How to check pressure gauge on boiler?

dcha

I have a single-pipe gas fired steam system. I think the normal pressure range should be between 2 and 5 psi. When do I check it though? When the boiler is fired up? What should the psi read when it's just sitting on standby (boiler is on, but no steam yet).

Unknown

zero

The reading would be at it's high point with all of the radiators hot (which we haven't got it to do, yet) and when the boiler cycles off.

Until the vents close on the last radiator, the system is still "open" to the atmosphere, and won't build pressure.

Noel

Brad White

Zero Part 2

As Noel said, when off and vented (vacuum relieved and at atmospheric pressure), the gauge should be at zero. Compound gauges (which read positive PSI and negative inches of mercury) are handier because there is no "pin" at zero.

I like compound gauges because if you do pull a vacuum (stuck vents for example) you can tell. Plus you can tell if you have "more zero than you think".

You may also have a "zeroing screw" to re-set the needle to zero should it have come out of calibration, regardless of type.

The other part of the post I wanted to address was your statement about 2-5 PSI operating pressure. Way too high. A pound or less should do it. Your "A" dimension"? That is based on the height of water stacked over a pound of pressure. If you run higher pressures you will force water up into your mains about 28 inches for each pound in your boiler. Crank it down.


The challenge now is getting a really low pressure gauge, one reading from zero to 16 or 32 ounces, 1-2 PSIG. Look at Winters Gauge, Ashcroft and Trerice under specialty or low pressure gauges.

Unknown

It's a one piper, Brad

There's almost as much pressure pushing down on the water out there at the end as there is pushing up (only line losses being the difference).

I still agree with what you said, though.

Noel

Fred Harwood_2

Steam Pressure

Most gauges start at 2 psi, which often is higher than a one-pipe needs. If you're building more than 2 psi in a one-pipe, you might want to know why. If you temporarily connect a clear plastic tube to your boiler drain, raise the open end to near the floor joists, and then measure the distance from the glass water line to the highest point of the water in the tube during the cycle, each 7 inches of water equals 4 ounces of pressure, and 4 ounces often is plenty.

If you push water out the top of the tube, you might consider down-firing the boiler by 10-15 percent, after checking your mains and radiator vents to ensure that they're functioning; if the air can't get out, steam can't get to the radiators and condense, and pressure will build.