Question about MEM Corliss

[Jasonb]

I've had a question from someone who hopes to build the MEM corliss at 1.5 times size and wonder if those involved with the design or anyone who has made it can comment.

It will be run on steam and looking at the drawings there is quite a large void at each end of the cylinder between end of cover and the piston at the full extent of it's travel. This is generally regarded as not ideal for efficient running so would it be better to have longer spigots on the cylinder covers to reduce these gaps to a minimum with due allowance for steam to get into the cylinder?  This is what is shown on the Thorp drawings and Simon's corless build also has a deep end cover.

Thanks in advance, J

[gbritnell]

I haven't looked at the porting relative to the end of the piston stroke but possibly the piston rod end could be adjusted and a longer piston made. Either way would reduce the head space.
gbritnell

[Jo]

I've had a question from someone who hopes to build the MEM corliss at 1.5 times size and wonder if those involved with the design or anyone who has made it can comment.

It would seem they have downloaded the drawings from MEM so that implies they are a member. We normally ask members to participate before we help to solve their model engine problems 

Jo

[Jasonb]

He is using the ones that Julius did on MEW and following Vince's build there. Thought that it may help others by raising the point here.

Thanks George, the piston is quite narrow so could possibly be thickended up but as there is 1/4" space each end and the passages are a long way in I think the thicker covers would be better.

[Jo]

He is using the ones that Julius did on MEW and following Vince's build there. Thought that it may help others by raising the point here.

We won't hurt or embarrass him if he joins and posts about his build of our engine here    It would also enable him to ask all of his questions without the problems associated with interpretation from having a "piggy in the middle"

Jo

[Jasonb]

He is a member but for some reason does not seem to want to ask here, does not post much on other forums either. Not everyone likes to be active on forums and I was just trying to be helpful.

[Jo]

If people do not post for a long time the forum software may assume they have died 

Jo

[Jasonb]

Yes I think he said he had to reset his registration.

[Jo]

  You mean he forgot his password.

Time out on posting will show as a deceased member the password will still work

Jo

[fizzy]

Hello all.

JB has been most helpful, as ever. I lost my password so asked on another forum. The Corliss is a project away from work (I make and supply steam boilers to trade and public) and i have yet to decide on a gas or coal boiler. I think it will go gas as there wont be much demand for steam and keeping a small coal fired boiler going can be less than easy. Im slowly re-drawing all the plans in a cad format that I like and tweeking a few changes as I go. Ive decided to turn the end covers thicker to fill the dead space as there is a lot of it. Having no joy finding a suitable piece of steel for thw 12" dia flywheel - any ideas?

[Jo]

Hi Nigel,

Last time I needed a 300mm diameter flywheel I turned the rim off of one from Bruce engineering.


In Bob's original design for the MEM Corliss the end covers stuck into the cylinder by 3.2mm . The port is 1.6mm wide and is drilled at an angle of 15 degrees, there is 2.7mm from this port to the inside face of the cover. The Piston comes 1.2mm from the edge of the port. So the "gap" at the end is 5.5mm wide.

Depending on how accurate your drilling of the ports is you could increase the cover spigot to 4.75mm leaving a 4mm gap but you have less wander space with your 1.6mm drill.

Remember this is a Corliss not a slide valve engine so with a smaller end gap the time to fill the volume at the end will reduce so you may have to operate on a higher pressure to get sufficient "energy" in the volume of air/steam that gets into the cylinder on each stroke.

Jo


P.S The Arnold Throp Corliss engine has a 2mm scallop on the end of the deeper cylinder cover leaving a 4mm "gap" either end of the stroke.

[Jo]

Just checked Julius's drawings there is 5.5mm gap on that one.

Jo

[Jasonb]

I don't see that the accuracy of the drilled passages really comes into it as the cover can be notched or have axial clearance in much the same way you would to the cover of most slide valve engines. Thorp uses both methods. Gap does not need to equal port width, it's the area that matters and provided that is not less than the ports there will be no restriction to flow

Also can't agree with your figures for the Southworth, looking at my Fleet drawings the cylinder is 3.875 long. Now if we subtract the stroke of 2.25", piston 0.5" and the two covers at 0.5" each we get 3.875 - 3.75 = 0.125 total clearance or 0.062" each end that's 1.6mm on a larger diameter cylinder. yes there is some counterboring for the piston nut and steam flow clearance added but generally only a small amount of end clearance.

Not sure how you got your sizes for teh MEM engine either? Cylinder is 2.5" long. Less SStroke of 1.5", 2 covers @ 0.125" and piston @ 0.25 gives 2.5 - 2 = 1/2" total so 0.25" or 6.35mm clearance between covers and piston at each end.

[Jasonb]

As for Julius again I get different.

Cylinder is 148mm long. Stroke of 86mm, 2 covers @ 19mm each and a 19mm piston gives 148 less 143 = 5mm total so 2.5mm each end These have the axial steam clearance like the Thorp.

[Jo]

I don't see ...

Also can't agree ...

Not sure how you got your sizes for teh MEM engine either..

As for Julius again I get different.

I was only trying to help 

Jo

[Jasonb]

I'm sure you were but could not see how you got your "helpful" figures, could not even blame them being in imperial as Julius' ones were in metric

Coming back to the point about restricting the flow of steam, on the MEM one the drilled passages are going to be the main restriction, as Fizzy is going to be upscaling his one there should be room to get a suitable cutter into the bore and have a slot as per the usual full size practice and the Thorp model.

Any thoughts from the wider membership?

[Ramon Wilson]

I would be reducing it to around 1.5 mm too if running on steam. The Throp Corliss has similar as you say but appears to not be enough to be able to get sufficient volume of air in in the short cut off period.

The MEM Corliss is a very nice and buildable subject but to me it has one unsatisfactory design fault. That is the main crankshaft bearing supports. I can't see any full size engine having a crankshaft and bearings sitting a top a narrow pedestal - much narrower than the actual bearing. To me this needs to be reversed to give more substance to this area and probably more so with the extra mass of the 12" diameter flywheel.

On one of the videos of this design the pedestal can clearly be seen flexing in relation to movement of the crank which to my mind reinforces that thought. Were I to build one this is one mod I feel I would need to make to what is otherwise a very nicely designed engine.

Regards - Tug

[Jasonb]

Thanks for your thoughts Ramon and also correcting my spelling

I'd not looked that closely at the bearing support but having done so would tend to agree. Options would be to make something more substantial in metal with about a 2" long bottom or to sit the existing bearing block onto a solid "foundation" but I think I would go for the former and match the support for the main frame of the engine to the outrigger one.

As for your flywheel Fizzy I wonder if one could be rolled from say 50 x 6 black bar, you would be upto the welding job. Once built up into the rest of the flywheel a light skim of the outer face and edges should clean it up OK. The traction engine guys often roll two pieces about 3/4 of a circle each and then cut to give to matching halves which does away with the bits at the ends of the bar that does not roll to the same radius. If you wanted to add a bit more interest the flywheel could be made to look like a two piece one with some dummy joint flanges.

Being quite wide but thin section you could possibly modify a shepherds/hen hut wheel casting, some 12" ones on e-bay.

[fizzy]

Thanks JB. At the moment im toying with buying a 'normal' flywheel for the inner gubbins and using an outer sleeve. Recon it would need to be at least 6mm plate if rolled as inside and outside would need skimming....dont know if youve ever rolled 6mm plate but its an industrial process if done cold. Brain working as I type.....some 2" x 8mm flat bar would round a former (I have a few BIG lumps of ali for end plate formers) with the help of a large amount of OXY heat would (Might) work, do two of them as you suggest....would just need to find someone to weld them together 

[pgp001]

Fizzy

I have sent you a PM regarding your search for a flywheel.

Phil

[fizzy]

The main parts excluding flywheel and supports are all completed, but i had big problems trying to get a parallel bore. Got there in the end but at the cost of oversized bore and awful finish.  Not too worried about the finish as having built a few bigger engines I have found that using graphite string (the 6mm square section stuff) works just as well as rings at low pressure and will work with a poor finish when running with wet steam. If it isnt good I will get some new honing stones, clean it up and make a new piston so not too much to lose. There is about 40 thou between the valve and the bore at its thinnest point, not something I wanted.  I will add some photos as soon as I remember to take the camera into the workshop. I had forgotten how much pleasure there is in making something for yourself instead of for a customer....and forgotten how dirty cast iron is to work with. Happy new year to one and all. Fizzy