Trillium Furnaces - ITT RV18AA02 - Fiberglass RV


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Old 08-18-2018, 12:17 AM   #1
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Name: Dave W
Trailer: Trillium 4500 - 1977, 1978 (2), 1300 - 1977, 1973, and a 1972
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Trillium Furnaces - ITT RV18AA02

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.

Related threads:
75 Trilium furnace gas valve
Trillium 1300 duotherm gas control

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.
Attached Thumbnails
Disection - Gas Valve Process.jpg   Disection - Gas Valve - 01 - Back.jpg  

Disection - Gas Valve - 01 - Bottom.jpg   Disection - Gas Valve - 01 - Bottom 01.jpg  

Disection - Gas Valve - 01 - Bottom 02.jpg   Disection - Gas Valve - 01 - Front.jpg  

Disection - Gas Valve - 01 - Top.jpg   Disection - Gas Valve - 01 - Side Data Stamp.jpg  

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Old 08-18-2018, 12:19 AM   #2
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Name: Dave W
Trailer: Trillium 4500 - 1977, 1978 (2), 1300 - 1977, 1973, and a 1972
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The Coil

The electrical part of the valve.
Attached Thumbnails
Disection - Gas Valve - 02 - Coil 00.jpg   Disection - Gas Valve - 02 - Coil 01.jpg  

Disection - Gas Valve - 02 - Coil 02.jpg   Disection - Gas Valve - 02 - Coil 03.jpg  

Disection - Gas Valve - 02 - Coil 04.jpg   Disection - Gas Valve - 02 - Coil 05.jpg  

Disection - Gas Valve - 02 - Coil 06.jpg   Disection - Gas Valve - 02 - Coil 07.jpg  

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Old 08-18-2018, 12:22 AM   #3
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Trailer: Trillium 4500 - 1977, 1978 (2), 1300 - 1977, 1973, and a 1972
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The Diaphragm

You can see the orifice that feeds the thermostat valve. It is the very small hole, surrounded by circle, inside the bottom of the circle that the diaphragm sits in. The gas passage to the back of the diaphragm is the larger hole just below the orifice. The gas passage to the back of the diaphragm is the small slot cut in the diaphragm cover, near the bottom, as seen in the third picture. The pilot ports are just above the large circle that the diaphragm sits in. The larger port comes from the pilot slot in the plug valve. The smaller port above it goes out the needle valve then to the pilot connection on the top of the valve.
Attached Thumbnails
Disection - Gas Valve - 02 - Diaphragm 00.jpg   Disection - Gas Valve - 02 - Diaphragm 01.jpg  

Disection - Gas Valve - 02 - Diaphragm 02.jpg   Disection - Gas Valve - 02 - Diaphragm 03.jpg  

Disection - Gas Valve - 02 - Diaphragm 04.jpg  
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Old 08-18-2018, 12:26 AM   #4
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Name: Dave W
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The Knobs

This should be split into two subjects. The thermostat valve and the selector valve. Oops.

The fifth and sixth pictures are meant to show the thermostat valve in the closed and open positions.
Attached Thumbnails
Disection - Gas Valve - 02 - Knobs 00.jpg   Disection - Gas Valve - 02 - Knobs 01.jpg  

Disection - Gas Valve - 02 - Knobs 02.jpg   Disection - Gas Valve - 02 - Knobs 03.jpg  

Disection - Gas Valve - 02 - Knobs 04.jpg   Disection - Gas Valve - 02 - Knobs 05.jpg  

Disection - Gas Valve - 02 - Knobs 06.jpg   Disection - Gas Valve - 02 - Knobs 07.jpg  

Disection - Gas Valve - 02 - Knobs 08.jpg   Disection - Gas Valve - 02 - Knobs 09.jpg  

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Old 08-18-2018, 12:28 AM   #5
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More Knobs

The rest of the knobs set.
Attached Thumbnails
Disection - Gas Valve - 02 - Knobs 10.jpg   Disection - Gas Valve - 02 - Knobs 11.jpg  

Disection - Gas Valve - 02 - Knobs 12.jpg   Disection - Gas Valve - 02 - Knobs 13.jpg  

Disection - Gas Valve - 02 - Knobs 14.jpg   Disection - Gas Valve - 02 - Knobs 15.jpg  

Disection - Gas Valve - 02 - Knobs 16.jpg   Disection - Gas Valve - 02 - Knobs 17.jpg  

Disection - Gas Valve - 02 - Knobs 18.jpg   Disection - Gas Valve - 02 - Knobs 19.jpg  

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Old 08-18-2018, 12:29 AM   #6
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Name: Dave W
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All the Parts

Last picture. Every part in the valve.
Attached Thumbnails
Disection - Gas Valve - 02 - BOM.jpg  
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Old 08-18-2018, 02:29 AM   #7
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Thanks for the last chuckle of my day Dave. I do the same thing but I tell my wife I'm just putsing in the garage.
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Old 08-19-2018, 01:46 PM   #8
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Thanks for doing this teardown, it is immensely beneficial to see the workings of these.
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