Is This Water-Hammer? 1

[RedRover]

I just measured 120 psi on the outdoor faucet located just above the water service entry point to my home. I then removed the water guage and opened the faucet for a few seconds and tested the pressure again. This time it read 40 psi. The house is in Texas, in a rural area, but it is city or county water, not a well. It is a slab construction, one story house and the water enters through the slab (no basement). My neighbors do not have this problem. If it is water-hammer, the problem was observed before we hooked up the washing machine or the ice-maker and before we ran the dishwasher. In fact, it was mentioned in the house inspection report, but we all thought it was just a faulty relief valve on the water heater (where we first noticed the problem). We've been in the house for about 2 1/2 years and the problem still exists, long after the valve was replaced. That did not fix anything. I haven't taken the problem seriously and haven't persued it, but today I decided to measure it at the outdoor faucet and 120 psi is a problem, but as I said earlier, after it runs for a few seconds the pressure drops to 40 psi. So, is this water-hammer, and any ideas on how I can fix it? Thanks in advance for any advice you folks may have.

 

[hydrae]

RedRover
My first thought is it is thermal expansion, is there a check valve on the service line to the house, it may be at the meter, under the meter, or a double check backflow assembly just after the meter or installed in the garage. It may also be a pressure reducing valve which acts like a check valve, and it has a very small leak which allows the pressure to build during time of no use. Back to thermal expansion, The water inside the hot water tank enters cold and when is heated the water wants to expand, with a check valve, it cannot expand so the pressure builds until the relief valve on the hot water tank(set at 120 PSI) relieves any additional pressure. In houses without check valves a small amount of water would flow backward through the meter to relieve this pressure.
The solution is a expansion tank, and the uniform plumbing code require the installation of expansion tanks when check valves are installed on service lines. The tank does not need to be very big.

Hydrae

 

[cvg]

I would take the problem seriously, as home plumbing systems don't fair very well at 120 psi. If the system springs a leak at night or while you are away, you will be facing very serious flood problems in your house.

 

[semo]

I would also install an expansion tank. There were probably no hammer arrestors placed in the waterline during the house construction. You can probably place the expansion tank inline near the water heater.

We always call out for backflow preventing meter bases on our rural customers. When a home (previously using a private well) is connected to a water system, we don't want an unknown cross connection to place contaminated water into the system.

With the homeland security stuff coming into play, I think backflow prevention will and should become a more common standard in water services.

 

[TrevorP]

This is not what I understand by water hammer. Water hammer is caused by sudden valve closure etc., that causes a short transient build up of pressure, putting undue strain on pipework. What you appear to have is a 'high pressure' situation. If, as has been suggested, this is caused by a check valve in the feed line, an expansion tank is a good solution. Another (perhaps cheaper) solution might be to install a relief valve set at say 50 psi. Make sure it's in a location that is unlikely to freeze, but where water drips will not cause a problem (e.g. route it to a drain).

 

[RedRover]

Guys, I just wanted to say thanks and let you know that your advice worked. I installed a pottable water thermal expansion tank according to the manufacturer's instructions and now I have a steady, consistant pressure of 40 PSI on my outdoor faucet--down from the 120 PSI reading that I was getting before I installed the expansion tank. Thanks again for your help.

 

[btrueblood]

RedRover,

Good job. I just wanted to post to say don't just install a lower-setpoint pressure relief valve. Most relief valves (maybe all) are not really intended/designed to suffer repeated "relief" events over long periods of time. The repeated "puffs" of hot water can cause erosion of the valve seat, resulting in a steadily increasing leak rate past the valve. Been there, tried that, bought the tank.

Ben T.

 

[TrevorP]

Ben T.
This is a cold water application rather than a hot water one. I wouldn't have suggested it for a hot water application. Nevertheless, it is fair to point out that a relief valve could still fail over time, and this was omitted from my original post. Failure should be after several years, however.
In any case, the expansion tank is installed and works fine.

 

[KRSServices]

When you observed the guage on the house....what did it do, specifically? Did it rise from 40 psi to 120 psi at a steady rate, or did it bounce?

When you noticed these spikes or when closing (running) water fixtures, do you hear an audible pipe "bang"?

How often did the spike occur? Was it at a particular time(s) of day? Were any water fixtures operating at the time...say a toilet, shower or sink?

Have you noticed little puddles around your hot water tank, or does your tank discharge after peak periods?

You mentioned rural area, how close are your neighbours, in terms of proximity and are they higher in elevation that yourself?

Did you contact the municipality? And if so, what was their comment?

Relative to the rest of the system, how are you situated - say at the bottom of a hill or the low end of the subdivision? Where is the pump station/reservoir relative to your residence?

I ask all these questions, because if your HWT (hot water tank) is relatively new, it is entirely possible that you have not resolved your problem, merely postponed an issue arising from pressure flucutation of the municipal system. Your static pressure of 40 psi indicates that you are at some higher point in the water system. I say this because the "normal" operating pressure is usually set to about 60 psi. Now in the case of hills, you may be on the limit of your pressure zone, and the municipaity may have a pressure reducing valve, or PRV, regulating your zone. If this is the case, the PRV may not be set correctly or may be faulty (pilot valve, etc.) and may cause surges, particularly when pumps are switched on for reservoir filling or fire demand (say line flushing operations). Unless, like you have done, a gauge captures what is happening at the neighbours residence, it is difficult to tell when a surge occurs off-peak. During the peak...residences will notice stronger flow from taps. When a nasty spike occurs...the hot water relief valve will open and discharge water...so it is usually reported as a complaint.

If the origin is municipal, you should have installed an inline PRV on your service line. By the same token, if the problem is municipal and your expansion tank fails, you system could be damaged as well. Just my thoughts.

KRS Services

http://www.krs-services.com