Increasing steam pressure--help with banging pipes

Saldanah

We have a two-pipe system in our building with 14 floors. A couple of apartments on the second floor experience banging of pipes. We have tried a number of fixes but to no avail. It so happens that we had reduced the boiler steam pressure from 2 psi to 1 psi a few months ago, and the banging seems to have gotten worse with the reduction in steam pressure. Coincidence or explainable?

An engineer said a slight increase in pressure can improve the flow of steam through supply lines, potentially helping to sweep out condensate pooling in areas with minor pitch issues or resistance. And increasing pressure slightly may also enhance the performance of steam traps by creating a more effective pressure drop between the supply and return lines, and that can improve condensate drainage.

Should we try going from 1 psi to 1.5 or 2 psi? We clearly need to fix the pitch issues where they exist, but need some near-term relief from the banging.

What is your experience with slight increases in the pressure?

Thank you.

Jamie Hall

The good news is that the banging was there before you decreased the pressure. The first thing I think I would check would the traps on all the affected radiators; your engineer may be correct in thinking that one of them may be sticking.

He may also be right in that the slight change in velocity may be affecting where condensate pools. Along those lines, can you determine when, during a heating cycle, the hammer is present? That will give you a very good idea as to where in the system the problem may be, as slight pitch problems or sags in the supply lines will usually only hammer a few times while the system is coming up to temperature, and will stop once the runouts or mains are hot. A hammer late in the cycle suggests returns…

Saldanah

Thanks Jamie. Here is the pattern of banging: a few very loud bangs as the system is coming on—supply lines are getting hot, and return lines are cold. And then the rest of the clicking and dull banging is in the return lines where you can hear the water surging as it bangs. Would increasing the steam pressure slightly help with one or the other?

Jamie Hall

Probably not much… if any. The very loud bangs are almost certainly somewhere in one of the runouts (possibly, but not likely, in one of the basement mains) which has lost pitch. A sag. A loose pipe hanger. One way — if you are patient — is to trace the flow of steam through the system as it is warming up. You can do this by hand unless things are out of reach (or too well insulated. No good deed goes unpunished…) and if you find a pipe which is beginning to get warm and then whang… you may have found it.

The other noises later may just be expansion related. Equally annoying, but more random and happening after things have really started heating up, rather than as things are heating up.

Saldanah

A bit more context. We learnt from the boiler company that they took down the pressure from 3psi to 1 psi in April, towards the end of the last season. Oddly enough, the banging increased soon after. This is the pattern:

• After the boiler has been shut off for a few hours due to the lower temperature threshold at night, the supply lines seem to be behind the loud banging when the boiler comes back on in the early morning hours.
• When the boiler cycles continuously during the day, turning on and off, we do not hear that initial banging in the supply lines. The banging is only heard in the return lines.

We might have pitch issues in the concealed ceiling of the retail space at ground level. Ideally we should open that up (asbestos wrapping notwithstanding), but as a workaround we are trying to figure out if a modest increase in steam pressure (say to 1.5 psi or even 2 psi) would make a difference in "pushing out" condensate and reducing the banging in the supply and return lines.

Mad Dog_2

More likely Wet Steam and some pitch issues. Mad Dog

Jamie Hall

A few observations…

First, what actually is the boiler pressure when starting up from the overnight hours? I'm going to be that if you have a low pressure gauge on there (you should) you may find that in that startup period when the mains bang that the pressure is still very low — half a pound or less. If this is true, then changing the pressure settings on the pressure control will make no difference at all.

Second, the combination of only hearing it really enthusiastically when the system has been off for a while, and not when it's turning on and off during the day, suggests that what is happening is that when starting with the pipes cold a good deal of condensate is forming in one or more of the mains as they heat up. It will, after all! And that that extra condensate from the cold mains is enough to build up somewhere and get caught up and pushed along to make the bangs. When the pipes are already warm, during the day, you don't get that extra condensate — and you get less banging, if any. I've seen just this sort of thing happen in other installations.

This may happen even if the pipe(s) in question is too flat — it doesn't have to be sagged (although that certainly won't help!) never mind reverse pitched. It can happen in parallel flow mains which are too flat, though it is much more likely to happen in runouts which are — so far as condensate created during warmup — by definition counterflow. Nor does it have to be a particularly long flat section to be a problem — one of the worst I've hit was a three foot long horizontal section between two vertical risers which was dead level.

EBEBRATT-Ed

Chances are you either have a pitch issue or some bad traps. The bad traps are probably NOT on the radiators that are banging. Other traps blowing by will pressurize the return lines from the rads that are banging because they pressurize the return lines and the banging rads are not draining. I would just start changing all the trap innards. Doesn't cost much and should be done as part of maintenance anyhow