Unusual Corliss

[Caber]

Well all the parts are made and engine norms disassembled for paint. I have tried posting a couple of times but the posts have vaporised. Here is assembled engine

[crueby]

Looking great! Really like the details on the valve pieces. 

[Caber]

Thanks!

Next question is what to use as gasket material. The stuff I have is a bit thick for this size of engine and will create some issues with the smaller parts!

[modelsteam]

Hi.  I use .25mm  PTFE sheet. It's easy to cut with a craft knife and punch holes in . It's works for me. Sample quantities are available on Ebay.
        Good luck with your Corliss .
                Chris

[Caber]

I decided to go with oiled paper gasket material that is about 2.5thou for dimensionally critical gaskets I found a small sheet among my existing gaskets.

My next problem is setting up the valve gear. The working end is straight from the MEM drawings but the operating linkage is all to my design. I have struggled a lot with trying to resolve the angular movement required to operate the valves in the cylinder block. My thinking was I needed to open and close the drillings forming the port between valve chest and cylinder but have come to realise that I need the valve to control the opening of the valve chest to the valve shaft. I presume this is a compromise for the model as efficiency wise this massively increases the volume of steam to start moving the piston. Looking at it this way with an angular offset of 15degrees for the ports, a valve chest opening of 45degrees the effective angular movement of the valve is 30 degrees less a bit to stop overrunning the cylinder ports.

When I try and work out the angular displacement at the valve from the  MEM drawings I get 60.1 degrees which seems wrong. The most uncertain measurement is the effective length of the valve lever which is not dimensioned on the drawing. I am scaling that as 0.3”

I would be grateful if anyone could idiot check my thinking on the valve angles or advise how they managed with setting timing and what angular displacement they have on their engine!

[Caber]

So I think I understand how to do this. I made a cut away model of the valve and valve chest to see how it works and realise that the eccentrics need to be at 90 degrees to the crank and advance is controlled by the rotational position of the valve in the chest. In a full size engine the valve would act against the ports but here it acts against the steam chest aperture. In a proper Corlis the advance is fixed by the valve position and cut off by the trip mechanism that I may come back to on mine once it is running. The major issue is setting the exhaust valves as I don’t know what overlap I need to make the valve steam tight. Currently my geometry gives a rotation of about 35degrees which seems adequate to keep the valve open as wide as the port area for most of the stroke. Timing to get the opening close to bottom dead centre but steam  tight during the previous power stroke will be the challenge. As there wants to be marginal advance on the inlet and it is possible to take the inlet cover off when the engine is erected is a bit less of an issue😃

[Admiral_dk]

Aha moment are always revealing  and usually enjoyable too.

Per   

[Caber]

It’s finished! For now. I am contemplating a governor and trip gear but that needs a lot more design thinking as I have strayed so far from the MEM drawings!

I might also add handrails and lubricators like the prototype I have been following but for now it is done.

My workshop compressor is defunct so when that is sorted I will get it running and put up some video.