Delta shower valve performance curves?

Discussion in 'Shower & bathtub Forum & Blog' started by Runs with bison, Sep 3, 2009.

  1. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    Do any of you have access to/can point me in the direction of Delta shower mix valve performance curves? These are 1994 vintage, single knob, don't know the model number, but believe they are pressure balanced/compensating. I'm looking for pressure drop vs. flowrate for the valves.

    The reason for this is that I'm trying to troubleshoot some low flow readings I'm getting from some showerheads. House pressure with one running appears to be 60-68 psig depending on which floor the shower is located. I've worked through pressure drop for the piping with line sizes and equivalent lengths, so the only remaining unknown is pressure drop across the shower valve. I'm wondering what it should be...vs. what I might see if I insert a tee and gauge in the shower arm to read the pressure during shower head operation.

    Presently, I can't explain why the flows are so far off the new showerheads' performance curves.
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,684
    Location:
    Cave Creek, Arizona
    pressure

    We do not know where, or how, you are measuring pressure, so your entire theory could be wrong. A gauge at the shower head will only measure the residual/back pressure caused by the head, and nothing about what you are trying to determine. In other words, without a head the pressure would be zero, with the head attached it would indicate some pressure value, but it would change depending on which type of head you had installed.
  3. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    Multiple places, cross checking using a Watts pressure test gauge. Other than the potential for a bad gauge, there is not much chance that I'm wrong about the house pressure. I can measure pressure before and after the PRV (multiple places on the latter) with trickle flows to verify the high DP of the PRV itself in any dynamic state, as well as during shower operation to again determine system pressure.

    I've also worked through the DP for various flowrates of the entire supply system after the PRV. They are negligible at the line sizes and flowrates I have. I'm also correcting for DP loss with elevation.

    Incorrect. A gauge at the shower arm on a tee with the showerhead will give me exactly the piece of information I'm missing: the dynamic pressure to the showerhead at a given flowrate. That is what the showerhead flow curves are based on, the dynamic pressure at the showerhead supply. That residual/back pressure caused by the head will tell me how much DP the Delta valve is causing--when combined with my other pressure measurements.

    In fact, if I put several different shower heads (or a valve) in and bucket test and read pressure at the tee, I should be able do develop the missing performance curve for the Delta as well as compare the showerhead performance curves.

    Yes, it had better change depending on the flowrate of the shower head installed. That's why I'm trying to find where Delta hides their performance curves.

    Right now I'm working backward from the curve for another showerhead I have installed which suggests the Delta's are taking ~30 psi of drop at 1.3 gpm. :eek: That seems unreal and is why my next errand is go get a tee and adapter to determine what the actual pressure is.

    I expect the showerhead to take a very large pressure drop. What I do not expect is the shower valve to take just as large a pressure drop at low flows with the showerhead in place since the showerhead should be the primary restriction. Presently they appear to each be taking about 30 psi of drop at a low flow. I was expecting about 5 psi out of the Delta.

    If on the other hand the showerhead is getting close to house pressure, but is flowing much farther back on its curve, then I know the showerhead is defective.
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,684
    Location:
    Cave Creek, Arizona
    pressure

    IF the HOUSE pressure is fluctuating, it has NOTHING to do with the shower valve. It us usually caused by a failing PRV which cannot deliver the flow when the shower valve is operating. IT can respond to minimal flows without any effect on the pressure, however. That is the very test I use to evaluate a PRV.
  5. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    I wish that was the problem, but perceptible fluctuation in flow has not ever been a problem in the house. The PRV isn't helping because it forces me to run a higher static pressure to maintain desired dynamic system pressure. However, its contribution is a smaller factor than some others.

    I picked up a tee, an adaptor and a second gauge from a different manufacturer. So now I can indeed see the pressure in the shower arm while it is running. Unfortunately the initial results are a mixed bag and are going to require some follow up. The gauges are not that far off from one another about 2-3 psi.

    The Delta fixture is fairly high DP, but is not the source of this particular problem at low flow. The PRV is already a known problem, but can hold 75-80 psi at about 1.25 gpm while the testing is occurring. The shower arm pressure is around 58-62 psi. The Delta takes between 5-7 psi drop once elevation change is subtracted. With a 2.5 gpm fixture at 2.25 gpm measured the pressure in the shower arm is 38 psi, the house is running at 67 psi. I'm revising the elevation difference to 8-9 psi, and at 2.25 gpm actual the pipe DP is about 1.5 psi. This yields a Delta fixture DP of ~19 psi @ 2.25 gpm. The Delta fixture is tied with the PRV as far as its impact on the dynamic pressure in the shower arm.

    Looks like the low flow showerhead is the guiltiest party, running well below its performance curve. At this dynamic pressure it should put out about 1.59 gpm but is coming up a critical 21% short.

    I'll repeat on the lowest level shower which has the same model Delta shower valve and is only a few feet from the outside gauge (I actually have two widely separated points for gauges outside so I have some nice checks.) This will provide cleaner data. I might even stick a valve on the end of the tee to verify dead head delta between the gauges.
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,684
    Location:
    Cave Creek, Arizona
    Prv

    IF the PRV does not maintain the same pressure, or close to it, under both dynamic and static conditions it IS defective.
  7. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    I never said it wasn't. However, it is not the source of this problem. I still have good reason to repair it, but it won't fix the showerhead issue.
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,684
    Location:
    Cave Creek, Arizona
    pressure

    I am not even sure what the showerhead issue is, because ANY Delta valve will deliver MORE water than a showerhead is designed for.
  9. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    And if it doesn't? Then perhaps there would be reason to replace the shower valve. Or if one wanted to know what the dp should be for a specific flowrate to determine what showerhead supply pressure to expect with a given dynamic PRV pressure... As it is, the Delta can be a pretty large restriction: about 20 psi loss at 2.25 gpm in my measurements. (Wouldn't be at all suitable for low supply pressures with 2nd/3rd floor as it would begin starving the showerhead.) At 3.46 gpm it is pretty much tapped out at 48 psi loss across the Delta valve. That's not a major factor here as I have enough supply pressure to work with at the reduced flows I am targeting.

    When one is trying to determine where the problem is, it is best to have performance curves for the components, hence my request. That way someone with some experience designing and troubleshooting distribution systems can actually identify the offending component rather then play part swapper on other things that won't fix the fundamental problem.

    As it is, my test worked, and is apparently the same arrangement as that of the designer of some of the showerheads. He has an idea of what the problem might be and is sending some parts.
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