50 psi Drop When the Toilet Flushes?


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Old 03-11-08, 08:03 PM
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50 psi Drop When the Toilet Flushes?

Two story 1990 home. We have lived in it for only 6 months, so still learning the ins and outs.

When showering upstairs, the water is reduced to an unusable trickle when someone flushes the downstairs toilet. There is no similar reduction (it lessens, but not to such a dramatic extent) when using the downstairs bathroom sink faucet, the kitchen sink, outside hose bibbs, etc.

I hooked a pressure gage to the hose bibb that is right above where the home main enters the house: static pressure, 110 psi (I don't think this high pressure was due to thermal expansion, since it would return to 110 psi immediately after shutting off cold water). Flowing pressure (i.e. when a bathroom faucet is on) about 60 psi.

This static pressure is too high, obviously, so I went to check the PRV next to the city meter. It was completely buried in dirt, so I spent an hour digging it out. It looked awful and the screw was rusted (the PRV was likely as old as the house, so about 18 years). I went to Home Depot and bought a 3/4" Watts PRV, and put it in (luckily it was exactly the same size). I adjusted the screw down a little and checked the pressure at the hose bibb again: 80 psi static.

When I turn on the faucet in the downstairs bathroom, the pressure gage reads about 70 psi at the hose bibb. However, when I flush the toilet in the bathroom and toilet begins to fill, the pressure gage reads 30 psi! What is up with this huge pressure drop? Is it possible that the toilet has a much higher flow rate than any faucet downstairs? Could this explain it?

Sorry for the long-winded story, but I am totally befuddled.

Ed.
 
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Old 03-12-08, 07:05 AM
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Bad plumbing job with not having large trunk line with smaller branch lines, or clog/restriction somewhere at the beginning before first toilet, I'd say.

What are your pipes made of? And is this something that has recently occured, or has it always been like this?

Do you have full house water filtration that imediately cuts water volume down to say 5 gpm max? What can happen if you do, is the filter acts like a clog. Since 5 is max, then the first downstairs fixture is still able to have a lot of that volume come out, which drops the available volume to the harder- to- push- upstairs fixtures. I recently went through such a case with a lady on a well. Same problem, basically, as you.
 
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Old 03-12-08, 09:17 AM
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The pipes I can see (under the sink, etc) are copper. We have always had the problem, where that one toilet has such a large effect on the rest of the pressure in the house. I was hoping the new PRV might fix it, but no joy.

As far as I know, there is no whole house filter. I have difficulty figuring out the general plumbing layout because we are on slab.

Thanks for the input,

Ed.
 
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Old 03-12-08, 02:06 PM
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Pipes under the slab? Got crushed maybe?, or kinked at some point? I presume you have no noteworthy leak, based on your static pressure, unless static pressure was never taken at a faucet as it comes back up out of the slab? And remember what I said about solder in the pipe. Or even some rock or ? got in the pipe during construction. Definitely some restriction in the line to be causing this.
 
 

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