Office of Steam Logo_1

Author Topic: Cheaper compound engine? Double expansion engines  (Read 208 times)

CBWho

  • Full Member
  • ***
  • Posts: 562
  • Location: Minnesota
Cheaper compound engine? Double expansion engines
« on: August 17, 2019, 08:17:39 am »
I don't have a double cylinder engine yet.
I'd like to get one (boiler optional) and ideally double expanding. Anybody makes those reasonably priced? My preference is non oscillating but oscillating will do
As for simple twin cylinder engines in my price range, I see PM Research's twin cylinder kit (is this reversible?), Jensen 55, or Wilesco twin cylinder marine engine.

I've been doing a lot of reading about steam engines. The more advanced ones double or triple expanding.
The Märklin 16051 is a double expansion. From what I've read typically (at least 1 example), the high pressure HP cylinder has a diameter of 3 and the low pressure LP cylinder has 5. Which corresponds to a low pressure cylinder with 3 times volume.

However, the Wikipedia article states: In non-condensing engines, the HP:LP volume ratio is usually 1:2¼.


But one can assemble expansion engines with same size cylinders, I've read somewhere that some just dumped the steam from the first HP into 2 LP cylinders. Which backs the ratio from Wikipedia. (So just use 3 Mamod cylinders?)

If the cylinders are 180 degrees out of phase (Woolfe compounding), then the plumping is simple.

But for self starting, one needs 90 degrees phasing with buffers called receivers.

http://ecoursesonline.iasri.res.in/mod/page/view.php?id=2450

In order to reduce this pressure variation, the receiver is made at least 1.5 times the H.P. cylinder volume.

Swift Fox

  • Full Member
  • ***
  • Posts: 546
  • Location: Leicestershire, UK
    • Swift Fox Steam Co
Re: Cheaper compound engine? Double expansion engines
« Reply #1 on: August 17, 2019, 01:49:49 pm »
It is one niche that has yet to be filled IMO, no toy steam manufacturer save the Marklin repro offered compounding. I had a little play around with simple compounds awhile back but using separate engines. I think you could possibly make one using Jensen parts if you were creative enough. I'm not sure if this is something CMS might offer as a future model, it might be worth dropping them a line. Otherwise you main option is Stuart models or possibly AJ Reeves as i know they offer compounds in their engine ranges.

https://www.officeofsteamforum.com/collections-pictures/jensen-65-acting-as-a-primitive-compound/
Your nose is before your eyes, so trust it first!

CBWho

  • Full Member
  • ***
  • Posts: 562
  • Location: Minnesota
Re: Cheaper compound engine? Double expansion engines
« Reply #2 on: August 17, 2019, 03:43:54 pm »
Thank you for your reply! :)
I like your experiment.

CMS: https://www.chilternmodelsteam.co.uk/index.php?route=product/product&path=61&product_id=53
This mentions a simple twin cylinder that is reversible by supplying steam to the exhaust port... They offer a valve to accomplish that.

We can do compounding with identical cylinders but as a 3 cylinder. I am contemplating making a 3 cylinder Mamod engine. 1 HP, 2 LP.

I've been browsing the CMS website and they look to be high quality and well priced. The only drawback is that I prefer twin flywheel engines and the cranks are cut short :(

Swift Fox

  • Full Member
  • ***
  • Posts: 546
  • Location: Leicestershire, UK
    • Swift Fox Steam Co
Re: Cheaper compound engine? Double expansion engines
« Reply #3 on: August 18, 2019, 02:55:41 pm »
CMS do produce some nice kit at reasonable prices and it is great to see they are made here in the UK. They are also very focused on education so i'm hopeful they may release a compound engine at some point in the future.

The quad mill engine they have in development looks interesting:

https://www.chilternmodelsteam.co.uk/index.php?route=information/information&information_id=13
Your nose is before your eyes, so trust it first!

CBWho

  • Full Member
  • ***
  • Posts: 562
  • Location: Minnesota
Re: Cheaper compound engine? Double expansion engines
« Reply #4 on: August 18, 2019, 08:37:33 pm »
Reading about CMS engines, they are reversible by switching the steam flow. To me that seems like a smart method. Are all steam engines without a slip eccentric reversible by switching inlet to outlet? Or is there something different about the linkage they use?

I road in a steam boat today and it uses a Stephenson's linkage to reverse the engine. The traction engines I drove use Woolf linkage. But I cannot think any that reverse the steam flow. Why not?

Someone mentioned that CMS doesn't use slide valves but instead use piston valves? Did they imply round round slide valves like Wilesco? (I see little wrong with round rod valves.)

RedRyder

  • Administrator
  • Hero Member
  • *****
  • Posts: 4313
  • Location: Connecticut - USA
Re: Cheaper compound engine? Double expansion engines
« Reply #5 on: August 18, 2019, 09:05:25 pm »
This is a neat project and you will appreciate it most when your engine is working hard.