I haven't updated this for a while because I have been hoping to find a way to implement a governor controlled valve release. That search continues. But in the meantime there are other things to do. It must be remembered that Corliss engines were designed to run at between 60 RPM and 160 RPM under load. Corliss engines were meant too run at high steam pressure with the throttle wide open and the speed (and power output) governed by short burst or high pressure steam with precisely timed valve opening and closing. The precision is the key. The precision is possible because the valves at each of end of the double acting cylinder can be adjusted independently and the timing adjusted to perfection.
That is not really possible with a slide valve engine. The timing of a slide valve engine is fixed by the fixed dimension of the valve. The cylinder halves can be balanced but each side cannot be optimized without remaking the valve. To run well at low speed, each cylinder half must carry its half of the cycle and deliver the crank to the opposite half with enough momentum to reach the point where the load can be picked up and carried by the other half. That is hard to do on a small model because it usually means dissassembly of the valve chest.
On a Corliss engine, the overall performance is affected by the design of the linkage from the eccentric to each valve edge. It includes the eccentric throw and advance angle and the geometry of the wrist plate but each individual valve can be fine tuned by adjusting the length of the rod between the wrist plate and the valve lever arm. That can be done without disassembly if the rod is made with right and left hand threaded ends as a turnbuckle. I don't know if left hand taps and dies are available in #2-56 or 1.5mm thread size.
If the rod length is fixed, the adjustment could be made by rotating the valve lever arm on the valve spindle. This is never done in full scale practice where the lever arm is always keyed to the spindle. It is difficult to imagine that a reliable clamping method could be devised at small scale. I devised a way to firmly fix the lever arm to the spindle (loctite) and still allow adjustment by rotating the valve edge on the spindle within the bore. This method has no basis in full scale practice but I think it is far more reliable that moving the lever arm on the spindle.
Details of this valve design are shown earlier in this thread but the adjustment is easy. The back side valve bonnets are removed, revealing the adjustment mechanism. I don't completely remove the bonnet. I remove all but one bottom screw and rotate the bonnet so that it reveals the adjustment but prevents the valve from sliding out of the valve bore. In fact, the engine can be run under power with the valve covers open with only minor, if any, air loss. Try THAT! with a slide valve. I have no experience with steam.
There may be better ways to do this but here is my methodology using a calibrated and certified 75 year old eyeball to measure the crank angle. I set the crank at TDC and then with the throttle valve open and the regulator set to 100 PSI and then, holding the flywheel, slowly rotated the crank past TDC untill I could feel the valve open and attempt to drive the crank. I adjusted the valve to achieve opening with the smallest angular advance past TDC. I then rotated the crank 180? to BDC and using the same method, adjusted the steam valve for the rod end of the cylinder.
Setting the exhaust valves was not as clear cut. I was not as concerned with closing the valve early to provide compression cushioning but I wanted to be sure that it was fully closed when the steam valve opened. I could clearly hear the high pressure air blowing through the cylinder by listening to the exhaust pipe. I thought about sticking the exhaust pipe in a glass of water and watching for bubbles but i didn't.
By tweaking these adjustments, I was able to achieve reliable operation at 60 RPM or less under no load. During all of these test, the local air regulator was wide open and the gauge was reading between 125-150 PSI and the air flow controlled by the globe valve at the top of the cylinder. The globe valve was modified to give finer control with a tapered seat and stem, not as severe as a needle valve, but still slower opening and secure closing.
Here is the result:
Before I can give control over to the governor, some modifications need to be made. The crankshaft pulley needs to be larger to increase governor speed and all of the control linkage needs to be tightened up. There is a lot of lost motion due to sloppy fits. There is plenty more to do. Oilers, guard rails, piping. And, oh yeah, release gear.
Well, its got dash pots. I guess you can call it a Corliss!
Jerry
Wow! That was a long post. If you read the whole thing, you deserve some entertainment! Sorry, my tutu has a beer stain on it.