Flushing toilet drops water pressure to almost zero


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Old 11-25-08, 09:56 PM
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Flushing toilet drops water pressure to almost zero

Hi,

We have a two-story house with basement, with a private well. The problem I have is that when we flush one of the toilets, the water pressure drops to almost zero. The shower can be running with a nice, hard, steady pressure, and keep running for a long time with no noticeable pressure change, until you flush a toilet. Then it drops to a trickle -- I'm not exaggerating, the water literally trickles out of the shower head. It will continue trickling, even long after the toilet has finished flushing, until you shut it off, let it sit for a minute (more likely two), and then turn it back on.

The same problem occurs with the bathroom and kitchen faucets -- they drop to a trickle when a toilet is flushed.

There did not seem to be a problem with the pressure tank, but just to be sure, I recharged it tonight. The pump kicks on at 40 PSI, and off at 60 PSI. So I shut off the well, opened a basement faucet until the water stopped running, closed the faucet, and pressurized the tank to 38 PSI. When I turned the well back on, it ran until the pressure hit 60 PSI, and shut off. I ran the basement faucet full open, and the pressure in the tank s-l-o-w-l-y dropped until it hit 40 PSI, then the well turned on, and the pressure made its way back up to 60 PSI. So far, no problem.

Turned the faucet off and went upstairs and turned on the shower. Got a nice, hard, steady stream of water. Flushed the toilet . . . . shower dropped to a trickle.

I don't get it. A toilet uses what . . . two or three or maybe four gallons of water? And gets fed by a 1/4" pipe?? What the heck is going on here?

By the way, there are a water softener and a sulfur-removal filtration system right after the pressure tank. But I've got the valves for those on bypass for right now, so they're not the culprits.
 
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Old 11-26-08, 02:23 PM
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When did the problem start? Was any work done at that time? How does the pressure tank work? Does it invlove compressed air like high rise sprinkler systems? I think that's where I would be looking.
 
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Old 11-26-08, 02:46 PM
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It's not related to any work on the plumbing. In fact, it will be OK for a long time, then it will consistently cause problems for days or weeks, then it will be OK again.

The pressure tank is in the basement and is pretty standard for private well installations. There's an air-filled rubber bladder inside which maintains the water pressure inside the house. When the pressure drops to 40 PSI, the well turns on and pumps more water into the tank, until the pressure hits 60 PSI. Then the pump shuts off, and the air pressure in the tank forces the water through the system as it's used. As water gets used, the pressure gradually drops, and when it hits 40 PSI the well turns on again. Lather, rinse, repeat.

I don't think the pressure tank is the problem, because I'd expect there to be an even worse problem when I run the washing machine or use a garden hose, which would draw even more water at a faster rate.

I was at the hardware store for something else and talked to the guy there. He suggested putting an air gap between the toilet supply valve and the supply line. For less than 10 bucks in parts (a tee, two nipples, and a cap), it's worth a shot.
 
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Old 11-26-08, 03:08 PM
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I'm not familiar with pressure tanks used in wells. How does that "air bladder" work? Could the air flow become restricted from time to time?
 
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Old 11-26-08, 03:28 PM
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It sounds like you may have a restriction somewhere in the line from the pressure tank to the house. Since it affects a both hot and cold water it has to be before the Water Heater. It could be a buildup of debris, or Bacterial Iron. Is there a place where the water line necks down from say 1" to 3/4". That would be where I'd start. What happens if you partially close the toilet shutoff valves to slow the flow to fill the tank?
 
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Old 11-26-08, 03:34 PM
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Think of a big inflated balloon inside the top half of the cylindrical tank. As the tank fills with water, it compresses the "balloon". The balloon wants to expand to its normal size, so when a faucet is opened, the force of the expanding balloon pushes water through the plumbing. As water is pushed out of the tank, the air pressure in the "balloon" drops. When the pressure drops below a preset point, the well turns on and pumps more water into the tank, compressing the "balloon" again.

There's a valve (like a bicycle valve) connecting the balloon to the outside of the tank, so you can add pressure to it externally, as they do tend to lose pressure very gradually.

Insufficient pressure in the bladder (or "balloon") would be revealed by overall low water pressure in the house, and/or excessive cycling of the pump. If there's not enough pressure, a relatively small amount of water usage will cause the pressure to drop enough to make the well turn on, and conversely, it will only take a relatively small amount of water to compress it enough to reach the shutoff pressure.

Again, the pressure in the tank is unlikely to be the culprit in this case, as the problem is specific to flushing the toilets.
 
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Old 11-26-08, 03:40 PM
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Originally Posted by dhamblet View Post
It sounds like you may have a restriction somewhere in the line from the pressure tank to the house. Since it affects a both hot and cold water it has to be before the Water Heater. It could be a buildup of debris, or Bacterial Iron. Is there a place where the water line necks down from say 1" to 3/4". That would be where I'd start. What happens if you partially close the toilet shutoff valves to slow the flow to fill the tank?
Thanks, I tried that this afternoon. Partially closing the shutoff valves helped some, but of course I had to shut them all the way to completely eliminate the problem. Wouldn't a buildup of debris cause a more general problem, not just when toilets are flushed? That's what has me really confused.

Did you see my comment about the recommendation to put in an air gap? The way it was explained to me kind of made some sense . . . in any event, it's cheap and easy to implement, and equally easy to undo if it doesn't help. Any thoughts on it?
 
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Old 11-26-08, 07:18 PM
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Originally Posted by jwnewman View Post
Thanks, I tried that this afternoon. Partially closing the shutoff valves helped some, but of course I had to shut them all the way to completely eliminate the problem. Wouldn't a buildup of debris cause a more general problem, not just when toilets are flushed? That's what has me really confused.

Did you see my comment about the recommendation to put in an air gap? The way it was explained to me kind of made some sense . . . in any event, it's cheap and easy to implement, and equally easy to undo if it doesn't help. Any thoughts on it?
So even if you close down the toilet valve to fill very slowly it still dumps pressure to the shower when you flush? I was thinking a debris blockage would allow water thru but at very low volume so the pressure would build up in the house until it was dumped some way, say by the toilet then the blockage would prevent full flow. Not sure how an air gap would help. It sounds to me like you have a volume problem, there is not enough water being delivered by your water system to support the use of more than one fixture. I suspect it is better on the lower floors of the house than upstairs. We have Bacterial Iron in our well water and before I put in an Iron Filter we used to get a lot of orange crud building up in our pipes eventually clogging them.
 
 

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