Ryder-Erricsson Displacer

[fcheslop]

Hi all,In slowly remachining a set of 2inch castings for the Ericsson Stirling engine that I recieved in a swap via David Jones
Now at the stage of machining a liner when I find a supplier for the tube
The question is has there been any alterations to the diameter of the displacer as a 1 3/4 dia displacer in a 2 inch bore just seems small to me and I had thought about going up to 1 7/8
many thanks

 

[Blogwitch]

F,

I have a Robinson casting set to make, same sort of principle as yours, and like everything else like that I do, I research how the engine works first, rather than following blindly what is shown on the plans.

One of the main deviations that I will be doing with mine is rather than the displacer piston being a sealed unit, it will have lots of holes drilled around it's periphery and will be filled with wire wool. This has been proved to make the Robinson engine work more efficiently as the piston acts as a regenerator. In fact, the original full sized engine had a wrapped wire mesh displacement piston.

I am sorry, but I don't know if it will work with yours, but it might be worth exploring.

John

 

[fcheslop]

Hi John, thanks for the reply like you Im familiar with the Stirling principal but just had this wee niggle that I had seen a mod maybe not. The Ryder has had all the rather sloppy tolerances tightened up and due to some poor machining read butchered with a knife and fork she is now nearer scale.I still have some pics from a restoration I did on a full size one 20 years ago
Instead of drilling lots of holes I had thought of using a porous material for the displacor like pumice its just stopping any bits of grit coming from it and getting into the gubbings or making it like a stack of CD discs.
I did start building a Westbury designed Robinson but at the moment it languishing under the bench with the spiders as the drawings are just total rubbish with so many errors he could never have made it. I will return to it over the next year as Im clearing up all the part builds
Best wishes always
frazer

 

[Blogwitch]

Frazer,

The Westbury one has been proven NOT to work unless a lot of design changes are carried out. Have a read of the attached PDF.

When you come to resurrect your Robinson, give me a shout and I should be able to send you what I have. I do have a very old drawing that has helped me a lot to decide what to do, like where to put the chimney(s) and how to get the constant velocity regulator working correctly.

Maybe a couple of copper coloured metal pan scouring pads (not the Brillo type with soap on) could be used, surrounded by a ring of thin brass sheet or tin plate to make it neat and some fine SS mesh at either end, then your rod through the whole lot. There are many ways to do things, just coming up with the right one is the problem.

John

View attachment Robinson.pdf

 

[BobsModels]

Hi

I recently built this engine. I made the displacer piston 1.875. I have attached a PDF describing how I did it.

Here is a link to a Dropbox description of my entire build with a description of all the modifications I made and why. If you get
a request to logon or create an account just hit the "no Thanks" at the bottom of pop up. Then just hit
the download button in the upper right to get the file, it is big about 25mb.

https://www.dropbox.com/s/fzv8noejdirmrqd/Rider-Ericsson%20Hot-Air%20Pumping%20Engine%20Build%20Complete.pdf?dl=0

Bob

View attachment Rider Ericsson Displacer Only.pdf

 

[fcheslop]

Hi Bob , thanks for that its greatly appreciated .It must have been youre build I had seem on the other channel but since I left I could not see the pics
I like youre added detail and the more realistic pump arrangement . I intend on building her with the oil/gas firebox so this will do away with another problem.Not sure if you mentioned it in the build what did you use as the piston seal I know the original engines had an oiled leather seal but not sure if this will work in a small scale model. In a perverse way because these casting are already butchered I ended up taking the attitude of nothing to lose and just build from previous experience although it would have been easier just to scrap them and machine from bar stock .We live and learn or so they say it just seems the older I get the less I know

Hi John , thats very handy and confirms what Iv already discovered to my cost
I dont mind the odd error but when you start to do the maths and he didnt even get the basics right its infuriating to say the least. Im just not in a position to waste money making good parts to bin them.
I do plan on restarting a build so any information you could share would be great.
Many thanks to both of you
kind regards
frazer

 

[BobsModels]

I used graphite string, ie old fashion packing yarn for the piston seal. It was recommended for the low amount of friction and easy to make. Just undue the small strings from a large packing string and make several wraps.

I use silicone oil to lubricate the piston. I do this so any oil that gets down to the hot tube end will not form a carbon film as it is burned away and thus becoming an insulator right where you want max heat transfer. That is also why I used a copper end cap on the hot tube, ie max heat transfer.

Bob

 

[fcheslop]

Thanks Bob ,Iv just seen the mention of it in youre right up
Im slowly getting there:thumbup:
cheers