# Water hammer



## newyorkcity (Nov 25, 2010)

What could be the causes of water hammer in this scenario:
-you hear it in the basement only
-6 story, 72 family building
-flushometers
-3" domestic water main with a pressure tank
-the problem has been since the last 3 weeks only
-when someone flushes, there is a bang in the basement piping, not upstairs, and it does not -happen if the toilets are flushed again within 3-5 minutes.
*could it be a loose stem banging with the fast closing flushometers?


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## Gettinit (May 9, 2012)

newyorkcity said:


> What could be the causes of water hammer in this scenario:
> -you hear it in the basement only
> -6 story, 72 family building
> -flushometers
> ...


Bad hammer arrestors. Air charge lost in the pipes being used as hammer arrestors. 

If there is a loose stem it has been my experience that it would have completely come undone.


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## Gettinit (May 9, 2012)

If there were not so many flushometers they make diaphragms that helps to reduce we're completely and water hammer if there were no way to get a hammer arrestor in its proper place.


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## newyorkcity (Nov 25, 2010)

Good point - most of the building has been repiped with no air chambers or water hammer arrestors, but it couldn't hurt to drain down the building and refill to empty the air chambers, if they exist.


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## Gettinit (May 9, 2012)

newyorkcity said:


> Good point - most of the building has been repiped with no air chambers or water hammer arrestors, but it couldn't hurt to drain down the building and refill to empty the air chambers, if they exist.


I would put it in writing that I will not be responsible for any flushometers that need to be rebuilt. I am certain you will have some to get trash in and need to be replaced. If that was the case I would go back with those special diaphragms as an extra precaution.


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## stillaround (Mar 11, 2009)

What kind of pressure tank...typical tank with air compressor???? That eliminates all piping before the tank. Assuming the level is proper in the sight glass, look for the longest run after the tank.


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## Gettinit (May 9, 2012)

Is there a PRV in the sixth floor or roof? If they are over sized they will chatter when new and get worse with age since they may be just barely opening on low flow conditions.


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## Mississippiplum (Sep 30, 2011)

The pressure tank could be waterlogged, that could cause chattering/hammering

sent from the jobsite porta-potty


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## newyorkcity (Nov 25, 2010)

No prv, and the pressure tank is 2/3 full of water. How do you figure out what the air pressure should be?


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## pilot light (Apr 21, 2012)

Iam going to go with a quick closing malfuntioning solenoid valve.:thumbsup:


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## Gettinit (May 9, 2012)

newyorkcity said:


> No prv, and the pressure tank is 2/3 full of water. How do you figure out what the air pressure should be?


You cannot do it while there is water pressure on it. If it is part of a booster pump set up, consult the manufacturer. They will have the drawings and what the engineers determined for your correct pressure for that particular building. If this is a booster set up the tank should be on the top floor and pumps in the basement.


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## stillaround (Mar 11, 2009)

newyorkcity said:


> What could be the causes of water hammer in this scenario:
> -you hear it in the basement only
> -6 story, 72 family building
> -flushometers
> ...


 At your convenience check out some of the science on water hammer. The formulas are hairy but some of the basic concepts can help track out a source.
Water hammer initial pulse is caused by an uninterupted mass of water quickly shut off. The mass ( weight ) of that water creates a spike in pressure and can bounce back and forth at very high velocity. Long piping runs as in the basemant could be "interrupted" by changes in direction or anything that can relieve the physics of the situation, like WHA's....some severe conditions are best served by an engineer. Check the end of a long horizontal for arrestors and remember , the longer the uninterrupted run and the quicker the closing..the worse it gets.


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## user8031 (Dec 14, 2011)

Air chambers are garbage, and pretty much serve no purpose. The air hammer arrestor or mechanical air chambers are permitted here in Michigan, unlike the "air chamber". But even those have a shelf life and eventually fail. Perhaps you could have some sort of failure going on. You would be surprised how many plumbers think they last forever. Just trying to help, based off of your description. Good Luck.


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## Don The Plumber (Feb 14, 2010)

stillaround said:


> At your convenience check out some of the science on water hammer. The formulas are hairy but some of the basic concepts can help track out a source.
> Water hammer initial pulse is caused by an uninterupted mass of water quickly shut off. The mass ( weight ) of that water creates a spike in pressure and can bounce back and forth at very high velocity. Long piping runs as in the basemant could be "interrupted" by changes in direction or anything that can relieve the physics of the situation, like WHA's....some severe conditions are best served by an engineer. Check the end of a long horizontal for arrestors and remember , the longer the uninterrupted run and the quicker the closing..the worse it gets.


 I don't think it has anything to do with any long piping runs, or anything at all, with changes of direction, or the way any of the existing piping system is installed. Why do i think that? Cuz the OP said it only started to do this 3 weeks ago.

IMO it has to be a valve or diaphram of some type, that went bad. Or it could be something as simple as a loose washer in a supply valve, or a hose that was left on, that has a vac breaker. Could be a bad RPZ or PVB on an appliance or lawn sprinkler sysem. Very tough to find in this large of a complex.


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## stillaround (Mar 11, 2009)

Don The Plumber said:


> I don't think it has anything to do with any long piping runs, or anything at all, with changes of direction, or the way any of the existing piping system is installed. Why do i think that? Cuz the OP said it only started to do this 3 weeks ago.
> 
> IMO it has to be a valve or diaphram of some type, that went bad. Or it could be something as simple as a loose washer in a supply valve, or a hose that was left on, that has a vac breaker. Could be a bad RPZ or PVB on an appliance or lawn sprinkler sysem. Very tough to find in this large of a complex.


Don, he called it a water "hammer"....not a chatter. Thats how I proceeded sight and sound unseen....I'd also be willing to quote the job over the phone:laughing:..I had to call an engineer who specialized in water hammer once here in sunny Florida....so naturally I felt qualified to teach....

I dont know what noise was heard....I still would look close to the end of a long run, and charge the customer for that:thumbup:....a sloan valve closes not all that quick anyway.....a supply valve almost closed..best bet.....bad rpz and "hammer" in the basement only doesnt fit quite right for me.

Remember, he said it had a tank with air....that limits outside irrigation.


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## gear junkie (Jun 20, 2008)

What is the water pressure readings before and after the 1st toilet flush?


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## Don The Plumber (Feb 14, 2010)

stillaround said:


> Don, he called it a water "hammer"....not a chatter. Thats how I proceeded sight and sound unseen....I'd also be willing to quote the job over the phone:laughing:..I had to call an engineer who specialized in water hammer once here in sunny Florida....so naturally I felt qualified to teach....
> 
> I dont know what noise was heard....I still would look close to the end of a long run, and charge the customer for that:thumbup:....a sloan valve closes not all that quick anyway.....a supply valve almost closed..best bet.....bad rpz and "hammer" in the basement only doesnt fit quite right for me.
> 
> Remember, he said it had a tank with air....that limits outside irrigation.


 Yea I know its hard to decipher whats happening, just by a description, from someone else. Kinda like when HO calls & says their toilet is broken.

But just because it has an air tank, don't necessarily mean it has air in it anymore. In fact it could be the air (expansion) tank, that is the whole problem too. Who knows. Be interesting to find out what it was, if they ever figure it out.


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## 89plumbum (May 14, 2011)

I'm sure you've thought of this, but was any plumbing work done 3 weeks ago? Maybe a tenant repared/ replaced an angle stop & did not open it all the way?


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## Gettinit (May 9, 2012)

89plumbum said:


> I'm sure you've thought of this, but was any plumbing work done 3 weeks ago? Maybe a tenant repared/ replaced an angle stop & did not open it all the way?


It would ne easy enough to post a sign at the mail boxes.


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## newyorkcity (Nov 25, 2010)

The water hammer is still happening. The building is three buildings combined, with one 3" water main and booster tank. Also with a garbage compactor room in each basement. 
Each of the three compactor rooms have three sprinklers, a rising stem gate valve, check valve and a vacuum breaker in each. 1 1/2" branch line off the domestic in the basement.
The super informed me that when he shuts the gate valve to the compactor room sprinklers, the water hammer from the toilets stop.
1) Why is this happening now after +80 years?
2) The risers have been drained and refilled to empty the air chambers. No difference.
3) A WHA after the check on the sprinkler branch = no difference.

What do you think? A WHA on the domestic before the sprinkler branch?


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## plumbing ninja (Jan 15, 2012)

newyorkcity said:


> What could be the causes of water hammer in this scenario:
> -you hear it in the basement only
> -6 story, 72 family building
> -flushometers
> ...


Could it be an occupancy issue! A lot of residents away on vacation? I had a high rise tower with a lot of empty floors! The flows were so low the system was never designed for it? We installed low flow PRV's in parallel to the main prvs set slighlty lower on the downstream!


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## OldSchool (Jan 30, 2010)

newyorkcity said:


> The water hammer is still happening. The building is three buildings combined, with one 3" water main and booster tank. Also with a garbage compactor room in each basement.
> Each of the three compactor rooms have three sprinklers, a rising stem gate valve, check valve and a vacuum breaker in each. 1 1/2" branch line off the domestic in the basement.
> The super informed me that when he shuts the gate valve to the compactor room sprinklers, the water hammer from the toilets stop.
> 1) Why is this happening now after +80 years?
> ...


Might be the check valve ...


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## U666A (Dec 11, 2010)

What makes you think the air chambers were emptied?


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## newyorkcity (Nov 25, 2010)

*good point*



U666A said:


> What makes you think the air chambers were emptied?


maybe they're not. not accessible to vent 'em.
hmmm....


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## U666A (Dec 11, 2010)

newyorkcity said:


> maybe they're not. not accessible to vent 'em.
> hmmm....


Just a thought... Finger over a straw theory.


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## newyorkcity (Nov 25, 2010)

*Problem fixed*



OldSchool said:


> Might be the check valve ...


Changed the swing checks to spring checks and the banging stopped.


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