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Pneumatic thermostat “puffing”

RPK
RPK Member Posts: 112
in THE MAIN WALL
I just replaced a Honeywell TP971A 2003 pneumatic thermostat (like for like). It’s a day/night heating thermostat. The old one would not come out of night mode automatically when the supply pressure changed from 13 to 18psi. The new one works, but when it’s in night mode pressurizing the branch it “puffs”. 2-3 times per second, eventually it stops doing this once the branch comes up to (or close to) the pressure it’s shooting for. This thermostat controls pneumatic valves on 4 steam convectors. The other thermostats (same model) don’t do this. I did find and repair a pinhole leak in a pneumatic line at one of the convectors. The air is nice and dry and supply pressure appears to be steady. Should I return the thermostat or am I missing something. The one I replaced never did this.

Comments

  • JUGHNE
    JUGHNE Member Posts: 11,157
    Is your day setting 13 and night setting 18?
  • RPK
    RPK Member Posts: 112
    edited February 2019
    Yes, day is 13 and night is 18. So what I meant to say is the old one wouldn’t come out of night mode when the supply pressure dropped from 18 to 13.
  • JUGHNE
    JUGHNE Member Posts: 11,157
    Could you switch with another known to be working OK stat in the building? See if the problem goes with the T-stat or is at that wall mounting location
    Grallert
  • RPK
    RPK Member Posts: 112
    Of course, swap it with a working tstat,, why didn’t I think of that?! And they’re so easy to swap, just snap right onto the sub base.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,950
    Possible the length of the branch line is different. Maybe a restrictor would calm it down
  • RPK
    RPK Member Posts: 112
    So the restrictor would just go on the thermostat outlet to the branch? When would a restrictor normally be required?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,950
    @RPK, a restrictor would not be normally used their. They are used on transmitters sometimes or other 1 pipe controls that bleed off they just slow down the action a little bit.

    Just something you could try
  • RPK
    RPK Member Posts: 112
    Thank you EBEBRATT-ED-Ed. By the way, can you recommend any good resources on pneumatic controls? I think RSES has a book on it.
    ComfEffic
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,950
    have some stuff will look. I know Honeywell has a book
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,950
    edited February 2019
    @RPK

    Google Honeywell #70-6925 You can download their complete manual.
    ComfEfficratio
  • RPK
    RPK Member Posts: 112
    Thank you for the tip!
  • Mike_Sheppard
    Mike_Sheppard Member Posts: 696
    @EBEBRATT-Ed thanks for posting that. Looking forward to reading it.

    Picture of my current pneumatics collection.
    Never stop learning.
  • ratio
    ratio Member Posts: 3,733
    @EBEBRATT-Ed, thanks, that's great.

    @Mike_Sheppard, don't keep me waiting after a teaser like that—how 'bout some closeups?

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,950
    @Mike_Sheppard , jealous!!!!!!!!!!!!!!!!

    All I got is a squeeze bulb and some fittings, a couple of thermostat adapters and a gage.

    But around here most of the pneumatics have been ripped out of most of the buildings

    Always liked Pneumatics. Can't claim to be an expert at it but I got by could do a receiver controller etc. Most of the problems are fairly simple..............usually
    ratio

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