Pressurtol Setpoint Refresher Question

KarlW

As I get ready for the heating season, I have a pressuretrol setpoint question for the experienced folks in this group.

On the coldest days with my boiler running full bore and all radiators open, I operate at 0.7psi.

Of course, this only happens a few times a year. The rest of the year, the thermostatic valves in my house open and close as needed and the system is 95% of the way to working in a fully-zoned manner.

After a lot of fuss last year, I managed to beak my "old (circa 2019)" vaporstat (the 0-4psi model) but jury-rigged my original (circa 2012) pressuretrol to shut off at about 1.5psi and turn back on close to zero. Unfortunately, this is just from the random turning of the calibration screws and is not precise.

This season I'd like to bring it back to actual control. I plan on purchasing the L408J1025 Vaportstat - the one from 0-16oz with a 0-16oz pressure differential. Here's my question:

1. Is this the right vaportstat model? (again, my equilibrium point is 0.7 psi)
2. What do I set the main and differential pressures to avoid over-pressurizing my system?
   1. I get incredible water hammer at about 2psi which can happen easily with all my thermostatic valves closed while I only heat a couple of rooms.

Thanks in advance, and this group has been very accommodating in humoring my posts/questions.

Jamie Hall

Yes, that's the right model. It is subtractive, so try it with the main scale set a 0.8 psi with a differential of 0.4 pso.

Mount it and a sensitive pressure gauge (0 to 3 psi is good enough) on the same pigtail so you can really see what it;s doing.

KarlW

I'm ordering a new pressure gauge, but the 0-5psi one I had is what helped me zero in on the 0.7psi.

Code needs to be changed to require 0-5psi for steam boilers instead of 0-30.

Jamie Hall

The 0 to 30 is there because the pressure relief specification for residential steam boilers is — and probably should remain — 15 psig, and you need a gauge going to twice the pressure relief setting.

Most folks just add a 0 to 3 or 0 to 5 for control observation.