Two pipe vapor system with vapor stat: to cycle or not to cycle?

Doesn't make sense to me that at 11oz you get a 3 :18min run time and at 12oz it will not cycle on pressure.

2:19 from start of boil to shutdown? No. Something is seriously wrong with the venting. Or, possibly, the piping to the main vent.

You say this is a vapour steam system. How, exactly, are the mains and dry returns vented? I've looked at the previous thread, but it isn't clear to me what was done about main and dry return venting.

The main vent on the dry returns, whether there are crossover traps from the mains to the dry returns or not, should NEVER close — never see steam at all. Once the boiler fires, you can feel the progress of steam along the mains — 20 feet per minute is not a bad sort of ball park figure — and that should be steady progress. If there are vents on the mains, they should close when steam hits them — likewise crossover traps.

I can't help but think that somewhere in there there is a significant restriction — but what it is I couldn't say without really looking at the system.

There is another possibility, however, which has occurred to me. Where are the vapourstat and pressure gauge connected? If they are connected directly to the steam chest — which is the usual connection, through a nipple or through the sight glass — is the vapourstat responding to real system pressure, or is it responding to pressure oscillations in the steam chest? If the pressure gauge is on the same pigtail, is it bouncing around as steam is rising, or is it rising steadily? Note that this is not related to surging water level! If the pressure gauge is bouncing around, it is likely responding to steam pressure variations as bubbles form and burst, not to the steady pressure found in the header — and the mains. This could be the cause of the quick shutdown, as vapourstats are quite sensitive to pressure spikes of this sort. There are ways to cure this problem. The best is to connect the vapourstat and low pressure gauge to the header, not to the boiler. Another is to use a snubber on the pigtail, but that is problematic as snubbers have a way of clogging.

Whatever, it ain't right.

If the return fitting area of the radiators isn't getting steam hot then the higher pressure is ok. the reason you need a vaporstat on a vapor system is to keep the pressure low enough that the metering device on the radiator limits the amount of steam fed to the radiator to an amount the radiator can fully condense so that it doesn't reach the returns.

The second reason is to keep the differential between the supply and return low enough that steam can't push through the water seals on any drips from the mains and in to the returns. this may or may not apply to your system.

In the other thread Steamhead wrote;

" @motordiscord628 et al, this is a Kriebel system. You can find it in chapter 15 of @DanHolohan 's "The Lost Art of Steam Heating".

"The Vapor Vacuum Heating Company" was the company the Kriebels set up to market their system. It was located in Philly. "

Which seems reasonable to me, so no crossover traps and/or thermostatic radiator traps, just a Union Elbow with a Baffler and a missing Vapor-Vacuum controller.

With the Baffler valve I would think venting would not much of an issue, except the main may not be uniformly filled first. That air needs a place to go to leave the system. So where is the new main vent installed.

In principle a Hoffman Equipped system could run without crossovers — so long as the rampup in firing rate was slow enough. Whether early ones had them or not, I wouldn't care to say — but radiator traps were, I think, always part of the deal — and since crossovers are the same as radiator traps…

Whatever, though, as you say, the one and only vent on such systems (and a number of others) must be on the dry returns at or very very near the Differential Loop or whatever other widget may be in there. That's what makes them work…

The "running faucet" sounds more like it might be steam and air pushing through the pipe and especially through the vapor valve and telegraphing through the pipe because it is uninsulated. The amount of condensate produced by the pipes should be in the order of drops per second.

Or the valves all need to be open a bit more proportionally and the pressure lower.

Steam in the returns can cause radiators to not be able to vent and heat or banging so you don't want steam in the returns as @Jamie Hall said. Most vapor valves have some sort of stop or way of positioning the handle or needle valve that allows you to keep them from opening beyond the amount needed for the connected EDR. I think a few systems have different size valve for different sizes of connected EDR.

No, boiler too big pressuretrol short cycles the boiler.(at least that's how it's supposed to work)