# PEX and Water Hammer Arrestors



## jar546 (Feb 21, 2020)

Is there an exception that precludes the use of hammer arrestors when using PEX or other similar tubing for water supply to quick close valves?


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## mark handler (Feb 21, 2020)

There is no exception, that I can find, in the Code. But both the California and International plumbing codes say the Water-hammer arrestors shall be installed in accordance with the manufacturer's instructions.

IMHO, there is no need due to the expansion capabilities of PEX. But that is not Code.


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## jar546 (Feb 21, 2020)

I agree.  We have had some plumbing inspectors that won't enforce water hammer with PEX due to the very reason you point out but that is not consistent with the code.  If this was a non-issue I assume there would have been an exception by now.


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## Rick18071 (Mar 4, 2020)

Only required for quick-closing valves. Can you build a house with only slow-closing valves?


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## Gregg Harris (Mar 6, 2020)

Excess velocity of the water and loose strapping can also cause water hammer along with quick closing valves and loose washers on faucets.


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## Glenn (Mar 12, 2020)

mark handler said:


> There is no exception, that I can find, in the Code. But both the California and International plumbing codes say the Water-hammer arrestors shall be installed in accordance with the manufacturer's instructions.
> 
> IMHO, there is no need due to the expansion capabilities of PEX. But that is not Code.


A water hammer arrestor is not for expansion.  It is to stop velocity.  The PEX would not expand to absorb that force.


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## mark handler (Mar 13, 2020)

Glenn said:


> A water hammer arrestor is not for expansion.  It is to stop velocity.  The PEX would not expand to absorb that force.


When a valve closes quickly and stops the flow, that momentum shakes and pounds pipes, through pressure. The PEX will absorb that force.


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## Glenn (Mar 13, 2020)

mark handler said:


> When a valve closes quickly and stops the flow, that momentum shakes and pounds pipes, through pressure. The PEX will absorb that force.


I'm not arguing that a flexible pipe can't handle the movement from water hammer.  I'm arguing that the expansion capabilities of PEX will not stop water hammer from happening.  Different discussions.  Stopping water hammer from occurring or tolerating the movement from water hammer.


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## jar546 (Mar 13, 2020)

I am waiting for the code to reflect an exception for PEX.  Until then water hammer arrestors are required.


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## classicT (Mar 13, 2020)

PEX can absolutely handle the water hammer, it can even withstand the line freezing solid.

The problem is that water hammer can cause extensive damage to valves and end-point systems, even if the supply line is PEX.


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## Rick18071 (Mar 13, 2020)

Most homes in my area have wells. Is there an exception that precludes the use of hammer arrestors when using a pressure tank when you have quick closing valves?


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## classicT (Mar 13, 2020)

Rick18071 said:


> Most homes in my area have wells. Is there an exception that precludes the use of hammer arrestors when using a pressure tank when you have quick closing valves?


Still best to have the arrestor at the quick acting valve; after all, water hammer is caused by the sudden change in velocity of the water. A pressure tank will often be a significant distance from the quick acting valve, so it will provide limited, if any, benefit.


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## classicT (Mar 13, 2020)

Check out this article...it provides a decent breakdown of the engineering and justification for placement of hammer arrestors.

https://www.pmengineer.com/articles/85460-water-hammer-arresters-sizing-and-placement


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## jar546 (Mar 13, 2020)

Rick18071 said:


> Most homes in my area have wells. Is there an exception that precludes the use of hammer arrestors when using a pressure tank when you have quick closing valves?



I'm not aware of that exception.


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## Ed Cooke (Mar 19, 2020)

3-19-20: California Plumbing Code section 609.10 is not adopted by the state agency, HCD1 and 2, which is the code of the hammer arrestor. See the Division I administrative section,1.8.2.1.1 in the code for that language as to who adopts or does not adopt certain sections. For those who want the short answer, not required in residential units containing sleeping accommodations, unless your jurisdiction has adopted it and registered that with the state.


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## classicT (Mar 19, 2020)

Ed Cooke said:


> 3-19-20: California Plumbing Code section 609.10 is not adopted by the state agency, HCD1 and 2, which is the code of the hammer arrestor. See the Division I administrative section,1.8.2.1.1 in the code for that language as to who adopts or does not adopt certain sections. For those who want the short answer, not required in residential units containing sleeping accommodations, unless your jurisdiction has adopted it and registered that with the state.


Might be so in Cali.....but good luck with that elsewhere.


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## Gregg Harris (Mar 19, 2020)

jar546 said:


> I'm not aware of that exception.


Exspansion tanks nor pressure tanks a designed to control the absorbtion of the velocity of the water. Hammer arestors are of a specific designe to absorb the shock and are location specific to function correctly.


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