residential water hammer 1

[bigwaterbill]

Will reducing water pressure from 80 psi eliminate water hammer? What pressure would be needed? Any and all suggestions appreciated.

1/2 copper cold water supply line coming off 3/4 main line. Feeds 9 cold water fixtures and all cause water hammer at the tank-less water heater. All fixtures are within 12 feet from each other. Longest line is 14 feet.
Flow rate at the end of this line at hose bibb is 7.46 gpm. There is no PRV, expansion tank, check valve is the system. City water system with 5/8 water meter without back flow valve.

Thanks

 

[btrueblood]

It will help, but may not completely eliminate, a water hammer problem. Water hammer is happening because the flow velocity, just prior to valve closing, is too high - or in other words, the valve is closing too quickly for the velocity. What exactly are the cold water fixtures - solenoid type faucets, or standard globe valve type?

Suggestions? Any or all of the following:

- Add a flow restrictor (plumb in a needle valve, so you can adjust) upstream of the fixtures, (and yes, a pressure regulator would do this also, though more expensively)
- add an air column or similar damping device, just upsteam of first fixture,
- Change the fixtures to slow-closing (anti-hammer) faucets/valves, and/or put flow restrictors on the faucets.

 

[bigwaterbill]

Front load washer (solenoid)
Kitchen sink, lav, laundry tub (1/4 turn type)
Hose bibb (old globe type)
Bath shower ( single knob cartridge type)
Toilet ( Korky fill valve)

 

[nackra]

http://www.plumbingsupply.com/waterhammerarresters.html

follow-up to btrueblood suggestions

 

[LittleInch]

Btrueblood is correct, velocity causes water hammer our surge, but it is driven by pressure difference. Also surge pressure adds to existing pressure.

So yes inserting a single main pressure regulating valve will reduce velocity, maybe down to 20psi given that your piping runs are short and hence not much pressure is lost. This will be trial to see what pressure is enough to keep the users happy, but reduce your velocity. You don't say if there is any height difference but if small shouldn't affect the flow too much.

The flow rate you give works out at about 15fps. You want to aim for less than 10, preferably 7 to 8.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[PEDARRIN2]

Since 80 psig is typically the highest pressure allowed by plumbing codes, I would be surprised if you do not already have a pressure reducer near the meter. This typioally is not a dynamic device, it doesn't maintain the 80 psig, but makes sure downstream pressure is less than 80 psig.

I have high pressure at my house and have one.

Since your washer is the only device with a solenoid, i would suggest installing a washer box that has an integral water hammer arrestor.

Look here (

http://www.ipscorp.com/plumbing/watertite/supplyvalve/washingmachine/wmoutlet)

 

[LittleInch]

Quarter turn taps close pretty fast as well though...

Meter pressure regualtor / reducer probably makes sure it's no more than 80 psig, but fully open below this.

No dishwasher?

Those little arrestors in nackra's post look pretty neat though.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[bigwaterbill]

By throttling the shut off (globe type stop waste valve) upstream of the water meter I can reduce the pressure spike by 40 psi. Before it would spike from 80 to 140 psi now it spikes only 20 psi over 80 when a cold water valve is closed quickly. Is this an acceptable range?
Betrueblood suggested a needle valve. Could a 1/2 in. stop waste valve(globe type)be substituted for the needle valve and be plumbed into the 1/2 in. line supplying those fixtures? Easy and inexpensive to find at any hardware store.
I did take flow rates (bucket and stopwatch method) at each fixture. I'm sending this info. to Sioux Chief (manufacturer) to size water hammer arrester/arresters. Also, looking into flow restrictors for faucets.
The tank-less WH is where the hammer shock ends up and makes the water hammer noise. The tank-less is isolated on the 3/4 in. main supply. Would the addition of a 1/2 in. check valve at the beginning of the 1/2 in. line serving the offending fixtures isolate the shock wave and dissipate the energy into the water hammer arrestors? Is this an option?
The reason I bring up the check valve is that I placed a screw-on 40 psi pressure regulator (RV camper type) to the hose bibb and generated water hammer with a spring loaded garden hose nozzle at the tank-less WH. I'm afraid if I go to the expense of pressure regulator down stream of the water meter I may not have resolved the problem without the addition of the water hammer arrestors. Go with water hammer arresters and flow restrictors and proceed from there?
Any thoughts on throttle valve (globe type) and check valve install?

Thanks

 

[LittleInch]

The acceptable range is the point at which the hammer stops, but given that it sounds like you're regualrly exceeding the max presusre domestic fittings are designed for you will eventually damage something by means of fatigue loading.

The issue with any single flow restriction on the incoming line(valve, flow restrictor etc) is that it doesn't alter the base pressure when no flow or only one outlet is operating, but could significantly restrict the flow when more than one was open. that's why the pressure regualtr was suggested, but I can appreciate it may be a bit pricey.

A check valve might work, but only if sprung loaded and might just disintegrate after too many shock closures. NRVs (especially domestic ones) are not really designed to slam shut more than a few times. The individual outlet needle valve or globe valve sounds like the next best idea as you can "tune" each one to avoid the water hammer without restricting flow too much. You really do need to screw it down quite a long way and as said before, aim for less than 10fps or about 3-4 gpm full flow. Any of the quarter turn valves you can swap put for a globe type valve as well as the flow restrictor / needle valve will also help a lot as the flow shut off is much smoother.

If the issue is the water heater I would put your first surge arrestor on the line to the water heater and se eif that works before adding any others.

Anything you do to restrict flow will mean that things take a little longer to fill at full flow,but in realirty, your system is going too fast.

The only other option is to fit 1" pipe, but I guess that's worse than anything else. They will have fitted 1/2" because it cost less and at that inlet pressure, you don't need anyhting bigger for pressure drop, but it is the root cause of your excess velocity. Double the diameter and for the same flow your velocity drops by a factor of 4.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Artisi]

The water hammer arrestors already posted are the norm for systems with water hammer. Usually fitted at the far end of the line if possible.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[btrueblood]

If the house is a few tens of years old, it likely has old-style water hammer arrestors, in the form of dead-headed pipes (air traps). These can leak air over time, or the air may dissolve into the water and dissipate. You can try turning off all heating fixtures, then draining the plumbing completely dry, and then slowly refilling it by opening a tap near the topmost point of the plumbing - this should recharge all those deadheads with air. Just be careful to bleed water out from every fixture after filling, as trapped air can cause surge flow and shake the heck out of the pipes too.

My worry with pressure regulators is that it can be tricky to size one - but if you know your min. and max. expected flow and desired pressure reduction, you can take a shot at it. Just remember that a grossly oversized regulator can squeal when it is flowing high differentials near shutoff, and an undersized regulator can also sometimes chatter. Be ready to try a couple different sized regulators, and don't skimp on the price.

 

[chicopee]

The problem also stems from having 1/2" line feeding 9 fixtures. It would have been better to have a 3/4" line with 3/4"X3/4"X1/2" T fittings for each fixture fed by a 1/2" line.

 

[Artisi]

chipopee, fair comment re line size, and others commenting about flowrate, assume this is a domestic setting and would never expect all 9 fixtures being open any one time let alone opening and closing simultaneously - likely there could be 2 operations fairly close together with 2 simultaneous opening / closing extremely unlikely.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)