The things I do for.... fun?
I have an unusual interest in taking things apart. Putting them back together, less so.
I have stared at the gas valve that is installed in almost every Trillium
trailer that I have seen. Trillium
was fond of Duo-Therm who seems very fond of the ITT RV18AA series of gas valves.
The photos are from the dissection of the defective valve that was part of the transaction in the first related thread. I have no idea what was wrong with it. There was no obvious flaw. I may have been able to fix it, but I have now sent out parts from it. So it is now just parts, let me know if you need something other then the diaphragm from the control valve.
The first picture is actually a process flow drawing that I did. It may not be correct, but it is my best guess.
I still can't quite figure out the operation of the main control valve. I get how it closes, the thermostat valve closes and line pressure slowly flows through the orifice to pressurize the back of the diaphragm at the same pressure as the front of the diaphragm. This allows the spring that is behind the diaphragm to push the flat surface of the rubber diaphragm to press against the valve seat. The opening is similar. The thermostat valve opens, and then vents the space behind the diaphragm to the discharge port of the valve. When the valve is closed, the discharge port should be at atmospheric pressure. The orifice prevents the flow of gas that would re-pressurize this space. The resulting pressure differential then pushes the diaphragm off the valve seat. What I am having trouble with is, how is this pressure difference maintained, when the control valve is open, and the pressure on either side should be the same? Maybe the valve acts a bit like a regulator. It only opens enough to allow the gas to flow to the burner, but at a lower pressure then the supply pressure.
I hope someone can comment on this.
The control sequence kind of goes like this:
- The operator turns the three way, plug style, selector valve to the pilot position. This lines up a very small slot on plug with the pilot port, but the main port remains closed.
- when the push button, (selector knob) is pressed, it opens the pilot override valve, allowing gas to flow to the pilot port, through a needle valve adjustment.
- When the pilot is lit, it heats up a thermocouple, (K type?). This generates enough power to allow an electrical
coil to hold the spring loaded, pilot override valve in the open position. The drawing should show some sort of mechanical interlock between the selector valve, and the pilot override, but I don't know how to show that.
- The push button is released, but the pilot remains lit, and the selector valve can now be turned to the ON position. This allows gas to flow to the control valve chamber, and now the valve is in automatic operation.
If the pilot light
goes out, then there is no power to the magnet, and the pilot override valve closes, the gas is thus completely shut off. The power that holds open this valve is millivolts, at milliamps, likely, milliwatts.