Two Pipe steam with in wall convectors, gravity loop at the end of the main.

Call_Me_Al

Call_Me_Al ✭
I replaced a failed steam boiler that has a gravity loop at the end of the steam main. The steam main is 58" above the boiler water line. I believe I need 60" from the boiler water line to the end of the steam main. The boiler water level on the old boiler was the same as the new one. The system is working and the convectors are getting hot. I have the pressure trol set to cycle at a 1-1/2 psi. There are two end of main air vents. One on the dry return and one on the end of the steam main. The air vent on the steam main will not stop releasing air. Its very noisey. I am not sure what to do to correct the problem. The end of main vents are Ventrite #35. They are brand new. Are these the right vents for this system? If I need to move the gravity loop. I am not sure how to do it without demolishing one wall of finished basement. Its located in a finished wall in a closet.

Jamie Hall

You have enough height, seems to me, if the pressuretrol cutout really is 1.5 psi (32 inches needed). If that is the cutin, though, with a 1 psi differential, you don't. Can you double check that the cutin is 0.5 psi and the cutout is 1.5?

Can you further describe what you mean by a gravity loop? Do you mean a "U" between the steam main and the dry return?

The vents are almost certainly too small. Probably way too small...

Call_Me_Al

The dry return is parallel to the steam main. Both pipes have a tee at the end of the main with a vent on top and are tied together at the bottom . (At 58" , there are two tees with a union in the middle, and 3"& 6" nipples and caps for cleanouts, that connect to the wet return. )

Jamie Hall

Ah. There is a wet return. Splendid. Then the vertical pipes count as drips, and all is well. Nice of them to give you cleanouts...

But do check the pressure; remember that the outside calibration on a pressuretrol is the cutin pressure, and the differential (dial on the inside) is additive!

Call_Me_Al

I will double check the differential setting.
I have watched the boiler cycle on and off. The pressure gauge reads 1-1/2 psi when the boilers shuts down. The end of main air vent on the steam main will not close. The boiler looses pressure and fires up again.
The boiler is also using a lot of water. I assume its because the air vent is not working the way I am expecting to work. I did check for leaks and could not find any. (According to the manufacturer the boiler should use 10 gal/month.) The meter is reading 10 gal after one week.

Fred

The main vent that is not closing is faulty. Try to take it off and clean it or replace it. As has been said, you probably need more venting but they should all close and will lose a lot of water if they don't. Is the boiler shutting down on pressure or is the thermostat being satisfied? If the boiler shuts down on pressure, It will shut down when you hit the 1.5 PSI (Cut-out) and then start back up when the pressure gets down to the Cut-in pressure of .5 PSI until the thermostat is satisfied. That may be due in part to inadequate main venting. It may also be due to the boiler being over sized. What is the Sq. Ft. Steam rating on the boiler? Do you know the total EDR of your radiators? You need to compare those two numbers to determine if/how much the boiler may be over-sized.

Jamie Hall

If the boiler is cycling on pressure, you can and should expect it to do exactly what you say it's doing. That's normal.