Bi-Metal Control Valve With Heater

[glitch]

I picked up a new-to-me heater for the workshop, manufactured sometime in the 1960's. It's a gas heater, but they didn't have combination gas valves back then, so it's got a separate pilot valve, regulator and electronic gas valve. Everything is pretty normal, except the gas valve.

The first oddity I noticed is that the nameplate said it was a 21V AC or DC valve. Its control transformer was also 21V. The transformer tested as good, so I connected it to the gas valve and...nothing. I removed the top of the valve to find what I thought was a standard solenoid gas valve, which lifts a plunger and opens what amounts to a poppet valve in the valve body. It showed a low resistance with my multimeter, but nothing moved when powered up. After taking a closer look, I realized that what I thought to be a solenoid coil was really a slide gasket, and that what I thought was the return spring and lever of the solenoid was a metal plate with a zig-zag of wire sandwiched between two pieces of mica!

After applying 21 VAC for around 45-60 seconds, the valve starts to move a little, and then snaps open. The supposed return lever is apparently bimetallic, and flexes up when heated, opening the gas valve. Just as it takes a while to open up when power is applied, it takes around 30-45 seconds to close when power is removed, as the bimetal spring cools down.

Has anyone ever seen a control valve like this? It's a new one to me!

 

[luckybob]

sounds like a standard furnace setup to me. I'm going to ask the stupid question; "is the pilot light LIT?" there should be a copper "wire" going from the gas valve to the pilot light, its called a thermocouple. They stop working OFTEN. If the pilot light wont stay lit, replace this and everything else should work.

 

[glitch]

Yes, after cleaning the pilot assembly, the thermocouple lets the pilot stand (there was some sort of insect nest in the air-gas mixer). What's weird is this bimetal device controls the /gas valve/, it's not a limit switch. When the thermostat turns on, it heats up the bimetal lever in this valve, and that turns on the gas supply to the main burner. The rest of the setup is normal (it's a Reznor unit heater...I don't think anything has changed in their gravity vent natural gas models since they created them!). It all works fine, just I'd never seen a control valve that operated in this manner, or that operated so slowly -- I'm used to putting the control voltage on the valve, you hear a click, and it's on. I'll see if I can take a picture of it later today.