Can anyone tell me what it is. I assume it has something to do with a a shutoff valve for the oil field boys (since that is where I got the truck from) but the switch on the dash is almost illegable. On the up side I can red "roda deaco valve ______ only, and the other position says "______ valve emergency only." Does anyone know what the blanks say?

Which position am I supposed to run it in? Does it hurt the performance at all? Can I or should I take it out? On the firewall there is a module marked "trombetta", I assume that is a part of it. Any help is appreciated.

Rodda decca valve is a positive air shutoff used in the oilfeild on diesel engines.

let me google that for you.= pictures (http://images.google.com/images?q=roda%20deaco%20valve&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&sa=N&hl=en&tab=wi)

let me google that for you = text (http://www.google.com/search?q=roda%20deaco%20valve&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&hl=en&ie=UTF-8&sa=N&tab=iw&tbo=0)

Diesels trucks do not have a throttle like gas vehicles do-- the engine RPM speed is controlled by injecting more fuel into the cylinder. If the engine gets more fuel-- such as a broken injector, or oil from the crankcase via a bad piston or other source-- the engine may keep increasing speed and there is no way to shut it down. It will keep screaming until it blows up. Some engines have a spring loaded flapper in the intake manifold that shuts off all air to the engine and stops the "Run Away" engine. It can be an automatic controled devise or manual lever activated. Others have a valve in the intake system to stop the engine. Many mechanics have a heavy piece of aluminum plate close by when working on diesel engines to close off the intake.

So the Rodda decca valve is a safety shut-off in case of a run-away engine.