Author Topic: Anything wrong with this?  (Read 2169 times)

Offline Paul

  • Full Member
  • ****
  • Posts: 37
Anything wrong with this?
« on: January 23, 2014, 08:31:12 PM »
It occurred to me that in a single acting engine the valve and piston could be hooked up so they have the same travel (and travel direction) if the valve was something like the attached, that is, a rod with about half cut away like a d-bit to allow the escape of steam with a transverse hole to admit steam at the appropriate time (valve in grey, piston in dirty mustard colour!). Is there anything obvious I've missed here, it seems too simple to work!

TIA

Paul

PatJ

  • Guest
Re: Anything wrong with this?
« Reply #1 on: January 23, 2014, 09:04:47 PM »
I build an steam engine like that years ago, and it works well.

I used an eccentric to move the valve.

The valve will move I guess roughly opposite of the piston movement?

Pat J

Offline Paul

  • Full Member
  • ****
  • Posts: 37
Re: Anything wrong with this?
« Reply #2 on: January 23, 2014, 09:19:44 PM »
Thanks Pat but I thought the valve could move in the same direction as the piston, ie as the piston moves left to right from so does the valve. I should have said - there'd be an opposed piston at the other end to shove it back the other way! Still seems too good to be true... maybe I'll make a mock up and see.

Paul

Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 11423
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Anything wrong with this?
« Reply #3 on: January 24, 2014, 01:15:26 AM »
Paul, it looks like the stroke of your piston and valve are the same. Generally the stroke of the valve will be much less than the stroke of the piston. In your example above the exhaust portion of the valve would cut off earlier than needed or desirable. Similarly the admission hole would only line up with the cylinder for a very brief time. The use of an eccentric allows the stroke of the vale to be less, yes still timed with the piston position though it will usually be somewhat out of phase and not identical to the piston movement. I am not sure I know what you are saying regarding an opposed piston at the other end.

Bill

Offline Paul

  • Full Member
  • ****
  • Posts: 37
Re: Anything wrong with this?
« Reply #4 on: January 24, 2014, 06:59:00 AM »
Cheers Bill. Yes I realised that the admission period would be short but running on steam (at this scale) I thought I could rely on expansion to get the work done. With regard to the exhaust I think it could be arranged that the exhaust phase is a bit longer and maybe assisted at the beginning by a  hole near the top end of the cylinder (!). I was thinking of an opposed cylinder as per this image with a scotch yoke between.

I've had success on air at very low pressure with this arrangement using an eccentric (actually a second yoke working as an eccentric) but thought it could be simplified further. What do you think?

Paul

Offline Paul

  • Full Member
  • ****
  • Posts: 37
Re: Anything wrong with this?
« Reply #5 on: January 24, 2014, 08:47:43 AM »
 :wallbang: Ignore me... I've got a better idea for the valve  ;)

Offline Alan Haisley

  • Full Member
  • ****
  • Posts: 663
  • Near Clayton, North Carolina, USA
Re: Anything wrong with this?
« Reply #6 on: January 24, 2014, 05:00:10 PM »
Paul,

You might be able to do something like this. Similar valves work with steam powered water pumps - Used with a double acting arrangement though.

Without the collars on the shafts to make it all automatic you could manually move the valve bar and take steam assisted motion off the piston rod. That would let you "manually" move a lever or whatever that has too much resistance for an unaided movement.

Alan
Near Raleigh, NC, USA

Offline Paul

  • Full Member
  • ****
  • Posts: 37
Re: Anything wrong with this?
« Reply #7 on: January 24, 2014, 05:27:03 PM »
Thanks Alan, that's almost exactly what I drew up earlier this afternoon!  :o

I've experimented with that type of valve before ...
list=UUVAZb701Oo_YMYv-ta7muKQ

I plan to make the yoke (the blue bit in the other image) straddle the valve rod or be a running fit on it (for support).

Cheers

Paul


Offline b.lindsey

  • Global Moderator
  • Full Member
  • *****
  • Posts: 11423
  • Dallas, NC, USA
    • Workbench-Miniatures
Re: Anything wrong with this?
« Reply #8 on: January 24, 2014, 06:12:29 PM »
That is certainly starting to look like a workable solution...simple and elegant!!

Bill