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Thread: Spa pump horsepower

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    Drew80's Avatar
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    Spa pump horsepower

    I have a 1,250 gallon spa with 8 jets, and I have a single speed 2HP pump that powers both it and my pool. The 3 jets in the pool are really strong, but the pump isn't strong enough for the 8 jets in the spa. The jet inserts barely spin and the water doesn't ripple at all.

    What HP pump would I need to get those things really moving?
    7,500 gallon gunite pool. 1,250 gallon spillover spa. Prologic 8. T-Cell 15 SWG. Hayward 350k BTU heater. Hayward cartridge filter. 2 HP Tristar pump. AquaConnect. TF100

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    mas985's Avatar
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    Re: Spa pump horsepower

    It depends on the flow rate requirement of the jets. Standard 15 GPM jets require a total of a 120 GPM which is very hard to get no matter what size pump you put on the plumbing unless you have very large pipe and don't go through the pad equipment.

    What size pipe did they use going to and from the spa?

    Is there a separate jet pump or does the water going to the jets also go through the filter?

    Do you know the flow rate requirement of the jets or the nozzle size of the jet?
    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: Spa pump horsepower

    2" pipe. Single pump, goes through the filter.

    I can't seem to find anything about flow rate for the jets. They're standard 3" Waterway jets, like this one: https://www.amazon.com/Waterway-Plas...QM00SS96GZE0RB

    ---

    Edit: Waterway's website says 10 GPM, so I need 80 total
    7,500 gallon gunite pool. 1,250 gallon spillover spa. Prologic 8. T-Cell 15 SWG. Hayward 350k BTU heater. Hayward cartridge filter. 2 HP Tristar pump. AquaConnect. TF100

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    mas985's Avatar
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    Re: Spa pump horsepower

    What is the filter pressure?

    Is the 2 HP pump a full rated or up rated version? What is the model number?

    Unfortunately 2" pipe is really much too small for a spa.
    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: Spa pump horsepower

    Quote Originally Posted by mas985 View Post
    What is the filter pressure?

    Is the 2 HP pump a full rated or up rated version? What is the model number?

    Unfortunately 2" pipe is really much too small for a spa.
    I disagree in some cases. My '95 Hot Spring Grandee has a 1 hp jet pump and a new replacement 1.5 hp pump on 1.5" lines each powering about 6 jets each. That's not very many jets but I get reasonable flow and pressure out of them despite the small line size and low horsepower. My system works okay because there are so few jets and each jet pump gets 2 filters each so you don't have any constriction on the intake/suction side. Up the number of jets significantly then you'll need a much higher discharge rate from the pump to compensate so more hp and bigger diameter lines would be needed there.

    In this case, the OP has a 2 hp pump on 2 inch lines and only 8 jets so I would think he should be able to get enough throughput on that system to make the jets work okay unless they really underdesigned that system.

    The first thing I would do is do a quick test running the jet pump with the filter off just to see if the filter is where the restriction is. If throughput increases significantly with the filter off then either clean or replace the filter.

    If the filter is not the issue then what other things could cause the system to perform poorly? Let's think this through. (Note: I am thinking here as if it's a standalone portable spa so some of the things I've listed may be N/A for your setup.)

    1. Restrictions in the pump suction and/or discharge lines either due to an obstruction or the lines being undersized (personally, I don't think they are for only 8 jets but it depends a lot on how long they are)
    2. Pump impeller worn out
    3. Pump impeller undersized (e.g. having a 1 hp impeller on a 2 hp motor)
    4. Pump motor being underpowered (design issue)
    5. Pump motor being weak from age and wear
    6. A leak in the suction and/or discharge lines
    7. Too much pressure drop through the system due to the suction and discharge lines being too long and narrow for the pump size. (I doubt this is it given it's a small sized tub and has 2" lines in and out of the pump. My tub is much larger and therefore the lines running to the jets are much longer and I have less hp and both the inlet and outlet lines from the pump are only 1.5".)
    8. Not enough current getting to the pump? (e.g. being wired for 240V but only getting 120? Is that possible? Corroded/oxidized wire connections in the GFCI box or at the pump possibly?
    9. Pump motor not turning enough rpms (e.g. it's a 2 speed motor only wired to run at the lower speed or the motor is a 1730 rpm one speed motor and is supposed to be a 3450 rpm motor.)

    That's about all I can think of. Out of all of the above, I would guess the most likely cause is the filter but fortunately, that's the easiest thing to test. How much do you know about the wet end and motor that's in there? Are they original to the tub? If you bought this tub second hand it's possible a previous owner replaced the motor or wet end or both with something that's incorrect like an undersized wet end or a motor with the wrong specs or got a motor that should work but wired it incorrectly so it's not putting out what it's capable of.
    I can take ANYTHING apart

    1995 Hot Springs Grandee
    500 US gallons (1,890 L) 104 F (40 C)
    Fibreglass construction

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    Re: Spa pump horsepower

    Quote Originally Posted by DangerBoy View Post
    I disagree in some cases. My '95 Hot Spring Grandee has a 1 hp jet pump and a new replacement 1.5 hp pump on 1.5" lines each powering about 6 jets each. That's not very many jets but I get reasonable flow and pressure out of them despite the small line size and low horsepower. My system works okay because there are so few jets and each jet pump gets 2 filters each so you don't have any constriction on the intake/suction side. Up the number of jets significantly then you'll need a much higher discharge rate from the pump to compensate so more hp and bigger diameter lines would be needed there.
    That is a stand alone spa and pipe runs are generally very short and use multiple runs. My comment was for in-ground spas that have very long runs between the pump and spa. Please don't confuse the OP.

    In this case, the OP has a 2 hp pump on 2 inch lines and only 8 jets so I would think he should be able to get enough throughput on that system to make the jets work okay unless they really underdesigned that system.
    80 GPM on 2" pipe is 8 ft/sec velocity which makes it well above recommendations especially for entrapment.
    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: Spa pump horsepower

    I read something that said 85 GPM is right around the upper limit for 2" pipe, so it seems like I should be ok-ish to bump up the pressure. That article is here: http://www.aquapoolstore.com/pumps/H...-Selection.htm

    The pump is a Hayward SP3215X20. It's uprated. I have no idea what that means.

    Side question - can I just cap off some of the jets to drop the GPM requirement?
    7,500 gallon gunite pool. 1,250 gallon spillover spa. Prologic 8. T-Cell 15 SWG. Hayward 350k BTU heater. Hayward cartridge filter. 2 HP Tristar pump. AquaConnect. TF100

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    Re: Spa pump horsepower

    You are quoting a pool store? Really?

    You can't always believe what you read on the internet. You can run at 85 GPM through 2" pipe if you really want to but there are several issues with that. First, for a spa and suction side plumbing in general, VGBA regulations that most states now follow dictate a maximum of 6 ft/sec velocity which is about 60 GPM in 2" plumbing. This reduces the risk of entrapment. Second, running over 8ft/sec greatly increases head loss significantly limiting how much flow rate a pump can produce.

    Again you can run above 6 ft/sec if you so desire. It just is not advisable and I wouldn't say it is OK!

    http://www.wvdhhr.org/phs/pools/Virg...h%20covers.pdf
    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: Spa pump horsepower

    So the mistake was that my pool builder chose to run 2" PVC to 8 jets, and it doesn't seem like there's any good way to fix that short of replumbing (which I'm not going to do). Can I just cap 4 of them to increase pressure on the others?
    7,500 gallon gunite pool. 1,250 gallon spillover spa. Prologic 8. T-Cell 15 SWG. Hayward 350k BTU heater. Hayward cartridge filter. 2 HP Tristar pump. AquaConnect. TF100

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    mas985's Avatar
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    Re: Spa pump horsepower

    Yes, that is probably your best bet. But I would just try caping two of the jets. That might be enough.

    But what is the filter pressure now?
    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: Spa pump horsepower

    It's dirty right now, so it's at 30. Clean is 20
    7,500 gallon gunite pool. 1,250 gallon spillover spa. Prologic 8. T-Cell 15 SWG. Hayward 350k BTU heater. Hayward cartridge filter. 2 HP Tristar pump. AquaConnect. TF100

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    mas985's Avatar
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    Re: Spa pump horsepower

    You really shouldn't allow the filter pressure to climb more than about 25% or 5 PSI. That could be part of the issue with the jets as it is reducing the flow rate significantly.

    I can estimate the flow rate for you and how it would change with different pumps and/or changing the number of jets as well as cleaning the filter but I need a bit more information:

    Distance from pool to spa?

    Height of the pump relative to the spa water?

    Is there a single run for the suction and the return for all 8 jets or are there multiple runs on both the return and suction side?
    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: Spa pump horsepower

    I'm sure the pressure doesn't help, but the jets are weak even when the filter is completely clean. As we've determined, there are just too many of them

    About 25' from the equipment to the pool returns. The spa is a spillover on the other side of the pool - that run is about 40'

    The ground is flat between the spa and the pump, so the rise is only about 1' from the top of the water to the intake pipe of the pump

    Single runs entering and leaving the valves. The spa has 2 drains and 8 jets, but those splits happen before/after
    7,500 gallon gunite pool. 1,250 gallon spillover spa. Prologic 8. T-Cell 15 SWG. Hayward 350k BTU heater. Hayward cartridge filter. 2 HP Tristar pump. AquaConnect. TF100

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    mas985's Avatar
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    Re: Spa pump horsepower

    At 30 PSI, the pump should be producing less than 60 GPM to the jets which is too little. However, if the filter is clean with a filter pressure of 20 PSI and assuming the skimmers and pump basket are also clean, then the pump should be producing over 90 GPM which should be more than enough flow rate for 10 GPM jets.

    Are there any valves which bypass flow rate around the jets?

    I would clean the filter & pump basket and get another filter pressure measurement to confirm.
    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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    Drew80's Avatar
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    Re: Spa pump horsepower

    How did you calculate this? I'm interested to see how each of these variables affects the output
    7,500 gallon gunite pool. 1,250 gallon spillover spa. Prologic 8. T-Cell 15 SWG. Hayward 350k BTU heater. Hayward cartridge filter. 2 HP Tristar pump. AquaConnect. TF100

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    mas985's Avatar
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    Re: Spa pump horsepower

    Using the spreadsheet in my signature.
    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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