Plumbing Zone - Professional Plumbers Forum banner

1 - 20 of 31 Posts

·
Super Plumbster
Joined
·
8 Posts
Discussion Starter #1 (Edited)
I was recently talking to an engineer about the hydrodynamics of "water hammer". If I have a basic single handle moen old style (non-positemp) shower valve at the end of a several hundred foot run of 3/4" PEX, CPVC, Copper, Etc. shutting off the valve rapidly, causes water hammer.

Will installing one or more swing joints in the run help eliminate water hammer??? And If so, why does the change in direction via a swing joint help eliminate this problem???

Obviously I could use a prefabed arrestor, air chambers, and other methods and/or devices to elimate this type of problem. I am just not sure how this swing joint concept works, if it does.

I am a 4th generation plumbing contractor in Central Florida w/ about 20+ yrs exp. and have always used other methods mentioned above to eliminate this type problem.

Wondering if someone could enlighten me on this swing joint concept, if it works.

Thanks,

Michael. CFC, CGC
 

·
Registered
Joined
·
843 Posts
If it's threaded pipe, I'd guess that the water hammer would mess up the threads after a while. Better to have slow-closing valves.
 

·
Always Something
Joined
·
1,369 Posts
That poster said the duel TK's were the cause of the hammer.....I'll bet that was his best educated guess. Tankless units do not aid or help remove hammer. At lease in all the ones I have installed and seen. Long runs with proper pressure will still hammer when the valve is slammed shut. Velocity plays a big part in it.
 

·
Always Something
Joined
·
1,369 Posts
I was recently talking to an engineer about the hydrodynamics of "water hammer". If I have a basic single handle moen old style (non-positemp) shower valve at the end of a several hundred foot run of 3/4" PEX, CPVC, Copper, Etc. shutting off the valve rapidly, causes water hammer.

Will installing one or more swing joints in the run help eliminate water hammer??? And If so, why does the change in direction via a swing joint help eliminate this problem???

Obviously I could use a prefabed arrestor, air chambers, and other methods and/or devices to elimate this type of problem. I am just not sure how this swing joint concept works, if it does.

I am a 4th generation plumbing contractor in Central Florida w/ about 20+ yrs exp. and have always used other methods mentioned above to eliminate this type problem.

Wondering if someone could enlighten me on this swing joint concept, if it works.

Thanks,

Michael. CFC, CGC
One of my first bosses used to tell me that at each turn the hammer's energy would dissipate. I would assume based on that theory that a swing joint would equate to enough turns at its operating pressure to dissipate the energy. I never installed one so...take it with a grain.

There was one time I couldn't get rid of hammer, I added a 3/4" line from the service riser about 150'. about 15' was above ground and braced with strut. The rest was about 20" below ground, that was a pex run. I brought it up against a footer and udes a drop ear'd 90 with a few tap cons....point is, there was no pipe wobbling around and when I hit the 1/4 turn hose bib to stop it would ping about 4 or 5 times all within maybe 2 or 3 seconds. Pressure was 70. It was just a hose bib line so I didn't spend a great deal of time on it and it wasn't worth it to arrest.

I think the engineers comments are correct in theory...but in real world...I dunno, I never used one.
 

·
Registered
Joined
·
12 Posts
For water hammer I wouild install factory made shock arrestors as close to the offending faucet as possible. Putting in the swing joints/offset would not hurt either but not sure if it wouild solve the problem. Size the arrestors according to manufacterers recomendations.
Roger
 

·
Registered
Joined
·
5,903 Posts
At my own risk Ill weigh in. Had to call an engineer who said he usually gets 1500-1800 for this stuff so with his angered english accent he walked me thru the basic causes of hammer. Large runs uninterupted have a weight of water that at quick close , that mass, creates a shock that travels very fast. The more the line can be shortened with arrestors the less mass for shock. The swing joints (imo) while slowing velocity a touch wouldnt do it.
 

·
Registered
Joined
·
356 Posts
Little formula for you to figure out how much pressure you have at the end of your run, you can change the variables to suit your application
dp = 0.070 v l / t (1)
where
dp = increase in pressure (psi)
v = flow velocity (ft/s)
t = valve closing time (s)
l = upstream pipe length (ft)
EXAMPLE

dp = 0.070 (5 ft/s) (300 ft) / (0.4 s)
= 262.5 (psi)
 

·
Banned
Joined
·
3,806 Posts
The process with the swing joints you are refering to is a good way to ease thermal expansion on long pipe runs, it will do nothing to prevent water hammer.
 
1 - 20 of 31 Posts
Top