Advice requested re pressure bouncing seen on 5 PSI gauge

Ken Johnson

Our home is heated with single-pipe steam. A week or so ago I went through the checklist to bring the steam boiler online for the winter. Circumstances limited the time available for the project, so I did only a minimal (30 minutes) skim.

The boiler is set with a Pressuretrol for 12oz cut-out, 4 oz cut-in. The boiler has two gauges installed, 0-15 PSI and 0-5 PSI. As the boiler pressure moved up toward 12 oz., I noticed the 5 PSI gauge needle bouncing back and forth, and the gauge clicking. Both new symptoms to me. I thought it likely that the gauge had failed, so I pulled it off, put in a plug, and ordered a new gauge.

When I installed the new gauge I fired the boiler and discovered that it wasn't the gauge after all, as the new gauge (Winters) did the same thing, but without the clicking. Turned the boiler back off until today.

Today I skimmed the boiler for 4.75 hours. When I skim the boiler I always take a 'before' sample at the start, and an 'after' sample at the end. The before sample did not look that great -- brownish water, and a cloudy surface. The after sample looks dead clear, probably clearer than I have ever seen it. So I fired the boiler. I am pretty sure that the amount of needle bounce is reduced, but still more than I remember. So I grabbed my phone and shot video of the gauge and the sight glass. Each 40 seconds, over at Youtube.

Gauge

Sight Glass

I know of two changes since bringing the boiler online a year ago (when I would have previously observed firing from a cold start). The shut-off valve on one of the radiators was replaced. The main vent was replaced: old -- Hoffman 4A; new -- Barnes and Jones Big Mouth.

Question: Is this more bounce or surge than I should have? If so, what can I do about it? More skimming seems like a long shot.

Jamie Hall

I don't see anything amiss there -- to be honest, I wish Cedric's water level was that stable when he's going full song.

If the vibrating needle bothers you (I don't think it should) you could try a snubber on the pigtail before the gauge, but they're often more trouble than they're worth.

ChrisJ

I'll see your bouncing gauge and raise you this




That's before I added a snubber to smooth it out.

Jamie Hall

I love it, @ChrisJ !

JUGHNE

I had the bounce issue for the gauge and the vaporstat at 8 ounces.
The main concern was that the vaporstat is mercury switch and come close to the vibration turning the boiler off early.

I stacked up two pigtails and secured the top one to the 2 1/2" main riser with clamps and rod.

ethicalpaul

I agree with Jamie, those videos look fine to me

mikeg2015

I bet if the starting water level is dropped even just a 1/2 - 1” it improves noticeably. But mid of sight glass is typical normal water line. My runs a lot smother and heats a little more even it seems when it’s about 1” below “normal” but still about 2” above min. LWCO trips near bottom of sight glass.

Does it have a drop header and/or two take offs?

My pressure is steady at 0oz, but there’s enough water sloshing around to vibrate all the near boiler piping very slightly. My sight glass moves more than that.

Hap_Hazzard

That amount of bounce is just due to the physics of boiling water. Steam bubbles forming and rising to the surface are going to change the volume. The only way to get less fluctuation would be to use boiling chips or something crazy like that. If you're worried about it damaging the gauge, just put a ball valve under it and only open it when you're standing there reading the gauge.