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