Pressuretrol Calibration

gehring_3

I have a Honeywell L404A Pressuretrol. The differential is subtractive. I want to set my cut out at 1.5 psi with cut in at .5 psi. Although the lowest numbers on both scales is "2" there does appear to be much further downward adjustment room below 2, so I estimated 1.5 on the Main with a 1.0 Differential.

The problem is my pressure gauge will read 2.5 - 3.0 before the unit cuts out (even though the unit shows a cut out well below 2). If I back the Main off even further (and there appears to be room as the indicator slides down well below 2) I have the problem where I can get the unit to shut off at 2 psi on my gauge, but then it won't tip back over even after all pressure has been released from the system.

I end up having to re-tighten (i.e. raise the reading on the main) before the mercury will tip back over and cut in.

The unit is completely level and my siphon loop is facing properly fore and aft.

Does the unit need to be calibrated or what am I doing wrong??

Thanks

will smith_2

Carl-Even though the Pressure-trol you've got may be the one either spec'd with the boiler, installed by a service tech, or recommended to you by a supplier, it isn't the best you could use. I prefer the Honeywell Vaporstat. It will give you the increments you'd like to see when setting up a low pressure system like yours. You'll aggrevate yourself using the one you've got. Good Luck!

joe_14

404a

carl
i thought the 404A was an additive pressuretrol was an additive setting control. just a thought


joe.

gerry gill

i'm with Will

best to use that pressuretrol as a high limit safety and install a vaporstat to run the boiler.

gehring_3

Vaporstat


Okay. So I'll go with a Vaporstat. What model do you recommend? I noticed Honeywell makes a 408A "SPST break on prerssure rise" and a 408B "SPST make on pressure rise."
Both are rated 0-4 psi which is what I think I want, but what is the difference between "SPST make/break on pressure rise??"

Also, Gerry - If I were to keep the Pressuretrol too where would I add the Vaporstat? "T" off the same boiler tapping or put it up on the end of my dry return? I take it they should then be wired in series. right?

will smith_2

Carl- When a control is designated to break on pressure rise, it means that when you get to a set pressure, a set of normally closed electrical contacts open, breaking the circuit. The L408A1157 should be just the ticket. You just need to tee it in and wire it in series with your high limit Pressuretrol like you figured. Hope this helps.

gehring_3

vaporstat


Thank you. I appreciate the help.

Dale

Gauge

First invest in a new gauge and or 404 pigtail, I don't trust the old ones to be clean. Then IMHO Most of the little gauges on boilers are pretty inaccurate at the low end. By code if the boiler has a 15# relief the gauge must be 30#. The code people aren't concerned with the low end. What I do is use a digital manometer or a 0-3 pound magnahelic to set the 404, I compare it to what the little gauge on the boiler reads and go from there. You won't get really accurate low end control with the 404 but pretty close if you set it up with a good gauge. The gauges I spoke of are pricy, if you buy a new standard 0-5 pound gauge at a plumbing supply store and put it in parallel with the one that comes on the boiler you can get pretty close. I don't like to wait for the boiler so I bench set the 404s with compressed air.

Kal Row

here is a tip from noel murdough of slantfin

get 5/8 clear plastic tubing (they sell 25ft of it for apx $5 at HD) and put a female hose connection at one end and connect to the boiler's drain, and hang the other end up to the ceiling near the sight glass,

then open the drain and measure the difference between the sight level and the hose's level - 28 inches is 1 psi, 14 inches is 1/2 pound etc

this will give you the most accurate readings

.8 psi should fill your system with steam – it you need higher pressure – check all your air vents, returns and supply headers for sag