Vaporstat/gauge selection advice

nicholas bonham-carter · February 2021

I can’t seem to find my old notes on which replacement Vaporstat (0-4 psi), to order. My present one is behaving in a peculiar manner, and causing a lot of short cycling, even though the low pressure gauge reads only a few ounces. Vaporstat (mercury) is set for 2psi, and diff is 8 ounces.
Also need a new low pressure 0-3 psi gauge, as it is too cold to have the boiler out of action while I try and investigate its strange behavior. Who has the best gauge now, as I can’t find the gaugestore.com website now. One of these devices is having trouble.
Another possibility could be that the gas company has raised the incoming pressure, and that the pressure regulator is not able to cope, causing the burner to be overfired, effectively oversizing the boiler. My plan is to get my boiler man to check the gas inlet pressure, and do a combustion test. If that checks out then I’ll order the replacements.
It has been rare for the pressure to rise over 10 ounces, until now.—NBC

ChrisJ · February 2021

Did you clock the meter?

As far as best, Dwyer Magnehelic by a lot.

nicholas bonham-carter · February 2021

Not yet, as I wonder if, with overpressure the results will be wrong.
Even the burners on the kitchen stove seem to have higher flames, but that is not a scientific measurement.—NBC

Jamie Hall · February 2021

Your existing vapourstat is a mercury type? If so, they don't break. However, they do get out of level -- and level is critical. If the vapourstat seems to be the cause of the short cycling, make sure the pigtail is clear and then, when you put it back on, make sure that it is really level -- and that the orientation of it and the pigtail is such that as the pigtail curls and uncurls with temperature that the level isn't disturbed.

ethicalpaul · February 2021

You can find a LOT of used (or new-old stock) Magnahelic gauges on ebay for about $30. They come in a wide variety of ranges and always measured in inches of water column.

So here's one that would show you up to about 1psi: https://www.ebay.com/itm/Dwyer-Magnehelic-4-Differential-Pressure-Gauge-0-30-Inches-Of-Water-Model-2030/274672948142

JUGHNE · February 2021

Do you have meter and reg in basement? Is reg vented outside, the vent could be frosted over....or outside vent/meter could have same problem.

Also MUD could have a sub station regulator that is over compensating for your area.
They might respond if someone reports pressure that is too high.
They are probably anticipate reports of low pressure this AM with your -20 overnight.

mattmia2 · February 2021

If you are running longer cycles because of it being unusually cold, especially if it is also windy, that could be causing it to run in a steady state that it normally doesn't, it probably gets shut off by the t-stat before the whole system becomes fully heated so the oversized boiler is less apparent.

nicholas bonham-carter · February 2021

The pressuretrol is shutting down the boiler on pressure, and is level, and before now, had no problems.
I think Jugne has the right diagnosis-overpressure from the gas company, or the frozen Regulator vent pipes.
Gas company say that this is probably due to the added propane in the winter mix of gas.-NBC

mattmia2 · February 2021

Propane will increase the energy content of a given volume of gas.

Vaporstat/gauge selection advice

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