Pentair / Jandy system pressure problem

[jrowlandesq]

My pool was rebuilt in 2005. The company installed all new Jandy equipment including a Jandy Stealth JHP 2.0 pump, the Jandy Aqua pure chlorine generator and several of their valves to control the pool/spa flow and the heater/solar flow. Last year I replaced the old filter ( the only thing that wasn't replaced when the pool was rebuilt). It is a Pentair FNS Plus 60. Lately I have been having a problem with the pressure in the filter. It has been going to 40 psi. I have taken the girds out and cleaned them 4 times at this point. I have "descaled" them per the instruction in the manual with a 6 to 1 water/acid mixture. I put the DE in by making a slurry and pouring it into the skimmer ( 6 lbs. ) The filter starts out at about 22 psi with clean DE. After about 3 - 4 hours of operation the gauge goes to 40 psi. I have run the filter with the grids out and it reads 20 psi. If I back wash the filter the pressure goes down to about 22 - 23 again but then goes back up to 40 after a few hours. I have checked the filter gauge accuracy by putting a pressure gauge on the hose bib that was installed between the pump and the filter and get exactly the same reading. I put a flow meter in the line after the filter and am getting a reading of approx 75 GPM with clean grids. The Pentair folks seemed to think that the flow rate of the pump was too much for the filter, which has a max flow of 120 GPM. I have installed a 1 hp motor on the pump and still get the same flow reading. Now I'm being told by Pentair that there may be some "oils or pesticides." I'm not sure how any of these would have gotten into the pool or if they'd cause the problem. Any ideas would be extremely helpful. Thank you.

 

[JohnT]

Welcome to TFP!

Depending on the specifics of the swap, changing the motor wouldn't change the flow. To reduce flow, you'd want to put a smaller impeller in the existing pump.

Rising pressure over time with a DE filter really sounds like it is removing something from the water. How does your water look?

 

[jrowlandesq]

Thanks for the welcome. Apparently someone ( I previously had a pool service) ran the system after back washing the filter without putting DE back in. There was a substantial amount of dirt in the grid fabric. After soaking the grids with some Cascade and brushing them I put it all back together and added the right amount of DE and the pressure stayed at about 24 psi. There was a substantial amount of DE in the bottom of the pool (from a crack in the manifold that I replaced) so I brushed it all to the main drain. The pressure eventually went up, presumably because of the addition of all the DE from the pool, so I'm going to backwash and refill with DE today.

I'm hoping that at least this problem is solved. Now onto the Jandy 1400 chlorine generator problem in another post.

thank you again