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Thread: Low PSI at Filter

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    Low PSI at Filter

    After having our pool reconstructed over the last 4 months, this morning we turned on the filter system for the 1st time. The PSI used to be up around 19-20. Now, it seems to be sitting at 10 PSI .. I let all the air out of the filter tank and it still doesn't seem to want to get higher. Otherwise, I have not opened up the filter at all since turning it off 4 months ago.

    The only difference in the new build is that we added a dual filter/drain in the deep end - that of course runs into the skimmer basket. There is a plastic hinged "valve" (not sure what to call it) that swivels over the hole in the skimmer - to allow the drains to suck water, or closed thereby no water flow through them. I have not tried shutting them off to see if that makes a difference - should it?

    What can cause a lower-than usual PSI in the Filter?

    Thanks in advance.
    30,000 Gal FIBER GLASS (over Gunite Plaster) Pool, Dolphin Nautilus PLUS Robot, (2) Cartridge Filter System (old), 1/2 HP Pump, Full Sun, Solar Heated, TF-100 Test Kit.

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    mas985's Avatar
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    Re: Low PSI at Filter

    Assuming nothing changed on the return side, lower then normal pressure usually means that you have additional head loss (restriction) on the suction side and since that is where they made some modifications, that is probably where the problem lies. More than likely it is the valve in the skimmer.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Low PSI at Filter

    What can cause a lower-than usual PSI in the Filter?
    1. Reduction of resistance on the pressure side (new returns, etc)

    2. Increased restriction on the suction side.

    3. A temporary and partial blockage (debris?) somewhere on the suction side or in the pump itself.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Low PSI at Filter

    If they ran new plumbing lines back to the equipment pad, which is fairly common on a rebuild/renovation, it is common to see lower filter pressure. This happens because modern standards use larger pipe than was commonly used years ago, thus less resistance to water flow. Similar reasoning applies if the pump was replaced.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Low PSI at Filter

    Thanks everyone ... So, is a lower PSI a cause for concern if there are no blockages or leaks? ie., should we consider increasing our PUMP size ..?? currently 1.5 HP ...
    30,000 Gal FIBER GLASS (over Gunite Plaster) Pool, Dolphin Nautilus PLUS Robot, (2) Cartridge Filter System (old), 1/2 HP Pump, Full Sun, Solar Heated, TF-100 Test Kit.

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    JasonLion's Avatar
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    Re: Low PSI at Filter

    If anything you want a smaller pump

    Low pressure is a good thing. It means higher overall system efficiency and lower electrical costs (if you optimize the run time).
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Low PSI at Filter

    There is a plastic hinged "valve" (not sure what to call it) that swivels over the hole in the skimmer - to allow the drains to suck water, or closed thereby no water flow through them.
    Given you had work done on the suction side of the plumbing only, I would double check that the valve they put in is actually working properly. Low pressure is also a sign of a restriction on the suction side of the plumbing.

    A float valve, if that is what you are talking about, can restrict the suction side and reduce pressure but that would be a lot.

    If the return side plumbing has not changed, then there is something wrong with the suction side plumbing.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Low PSI at Filter

    Yes, the "Suction Side" = the RETURN thru the Skimmer - the only thing changed. They had to re-plumb the pipe (filter) to the new skimmer. Yes, there is a float valve in the skimmer. We removed that and it didn't seem to change anything. Something curious though is that there definitely appears to be air in the filter. When we unscrew the pressure relase valve at the top, air escapes, eventually spewing water. We close it and about 5 mins later do it again only have more air escape ... Is that normal? Right now we're getting about 7-8 PSI ... not even the 10 from earlier.

    Side question: What would the "procedure" be to troubleshoot where air might be leaking in? Plug the Skimmer intake & pressure test at the pump?? Are pool repair companies able to pinpoint leaks in the system? or is it a **** shoot ??
    30,000 Gal FIBER GLASS (over Gunite Plaster) Pool, Dolphin Nautilus PLUS Robot, (2) Cartridge Filter System (old), 1/2 HP Pump, Full Sun, Solar Heated, TF-100 Test Kit.

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    Re: Low PSI at Filter

    We close it and about 5 mins later do it again only have more air escape ... Is that normal?
    No. That's a possibility I don't think we covered and probably should've been the first thing. You have a suction side leak....no doubt.

    The procedure is to start at the skimmer and work your way back to the pump until you find the leak. Obviously, wherever you were working is a prime suspect. They are sometimes simple and sometimes maddeningly difficult but that is almost surely the issue. Find that leak and your psi will go up.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Low PSI at Filter

    The filter air is likely getting sucked in from the pump lid. Can you see air swirling around in the pump basket?

    Both the air in the filter and low PSI indicate a suction side blockage. A blockage will cause the pump lid to leak air and it gets sucked in by the pump and passes it on to the filter. The workers might have dropped something in the skimmer pipe.


    FYI

    Suction side is from the skimmer/main drain to the pump

    Return side is from the pump back to the pool via filter and pool eyeballs (water returning to pool)
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Low PSI at Filter

    Thanks again Mas .. we opened up the Pump and cleared all the debris from the basket (there was some). Then primed it and started it up again, purged air from the filter. The Pump has no air in it - well almost none anyway ... a bubble at the crest of the lid, but really that is about all. Then again, we purge the air filter and nmore air comes out after a few minutes.. We also pulled apart the fiter to examine it for any blockage or debris and it was fairly clean other than a few tiny debris that I hosed off, then reassembled. I "suppose" there could be debris somewhere between the pump and the filter ????? ugh ... don't even want to start tearing apart the PVC connections, but might have to consider that next.
    30,000 Gal FIBER GLASS (over Gunite Plaster) Pool, Dolphin Nautilus PLUS Robot, (2) Cartridge Filter System (old), 1/2 HP Pump, Full Sun, Solar Heated, TF-100 Test Kit.

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    Re: Low PSI at Filter

    The filter and the connections to the pump are on the pressure side.

    Air gets into the system only from the suction side.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Low PSI at Filter

    OK, got it ... so it HAS to be between the Pump & the Skimmer is what you're trying to drill into my head ... ??

    Is there a way to reverse force water back OUT of the pump to the skimmer?? I don't see anything on the pump that reverses water flow. I suppose we could disconnect the pump and push a hose through the pipe??? any other ideas on how to verify debris isn't stuck in the line?

    Thanks again.
    30,000 Gal FIBER GLASS (over Gunite Plaster) Pool, Dolphin Nautilus PLUS Robot, (2) Cartridge Filter System (old), 1/2 HP Pump, Full Sun, Solar Heated, TF-100 Test Kit.

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    Re: Low PSI at Filter

    You can't reverse the pump. If the path is straight enough, you can MAYBE get a hose or a fish tape to go through but probably not. You can get a device called a Drain King @ HD/Lowes that will allow you to force water backwards but you will have to disconnect the pump.

    Even if you don't find debris, the leak is still in the suction side. It can be a valve, gasket water too low in the skimmer, drain plugs at base of pump, etc., but you will eventually find it and the filter will no longer fill with air.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Low PSI at Filter

    OK .. thanks .. will mush through this ...
    30,000 Gal FIBER GLASS (over Gunite Plaster) Pool, Dolphin Nautilus PLUS Robot, (2) Cartridge Filter System (old), 1/2 HP Pump, Full Sun, Solar Heated, TF-100 Test Kit.

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    Re: Low PSI at Filter

    Right now I think you should focus on the blockage instead of the leak. When the blockage is removed, the air leak may very well disappear because the blockage is causing very high suction.

    The drain king is a good way to clear a blockage but you can also try a hose wrapped with a wet rag stuck into the suction via the pump basket. No dis-assembly required.

    Also, have you removed the skimmer float and basket and looked instead to see if there is something obviously stuck in the skimmer pipe?

    Also, reading back at one of your posts, this didn't make sense:
    They had to re-plumb the pipe (filter) to the new skimmer.
    There is no pipe from the skimmer to the filter only from the skimmer to the pump. Can you please explain again in detail, what was replaced and what was not replaced and did they change pipe size too?
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Low PSI at Filter

    All they did was remove the previous skimmer, as part of the re-coping of the tiles around the edge of the pool. (We had it refiberglassed due to a major underlying crack in the gunite). There was a copper return line from the skimmer to the pump that is totally underground. They dug down & sawed off the old skimmer connection then connected a PVC pipe to the copper one and then connected that to the bottom of the skimmer - they added a bit of an elbow PVC as the line wasn't a direct line to the old location.). I saw him do this and frankly it looked "fine" ... but I'm no expert either. I suppose we could just dig up the dirt its buried in and examine it. But I don't believe it was resized in any way at all.

    Update: This morning the pump kicked in as scheduled. I removed the Float Valve that was in the bottom of the Skimmmer. Then checked the the PSI - it is solid at 10 PSI in the filter and plenty of water is flowing through the pump ... I didn't try opening the filter's pressure valve yet to see if/how much air is in it. My next test to see if it changes anything is to put the Float Valve back in ... thanks for the hand-holding .. (so based on previous comments, a solid PSI of 10 is fine?)
    30,000 Gal FIBER GLASS (over Gunite Plaster) Pool, Dolphin Nautilus PLUS Robot, (2) Cartridge Filter System (old), 1/2 HP Pump, Full Sun, Solar Heated, TF-100 Test Kit.

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    Re: Low PSI at Filter

    At this point NO, 10 PSI is not OK unless you can figure out why the filter pressure went down.

    My concern is that the filter pressure dropped from what it was before and since you did not change anything on the return side (water return to pool via filter), then the only explanation for the filter pressure drop is that there is more restriction on the suction side. So something got worse on the suction side when based on your description, things should have gotten a little better. The air in the filter also indicates that there is now higher suction on the suction side which again points to a suction side restriction. All the symptoms indicate a problem with the suction side. You could ignore it but I would try to figure why the pressure dropped.

    I would at least try a back flush with the hose and rag I described earlier.
    Mark
    Hydraulics 101; Pump Ed 101; Pump/Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, MaxFlo SP2303VSP, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: Low PSI at Filter

    Quote Originally Posted by mas985
    .. Also, reading back at one of your posts, this didn't make sense:
    They had to re-plumb the pipe (filter) to the new skimmer.
    There is no pipe from the skimmer to the filter only from the skimmer to the pump. Can you please explain again in detail, what was replaced and what was not replaced and did they change pipe size too?
    What I meant by that is they sawed off the end to the old skimmer and had to replumb it back onto the pipe that goes from skimmer to the pump. Yea, not directly to the filter ... there is a separate pipe from the pump to the filter, duh ... thanks again.
    30,000 Gal FIBER GLASS (over Gunite Plaster) Pool, Dolphin Nautilus PLUS Robot, (2) Cartridge Filter System (old), 1/2 HP Pump, Full Sun, Solar Heated, TF-100 Test Kit.

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    Re: Low PSI at Filter

    Quote Originally Posted by mas985
    ... you can also try a hose wrapped with a wet rag stuck into the suction via the pump basket. No dis-assembly required.

    Also, have you removed the skimmer float and basket and looked instead to see if there is something obviously stuck in the skimmer pipe?
    Can you explain the "wet rag" procedure? So we (1) remove the lid to the Pump basket, (2) remove the pump basket .. then specifically what do we do with the rag tied to the end of the hose -- is the point of the wet rag to wrap around the hose to create a sort of vacuum? You don't mean that we wrap a wet rag over the actualt FRONT of the hose where the water comes out, right?

    And yes, we removed the skimmer float & basket ... nothing obvious at the bottom where the water goes to the pump. In fact we did a wet/dry vacuum of it initially .. here was certainly debris in there .. and a bunch ended up in the pump basket as well ... which we cleaned out.
    30,000 Gal FIBER GLASS (over Gunite Plaster) Pool, Dolphin Nautilus PLUS Robot, (2) Cartridge Filter System (old), 1/2 HP Pump, Full Sun, Solar Heated, TF-100 Test Kit.

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