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Thread: Cooperative effort to determine individual head loss

  1. Back To Top    #1

    Cooperative effort to determine individual head loss

    It seems nailing down dynamic head loss is the most critical aspect of properly selecting optimum equpiment to run our pools. It also seems to be the most fleeting.

    Mark definitely has it understood, and I hoping the end result of the information he is working on is a quick and easy accurate way to tell us what we need to know If it is, what follows may be moot, but I'll throw it out anyway.

    I propose we band together and buy a head loss determining "kit" that we could each share. A vacuum gauge, flow meter and necessary fittings and adapters to make it work on most set ups, which can possibly be determined by those wishing to participate posting specific info on their pool and those educated in what it would take to do so figuring out what is needed. If enough people are interested it should bring down the individual cost to a reasonable level. My gut says $150 should more than do it, and if 10 people are interested, that's only $15 each.

    Once the kit is figured and a total cost determined, everyone wishing to participate would throw and equal portion of $ to the person chosen to purchase and distribute the kit. I formally nominate Dave, since TF test kits is already up and ready to go... do I hear a second?

    Anyway, once Dave (or whomever) has the money, he orders the stuff and puts the kit together. We "draw straws" to determine the order in which we get access to the kit. 1st up "orders" the kit from Dave, paying only S&H, but secures the entire cost of the kit with a CC. That way if it's not returned, their card is charged and a new kit can be purchased. Once #1 is done (they have a certain time frame to do so) they return it to Dave, who contacts #2, rinse, repeat

    I have no idea if this can even be done, but it's been on my mind so I wanted to put it out and see if anyone would be interested. I for one would LOVE to know my DHL once and for all. As I understand it, once you have it nailed down, it's a matter of simple calculations to figure how it will change based on the pump selected.

    Anyone?

  2. Back To Top    #2
    JasonLion's Avatar
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    Calculating your true flow rate is usually not critical, and it depends on so many factors that it is difficult to generalize from one pool to another. Keep in mind that a dirty filter can run 10 psi more pressure than a clean filter which translates into 23 feet of dynamic head variation between a clean and dirty filter. The errors in casual dynamic head estimates are often smaller than that, though the estimate errors can grow for more complex system.

    Automotive vacuum gagues can be gotten fairly cheaply, and when used in combination with a working filter pressure gague can tell you the flow rate. Vacuum gagues can be shared, but flow meters generally require making a hole in your pipe and so are more difficult to remove and thus tricky to share. A simple vacuum pressure gague, like this one will probably do. Shipping it around would cost a substantial portion of the original cost.

    With flow meters under $100, I would rather just get my own flow meter. Though I continue to not get around to actually getting one, so I have to wonder how important it really is to me.
    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

  3. Back To Top    #3
    mas985's Avatar
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    I would agree with Jason. Flow rates are not that crtitical and if you can get within 10-20%, that should be sufficient for turnover calcs.

    My goal is to come up with "rules of thumb" that would allow easy estimates of head loss from filter PSI measurements. I also wanted to create a model for those who would be upgrading their pumps and interested in how the head loss changes. From the information I have received so far, it seems that I can easily predict head loss to within 10% or so which should be good enough for estimating run times.

    With a cheap vacuum gauge, you can get even closer. Sears has one for about $20.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater, ThePoolCleaner

  4. Back To Top    #4
    Jason,

    flow meters generally require making a hole in your pipe and so are more difficult to remove and thus tricky to share.
    I was hoping one could be had that could screw into returns or something, so no pipe would be harmed in that gathering of data

    So, a good pressure reading and a cheap vacuum gauge reading should be all that's needed?

  5. Back To Top    #5
    mas985's Avatar
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    Quote Originally Posted by Rangeball
    Jason,

    flow meters generally require making a hole in your pipe and so are more difficult to remove and thus tricky to share.
    I was hoping one could be had that could screw into returns or something, so no pipe would be harmed in that gathering of data

    So, a good pressure reading and a cheap vacuum gauge reading should be all that's needed?
    Yes.

    In order of accuracy of flow measurement:

    1) Flow Meter - Error very small
    2) PSI and Vacuum gauge measurements - Error limited to accuracy of guages and head curve
    3) PSI only measurement with fudge factor listed in sticky (2.5-4.0 depending on plumbing) - <10% Error
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater, ThePoolCleaner

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