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Re: Gordon Cheape Compound

Posted: Sat Dec 01, 2018 4:25 pm
by dampfspieler
I have used pear and brass. The strips where glued together, sanded and varnished with EPIFANES.

Re: Gordon Cheape Compound

Posted: Mon Dec 03, 2018 9:13 pm
by Martyn39
Thank you for the photos and info. As far as the drain cock manifold is concerned here are a couple of photos as it is today. Essentially it is a piece of 7/8" square brass with a 10 mm stainless steel rod through a reamed hole. A bit fiddly to make to get an accurate fit and line everything up. Still left to do is to machine grooves in the stainless between the holes to seal each cylinder from the others with O rings, but I am still waiting for these to arrive.

Re: Gordon Cheape Compound

Posted: Mon Dec 03, 2018 10:28 pm
by Mike Rometer
I have similar drain cocks on my Locomotive and haven't found the need for intermediate 'O' rings. The steam oil and condensate is more than enough sealant.
Drain-cocks (11) (600 x 450).jpg
Drain-cocks (11) (600 x 450).jpg (61.43 KiB) Viewed 1073 times

Re: Gordon Cheape Compound

Posted: Tue Dec 04, 2018 3:31 am
by Lopez Mike
O.K., all of you experts out there. When a drain cock isn't right at the end of the cylinder but on the end of a tube, does that tube volume significantly affect the non-swept volume of the cylinder?

I suppose it depends a good deal on the relative size of the cylinder, it's existing unswept volume and the volume of the tube between the cylinder and the cock. Some engine designers have gone to considerable effort to minimize the unswept volume of cylinders.

Thoughts?

Re: Gordon Cheape Compound

Posted: Tue Dec 04, 2018 3:33 am
by Lopez Mike
I suppose the tube fills up with non-compressible fluids right away. All a moot point.

Re: Gordon Cheape Compound

Posted: Tue Dec 04, 2018 11:59 am
by RGSP
Lopez Mike wrote:
Tue Dec 04, 2018 3:33 am
I suppose the tube fills up with non-compressible fluids right away. All a moot point.
Given the drain tubes are uninsulated, I'm sure you're right, but it must add quite a lot to the unswept volume immediately after the cocks are closed. Perhaps that does minimal harm just when starting. The thing that occurs to me is that the drain tubes will need to be rated for full steam pressure, rather than diddly squat if the drain cocks are right by the cylinders.

Re: Gordon Cheape Compound

Posted: Tue Dec 04, 2018 6:15 pm
by Mike Rometer
Well mine are Kunifer brake pipe so I don't envisage any pressure problems :lol:

Re: Gordon Cheape Compound

Posted: Wed Dec 05, 2018 4:22 am
by fredrosse
Drain passages can play a significant part in heat penalties, depending on the arrangement.

Say you have an engine running at 125 PSIG (8.7 Barg) steam pressure, with a saturation temperature of 353F (178 C), exausting at atmospheric pressure, 0 PSIG, (0 Barg) with saturation temperature of 212F (100C).

The cylinder wall, steam inlet and exhaust passages, piston, piston rod, and all surfaces in close thermal conduction contact with cylinder steam pressure will be at about the average saturation temperature between the inlet and exhaust, in this case 282F (139C).

When the high pressure steam is admitted to the cylinder, it will condense like crazy on the metal surfaces, because the heat transfer coefficient for steam condensing is tremendous. The metal surfaces are heated up perhaps just a few degrees, as the time of exposure to high pressure steam is very short, less than one stroke of the engine. This initial condensation is the basic main thermal loss in almost all reciprocating steam engines, and with typical launch engines about half of the incoming steam is condensed to liquid water, and is not available to do expansive work in the engine.

At the end of the power stroke, the exhaust valve opens, and cylinder pressure drops to atmospheric pressure, and all of that initial condensation water , thermally connected to the steam cylinder, piston, exhaust passages, etc., now boils away, this is called re-evaporation of the wet cylinder walls, passages, etc. Again with a tremendous high heat transfer coefficient, lowering cylinder temperature only a few degrees.

Parts of the cylinder drain passages that run below 212F (100C), will fill up with condensate, and the trapped water will do virtually nothing, no initial condensation on admission, no re-evaporation on exhaust stroke. However, any parts of the drain passages that run above 212F (100C), will participate in initial condensation and re-evaporation. The cylinder drain passages must at least start right at the cylinder, very hot, so the passages here contribute to initial condensation and re-evaporation. Best to have the drain passage valve seat as close to the point of inlet drain collection as possible for minimum losses here. Very small passages also helps, less area for heat transfer, and less drain passage volume to collect new condensate on every engine stroke.

Re: Gordon Cheape Compound

Posted: Wed Dec 05, 2018 2:32 pm
by Mike Rometer
I don't think there is any argument that these things must make some sort of difference. The real question is, is that difference measurable, and even if it is, is it big enough to be of sufficient significance? It was accepted a long time ago that steam engines are inherently inefficient, so attending to the things that are significant is going to bring the biggest improvement(??) and should therefore be done first. I believe we still await the perfect valve gear for instance.

In my case I traded that (however) small problem, for a much less complicated/compact linkage, and simpler manufacture.

Re: Gordon Cheape Compound

Posted: Sat Jan 05, 2019 7:04 pm
by Martyn39
It's back to the engine after christmas. The drain cock system is fitted and plumbed in so the next job is to make the lubricator and design a linkage for it. I am currently looking at using the valve spindle as the driving force for the lubricator but any suggestions you guys have would be gratefully received.
According to Gordon Cheape the engine is designed to give 7HP @ 150 psi with mild superheat. As I said at the beginning I am unfamiliar with compounds and I am still learning but there seems to be a problem with lubricating an engine that has a condenser. What steps do you take to minimise oil contamination of the boiler feed water? This will not affect me as once the lubricator and the feed pump are fitted I shall move the engine on but I can't stop thinking about the solution.
We don't have this problem with locomotives as the steam is a total loss system.
I have run the engine on steam with a test boiler that is too small but it certainly runs better than when running on air.
Hopefully the larger test boiler will be built before the engine goes to the next owner so that it can be demonstrated running on steam.