Maximum water pressure in home?

14 years ago

I am responding to message that has been lost. Both justalurker and asosl were helping me. So for them, my status is as follows:

Hi Again,

Thanks so much for your patience, but I finally did get it, although I don't understands the principal of having the tank pressure equal to the water pressure. But I totally trust you guys and I did drain my system so there was zero water pressure. When I checked the tank water pressure it was zero. So I pumped it back to around 55 PSI and was very proud of myself. I turned the water on again, turned off all the faucets, put my tools, and ladder away and it suddenly dawned on me--why was the tank pressure at zero? So back up on the latter, put some spit on my finger and put it on the air valve. As you might have guessed there, was a very slow small bubble, but nonetheless a bubble. Since I have new valves for my car I started all over again. Turn the water off, open faucets, turn off water heater, replaced the air valve, repressurized the tank, and there was no bubble. So I'm now back to where I should be, but will have to monitor the maximum pressure in the tank, but I'm betting all is okay.

Now for the rest of the story. I live in townhome/condo complex and several years ago a unit had a water house spring a leak and caused a lot of damage. Since I was on the homeowners board at the time as well as I walk everyday including around our development. I talked with the owners and they mentioned that their insurance agent had noted 150 PSI--my well water pressure in my previous home had been about 30 PSI. Since I was suspicious I got on the web and that is when I heard the pressure inside the home should not exceed 80 PSI. In those forums/e-mail messages it was suggested that maybe their expansion tank was faulty. My response was "what's an expansion tank?". Well I soon learned the extreme need for not only a good expansion tank, but to even have an expansion tank if you don't already. The developer had never installed expansion tanks in any of 122 units. So we very hurriedly decided to not only install expansion tanks, but to also replace the pressure control valves as they were about 20 years old. We bought industrial quality control valves and new pressure tanks for all 122 units.

Because of that investigation I had purchased a pressure gauge and so installed it near my furnace and expansion tank. Without it I would not have known I had a problem. Now I worry about the other 121 units. How does one know, without a pressure gauge, when they are in trouble? Are there symptoms other than an exploding hot water tank? I'm surprised my hot water tank did not open it's safety valve.

One more aside that plumbers might be interested in is another problem we were having. Half of our units had high efficiency furnaces which have acidic drainage and the drain pipes were copper and several units had damage from dripping drain pipes. As you probably know copper will be eaten by the acid, soooooooooooooo we also replaced the copper drain pipes with PVC. I now know more than I ever wanted to know about plumbing. (:-))) Uncle Dewey

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Comments (6)

User
14 years ago
last modified: 9 years ago
Symptoms of thermal expansion can be toilets running for no reason, T&P valve on WH burping water for no reason, and repeated leaking of faucets for no apparent reason.

A tattletale gauge is cheap and it's a good item to have. I have one installed at the WH cold inlet.
User
14 years ago
last modified: 9 years ago
Here's some reading for you... http://www.hotwater.com/bulletin/bulletin45.pdf
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In a municipal water supply system the static head pressure on the system is primarily generated by means of water towers. Water exerts 0.434psi per/ft on a vertical column of liquid. (Vertical Static Head) In order to insure that the system will maintain the required code minimum of 45psi the support tower is 105' tall above average terrain to the base of the storage tank. (105' x 0,434psi= 45.57psi) The storage tank on the top of the tower may then be as much as 92ft higher. (0.434psi x 92' = 39.92psi) From this we can easily see that when the storage tank is empty we still have a static head pressure of 45psi, however when the tank is full the static head pressure at the ground level would be 45psi + 40psi = 85psi. The storage tank is then fitted with a pump controlled by a float system very similar to the fill valve in a toilet tank. Wherever practical the system is allowed to use the water from the tank during the day and the pumps are set up to refill the tank at night when the electrical supply for the pumps is on an off peak demand. Generally a municipal water supply will provide the highest static head pressure to your house early in the morning when the tank is full, but that pressure may decrease throughout the day as the water level in the storage tank drops. To this point we have discussed the pressure above average terrain however the actual pressure at your faucet is a net result of the physical differential between the elevation of your faucet and the top surface of the water in the storage tank. If your house is substantially above the average terrain elevation at the storage tank your water pressure will be less than the average for the community, and conversely, if your house is below average terrain your water pressure will be higher. By example, I am familiar with one community in W.PA where the town is built on steep hills. While the municipal water system can provide water pressures within the prescribed code range of 45-80psi for the majority of the community, there are neighborhoods at the bottom of the hills where all structures must be fitted with PRV's. On the other hand, some of the structures on the top of the hills actually require boost pumps to maintain code minimum. As you can see from this, during the course of a day the line pressure could vary by as much as 40psi, depending upon the actual level of the water in the municipal storage tank. For this reason we do not install pressure gauges on systems supplied by a municipal water supplier because the gauge would not provide any truly useful information, and it would only cause undue apprehension of the part of the untrained homeowner, which would then results in hundreds of unwarranted complaints to the water supplier.
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OK, i take it back. 1st. Before the copper pipe in the house, you may have galvanized pipe outdoors. The municipality has to replace it. ( "... i think its more a problem from the street as neighbors complain as well..." ) If the entire house was a low-flow (or low pressure) problem, this is the cause. It will be felt as a low pressure problem because of the restricted flow. This is called dynamic pressure. But before you turn on the tap, the pressure might be (static pressure). A pressure mater is inexpensive, easy to get at a hardware store, and easy to install. It will help you identify your problem more clearly. Or, you could just ask the city to change the supply pipes, since you and several neighbors all have the same problem. You have to let a fairly large quantity of water flow, in any case, to get really hot water to the sink "for cleaning pots and pans" The need is to get Hot Water to the kitchen. This does not depend on the 1st thing above. If the flow and pressure are low, it will increase the time you have to wait. But nothing will change this for the better. Except one thing: new city supply pipes (outside). The Distance between the kitchen and the hot water source is what determines the amount of wasted water before you get hot water. That, and whether the pipe is 1/2" or 3/4". Where is your tank? It is normal for the first several seconds to feel warm water, not hot. This is because the heat is being lost to the pipe at first. Once the pipe itself gets warmed up, the water temperature at the faucet is much higher. Hope this helps. Here is a link that might be useful: pressure versus volume, in 3/4in. or 1/2in. pipe
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asolo
14 years ago
last modified: 9 years ago
"The developer had never installed expansion tanks in any of 122 units."

I live in a large development mostly completed about 1989. Hundreds of houses. Street pressure is 127psi. All the houses have PRV's. NONE -- except mine, now, after all my troubles -- have expansion tanks. ALL of the water heaters are installed on slab with no plinth or drain-path in the event of leaking. Every one of these houses is -- like mine was -- a plumbing time-bomb.

The plumbers I brought in on-site to repair the damage and install plinth, drain-path, and expansion tank at my direction didn't know the codes or the reasons although the supervisor fessed-up when I questioned him. The city inspector couldn't have cared less about any of it. Justalurker was the one who set me straight...and helped me embarrass more than one plumber along my path. Seems to me we're all on our own.
User
14 years ago
last modified: 9 years ago
IIRC, the expansion tank requirement on closed systems became code around 92 or 93.
User
14 years ago
last modified: 9 years ago
More good reading... http://www.aohomeinspection.com/pdf/Thermal-expansion-control.pdf
asolo
14 years ago
last modified: 9 years ago
Didn't know that. Maybe should let plumbers and inspectors off the hook.

My disaster and repairs took place just a couple of years ago. Perhaps only requirement for them was to replace in-kind? Again, don't know, but happy to have repaired/replaced with better. I would prefer not to go through that again.

Maximum water pressure in home?

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