution would be to replace your pump's impeller with an impeller one size smaller. You can always put a smaller impeller on a motor. You just cannot place a larger impeller on the motor.