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Thread: how do i measure flow rate of water?

  1. #1

    how do i measure flow rate of water?

    I have a raypak above ground pool and spa heater I am newly installing, the instructions say I must have an external auxiliary bypass valve if rates exceed 70 gallons per minute. How do I measure flow rate?

    Thanks in advance for any advice

  2. #2
    Administrator JasonLion's Avatar
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    Re: how do i measure flow rate of water?

    Welcome to TFP!

    There isn't any easy way. What size pump do you have?
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    TFP Admin. Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  3. #3
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    Re: how do i measure flow rate of water?

    Can you hook up a hose to the return fitting so you can fill a 5G bucket. You can see how long it takes to fill the bucket and do the math. I know it's a bit primitive but it will give you an idea.
    18x36 Vinyl In-ground w/roman ends 27,400G, Hayward 3/4hp with 300# sand filter. Hayward heat pump heater

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  4. #4
    Senior Member mas985's Avatar
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    Re: how do i measure flow rate of water?

    Putting a standard hose on the return fitting will increase head loss significantly so the flow rate will not be very accurate.

    I can estimate the flow rate for you but I need the following information:

    Suction pipe diameter (e.g. 1.5", 2", 2.5")
    Average length of suction pipes
    Number of individual suction pipes from the water to the equipment
    Number and type of suction side valves
    Current Pump Make/Model
    Height of pump relative to the water level
    Pipe size between pump and filter (e.g. 1.5", 2", 2.5")
    Filter type, size and multi-port valve size
    Filter PSI reading at the desired valve settings and pump's highest speed setting
    Height of pressure gauge relative to the pump center line
    Heater - yes or no
    Number and type of return side valves
    Return pipe diameter (e.g. 1.5", 2", 2.5")
    Average length of return pipes
    Number of individual return pipes from the equipment to the water
    Return eyeball/jet inner diameter (e.g. 1", 3/4", 1/2") or Jets (e.g. 3/8", 7/16")
    Number of return eyeballs
    Optional: Pump suction reading (in-hg) - not necessary but improves accuracy
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study
    18'x36' 20k gallon plaster/gunite pool, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge Filter, 450 sq-ft EPDM Solar Panel, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

  5. #5
    Senior Member Richard320's Avatar
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    Re: how do i measure flow rate of water?

    Quote Originally Posted by traciejo@gmail.com
    I have a raypak above ground pool and spa heater I am newly installing, the instructions say I must have an external auxiliary bypass valve if rates exceed 70 gallons per minute. How do I measure flow rate?

    Thanks in advance for any advice
    Here's how I got a rough idea of my flow. I did mine to calculate how long to turn the water over so I could set my filter timer.

    I set the valves to suck from the spa and return to the pool. I stuck a ruler in there and got a depth from the seat, then timed it until it went down 6". Then I shut it down, reversed the valves, and measured how long it took to raise the water level again. I figured going both directions would give me the average since the lines are all different lengths.

    My spa is round. I broke out the tape measure and got the diameter, then crunched some numbers and came up with how many gallons I moved and how long it took to do it. Answer is GPM.

    In case math isn't your strong point, just post the measurements and someone can crunch the numbers for you.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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  7. #7
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    Re: how do i measure flow rate of water?

    Hello, this is my first post. The 1st poster in this thread, traciejo (my gf) posted while I was out shopping for some parts for the pool we are assembling, I was having her read the heater manual and see if she could help me figure out our install.

    Thanks for all the detailed questions to help us with an answer. I'm going to follow up with more info.
    AG 7300 gallons, 18ft Wilbar Industries “Summerfield” (but sold as a “Key West”)
    Filter: Millennium 22'' Sand w/ 1.5HP 1 speed 120V
    Raypak heater Model 130A (P-R130A-EN-C)

  8. #8
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    Re: how do i measure flow rate of water?

    Detailed questions that dovetailed from this thread here:

    many-questions-related-to-our-wilbar-18ft-ag-pool-install-t48479.html
    AG 7300 gallons, 18ft Wilbar Industries “Summerfield” (but sold as a “Key West”)
    Filter: Millennium 22'' Sand w/ 1.5HP 1 speed 120V
    Raypak heater Model 130A (P-R130A-EN-C)

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