Sarco Vapor heating system

Dennis Alvarez

I have a customer who has a Sarco vapor heating system that is acting up. The system has a alternating receiver & main vent in ceiling. It also has a standard pressuretrol & not a vaporstat as far a we can tell.

The problem we are having is that after the system cycles, the condesate returns to the boiler & the boiler cuts off. The boiler seems to be flooded, so when we drain it down a little, it fires. There seems to be a vacum when we drain it because it is not pretty.

We have cleaned the return piping near the boiler & replaced the (2) check valves under the alternationg receiver. We shut the water feeder off & the problem still persists.

Question 1: why is the boiler flooding?

Question 2: where should the site glass be (or water line) in regard to the alternating receiver?

Question 3: where does the vapor stat go in relation to water level?

Question 4: How much should I charge to drain down the boiler 5 times a day throughout the heating season?

Unknown

Vapor

1) The boiler is likely flooding because during the run cycle, condensate is likely stacking up in the returns behind the check valves, for some reason.

2)The waterline should be where the boiler manufacturer wants it to be. The reciever no longer is the only factor. The amount of water in the boiler is more important on a modern boiler.

3)The vaporstat can go beside the pressuretrol, in place of the pressuretrol, or out at the end of the supply main (which shows when the main vent closes, indicating pressure in the whole supply main). If you use an existing pressuretrol as a high limit and the vaporstat in series with the room thermostat, you have the best protection going. Don't use one pigtail for two controls, though.

4)If you get the pressure (in inches water column) lower than the height between the waterline and the lowest horizontal pipe going into the reciever and returns, the water will slide into the boiler without having to overcome back pressure from the steam in the boiler. The reciever will never operate.

Of course, if plugged returns are also slowing the return flow back to the boiler, that problem won't go away by itself. You need clean returns.

Noel

PS If the vent is a vacuum type, replace it with a vent like the #2 Gorton. The vacuum is no longer needed.

Steamhead

Check that main vent you found

and any others that might be on that system. I think Noel's right (as usual). It's probably a "vacuum" vent which was designed to let air out but not back in. These only worked well on coal-fired systems. With oil or gas, the vacuum appears long before the air is out, and can impair the return of the condensate. The Gorton #2 is the best replacement out there, but don't mount it where ambient heat might make it close too fast.

Lack of insulation on steam pipes can also cause a strong vacuum on shutdown, because the steam in these pipes condenses too fast.

If you find the Alternating Receiver is malfunctioning, get in touch with Tunstall Associates (www.tunstall-inc.com). They can rebuild it.

Unknown

Do the vaporstat first

You might find that the pressure never rises to the point that the reciever even needs to operate.

In that case, just leave it there for the continuity of the old design. The vaporstat does the same job, better. The piping around it is OK for getting the air to the vent, and the water never will rise into it.

Pressure is the problem....

Noel