Gallery, Projects and General => The Design Shop => Topic started by: picclock on August 29, 2010, 05:58:07 AM

Title: Through piston exhaust porting
Post by: picclock on August 29, 2010, 05:58:07 AM

Hi - First post here.

I'm "designing" a compressed gas engine to run from a wide range of pressures, and need it to have a low resistance exhaust gas path. So I've come up with an offset balanced valve which is located in the piston head and operated by push pins at the ends of the stroke. At the top of the stroke the valve is pushed closed. The gas under pressure, and inertia of the valve keep it that way until it reaches the push pin at the bottom of the stroke whereupon it is pushed open, in doing so the valve is canted to the right and differential pressure + inertia keep it open on the up stroke. The valve pivots about the gudgeon pin and the area of the left surface is about 5% larger than the one on the right. The weight of the right side is about 10% greater than the left ensuring that the inertia of movemement of the piston assists the valve operation. The pins would be spring loaded. The target engine speed is 800 rpm and its highest temperature will be about 35C. The valve seals are just captive nbr O'rings.

I have another problem I need to resolve in that the room for this device is very restricted and I would like to be able to connect and disconnect the crankshaft drive very easily for maintenance purposes (could be a lot of that :-)). Because the engine sits in a well grub screws would be very awkward (and I'd probably have a collection rattling around in the bottom before long).  So I'm looking for some sort of shaft quick connect/disconnect mechanism.

Well, this is the scheme. If anyone has any comments or suggestions for improvement I'd  appreciate it.

Best Regards


Title: Re: Through piston exhaust porting
Post by: cidrontmg on August 30, 2010, 04:53:12 PM
Iīve read your post a couple of times, and Iīm sorry I canīt figure out how the proposed exhaust valve is supposed to work. Maybe because Iīm not a native English speaker... But if you could supply some drawing, sketch, image whatever, it might help. A freehand sketch scanned would be fine, a 3D model would be fantastic  :) You might get a far bigger following, and lots of response. You know, :worthless:    :) :) :)


Ha! Now I see the sketch. Couldnīt see it before, donīt know why.
Title: Re: Through piston exhaust porting
Post by: picclock on August 31, 2010, 10:55:46 AM
Thank you for replying. I apologise for any confusion. I've attached another drawing which shows the piston in two positions, top dead centre and bottom dead centre. It also clearly shows the valve in the open and closed position,  and contains a few additional notes.

I plan to use an overhead sleeve valve with a centrifugal governor for the compressed gas input. I think that's fairly straightforward apart from the gas pressure seals.

Best Regards