steam return pipe hammering frequently

Pete_4

Hi,

I have a one pipe steam system. Lately, there are frequent hammering noise on the return pipe going back to the boiler. It starts to hammer (sounds more like a pop) frequently at the begining and at the end of the heating cycle. First, I checked the pitch on the return and it wasn't pitch perfectly. Now, I have rectified the pitch on the return but the hammering noise is even louder and goes for the entire heating cycle. Actually, the hammering continues at a slower pace even long after the boiler stops heating (about 90 minutes). Also, I observed some infrequent and minor hammering noise started to come from the long main after it cools down. Just to clarify, the hammering noise is not continuous but just a single bang and then stops. A contractor told me it was caused by high pressure on the system. Now I have lowered the pressure to 2.5 from 4.0, thought I am not sure if I did it correctly. What are the other possible cause for this problem?

Here is how I changed the pressure on the Honeywell PA404A pressure control (it is similar to the A404A model.)

Original setting: 4 psi
main scale setting indicator: ~2
Differential (a knob): pointing at 2
so i guess the total pressure is 4 (add the two together)

New setting: 2.5 psi
main scale settting indicator: ~1
Differential (knob): pointing at ~1.5

By the way, what does this mean on the Honeywell pressure control:
CUT OUT EQUALS CUT-IN PLUS DIFFERENTIAL
Is the sum of this equals the pressure on the system?

Thanks.
-Pete

gas man

water hammer

on the pressure-trol ,use the screw adjustment and lower it down till it just gets to the bottom. .05 raise it till to just see an air space! that should be .5 approx- the differential wheel - set at 1 - or between 1 and 2 (halfway unless your home is quite large - see how this works )

Steamhead

That return line

may have gotten plugged up, which would cause water to back up into the steam main. Then the steam hits the water, and BANG!

If you find it's plugged, I'd replace it.

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Pete_4

gas man,

Thanks for the advice. I lowered the pressure to 1.5 psi (.5 on the main pressure gauge and 1 on the differential wheel) but the hammering on the return still exists. To be exact, the loud hammering happens at the same location and which is about 11 feet away from the boiler. The length of the return is ~53 feet long from the main to the boiler. It is not an exact straight run, with two straight pipes connected by a slanted 's' about 1/3 the distance from the boiler. What are other the possible causes?

Thanks.
-Pete

Pete_4

Steamhead,

The return is less than 1 year old. The hammering noise always come from the same area on the return and it is about 11 feet away from the boiler. This section of the pipe, about 6 feet, which is below the sink/cabinet and the pitch looks good. I am totally confused as to why only the hammering occurs at that specifc area. It hammers once about every 50 seconds or so. It is quite loud too! Any ideas?

Thanks.
-Pete

Unknown

Sounds like steam

is hitting condensate somewhere . Is there a Hartford Loop and equalizer , and if there is , how high is the Hartford loop tee on the boiler ? If its too high , it could cause the banging in the returns . Also , you said there were 2 pipes connected with an S bend . Is this connection lower than the water level of the boiler ?

Pete_4

> is hitting condensate somewhere . Is there a

> Hartford Loop and equalizer , and if there is ,

> how high is the Hartford loop tee on the boiler ?

> If its too high , it could cause the banging in

> the returns . Also , you said there were 2 pipes

> connected with an S bend . Is this connection

> lower than the water level of the boiler ?



Ron,

Yes, there is a Harford Loop and equalizer. As for the Hartloop loop tee it is approximately about the same height as the bottom of the water line gauge. Nothing much really changed from a year ago when the new return was put in. The old return was underground and the new return is about 2-3 inch above ground but it is defintely much lower than the water level of the boiler, maybe 24"-30" difference. The two parallel connected pipes look like this:

from long main_________
________to boiler

Again, the hammer continues at the same spot but at a slower and slower pace as time goes by. It hammers even after when the boiler is shut off for more than 4 1/2 hours. However, the water in the boiler is still warm but the return pipe is already cold to the touch.

I just drained about 2/3 of the water from the boiler and I still hear the hammering noise once a while.

Thanks.

-Pete

Unknown

Hard to diagnose

this one Pete . Ive had that same scenario happen when I clean out return piping on a new install . With the isolation valve closed on the return , and the drain valve open , we get very loud knocking noises while the condensate get pushed out . But I dont remember hearing knocking noises with the system running normal in a wet return with the Hartford loop piped in the right height . Can you give us a little more info - what brand boiler , what pipe size is the equalizer and Hartford loop , and what size is the return piping ? And do you know the "A" Dimension ? Its the difference in height between the water line of the boiler and the end of the steam main , where it drops down into the return . You need at least 28 inches for it .

Unknown

Hard to diagnose

this one Pete . Ive had that same scenario happen when I clean out return piping on a new install . With the isolation valve closed on the return , and the drain valve open , we get very loud knocking noises while the condensate get pushed out . But I dont remember hearing knocking noises with the system running normal in a wet return with the Hartford loop piped in the right height . Can you give us a little more info - what brand boiler , what pipe size is the equalizer and Hartford loop , and what size is the return piping ? And do you know the "A" Dimension ? Its the difference in height between the water line of the boiler and the end of the steam main , where it drops down into the return . You need at least 28 inches for it .

Oh yeah , and what type of low water cutoff do you have ? If its a 67 , and the gauge glass is connected to it , and the bottom of the Hartford loop tee is above the bottom of the gauge glass - it might just be too high . With the boiler low on water - but not low enough to trip the LWCO , it could send steam into the return .

Unknown

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Unknown

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[Deleted User]

What was

the inside diameter of the old return pipe? What is the inside diameter of the new pipe? What is the length of the nipple that connects the last 90 to the equalizer?

Pete_4

Ron/gasman/steamhead,

Thanks for all the help and I appreciated the advice that you folks gave. After a day of meddling with the return pipe I finally figured the problem. It was something simple, and I mean simple! The culprit were the shims that were use to hold the pipe in place under the sink/cabinet . Somehow the pipe was grinding against the wood when the water inside the pipe is warm, maybe it is a cause of expansion/contraction. However, I suspected some minute amount of steams got into the return from the Hartford loop. I still hear some noise at the beginning of the heating cycle but it is minute. It might be that the pipe needs more pitch. For now I am a very happy camper that the hammering noise had subsided.

Again, thank you folks for the great insight or else I wouldn't be able to solve the problem by myself. Kudos to you all!

Thanks.
-Pete