The Case of the Recalcitrant Receiver

My friend Bruno was feeling besieged. A superintendent at a moderate-size co-op, he had several angry shareholders on his hands and a contractor’s quote for heating system repairs of more than $120,000 in his inbox.

It seems that water was backing up into the radiators on the first and sometimes the second floors, creating a discordant chorus of banging in the steam pipes. A vendor brought in to assess the situation had recommended extensive – and expensive – repairs.

Bruno didn’t know what the solution to his problem was, but his gut told him that it should not cost $120,000. Remembering some help I had given him a few years before, he asked me for a second opinion.

I recalled the building clearly because it had a very unusual heating system – two-pipe steam with an alternating receiver. Unlike most steam systems, it employed a combination of pressure and check valves to push the steam condensate back into the boiler.

After the steam in a heating system gives off its heat via the radiators and condenses back into water, it needs to find its way back into the boiler to be made into steam again. With an alternating receiver, this condensate stacks up in a vertical pipe until it reaches the receiver and moves a float inside it. This opens a valve and allows steam into the receiver.

The steam pressure, along with the weight of the stacked-up water, is enough to force the condensate back into the boiler. The check valves make sure the water moves toward the boiler instead of away from it.

For some reason, this fairly simple and effective system fell out of favor decades ago, and many people in the heating industry have never encountered one, except perhaps in books.

This is a big problem in the heating business. A contractor sees something he doesn’t recognize, and, instead of finding out what it is and why it’s there, he just tells the client to rip it out and install some new, expensive thing that he sort of recognizes.

I was immediately suspicious of this big-dollar proposal, since the “repairs” had almost nothing to do with the unique features of the system. It’s true that parts for alternating receivers are difficult, if not impossible, to find. But surely we could be more creative than simply splashing over a hundred grand at the problem?

The first thing I looked at when I reached Bruno’s building was the boiler’s pressure control. Whenever you have steam condensate mysteriously backing up into apartments, there’s a good chance excessive steam pressure is involved. One of the most durable myths in boiler-land is that more steam pressure is better than less. Having more is the American way, right?

What many folks in boiler-land don’t realize is that the opposite is true. When designed a century ago, the steam-heating systems in our buildings were made to operate on ounces of pressure. More than that is not only unnecessary but can be counterproductive, especially in two-pipe systems.

Why? Because in two-pipe systems, after the steam has given up its heat, condensed, and passed through the steam trap in your radiator, its pressure is zero. To make it back into the boiler, it needs to overcome the pressure inside the boiler. Without some sort of help, that water will stack up in the returns until the water column pressure is greater than the boiler pressure. So, the higher the pressure in the boiler, the more problems you are likely to have in pushing the condensate back in.

Since a column of water just over 2 feet high generates a pressure of 1 pound per square inch (psi), you’d need a column of water about 12 feet tall to overcome 5 psi. This particular boiler room actually had 12-foot-tall drip legs in the return system, plus about 5 psi of steam pressure for the alternating receiver to work with. But the problem remained.

Multiple Causation

After we turned down the pressure settings we began to look for additional causes. Bruno called in a service company to inspect and adjust the receiver, but the guy it sent promptly broke one of the pivots inside the unit (see photos), so Bruno decided to do the work himself.

He cleaned out years of accumulated gunk in both the receiver and the two check valves, buttoned the system back up, and let it rip. Son of a gun, all was back to normal. No more banging or backed-up condensate, and no need to spend $120,000.

So what had been going on? There was so much crud in the receiver valve that steam could not enter it to provide a boost. And the crud in the check valves prevented free movement, so that much more than 12 feet of stacked-up condensate was required to overcome the 5 psi in the boiler.

The moral of the story? Next time someone tells you it’s going to cost big money to fix something, make sure they can explain exactly what’s wrong and why their solution will address the problem. If you don’t understand their explanation, chances are they don’t, either – time to call in someone else!