Compression fittings max pressure?

[loco]

Hi all!

after not being able to get my rather large engine up to max power on gas, I'm hoping to run it off liquid propane by inverting the tank. I have also added some valves as a very crude method of throttling the engine. I have two valves that allow for a precise idle setting and a full power setting.

However, I can forsee a couple of problems:

1) The tank has no regulator on it, so when the valves are closed, they're going to need to be able to take the full pressure of the tank... which is a lot.

2) With the liquid gas going through, it's going to get very cold. This could cause a valve jam

3) I've got to somehow start the engine on liquid gas, which was tricky last time.

Here's the somewhat comical valve arrangement:
http://www.frenchgeek.com/imageslg/pjupdate5lg.jpg

Any suggestions or ideas on running on liquid would be very much appreciated.

Edit: I'm using 1/4" fittings I think