+ Reply to Thread
Results 1 to 7 of 7

Thread: How to Calculate Feet of Head...???

  1. #1
    Sherra is offline Lifetime Member Weir Watcher Sherra 0
    Join Date
    Dec 1969
    Location
    South Carolina, United States.
    Age
    50
    Posts
    184

    Question How to Calculate Feet of Head...???

    How exactly would I calculate the feet of head for my pool? I've heard the term and seen it on the performance curve graph on my pump but have no idea how to figure out what it is for my pool. Is there a formula I should use to figure this out?
    Sherra
    Kershaw County South Carolina
    18x34 IG 2' radius rectangle vinyl liner (approx 27,500 gal) 1 1/2" pipes installed March 2006
    (previous AG pool owner)

  2. #2
    mas985's Avatar
    mas985 is offline Lifetime Member Whizbang Spinner mas985 3 stars mas985 3 stars mas985 3 stars
    Join Date
    Dec 2004
    Location
    Pleasanton, CA
    Posts
    1,423

    Default

    It sounds as though the pool is not complete so you cannot measure it. With an existing pool you can measure existing head via the filter PSI and pump vacuum. However, you will need a vacuum gauge which you can get at Sears or OSH in the auto hardware section.

    Some builders use 50' or 60' of head as a standard pool build but depending on the design, this can be way off. Also, most pool builders do not have the ability to do a head calc. You could hire a hydraulics engineer to perform one but it will be expensive. They also don't tell you that head is dependent on the flow rate through the pipes and the pump flow rate is dependent on the head. This is a circular calculation which requires an interative solution.

    Also, the exact calculation is quite complicated and requires detailed knowledge of all the pipe size & lengths plus all of the fittings and equipment losses. If you are up for it there are some good references to get into the details but it does have a steep learning curve. I have detailed spreadsheets which do the calculations but again, the inputs need to be pretty accurate.

    This approach may be best suited for your situation:

    http://www.poolplaza.com/pool-pump-sizing-2.shtml
    http://www.poolspa.com/publications/...ries/pumps.htm
    Last edited by mas985; 04-11-2006 at 06:46 PM.
    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

  3. #3
    Sherra is offline Lifetime Member Weir Watcher Sherra 0
    Join Date
    Dec 1969
    Location
    South Carolina, United States.
    Age
    50
    Posts
    184

    Default

    My pool is complete. I've had water in the pool and the pump has been functional since March 13th. They poured the deck Thursday (I guess I should change my signature to take that part out). I could figure out what the measurements on the lengths of the pipes are within a couple of feet accuracy. I've got pictures of most of the plumbing before they backfilled also. I'm just trying to figure out how long I REALLY need to run my pump each day.
    Sherra
    Kershaw County South Carolina
    18x34 IG 2' radius rectangle vinyl liner (approx 27,500 gal) 1 1/2" pipes installed March 2006
    (previous AG pool owner)

  4. #4
    Sherra is offline Lifetime Member Weir Watcher Sherra 0
    Join Date
    Dec 1969
    Location
    South Carolina, United States.
    Age
    50
    Posts
    184

    Default

    OK, I did a little more reading on those sites you linked, and it looks like my maximum flow rate is going to be about 42 GPM anyway because I've got 1.5" PVC pipe, so it looks like even assuming I could be running at my max flow rate I'm going to need to increase the length of time my pump is running... Thanks for the info!
    Sherra
    Kershaw County South Carolina
    18x34 IG 2' radius rectangle vinyl liner (approx 27,500 gal) 1 1/2" pipes installed March 2006
    (previous AG pool owner)

  5. #5
    mas985's Avatar
    mas985 is offline Lifetime Member Whizbang Spinner mas985 3 stars mas985 3 stars mas985 3 stars
    Join Date
    Dec 2004
    Location
    Pleasanton, CA
    Posts
    1,423

    Default

    From your pictures, it looks like you have separate runs for suction and return which means you will have 1/3 of the total flow in each run. This is a good thing for 1.5" piping which is pretty small. So three runs of 1.5" pipe is close to the same loss as 1 run of 2.5" pipe.

    Given that you are running your pump, what is the filter PSI? Multiply this by 2.31 to get return head. Suction head you can estimate from the web site and it should be fairly accurate. However, my guess is you probably have about 10' of suction head give the pool configuration.

    Also, the 42 GPM is the maximum "suggested" flow rate for a single pipe and probably not what you may actually have. To get the flow rate, you must determine the head of your plumbing and look up the flow rate from your pump curves. This value could be well over 42 GPM. But since you have three pipes, you can go much higher.
    Last edited by mas985; 04-12-2006 at 01:00 PM.
    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

  6. #6
    Sherra is offline Lifetime Member Weir Watcher Sherra 0
    Join Date
    Dec 1969
    Location
    South Carolina, United States.
    Age
    50
    Posts
    184

    Default

    I believe I've only got one return line leading from the filter which then "t's" off at the returns. That's the way it looks from the pictures I didn't put on my Yahoo site anyway. I'm guessing their logic on that is because you're less likely to get a clog in a return line??

    My pressure reads about 15-17 right after backwashing.
    Sherra
    Kershaw County South Carolina
    18x34 IG 2' radius rectangle vinyl liner (approx 27,500 gal) 1 1/2" pipes installed March 2006
    (previous AG pool owner)

  7. #7
    mas985's Avatar
    mas985 is offline Lifetime Member Whizbang Spinner mas985 3 stars mas985 3 stars mas985 3 stars
    Join Date
    Dec 2004
    Location
    Pleasanton, CA
    Posts
    1,423

    Default

    The loss between the filter and the tee is small compared to the loss over long lengths of pipe and through other fittings. Their design is fine and some perfer that over the single large pipe. Either way, the loss is nearly the same so I would not concern myself with that.

    With that PSI setting, you have about 47 feet of head in your pool using 10 feet for the suction head. Now look at your pump curve in your manual to determine the flow rate.
    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

+ Reply to Thread

Similar Threads

  1. Can someone help estimate my Total Resistance to Flow (Feet of Head)
    By 1PoolNoob in forum Pool Equipment & Operations
    Replies: 8
    Last Post: 06-09-2013, 12:17 PM
  2. AGP and 1hp Pump... Calculate Turnover?
    By Solarius99 in forum Pool Equipment & Operations
    Replies: 1
    Last Post: 06-20-2011, 08:53 PM
  3. Formula to calculate expected Pool Water Temperature???
    By TheG$ in forum Pool Equipment & Operations
    Replies: 2
    Last Post: 05-11-2007, 06:18 PM
  4. How do you calculate head?
    By Rangeball in forum Pool Equipment & Operations
    Replies: 21
    Last Post: 07-17-2006, 11:32 AM
  5. How to calculate the size of my pool
    By Sunny32504 in forum Testing and Adjusting Pool Water Chemistry
    Replies: 1
    Last Post: 06-09-2006, 10:16 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts