Strange water pressure issues.

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jpbordeaux87

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This gentleman whom I was working for today is insistent that his water pressure problems are not related to his ultraviolet filter, but to the piping that he had done on his house. Every fixture in his house has good pressure other than the bathtub that he ran 3/4 cpvc to. When you turn the bathtub on, it has very low pressure, and causes all the other fixtures in the house to lose pressure almost entirely.... It is only a fifty foot run from the pressure tank (which has great pressure at the boiler drain) to the bathtub that has terrible pressure. Here is a basic diagram. http://i.imgur.com/SKrV8aH.jpg Any thoughts would be appreciated! Thanks guys.
 

Reach4

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I would add either another boiler valve (where you could attach a gauge) or just a pressure gauge at the output of the UV filter.

You could also raise the pressure switch from 30-50 PSI to 40-60 PSI, or 40-60 PSI to 45-65 PSI.
 

LLigetfa

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Don't confuse flow and pressure. When there is a flow restriction, such as a long undersized pipe run or a flow limited device such as a UV filter, the pressure only drops as the flow increases. Tub fillers generally have greater flow rates and so can rob the rest of the outlets of pressure.

When my wife fills her soaker tub the iron filter and water softener become the choke point and the pressure drops immediately. Also, the well pump GPM cannot keep up with the demand.
 

jpbordeaux87

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I would add either another boiler valve (where you could attach a gauge) or just a pressure gauge at the output of the UV filter.

You could also raise the pressure switch from 30-50 PSI to 40-60 PSI, or 40-60 PSI to 45-65 PSI.

Good plan. I will try this. Can you think of a reason the pressure drops off dramatically at the other fixtures even though the tub is only trickling water out? It doesn't seem like there is enough flow from the spout to rob the other fixtures of their pressure.
 

Reach4

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No. I presume that the flow is enough to rob the available water. If you are seeing something other than that, I would have no theory.

I don't know if those UV filters have a flow limiter to force sufficient contact time of UV to the water. It would make sense if they did, but I don't know how they actually build these things.
 

Jadnashua

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There are a few full flow water outlets in a home...pretty much all faucets, showers have flow restrictions in them. But, a tub filler is generally not restricted, so can take all that it's own valve can provide. 3/4" cpvc is only slightly bigger than 1/2" copper ID. Depending on your static supply pressure, you could expect about 5gpm of full flow from each of the hot and cold lines, but unless you have a 3/4" tub filler valve, you'd probably top out at about 8gpm, depending on how much hot/cold you're mixing.

Typically, a hose bib going outside is unrestricted, as could be those feeding your washing machine. YOu can get an idea of the max flow through your system by using a big bucket on one of those outlets and time it. My guess is that you have a restriction, probably the filter, that is limiting your total flow through the pipes, and you can only keep up the flowing pressure when the outlet is equal or smaller than the supply can provide, otherwise, the pressure will drop. Think soaker hose...lots of outlets, not all that much inlet verses feeding a hose nozzle that is partially closed down...water goes much further from the nozzle than the soaker hose where it dribbles out because of flow rates...the inlet pressure is the same.
 

hj

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If opening the tub valve causes the storage tank to lose its pressure, which would then affect all the other fixtures, then it is a tank or pump problem. If its pressure remains high when everything else is low then it is a restriction between the tank and the faucets.
 

Reach4

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I interpreted " pressure tank (which has great pressure at the boiler drain)" to mean that there is great pressure at the gauge at the pressure tank, even when the tub is filling.

It seems to me that everybody posting, including the OP, thinks that the UV filter is causing the pressure loss during the high-flow conditions. The OP will try to explain the situation to his customer, who doesn't want to believe that the UV filter is the problem. The OP wants to eliminate other potential explanations first.
 

LLigetfa

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I interpreted " pressure tank (which has great pressure at the boiler drain)" to mean that there is great pressure at the gauge at the pressure tank, even when the tub is filling...
That is only an assumption. Even if the pressure at the tank drain is good, it is still dubious. For example, my tank has three individual ports on it, an inlet, an outlet, and a blowdown (drain) so if the pressure at the drain drops, then I know the pump cannot meet demand.

If the tank uses a single port with a tank Tee, then a flow restriction at the tank port can complicate the prognosis. Whenever there are inline flow restrictions such as filters, it is advantageous to have pressure gauges on both sides of the filter.

Pressure drop due to friction losses can be complex to diagnose because the friction loss is summed from all the components in series. On my system, the first flow restriction is the micronizer before the hydro-pneumatic tank. The second is the line from the tank to the iron filter which tends to build up with iron. The third is the iron filter itself. The fourth is the softener. The fifth is the piping, and the last is the fixture.
 
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