Need help diagnosing water pressure problem


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Old 08-21-11, 12:09 PM
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Need help diagnosing water pressure problem

We moved into our house a year ago and have been experiencing water pressure issues ever since. I need some help figuring out where the problem might lie. I'll do my best to describe the symptoms as well as the complete plumbing system.

Symptoms:
1. When you turn the water on at a faucet, there's about 1 second of strong pressure and then, over the next couple seconds, the pressure decreases significantly.
2. Occasionally, the pressure in the shower drops to less than half of normal. You can turn the water off and back on but the pressure will still be terrible. The next day, it will be back to normal.

System:
The house is 8 years old. It has city water.

The meter is out at the curb, down several feet. A copper pipe enters the house through the basement wall. Immediately, there's a shutoff valve and then a PRV. After the PRV, it changes over to 1" PEX. That 1" PEX travels about 20 feet to the mechanical room where it goes into a small "Manabloc" manifold which feeds 1/2 PEX to the two outdoor spigots, the kitchen sink, and the ice-maker.

After the manifold, the 1" PEX continues to a water softener. 1" PEX comes out of the water softener and then goes to both a large Manabloc manifold and to two water 40 gal water heaters (1 is 8 years old, the other is only a year old). The hot water feeds back to the manifold. From the manifold, individual runs of 1/2 PEX feed all the sinks, toilets, showers, etc.

Comments:
1. I've bypassed the water softener to see if that was the problem. It didn't seem to make a difference.
2. When a plumber was here for something else, I had him check the water pressure. It was 70psi at one of the outdoor spigots, but he didn't do anything like turn the water on somewhere else in the house to see if it dropped.
3. There's no expansion tank anywhere.
4. Another plumber that was here suggested that the problem might be a bad PRV.

I'd appreciate any ideas y'all have.

Thanks.
 
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Old 08-21-11, 03:50 PM
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I'd say 95% it's a bad PRV. The fluctuating pressure indicates that it is likely that. The good thing is that new PRVs aren't all that expensive, and depending on how they are hooked up, can be reasonably easy to replace.

You should also probably have an expansion tank somewhere. Usually, these are installed near the water heater. As the water expands as its heated, it has nowhere to go since the PRV acts as a check valve. Obviously, you don't want the pressure in the pipes building too much.
 
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Old 08-21-11, 07:55 PM
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I totally agree with Zorfdt.
 
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Old 08-22-11, 09:52 PM
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Thanks. I'll look into replacing the PRV.

With regards to the expansion tank - should that be installed before or after the water softener (or does it matter)?
 
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Old 08-23-11, 12:12 AM
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The expansion tank should be installed in the cold water supply to the water heater, after the shut-off valve to the heater.

cold water supply>shut-off valve>expansion tank>water heater inlet
 
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Old 08-23-11, 10:57 AM
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And just a note. The air in the expansion tank should be set to the same static PSI as the home.

So if 70 psi, set the air in the tank to 70 psi. ( They are usually only preset to 40psi)

Mike NJ
 
 

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