Back pressure

  • Last Post 30 January 2017
  • Topic Is Solved
GrandpaChuck posted this 25 January 2017

 My Hayward sand filter gage shows 30psi.  I have rebuilt the filter and the pump/motor, but pressure remains the same.   I opened the return line union and pressure drops to 10-12 psi, so flow seems to be constrained in the return line.  Back flushed the 3 jets, but none were blocked.  Removed the balls in the jet outlets and pressure dropped to 28psi.  Dug up return line to inspect it.   It is a 45 ft run of 1.5" PVC to the pool, then it is reduced to a 1" PVC pipe. The1" pipe has a 40ft run to the first of 3 jets, then another 25ft to the 2nd jet, and another 15 ft to the 3rd jet.    The pipe essentially makes a 360 deg loop around the pool, with 1.5" along one side, and then 1" around the other 3 sides to feed all 3 jets.   I think all this pipe is what is causing the back pressure.

I plan on  shortening the initial 45 ft run of 1.5" to 20ft put a T in and run the 1.5" about 5 ft to jet#3 and drilling out the small jet#3 and installing a large diameter jet (how large can I go?).  I would also put a T in near the Jet#3 to allow also attaching the current 1" return to be fed "backwards" over to jets #2 then to #1.  

Then from the T to Jet#1 from the 1.5" return pipe, continue 1.5" another 15 ft and install another T to go over to the pool and drill a new hole in the pool for a new 4th jet that will be a large one also.  Then extend the 1.5" 10 ft to the reducer and tie into the existing 1" pipe to feed the other 2 jets. Replumbing the other 2 jets would required tearing out the entire pool deck.  

This would result in a ring around the pool that is 1/4th 1.5" pipe with two large jets off of it, and 3/4th of it  1" pipe with two small jets off of it.          Hopefully that would reduce the back pressure.  What are your thoughts?

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InyoRob posted this 26 January 2017

Hello GrandpaChuck - We'd be glad to assist you. Before you change all of the plumbing, let's back up and make sure we didn't miss anything simple. Was the sand replaced? Did you use the proper #20 (.45-.55mm) silica sand? The wrong sand can cause higher pressure.

What was your normal PSI before it jumped to 30? At 30 PSI, is the flow coming out of the jets lower than it used to be when it ran at a normal PSI? If it is, the gauge must be working. If the flow is the same but the PSI is higher, the gauge needs to be replaced.

Perhaps the HP of the pump is too high. You could try replacing the impeller with the next size down. This will reduce flow and the PSI.

Again, we suggest looking for other solutions before you start redesigning the return side plumbing.


GrandpaChuck posted this 28 January 2017

Hi Inyo Rob! - Thanks for the reply.  its been at 30psi ever since we bought the house in 2005.  I have replaced the sand with the proper amount of #20 silica sand and verified the spider in the filter is clean and unobstructed.  The spider valve is also clean and in proper working order.  The gage has been replaced 3 times.  All have read 30psi.  The flow from the jets has always been the same as long as we have had the pool.  The pump motor is 1hp, and the impeller is also for a 1hp pump.

The reason I am trying to solve this is I have 10 solar panels (each is 4' x 10') and an automatic flow valve and temp sensors that I want to set up for solar heating for the pool.   The panels will not be on the roof.  They will be on angled racks on the ground, aimed at the proper angle and azimuth for my latitude. I am planning feeding the panels in parallel, however, I am concerned that adding the panels will potentially raise the back pressure and with it already at 30psi, the system will fail due to too much back pressure....  I think a 1hp motor/impeller is not going to be be oversized, considering the need to feed the solar panels, but must admit that is only a guess on my part...

The length of the 1.5" and then the reducer to 1" and the excessive length of the 1" line with the return line going all the way around the pool rather than taking the shortest route with larger pipe seems like a better approach than what seems to be a workaround to probably moving the pump/filter to a location further away from the pool?


Hope this helps....   And thanks for any thoughts on what I should do to make sure that adding the solar panels will work acceptabily...



InyoRob posted this 30 January 2017

I would agree that the reduction from 1.5" to 1" pipe is causing most of your problems. Using 1" pipe near the jets is not common. I'm not sure why the builder did that.

Changing the 1" to 1.5" should alleviate that back pressure. Come back and let us know how it turns out. Good luck!

GrandpaChuck posted this 30 January 2017

Hi InyoRob!


Thanks for the reply!

The pool is about the same age as the house (circa 1968).  Looks like the pump eq used to be at the location that the reducer is at, so when they moved it (pre-1975) to its current location they lengthened the return line by 45 ft but at least used 1.5" pipe.

Will let you know how things come out!


Thanks again for the replies!