I seek an alternative mechanism that will convert rotary motion into linear motion in the same way as a rotary govenor does on a steam engine.This is to control a needle valve proportional to r.p.m

One method is a hydraulic governor.  The rotating shaft drives a gear pump that circulates oil.  There is an orifice in the discharge line of the pump.  The oil pressure upstream of the orifice will be proportional to the shaft rpm.  This pressure signal can be used to control a linear hydraulic actuator on the valve.  This is similar to how the governor on a steam turbine works.

Just another thought.  If you replace the fixed orifice I mentioned above with a needle valve and use a spring return actuator on your gas valve, then the needle valve will effectively become your throttle.  You may also want to consider a needle valve in parallel with a fixed orifice.  Without the orifice in parallel, it would tend to drive your gas valve wide open if the needle valve is closed.

A possible solution for the oil tank is to use an accumulator.  This is a small pressure vessel with a piston or diaphragm that separates the liquid from a pressurized gas.  It is pressurized with nitrogen, and then the oil is pumped into it.  The system will then have to be bled free of air.

MORE NEWS