PSI Drop after using Waste setting

[BK MAC]

I've been keeping my neighbors pool chemistry in check until he finishes remodeling his new home and moves in. We just had a lot of rain dumped on us so I went over to check on the water level in his pool. As it was still raining heavily and the water had reached the top of the skimmer I set the filter to waste to dump some water out of the pool. I noticed after doing this that the pressure in his sand filter went down about 3 psi. My question is this. If the system is pulling air (which I suspect it is) is it possible for the waste setting to relieve the filter of this air pressure? Is there another potential cause of this psi drop? A bit of background on my neighbors pool. 20 x 40 IG vinyl pool with only one skimmer acting as a return source to the pump/filter. 2 returns which I often witness discharging air bubbles. Single speed pump that runs 24/7 and no relief valve on the sand filter. SWG, and an ionizing system (which I took the liberty to unplug).

 

[Texas Splash]

Let's make sure we're talking about the same thing. First, when you put the MPV on WASTE, you are essentially bypassing the filter. Water gets pushed directly out to the waste line, so it's understandable that the psi would fall during that time. But once you put the MPV back to the FILTER setting, the psi should go back to normal.

As for the air question, if there is air in the system, it's coming from somewhere between the skimmer and the pump pot (wet end). If air is getting sucked "in", then it will continue to get pulled inward regardless of the setting of the filter. As for what we might refer to as a normal amount of air in the filter, the air bleed at the top (if installed) should take care of that. The WASTE setting should not have any influence on bleeding air from within the filter itself.

 

[BK MAC]

Let's make sure we're talking about the same thing. First, when you put the MPV on WASTE, you are essentially bypassing the filter. Water gets pushed directly out to the waste line, so it's understandable that the psi would fall during that time. But once you put the MPV back to the FILTER setting, the psi should go back to normal.

Yes, we're talking about once we go back to FILTER after going to WASTE. There was a 3 psi drop.

One other item that MAY have a bearing on my psi drop.....while I understand WASTE bypasses the filter, I wanted to make sure I was correct in that assumption before going back to FILTER (since it's not my pool to make a mess of). As a precaution, I did RINSE briefly to check the glass and make sure all was clear. As RINSE water does go through the filter and exits via the waste line, would it take the air with it ?

 

[Texas Splash]

As RINSE water does go through the filter and exits via the waste line, would it take the air with it ?

Since RINSE runs water through the filter the same way as the FLTER setting, it might take some air with it out to waste, but I wouldn't think it would be significant.

 

[BK MAC]

Just as a follow up....... I went over to my neighbors house this AM to check on things. Filter pressure was 12.75 psi. I decided to see if I could get the pressure to reduce using only the RINSE cycle. All I did this time was run the filter through a 20 second RINSE cycle. Other than turning the power switch on/off and turning the MPV handle, nothing else was touched. When I switched back to FILTER, psi had dropped back to 9 and return lines picked up in intensity. Just my observation, not sure if this proves air will be ejected during the RINSE setting. I understand your point about water flow in the filter during RINSE / FILTER. That said, the pump runs 24/7 on FILTER and the psi rises during that time, but drops after doing a RINSE. ???????? The reason all of this peaked my interest was because I was fairly certain the filter did not need backwashed from debris build up and that air was the issue for psi rise.

 

[Texas Splash]

Good to know. I wonder if anyone else will chime in with similar experiences.

 

[cowboycasey]

You are cleaning the filter getting all the gunk out when you rinse.. that is why the PSI is dropping.. happens when you clean/backwash the filter

 

[BK MAC]

You are cleaning the filter getting all the gunk out when you rinse.. that is why the PSI is dropping.. happens when you clean/backwash the filter

Would gunk still be pushed out without first going through BACKWASH ? Glass was clean during the 20 second RINSE. I assumed RINSE and FILTER were pretty much the same flows with the exception of where they exit the MPV. That's why I'm puzzled at the psi drop.