Vapostat or Pressuretrol Settings

vaporvac

I have a gas two-pipe trane vapor vacuum system that I'm trying to

> restore.  Pls see prior post for details.  Anyway, does this have a

> vaporstat or a pressurtrol on it? Tthere is a small instrument called a Pressure Control by white-Rodgers Mfg. calibrated in oz. with a differential marking behind it as well as some sort of pressure

> gauge with positive poundage and negative inches (for the vacuum, I presume).  What is this

> showing exactly  and how should it be set for my system?  I currently

> have it a 5-6 with a diff. of 2 for no reason in particular.  I'm

> trying to get all radiators to heat  equally without banging..  Please see schematic of

> piping if helpful. Thanks.

vaporvac

Anyone there

Has anyone thought about my question. I'M STICKING With steam so I need some help, please.

Jamie Hall

If the control really is

calibrated in ounces, the settings you have should be about right.  I have to confess that I've never run into a White-Rodgers pressure control.  What this gadget does, though, is turn the burner off when it reaches a certain pressure in the system -- and vapour or vapour vacuum systems work best at the kind of pressures you are working on (and may not work at all on higher pressures, for that matter).  Depending on how closely the boiler is matched to the load, it may never do anything at all.



The pressure gauge is a lovely thing.  Hang onto it!  Is it calibrated in pounds pressure and inches vacuum?  If so, I doubt that you will ever see the needle even move on the pressure side.  Shouldn't, anyway.  You may, depending on what kind of vents you have, see it drop into the vacuum side when the burner shuts off.  The gauge doesn't need any setting.

vaporvac

What do they do?Should I keep them?

Thank you Jamie. I've decided to keep my old system and am trying to figure it out to make sure the new boiler is compatible.  I've been reading that these old controls are better, so should I keep them when I get a new boiler or replace them with what? 

BTW, what exactly does the pressure control and differential do and is it the same as a Vaporstat? 



Jamie, you are right in that in does go negative when the boiler goes off, but it will go to maybe 1/2 pound when on.  Is this normal?.  thanks all.



Colleen

Jamie Hall

I'd say to keep them...

if you can, and if your installer (and any local building officials) will let you.  Those folks can get a little sticky now and then about antique equipment, sometimes with very good reason.  But if it's working -- which it certainly seems to be from your descriptions -- I'd keep them.



It is quite normal for the pressure to rise to about half a pound or so when the boiler is running and, in an intact Trane system, to drop into a vacuum when the boiler shuts off.  The beauty of those old pressure vacuum gauges, like the one you have, is that they tended to be more accurate in the low pressure ranges than the new ones you can get.



Your pressure control is essentially the same as a vapourstat in terms of what they do.  Not having actually seen a White-Rodgers, I can't say if they're mechanically similar or not!  However, the function is the same: they sense the steam pressure and, at a certain upper limit they will turn the burner off.  Then, as the pressure drops, eventually they will come to a lower pressure and turn the burner back on again; the difference between the two pressures is called the differential.  The objective of the exercise is to match the average steam production of the boiler, over a period of minutes, to the steam demand of the system.  I am not sure whether the White-Rodgers is set up so that you set the cut in pressure (in your case, you have it set to 5-6) and the differential (in your case, 2) is added to it -- which would give a cut out pressure of, say 8 ounces (this is called an additive differential) -- or whether the main scale is the cut out and the differential is subtracted (called, with a singular lack of originality, a subtractive differential).  In your case, it doesn't make any difference. 



Your new boiler should be sized to match the radiation in your system; if you can't find a good steam pro. in your area, we can help you help your contractor with that.  It is essential that the near boiler piping be exactly as the boiler installation manual says it should be -- or better.  Non steam people often take short cuts here, with disastrous results.  The other slightly obscure essential with a new boiler is that the water line of the new boiler must match the water line of the old one, within an inch or two -- so make a record of the operating water line of the old boiler before you start messing with things!  You may find the new boiler will need to be raised somewhat.



You certainly, as I said above, can use the old controls on your new boiler, assuming your building code folks will let you.  However, I would suggest that you also have a standard pressuretrol with a manual reset as a back up safety, set to about 5 psi.  It should never operate -- but if something did go wrong with the main low pressure controller, it's nice to have.  If they won't let you use the old White-Rodgers, yes you should get a vapourstat.  They are subtractive differential (see above), so I would set it at a cutout of 6 ounces with a 4 ounce differential.  That would work fine.

vaporvac

can setting lead to short cycling?

Thanks again Jamie for a wonderfully complete, but concise explanation.  I've posted a question on short cycling and a pdf of my boiler piper on two othe rvery  posts.  I think there's also a picture of the white rodgers unit.  Your insight on these latest posts would be most appreciated.



thanks.



Colleen

Jamie Hall

The main reason

for a boiler turning on and off at short intervals -- a minute or so -- near the end of the cycle is that it is producing more steam than the system can condense.  If it is doing it closer to the beginning of a cycle -- say in the first 15 minutes or so of a run -- there are two main possibilities: either the boiler is significantly oversized for the radiation or there are serious venting problems (the vents simply can't let the air out as fast as the boiler makes steam -- but this is actually rarer than folks sometimes make it out to be).



In an ideal world, the boiler and burner would be so closely matched to the radiation that it would never cycle on pressure.  However, for a variety of good practical reasons this is rarely the case, and the boiler is very slightly oversized for the system.  In that case, on a long run (say coming out of a setback, or something like that) it will cycle on and off.  It's not ideal, but with our on or off burners, it's the best that can be done.



When you install your new boiler, if you have a really good steam man he should be able to size it accurately to the radiation -- and then adjust the burner to match even more closely.



I'll go look at the picture of the White-Rodgers unit here in a few minutes...



Just went and looked at that White-Rodgers unit.  I love it!  Nice big diaphragm in there to give plenty of power, and a nice solid mechanical contact set.  Nice...

Dave in QCA

here is some good information on your system

http://72.3.142.104/article/163/Older-Steam-Heating-Systems/1392/Trane-Heating-Specialties-for-Vapor-and-Vacuum-Systems



Above is a link to a very good brochure that show in detail, all of the parts of your Trane system.  Perhaps you have already seen it.

I have been reading your posts, and trying to determine when you are getting the short cycling.  Is it at the beginning of a heating cycle, or only after the system and radiators are fully heated?  If at the end of the cycle, it is somewhat normal, but the frequency of the on-off cycling seems a bit rapid.  Perhaps a little bit greater differential on your vapor stat would help.

Also, are all of your radiators heating?  If not, that tends to amplify any boiler oversize condition that you may already have.  If you are looking at a replacement, you certainly want to do a radiator survey, in fact, it would be a good thing to day anyway, so you know how the current boiler is matched to the system.  You could clock the gas meter and see exactly how your boiler is firing.  The picture of your boiler that shows the gas controls (from an earlier post) is very dark and fuzzy, and hard to see.  But, I do see a regulator, and your probably could adjust it down to decrease your firing rate if that is necessary.  I can't tell whether your gas valve is a one or two stage valve.  There are many boilers with 2 stage valves, that are not operating as such.  You might have an opportunity to utilize the 2 stage aspect of the valve to reduce the firing rate and stop the short cycling.   Just listing off a bunch of thoughts and possibilities here.

You also mention that you have some banging.... is that occuring in the radiators?  You may have some bad radiator traps.  If you have to replace, make sure you pick a trap that vents the same as the old Trane traps.  Better, yet, just repair the old trap if parts are available.  You could give us some trap information and folks on here will help you find parts availability information.



You're gonna love your heating system!