A beautiful old vaporstat, but.....

tmw

I scored a NOS Honeywell L408B a few months ago. It's over 50 yrs. old in an unopened box.  I tried to hook it up this morning only to find that the thing breaks contact on pressure <span style="text-decoration:underline;">drop</span>.  Is there any way to use this thing on my vapor system that currently runs on a breaks-with-pressure-rise vaporstat?

Jamie Hall

You could

rig an SPST relay in there, normally closed.  Power the coil independently through the vaporstat, and run the boiler wiring through the contacts.  Make sure you have enough current rating in the contacts, and check the coil current and voltage ratings too.  Then when the vaporstat is at low pressure, it's open and the relay contacts are closed.  And vice versa...

tmw

OK, got it.

Thanks. What was the reason that this control was made to operate like this?

Steamhead

Some systems with unit heaters

 would use these things to keep the heaters' fans from running unless there was pressure in the system. I prefer to use temperature controllers for this, that way you can run at extremely low pressures as long as the steam has actually gotten that far.

tmw

Steamhead..

are you as heartbroken as I am?