Vaporstat vs pressuretrol

Fizz

Currently have a pressuretrol on vapor/vac system(Richardson).  Is it wise to switch to vaporstat?  How difficult are they to replace as no one in area is familiar with vap/vac system?   Current boiler is Weil-Mc oil, recently converted to gas.

Rod

Vaporstat

Hi- Vaporstats allow you to operate your system at very low pressures.  Most  vapor systems can operate at ounces of pressure. A Pressuretrol's accuracy gets a bit "funky" at very low pressures so that the reason most people with two pipe or especially vapor systems go to Vaporstats.  Installing one is quite easy as all you need to do is to swap out the pressuretrol.  Ideally you leave the pressuretrol connected in series with the Vapostat and set the pressuretrol's  cut off at  3 or 4PSI. The Vaporstat will do most of the work at around 1 PSI or less but if for any reason the Vaporstat fails, the pressuretrol would then cut off the burner at 3 PSI. If you need more info let us know and I'll post the Vaporstat manual. Also unless you already have one you probably need to get a low pressure gauge as they are much easier to read at low pressures. You will need to keep the 0-30 PSI gauge as code requires it.

- Rod

Hap_Hazzard

Call me a slacker, but...

I was going to buy a Vaporstat, but I got one of those low pressure gauges, and I noticed that the pressure rarely got above .5 psi before the thermostat cuts it off. It might be the amount of venting I have or it might be because the CycleGard shuts it down every ten minutes, but I've decided I don't need another control on there to limit the pressure to a level that's never reached anyway.

MotownSteamer

I vote no

I just went throughout this with my vapor vacuum system and agree with Hap. If your system is working (mine operates at about 1.5-3 ounces) your thermostat will shut it off before the limit controllers. I suggest getting a low pressure compound gauge (which are very obscure) and confirm your operating pressure. If its just a couple ounces, leave it alone and let the pressurtrol be a safety device.

Fizz

Help me

Don't understand why thermostat would shut burner at lower pressure? 

BobC

Properly sized boiler

If the steam boiler is sized to the amount of radiation in the building you will probably not develop any real pressure because the radiators will condense the steam just about as fast as it's made. You could see some pressure coming off a temperature setback in the morning.



Before spending a couple of c-notes on a vaporstat invest in a low pressure gauge (0-3 psi) to see where the boiler is operating at. The standard pressure gauges are useless at low pressure but you need to have them to keep the buiolding department and insurance guys happy. The low pressure gauge has to be installed as an auxiliary gauge on a pigtail and mounted at least 8-10" (?) above the waterline of the boiler so water will never reach it.



Bob

Hap_Hazzard

Thermostat

The thermostat shuts off the burner when the temperature reaches its set point. It doesn't care what your steam pressure is. If you can reach that temperature without building a lot of pressure, you don't need a device to limit the pressure, except in those rare cases where the pressure might exceed what might be considered a reasonable limit. For me, that reasonable limit is the lowest possible setting on a Pressuretrol: 2 psi. If my pressure ever gets that high, then the Pressuretrol would cut the burner, but my observation, after spending many hours crouched in my furnace room staring at my low pressure gauge, has been that it never even comes close. Maybe if it was 20 below outside and I left the furnace off overnight it might run long enough to build some pressure, but I'd never let that happen intentionally, and the thought of developing 2 psi of steam pressure in my heating system in response to some emergency doesn't keep me up at night.



But I have to say that I would not have been able to get my system working this well if I hadn't followed Nicholas Bonham-Carter's advice on main venting and reducing operating pressure. I used to think he was a little fanatical about it, and I still don't feel the need to be as focused on my pressure as he is, but if he wasn't as focused on it, and if he didn't take the time and trouble to measure and record his observations down to the last ounce and then share this wealth of knowledge he's developed with the rest of us, I don't think I ever would have appreciated how important these concepts are. I don't feel the need to know exactly how many ounces of pressure I have in my system at any given time, as long as it's well under half a pound most of the time, to know that every time I've done something that lowered the pressure, the performance has improved, and every time I've done something to improve the performance, the pressure has gone down.



So I want to be really clear that I'm not saying don't listen to these guys who say everyone should get a Vaporstat. DO listen to them, because they're really smart and you can learn a lot about steam heating systems from them. Just be critical about understanding your own needs and priorities.

Jamie Hall

As a general thing...

The above comments are right on -- if your system is correctly sized and vented etc., a vapourstat is, in most cases, a bit of a luxury.  So is a low pressure gauge.



There are a couple of situations, however, where that isn't quite true... (there are always exceptions!).  They occur in certain types of vapour systems.  If the system is depending on orifices to control steam flow, rather than traps, you need to keep the pressure in the ounces range as a maximum.  Or, if the system has devices, such as Hoffman Differential Loops, which are sensitive to low pressue (a Differential Loop will typically trip at 12 ounces or so, and shut down steam flow to the radiators for a while) you again need to keep the maximum pressure to ounces.  And in those situations you do need a vapourstat; a pressuretrol just can't function reliably down there.

Fizz

Richardson System(vapor/vac)

Thanks guys.

My system is a Richardson, a 2pipe vap/vac which uses a graduated supply valve wood handle operated at each rad, and a ball cock in ea return elbow of rads.  The system was touted as workable in vacuum, vapor or pressure set=up.  There are 11 original rads, with a bastardized valve on one, and 3 after-add-ons which have taditional steam traps.  My mains are vented with 2 #1 gortons and a #2 at the near boiler dry return, these of course replaced the original vacuum vents during coal burning days, now using gas convert in oil boiler.  I did see a retro-fit Richardson system on line, where a vaporstat replaced pressuretol.  The pressurtrol on my boiler is set at lowest setting 1/2 psi, but don't know if vapor would be more efficient.



Fizz

Jamie Hall

Sorry about this, but...

yours is one of the situations where a vapourstat would be genuinely beneficial.  Although you can make it work with a pressuretrol, at the higher pressures the control offered by the valves will be at best marginal.  If you can manage to keep the pressure down to less than 12 ounces, it's going to be happier -- and that means a vapourstat.

Fizz

Vaporstat installation

How difficult is it to install?  Will it completely replace pressuretrol?  So far haven't been able to find anyone with vaporstat experience.



Fizz

Hap_Hazzard

Vaporstat installation

You can either replace the Pressuretrol or keep it as a safety device. Many people do the latter, and if you search the forum you can find lots of pictures and discussions.



To install the Vaporstat and keep the Pressuretrol, you'll want to add on a new pigtail. How you do this depends on where and how your existing pigtail is installed, but you need to connect it to a tapping that's above the water line. Red brass pigtails are the best choice. McMaster carries some nice ones, but you can find them all over.



If you can find a 1/4" pipe union (also in brass) and a close nipple, it will make your life easier if you ever need to remove your Vaporstat (to make sure the pigtail is clear and has water in it, for instance).



Then you simply wire the Vaporstat in series with the Pressuretrol so either one can cut the burner if its set point is reached. If you set the Pressuretrol at 3-5 pounds, this means it will only come into play if something goes wrong with the Vaporstat.

Fizz

Good advice

Thans for input, now to find someone to do it.



fizz

Mike Kusiak_2

Low pressure gauge

Before you go to the trouble and expense of installing the vaporstat, I would first set up a low pressure gauge to see at what pressure the system actually operates at. If  your system pressure never rises above a few ounces before the thermostat is satisfied, the vaporstat limit will never be reached either and you will gain nothing.



Does your system pressure ever rise high enough to shut down on pressure with your current pressuretrol? If the boiler and firing rate are well matched to the radiation, the vaporstat may be unnecessary.

Fizz

Pressure?

Honestly don't know if pressure shut-down system.  Recently changed to gas gun in WM SGO-6 oil boiler, which is rated at 648 sq ft; my radiation is 518 sf, when using conversion chart that came with gas gun it called for firing at 140,000 x gph of oil unit which was 1.75, giving a btu rating of 240k.  Initially my installer fired at my radiation only, not considering boiler or gun conversion chart, and he fired at 157k, resulting in poor heat and short cycling.  I factored my radiation and boiler radiation rating as follows: 518/648 =80%, coming up with a firing rate of 192k.  My installer refired unit to 189k which is much better and no short cycling. 

haaljo

"The pressurtrol on my boiler is set at lowest setting 1/2 psi..."

Fizz, does your pressuretrol really have a 1/2 PSI marking on the dial?

There have been cases where they are turned so low that do not work resulting in no protection from high pressure.

Dave in QCA

Importance of a Vaporstat on 2-pipe

It is important when considering a vaporstat on a 2-pipe steam or vapor system to remember that the vaporstat is a safety limit device.  In normal operation, it may never trip and it might seem therefore that it has no real function or purpose.  However, that is not really the case.



In 2-pipe systems, remember that the return lines are all at atmospheric pressure, vented to atmosphere, or the pressure may be in a vacuum, if set up for vacuum operation.  But, there pressure is never above atmospheric.  This creates a potential problem in getting the return water to flow into the boiler.  As long as the boiler pressure remains low, usually less than 1 psi, you will be fine. (it all depends on what the elevation difference is between the return piping and the boiler water line)  But, if your return line is about 30" above the water line and something happens that causes the boiler pressure to rise to 2 psi, you now have condition where the return water will not flow by gravity into the boiler.  Many old 2-pipe systems have devices to deal with this, such as a return trap or on the Hoffman system, they had a device called a differential loop.  On my system, an old Dunham Vapor, whatever devices were originally present were removed when a boiler was replaced about 35 years ago.  The installer at the time knew that boiler pressure had to be dealt with, so they installed a condensate return pump.   For about 1/10th of the cost, they could have installed a vaporstat to simply limit the boiler pressure to 1 psi, but apparently they didn't think of that.



Now, in this thread, there have been a few comments about how a system can be so well balanced that it never builds pressure.  And, the assumption is made that in this case a vaporstat is not necessary.  However, consider that fact that you might have company that likes to sleep cool, and so they shut of the radiators in their bedroom.   Or for whatever reason, some of the radiators are turned off.  You system will no longer be in perfect balance, and the boiler WILL build pressure if it runs for a prolonged cycle.  You have to remember that all sorts of things can happen.  The electricity could be off for 12 hours, and when it comes back on the boiler has to warm the house up 20 degrees, because it's below 0 outside and the house really cooled down.  Running continuously for a prolonged period might cause the boiler to build pressure. 



At any rate, the time you need that vaporstat is when your boiler would otherwise start to build enough pressure to interfere with the normal gravity return of your condensate.  If you don't have some device in your system that will mechanically move that condensate into your boiler, you need a means to limit the boiler pressure.    A pressuretrol cannot function reliably at very low pressures.  A Vaporstat is what is needed.

Fizz

Pressuretrol 1/2 psi?

P-trol is set at mid-line between 0-1psi, not an absolute 1/2 setting.

Fizz

Richardson System(vapor/vac)

My system is a Richardson which originally called for a swinging check valve to prevent back-flow which has since been removed.  By going with v-stat, will quality of heat be compromised, as some in thread mention possible shorter cycles?

Fizz

Addendum

Forgot to mention, return piping is at least 40 in from water line.

Fizz

Low pressure gauge

Would a low pressure gauge replace or compliment current gauge?

Dave in QCA

follow up

The check valve was to prevent back-flow, but cannot for the condensate to flow in.  It will quickly stack up in the return lines if the pressure is too high.  The Vaporstat is not going to do anything unless you have a condition that pressure rises over its set point.  Yes, at that time, it will shut the boiler off until pressure drops, and that won't take long, then it will start to fire again.  Pressure may not take a real long time to come back up to the cut out again.  But, as you described your firing rate and your system, this is probably not going to happen much if at all, unless some of your radiators got turned off, and then, it will only occur during long firing cycles.

Most cycles are partial steam cycles and you probably don't even build 2 oz of pressure.

On elevation difference, you say you have 40".  You need 30" for each 1 psi.  So, I'd set the vaporstat for 1 psi and you should be fine and would have a little bit a margin left over.  

Fizz

Happier system

How will v-stat benefit system?  Also, pressure seems to be key, and when I converted to gas gun my installer wanted to increase pressure on p-trol which I refused to do per general consensus.  How can pressure be increased by p-trol setting?  I didn't think that had bearing on pressure, rather was safety feature to shutdown system upon reaching setting.



Fizz

Fizz

Happier system

How will v-stat benefit system?  Also, pressure seems to be key, and when I converted to gas gun my installer wanted to increase pressure on p-trol which I refused to do per general consensus.  How can pressure be increased by p-trol setting?  I didn't think that had bearing on pressure, rather was safety feature to shutdown system upon reaching setting.



Fizz