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Thread: pump not getting enough water flow for venture effect?

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    pump not getting enough water flow for venture effect?

    Split from no-more-bubbles-out-of-the-spa-jets-t39227.html
    Please start your own thread. Butterfly



    I bought a house with a 72" spa with overflow into 20'x40' pool and the spa air control has a winter plug in it and it looks like the threaded female pvc adapter was cracked off so they did not bother to repair. When I slowly release the plug... water shoots out. Can this be due to a weak 10 year old 1HP pump not getting enough water flow for venture effect? In SPA mode The six jets currently do not feel that powerful. FYI I did run my wet/vac blower into the pipe with the pool pump off and all the jet DID have air coming out so there does not seem to be a blockage.

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    mas985's Avatar
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    Re: pump not getting enough water flow for venture effect?

    Pumps don't really weaken over time so it just may not have been sized properly to begin with. A couple of questions:

    What is the pump make/model?

    Is the pump dedicated to the spa or is the a single pump for the pool and spa?

    What is the distance from the spa to the pump?

    What is the pipe size going to and from the spa?

    What is the pipe size for the air vent?
    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: pump not getting enough water flow for venture effect?

    Pump is Magnatek 7-177450-03 and its shared Qty 10 PI750.42.551with pool. There are automatic Jandy valves that close off pool 2"returns and 2"suctions while in SPA Mode. All plumbing is 2" above ground except for vent pipe is 1.5". Distance is about 25 feet pump to spa

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    mas985's Avatar
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    Re: pump not getting enough water flow for venture effect?

    Both the pipe and the pump are undersized for a spa. Up sizing the pump alone may help a little. Also, going through the filter makes the problem even worse. What is the current filter pressure when in spa mode vs pool mode?
    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: pump not getting enough water flow for venture effect?

    Replumbing is not an option because its under decorative concrete deck. The filter is a Sta-Rite System3 S8M150 filter; pool mode(all returns open, suction from spa closed off) i get 17 PSI at filter. Spa mode( only spa suction on and only return to 6 jets in spa) i get 20 PSI. I have an 2HP variable ePump that i want to install, but still trying to design and optimize above ground plumbing and equipment layout (using large sweep elbows, and elminitaing so many elbows by more direct routing of pipes.
    If i open the heater bypass valve the pressure drops to 11 PSI in pool mode and 16 PSI in Spa mode. Heater is Raypak C R335 EN 330,000 BTU
    I have a chlorine tablet feeder and a mineral cartridge feeder, and a polaris 280 with booster pump.
    i just bought a 2" PVC flowmeter that i am going to install today.

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    Re: pump not getting enough water flow for venture effect?

    The ePump will give you some flexibility to experiment with flow rates. The filter should be able to handle almost anything so that's good and if you use the heater bypass, you may be able to get some decent flow to the jets.

    using large sweep elbows, and eliminating so many elbows by more direct routing of pipes
    I wouldn't bother with sweep elbows, they don't change the head loss much to make a difference and they make a mess of the plumbing.

    Increasing the pad pipe size would have a much larger effect but still small compared to the rest of the plumbing. I doubt you would see more than a few % change in flow rate.

    I can run some simulations to show you the different effects that changing pipe will have.

    How many elbows are you considering swapping out?

    How much pipe length is on the pad?
    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: pump not getting enough water flow for venture effect?

    I have 30 sharp 90 elbows and 589" of 2" piping. I think I can reduce to 20 large sweep and shorten total length to about 450". Will the 2hp ePump have a significant effect on spa jets?

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    Re: pump not getting enough water flow for venture effect?

    You have 589" of 2" pipe on just the pad? That's 49 feet of pipe.

    Is the 30 90s all on the pad too?

    Can you post a picture of the pad plumbing?

    If what you posted was total 90s and total pipe, I am more interested in what portion of that is accessible on the pad.
    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: pump not getting enough water flow for venture effect?

    All on the pad!!! 8" here, 18" there... it adds up quick. i measured from the center of each elbow
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    Re: pump not getting enough water flow for venture effect?

    From the picture I am counting only about 20 90s, is the plan to change those that I can see? Some of those are on the pool side correct? What is the exact count for the spa only side? I count about 16.

    Also, how high is the filter gauge relative to the water level?

    Do you know the size of your spa jets (3/8" or 7/16")?

    Sorry, just trying to be as accurate as possible.
    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: pump not getting enough water flow for venture effect?

    Don't be sorry... I appreciate all your knowledge and help. I have been trying to figure this out for 7 months and had two pool guys come by... all with no help.
    I labeled all the elbows in the photo:
    There are 20 Elbows just for SPA mode alone... Can't do anything about the Jandy 3 way. So I think I can reduce to 9or 10 large sweep and 1 Jandy 3 way, plus a check valve that im not even sure if I need that???
    I noticed someone removed the flap in the check valve in between pump and filter....im guessing that the valve was not necessary and instead of removing whole thing, they just took out flap.
    All together there are 30 elbows on the pad (in the photo), I did not count one of the Jandy 3 way valves by the suction.
    I am not sure what size jets are.
    The filter gauge is mounted on top of the filter 68" from pad, so I say the most 7 feet above pool water level and 6-1/2 feet above the spa level.
    I also included a picture of the broken spa air control that has a winter plug in it.
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    Re: pump not getting enough water flow for venture effect?

    You should be able to drill the bolt out of the center of the plug.

    Anyway, I put together 5 scenarios and given the filter pressure you are experiencing now, I will assume a 3/8" jet because that probably is what was used. For a decent strength jet, each jet should have about 15 GPM or 90 GPM total. Here are the results:

    Current Setup: 11.6 GPM/jet - 70 GPM total

    EPump with current plumbing: 12.5 GPM/jet - 75 GPM total

    EPump with 10 - 90s replaced: 12.7 GPM/jet - 76 GPM total

    EPump with 2.5" pipe/fittings on pad: 13 GPM/jet - 78 GPM total

    EPump with pad bypass: 15.4 GPM/jet - 93 GPM total

    The last scenario, I assumed that 1/2 the flow rate bypassed the pad equipment and as you can see, that will give you the best performance plus it doesn't require much change. The heater should still work since it will have at least 46 GPM going through it plus with a valve, you can adjust it for optimal flow performance. The downside is that you would need another actuator that can be engaged when in spa mode but it can be wired in tandem with the existing actuator.
    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: pump not getting enough water flow for venture effect?

    I recently installed a flow meter as seen on the exit pipe of the filter. I am not getting 70 GPM according to meter.
    Pool Mode 79 GPM/ 17 PSI
    Pool Mode with heater bypassed 80 GPM/ 11 PSI
    Spa Mode 62 GPM/ 20 PSI
    Spa Mode with heater bypassed 64 GPM/ 16 PSI

    Getting back to the original question... Do you believe if I achieve higher flow rate reaching 90 GPM (with more efficient plumbing and 2HP ePump), then the spa air control will suck air in as opposed to it squirting water when I slowly open the winter plug?

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    Re: pump not getting enough water flow for venture effect?

    I don't have the exact model number for your existing pump so I had to guess at that but keep in mind that those type of flow meters have at best a 10% accuracy at full flow. So if that is a 100 GPM meter, the error range is plus/minus 10 GPM.

    With higher flow rates, the venturi's should draw more air. But the winter plug should be completely removed for proper operation.
    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: pump not getting enough water flow for venture effect?

    When I remove the plug in spa mode. The water comes gushing out

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    Re: pump not getting enough water flow for venture effect?

    Is the vent below water level? Where is it in relation to the spa and pump (height and distance)?
    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: pump not getting enough water flow for venture effect?

    Maybe about 4" avbove spa water level and about 8" from spa rim. Pump is on the pad about 25 feet away.

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    Re: pump not getting enough water flow for venture effect?

    Does anyone know what the spa air fitting looks like and where in the heck I can buy one? I seem to be finding only portable spa parts

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    Re: pump not getting enough water flow for venture effect?

    I forgot to mention that the PVC pipe is a one and a half inch diameter

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    Re: pump not getting enough water flow for venture effect?

    My previous house just had a 1.5" PVC pipe sticking out of the ground by the equipment with a hole cut in the side.

    Current house just has some 1/2" PVC pipe sticking out of the coping just above 3 bench jets ... they are loud and annoying but 2 of the 3 pull air in ... the 3rd stopped working correctly after a resurfacing ... but if I plug the returns the water will flow out of the air pipe (not sure how these are plumbed exactly).
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