Inconsistent water hammer

HammeredOut

I have a steam heating system and am getting inconsistent water hammer. By inconsistent, I mean that on most days there is no water hammer, but every once in a while (1 out of every 6 or 7 days) there is water hammer. I live in NYC and am thinking that the water hammer occurs when the temperature is really low, but I am not entirely sure about this. Does anyone have any recommendations as to what I should do/monitor to effectively diagnose/fix this? Some additional things that may be helpful:
1) I have a one pipe system
2) I remove water from the system about once every 10-12 days

nicholas bonham-carter

Unless you see that the waterline in the sight glass is above the halfway mark, don't drain water out unnecessarily.
Quite likely, this is happening when the boiler has to work harder in cold weather. Are you setting back the temperature on the thermostat during some periods of the day? Try leaving the thermostat set a degree or two lower than usual, and leave it at that setting, until the cause of this has been identified.
Next job is to isolate the area where the hammering occurs. Is it in the boiler piping, supply piping, or in one of the radiators?
Post back here when you have a better idea where the water hammer takes place, and we can advise.--NBC

Larry_52

steam boilers do not make water. If you are removing water due to increasing water in sight glass than there is a problem with the makeup valving.

Is the water hammer during boiler start or post shutdown?

Fred

I assume when you say you remove water, you mean you do a blow down to remove dirt/crud, right? As far as the hammer is concermed, are you sure it is hammer or possibly pipe expansion where the pipe might be rubbing against something?
As Nick suggested, see if you can isolate the area of the hammer/noise and check to make sure the main and/or radiator run-out has good pitch (Radiator run pitched back to the Main and Main pitched towards the return pipe at the end of the main. Make sure there are no sags in the pipes that might allow condensate to pool in that area.

Abracadabra

How much water do you remove every 10-12 days? Is the sight glass full? If so, there's your water hammer.

HammeredOut

NBC/Larry -
The temperature is set to 72 degrees throughout the day and 70 degrees from 11 pm to 6 am. From what I can tell, the water hammer is in the supply pipes. It occurs during mid-cycle when the boiler is running. At this point, there is steam going to the radiators and they are warm/hot and then the water hammer starts. The water hammer is towards the back of my house and lasts about 45-60 seconds. I'm going to try to monitor it more closely the next few times it occurs so that I can be more specific/provide additional details.

Fred/Abracadabra - I am doing a boiler blow down and removing about a quart to half a gallon of water. The water sight glass is not full and is around the halfway mark.

Fred

Check all the horizontal pipe runs in the area of the hammer. It sounds like one of those pipes isn't pitched so that the condensate can run back to the mains/boiler. Make suree the radiators have some pitch back to the supply pipe and the supply pipe has pitch back to the main and the main is pitched towards the return. Make sure none of the pipes have any sags in them.

ChrisJ

Do you have a wet return?
I.e. a return that runs along or under the floor?