Pressurtrol or Vaporstat?

AlexT

I have a one-pipe steam system, fired by gas. When I bought the system there was no low pressure gauge hooked up so I had no idea what the pressure was. I had always noticed a lot of noise in the system and it seemed the pressure was too high and air was being forced out despite closed vents.



So based on advice here, I hooked up a new 0-3 psi gauge and a fresh pigtail. The PA404A I have hooked up is set up for the minimum amount of pressure (i.e. cut-in at .5 psi and a differential of 1). As I suspected, the Pressurtrol is actually cutting out around 2.5psi instead of the set value of 1.5psi.



So now I know I need to replace it. Question is whether I should spring for a new Vaporstat, not knowing yet if my system will run on the lower pressures. I'm worried I may spend a lot and get a lot of short-cycling when I'm done. Any suggestions?



Also a related question - saw this P404A1X0A4 Pressurtrol on Ebay (<a href="http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230529932966&ssPageName=STRK:MEWAX:IT#ht_500wt_922">http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230529932966&ssPageName=STRK:MEWAX:IT#ht_500wt_922</a>) Looks like the older version of the PA404A, but I can't confirm that. Anybody know?

BobC

vaporstat

those old pressuretrols were better than the newer styles but the problem is can you be sure that this one is working? I don't know what range they worked over so be sure you know that before you leap.



I have single pipe steam and when my pressuretrol started to get flaky I bought a vaporstat and now run my system from 4 - 12 oz. I may dial it down more because the house heats just fine now. I was able to snag one of the last mercury bulb units, they should be better than the microswitch unit.



They do cost more, at least twice the price but they offer finer control than you can get with a pressuretrol.



Bob

AlexT

0-10 Pounds

According to the seller, it has a range of 0-10 pounds. One reason I was attracted to it was that 1

) it probably is a mercury switch

2) range is only 0-10 pounds instead of 0-15 for the newer style Pressurtrols.



I'm leaning towards a Vaporstat as well. I'm just worried about my system short-cycling like crazy. Good to hear your Vaporstat has worked out. I need to replace mine ASAP because I can tell the system is stressed at the current pressure level.

nicholas bonham-carter

short-cycling

as long as you have enough main venting, you should have no short-cycling during the air escape, and that is where you want an uninterupted burn to fill the mains with steam.

depending on how closely your boiler is matched to the radiation, you may cycle on pressure as the rads are condensing the steam on a less than design temp day.

can you perform the open pipe test to see what the behaviour would be without whatever vents you have now? put a ball valve where the vent is so you can shut it down when needed. the low pressure gauge will show you the back pressure as air is leaving.--nbc

AlexT

New Pressuretrol

So I decided to start conservatively and I scored a very inexpensive, new PA404 Pressurtrol on eBay. I installed it last night and the system behaves just as well under the lower pressure. Having watched the entire cycle in the basement, I think a Vaporstat is still in the cards. I noticed during the cycle that the pressure hovered around .5psi for quite a while before rising up to the cut-out. It seems that's the magic number to get steam filling the radiators.



Somebody mentioned an open-pipe test. I found another post where the test is that you run the system with the main-vent shut, and check for short cycling. What does this prove in the end? I'm reading "Lost Art of Steam Heat" right now and I haven't run into the test. Is it covered in the book?



-Alex

nicholas bonham-carter

open pipe test

the idea is to simulate the most main venting you could have-an open pipe. remove the main vent and put ball valves in their place. fire up the system, from cool, and observe the gauge as air is allowed to escape freely. there should be no short-cycling during the venting cycle, because the back-pressure is very low. this will be the effect when you put on enough main vents to get close to that ultimate lack of restriction.

naturally, when steam appers at the ball valve, close it, and use gloves.--nbc

jpf321

NBC - why the strikethrough .. error?

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