Vaporstat reliability?

ratio

I'm in the middle of adding a two-stage gas valve to my 26 HP boiler. I've heard that the new vaporstats with the microswitches are possibly unreliable - has anyone experienced one of these hanging up or not switching when they're supposed to? I haven't pulled the trigger yet, but I'm looking at a pair of Honeywell L408J1017 for on/off & high/low control.

I was using a bulit-up control using Dwyer 1823 pressure switches, but I must have got steam into one last season, because she didn't shut off when she hit what should have been the cut out. I could repair this, & add another set for second stage, but I am aiming for reliability at this point.

This is the heating plant for a school, safely & reliability are critical. Cost is secondary, but it's all coming out of my pocket, so if I'm going to drop coin on something like this I have to have a lot of confidence in it.

Fred

I've been using one for two or three years now without fail. I think they are pretty reliable but most of us who add them, typically keep our Pressuretrol in the same circuit, set at a higher cut-out just in case it does fail.

Jamie Hall

I can't speak to the microswitch variety -- but the mercury switch vapourstat which controls Cedric II is on its third boiler and well into the fourth decade of flawless service. There are several things to consider for longevity. First is mounting. It should obviously be on a pigtail -- but less obviously, my feeling is it should also be protected by a snubber (made for steam service) and, if possible, the pigtail should be on the header, not on the boiler.

Fred, however, is absolutely spot on on his comment: you should have a secondary pressurestat, set somewhat higher (2 psi or so?) -- and for a school, I would have a third (!) pressurestat, set at about 5 psi, with a manual reset (and no valves between it and the boiler -- just the pigtail), both hooked up conventionally on the boiler. Belt and braces? Sure. But you want a system which will let you know about failures! You should also have two LWCO's -- one with an automatic reset (possibly hooked to an automatic water feeder, though there are differences of opinion on that) and the other one, lower on the boiler but still safe, with a manual reset.

Abracadabra

I've installed probably over 100 vaporstats of the microswitch variety, and I've been called back to not more than 5 to find a vaporstat switch that's either not switching on pressure or switching at a pressure much greater than what has been set. So something at just under 5%. Whenever we run across a job with a mercury vaporstat switch we'll either reuse it or buy it off the owner if he's having it removed. If you can find a mercury vaporstat use it, otherwise a microswitch version will work ok. Just keep an eye on it. Like Jamie said, always keep the existing pressuretrol setup which usually includes two pressuretrols, one being the manual reset type.

ChrisJ

Fred said:

I've been using one for two or three years now without fail. I think they are pretty reliable but most of us who add them, typically keep our Pressuretrol in the same circuit, set at a higher cut-out just in case it does fail.

Your vaporstat trips a lot does it?

Fred

ChrisJ said:

Fred said:

I've been using one for two or three years now without fail. I think they are pretty reliable but most of us who add them, typically keep our Pressuretrol in the same circuit, set at a higher cut-out just in case it does fail.

Your vaporstat trips a lot does it?

I have it set to trip @ 8 oz. It may trip once every few cycles when it's -20 outside which is 2 or 3 days a year. I can live with that until my old, faithful boiler finally gives up the ghost. All other times I typically run at 2 oz. of pressure or less.

Fred

Abracadabra said:

I've installed probably over 100 vaporstats of the microswitch variety, and I've been called back to not more than 5 to find a vaporstat switch that's either not switching on pressure or switching at a pressure much greater than what has been set. So something at just under 5%. Whenever we run across a job with a mercury vaporstat switch we'll either reuse it or buy it off the owner if he's having it removed. If you can find a mercury vaporstat use it, otherwise a microswitch version will work ok. Just keep an eye on it. Like Jamie said, always keep the existing pressuretrol setup which usually includes two pressuretrols, one being the manual reset type.

Some new/old stock mercury Vaporstats available here:
http://www.ebay.com/itm/HONEYWELL-L408A-1132-VAPORSTAT-/251913717067?hash=item3aa73a454b

ratio

I think I've seen those, unfortunately I need the 0-4 lbs model. My Old Guy at the counter wasn't in today. There a good change he has I one in his pile of attic stock that I might be able to talk him out of.

If I can't get a pair of them cheaply, I'll just get the newer model. I'll be on hand for the first few minutes of runtime anyway.

For the record, I have a manual reset high limit set at about 3½ lbs & a Pressuretrol set at about 2-3 lbs (bottomed out on the scale) My target is a cut in of 1 lb & a cut out of 2 lbs. Also, the automatic water feeder had a low water switch in it, & a probe type LWCO on the other side of the boiler. Both work via test procedure, & functionally as well.

ChrisJ

Fred said:

ChrisJ said:

Fred said:

I've been using one for two or three years now without fail. I think they are pretty reliable but most of us who add them, typically keep our Pressuretrol in the same circuit, set at a higher cut-out just in case it does fail.

Your vaporstat trips a lot does it?

I have it set to trip @ 8 oz. It may trip once every few cycles when it's -20 outside which is 2 or 3 days a year. I can live with that until my old, faithful boiler finally gives up the ghost. All other times I typically run at 2 oz. of pressure or less.

Oh,
I just installed a Dwyer that is set to trip at 1oz and shut the system down for 5 minutes.

Abracadabra

ratio said:

I think I've seen those, unfortunately I need the 0-4 lbs model. My Old Guy at the counter wasn't in today. There a good change he has I one in his pile of attic stock that I might be able to talk him out of.

If I can't get a pair of them cheaply, I'll just get the newer model. I'll be on hand for the first few minutes of runtime anyway.

For the record, I have a manual reset high limit set at about 3½ lbs & a Pressuretrol set at about 2-3 lbs (bottomed out on the scale) My target is a cut in of 1 lb & a cut out of 2 lbs. Also, the automatic water feeder had a low water switch in it, & a probe type LWCO on the other side of the boiler. Both work via test procedure, & functionally as well.

Anything over 1psi is more of a pressuretrol than a vaporstat. At least in my eyes. Why do you want the 0-4psi?

ChrisJ

Abracadabra said:

ratio said:

I think I've seen those, unfortunately I need the 0-4 lbs model. My Old Guy at the counter wasn't in today. There a good change he has I one in his pile of attic stock that I might be able to talk him out of.

If I can't get a pair of them cheaply, I'll just get the newer model. I'll be on hand for the first few minutes of runtime anyway.

For the record, I have a manual reset high limit set at about 3½ lbs & a Pressuretrol set at about 2-3 lbs (bottomed out on the scale) My target is a cut in of 1 lb & a cut out of 2 lbs. Also, the automatic water feeder had a low water switch in it, & a probe type LWCO on the other side of the boiler. Both work via test procedure, & functionally as well.

Anything over 1psi is more of a pressuretrol than a vaporstat. At least in my eyes. Why do you want the 0-4psi?

I would think the 0-4 PSI vaporstat would be far easier to adjust than a 0.5-15PSI pressuretrol, no?

Why do they even supply pressuretrols with steamboilers?

KC_Jones

ChrisJ said:

Why do they even supply pressuretrols with steamboilers?

Because they are cheaper.

ratio

I've got a pressuretrol operating control, it's ...less than reliable... in it's setpoints. I dropped it off the adjusting screw once or twice trying to get the pressure set to 2 lbs on my 100" H₂O gauge.

This is a commercial boiler that can't fail (heating for a charter school), & needs a lot of TLC at the moment, so even thought I'd like to run it at the lowest pressure that I can, I've got to start it at a known-good pressure. After she's running good & most of the problems are fixed, then I'll try cranking it down. FWIW, she was running at 5-7 lbs when I took over...

ChrisJ

Like I've said before.

IMO a proper system uses the radiation to limit pressure.

vaporvac

IMO a proper system uses the radiation to limit pressure.

... and adequate venting. The two-stage gas valve should help keep the pressures inline with the radiation, but there's seriously no reason for such high pressure.

I have both types of Vstats on my twinned boilers, mounted in the header as @Jamie Hall suggests. One is @50yrs old, the other is maybe 4yrs, so too new to judge, but it seems to be accurate after calibrating. Perhaps someone here who's ditched their Vstats for the Dwyer control would be willing to sell you theirs. That's how I got my new one.

ratio

Well, this is a little more complicated than a residential steam system. While I have considerable load controlled by hand valves (i.e. residential style "controls"), I have about ten rooms on pneumatic stats & a steam -> water HX that feeds several more rooms. The building is two stories tall & the boiler is located about a third of the way along the long axis of the building, which is about 300' long. Kinda big, is what I'm getting at.

I picked 2 lbs because (after reading Dan's books), I think that's my best bet for the design pressure. There's too many problems that need corrected before I can stat cranking the pressure down. After I get off of make up water & get the boiler cleaned out, then I'll feel a lot more comfortable making those changes.

Everyone, I appreciate all your input & ideas. This is an ongoing project, & since I'm working on it after hours it's moving slower than it could. But I'm going to get this thing working even if it kills (or more likely bankrupts) me!

Jamie Hall

With that large a system, and particularly with the heat exchangers, you may well need to run 1.5 to 2 psi. A 0 to 4 vapourstat would be ideal as the primary control on that, backed up -- as I said earlier -- by a couple of pressurestats.

Also on that big a system -- make sure you have adequate venting. That can make a huge difference as to how well the system operates.