Vaporstat or a modified P-trol?

StudyingHard · February 2010

I have a 2-pipe Trane Vapor/Vacuum system, and want to get down into the 2-3oz cut-in range, with cut-out in the 8-12 psi range. Note: Keeping or ditching the Vacuum valves is a future decision, to be made after un-knuckleheading a few things.

<span style="text-decoration:underline;">Please comment on what you think of modifying the P-trol as follows:</span>

<ol><li>Remove the tab which shows the cut-in pressure, so that I can drop it lower than 0.5 psi, using the counter-clockwise screwdriver (thanks, Dan :-) That way, the bottom of the scale slot will not be the limiting factor in the low end psi.</li><li>Install the pigtail in the same plane as the p-trol case (not at 90 deg, as recommended) hopefully the heat expansion will tip the p-trol slightly and produce an even lower differential. I think the minimum diff is 1 psi, but I have not tried to set it lower.</li><li>I do have a low pressure gauge, so that I can see the effects of these mods.</li></ol>

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Why am I wanting to do this?</span> Because there have been questions raised about the integrity of the Vaporstat. Otherwise I would just go that way. See Gerry's thread:

<a href="http://www.heatinghelp.com/forum-thread/128249/why-do-Honeywell-vaporstats-suck-so-badly">[url=http://www.heatinghelp.com/forum-thread/128249/why-do-Honeywell-vaporstats-suck-so-badly]http://www.heatinghelp.com/forum-thread/128249/why-do-Honeywell-vaporstats-suck-so-badly</a>

I see from some of the posts that Vaporstats can be calibrated, but there were also some reliability questions Does anyone have anything good to say about the current production run of Vaporstats?

StudyingHard · February 2010

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jpf321 · February 2010

v-stat ...

after tweaking my "jeweler" screw as per Mr. Gill's thread posted above, my v-stat is spot on .. 5oz cut-out with a diff of 2oz. more importantly however, i don't tend to cycle on pressure except on very rare cold days .. and I have thrown out the idea of setbacks completely as it seemed after my data collecting, that it was causing wasted fuel consumption vs a single temp with no setback variation.

Jamie Hall · February 2010

So far as I've heard

The current Vaporstats are reliable. They do sometimes need calibration, however, which isn't all that hard to do (there is a calibration screw). I cannot advise trying to modify a pressuretrol to operate on lower pressure, as the mechanism is very different. It is adapted to be reasonably repeatable (that is, always trip at about the same pressure) at higher pressure ratings, where a variation of a few ounces isn't going to cause a problem. That same variation of a few ounces operating at very low pressure or differential is almost guaranteed to cause problems. Consider: if the cut in is 4 ounces and the variation in operation is plus or minus 5 ounces (good for a pressuretrol) sooner or later it simply won't cut back in on a cycle, giving all the symptoms of a lock out (including no heat!!!).

So... no, I can't recommend modifying the pressuretrol. Get a vaporstat and a good low pressure gauge to calibrate it with, and be happy.

Vaporstat or a modified P-trol?

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