Vintage pneumatic Fuel cut off engine timer

Greetings-  Does anyone know how to set up a vintage pneumatic type fuel cut off engine timer?  The one that I would like to use with a TD or Pee Wee 020 is nice and small/lightweight and it is branded "Spitfire"  I do not have any instructions for how it works and how to configure the fuel lines.  Photo is included.  Any advice is appreciated.

Well I wouldn't recommend using it at all-these timers (the airdraulic type-not just your particular branded one) were notoriously inaccurate and troublesome in their day-late 40s-to late 50's-and disappeared off the market very quickly when clockwork timers became readily available. The problem is they used rubber and leather parts internally-and neither material ages well.

There is no way you could use your example with a PeeWee...unless you are prepared to cut a hole in the tank and use an external fuel line. It could be used with a TD 020-but again you would have to a) find a place to mount it-so that means at best behind the engine in the fuselage-or hanging out in the breeze-but again behind the engine-and then the fuel line will be convoluted-you have to plumb the timer between the tank feed and the needle valve assembly-that's what the two fuel nipples on top of the timer are for-its simply a shut-off valve. Note that there are other types of timer operating the same way-some cut the ignition circuit on a spark engine, others crush the fuel line-but they all suffer from the same genera issues of unreliability and repeatability.

If your usage is such that you don't need an accurate engine run-then fine....but you could then achieve the same result with an eyedropper tank or a graduated coil of fuel tube-at a lot less hassle.

The reason such timers became notorious is due to their intrinsic design mechanism-they all work essentially on a 'syringe' system-there is a piston inside that is propelled down the body by a spring-which is compressed when the operator pulls out the operating lever....the piston uses leather or rubber gaskets to achieve a seal within the body-and the rate at which it moves down is governed both by the spring tension and an adjustable bleed valve at the base-normally adjusted by a needle valve-adjustment of which speed up or slows down the rate at which air can escape....and in turn determines the time taken for the piston to reach the limit of its travel-at which point the timer carries out its function. Sometimes the adjustment is built into the knob on the operating lever-but the principle is the same. Friction, dust lubrication all have a major effect on the reliability and repeatability...

Some brands-the UK 'Elmic' for example, had versions that triggered a sprung loaded arm that could pivot though about 45 or 90 degrees when triggered-and operate a separate shutoff mechanism on the engine when the timer operated. and some incorporated two functions-the second being via the aforementioned arm-so for example could operate an autorudder function as well as engine shutoff. Ingenious...but still a flawed concept.

ChrisM
'ffkiwi'