Any heating system guru's? water hammer problem

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Apr 19, 2004
New York
I have a lot of noise (slamming) from my heating system when the zone valves's definitely 'water hammer'. I had a plumber come in last year and replace all the zone valves (Honeywell) to no avail....he also installed one of these but it doesn't seem to help.....(it may even be worse).... Some guys on an online HVAC forum say that Honeywell ZV's are prone to this because they close fast. Does anybody think I would have better luck using Taco's or some other brand? PS: The valves are installed correctly (not backwards) as I know that installing them backwards can cause this issue. My entire system was replaced in 2009 so the ZVs I replaced were only 7 years old. Thoughts?
Anything you can do to purge air from the system could help, but I have not seen this particular problem. I work on hydronic heating and cooling water flows and one of the most common problems I find is air in the system. Is there a valve on a high point to purge air out when the pump is off?
Originally Posted By: knerml
Look into installing hammer arrestors in your lines.
Oscar: Thanks, I had a new expansion tank, scoop and several air bleeders installed so I don't think air is the problem. knerml: Thanks....So the Taco Bypass valve wouldn't do much?
Air in the line can be the solution, not the problem. Quite often there are standpipes above the water line in various locations throughout a building. The idea is that the air remains up top and cushions the surging water. Preventing water-hammer. When I have trouble with water hammer in my home, I simply shut off the water main, and use my shop vac to pull the water out of the house, by going around and opening shower valves and sink valves. I start at the farthest valve and work my way back. Note: A water hammer device needs to be upstream of the valve in question.
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In a hydronic system, the expansion tank allows for this. There should be zero air in the lines or convectors. With no air, there would be no hammer. I suspect the OP does have some entrapped air and a judicious bleeding will get rid of it along with the hammer.
low system pressure can be a cause as well, is your feed water pressure regulator working properly? Mine was stuck closed, and a trifecta of that, a failed exp tank, and a failed relief valve caused my system pressure to regularly drop to 0. Then the hammering would start.
Not a guru, but one thing I learned was air dissolves in water. In a standpipe or tank, where there is no diaphragm between the water and the air, the air will dissolve into the water over time, and the standpipe or tank will become filled solid with water. This happened at our old house where we had a well system. The diaphragm in the accumulator tank failed, the trapped air dissolved into the water and the accumulator tank became water bound. The system would short cycle because there was no air cushion in the tank. Water hammer arrestors work the same way. They have a diaphragm to separate the water from the gas charge. The failure mode is the diaphragm fails and the water hammer arrestor becomes water bound.
Also, the air will boil out of fresh system water over time, so bleeding does need to be done repeatedly over a period of days. Once the system is properly filled to something above recommended static pressure, to allow for the bleeding off of the inevitable air, there should be no possibility of hammer since there is only constant pressure at every point in what is a closed system.
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