water pressure varies


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Old 05-16-01, 03:06 PM
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I need help on this one. My sister's house has 1 1/4" steel water supply. They are approximately 300' away and downhill from the water meter with about a 50' drop in the elevation. My water pressure readings from the hose bibs has always been about 45 psi. They have complained of low pressure from the fixtures in the house. They also used to complain that the water heater was making sounds like someone crushing a pop can. (expansion and contraction I assume) The T -n- P valve on the heater recently started to leak so I replaced the TnP and added an expansion tank. Now they are very happy because the water pressure appears to have gone way up. If you run water for about 10 minutes then the pressure starts to drop again. Why is this happening? Is this increased pressure coming from the expansion tank? Is pressure compressing the balloon in the exp. tank and then it takes 10 minutes for the balloon to scrub off the excess pressure? Is this a setup excessively stressful on the plumbing? tips? opinions?
 
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Old 05-16-01, 03:15 PM
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Do you know what the pressure is at the meter?

A drop of 50' should give the pressure at the house additional 25 psi.

I don't think the expansion tank is a factor, it would take less time then you indicate for the expansion tank to even out in pressure.

Do you know if there possibly a PRV in the mainservice to the house? If there is, could be getting clogged up.
 
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Old 05-16-01, 03:19 PM
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No PRV
 
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Old 05-16-01, 03:22 PM
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Does this lose also take place with running the outside hobe bibb?
 
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Old 05-17-01, 03:03 PM
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I don't know. I haven't been back since she first showed it to me. I will need to get accurate pressure readings and time the pressure drop. I was just wondering if I was missing some general principle or law of physics that would explain the phenomenon.
 
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Old 05-22-01, 11:21 PM
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if you only have 45 pounds of street pressure and a 50 foot
drop in grade from your house to the street then by all means you will not have a pressure gain. your situation
will be improved only with higher street pressure. the friction loss will work against you in this application.
 
 

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