Single valve compounds

A special section just for steam engines and boilers, as without these you may as well fit a sail.
Post Reply
Ethelred
Lighting the Boiler
Lighting the Boiler
Posts: 36
Joined: Sat Dec 03, 2016 7:14 pm
Boat Name: Dixie

Single valve compounds

Post by Ethelred » Sat Dec 10, 2016 1:35 pm

As a naive autodidact I look at my compound and wonder about all that reversing linkage flapping about. I read that many builders spend as long on them as the entire rest of the engine. Surely I thought, you could put the valves in the middle and drive them off one artfully contrived linkage. It seems so obvious that there must be some good reason for not doing so. So that one gets parked in the nether regions of the grey matter and then I came across this:

Image[/URL]

This is the engine from the steam launch Advance

http://media.wix.com/ugd/3c78c8_c2de096 ... 739b8a.pdf
http://www.steamboatassociation.org.uk/page-1854442

It seems to be a Russian engine from the 1860's.
It appears to have one central piston valve with reversing gear.
Damn clever them Ruskies, but how do they do it?
It obviously works OK as it's pushing a reasonably sized boat for the engine capacity, so why isn't everyone doing it, or am I missing something.
I also noticed in a recent discussion on here, a reference to the Halcyon class destroyers, some of which had a shared piston valve between two cylinders.
Rob Lemon
User avatar
TahoeSteam
Full Steam Ahead
Full Steam Ahead
Posts: 813
Joined: Fri Mar 07, 2014 5:38 am
Boat Name: Wayward Belle
Location: South Lake Tahoe, CA, USA
Contact:

Re: Single valve compounds

Post by TahoeSteam » Sun Dec 11, 2016 4:20 am

I'm pretty sure the only way to do it with one set of valve gear is to either be a steeple compound, a wells compound, or have the crank throws 180* opposed. The problem with the options is the difficulty to start on TDC or BDC, similar to a single, which is not ideal when it comes to maneuvering. The way the Halcyon class engines worked is they had essentially two compounds bolted together with their respective 180* crank assemblies 90* opposed.
Ethelred
Lighting the Boiler
Lighting the Boiler
Posts: 36
Joined: Sat Dec 03, 2016 7:14 pm
Boat Name: Dixie

Re: Single valve compounds

Post by Ethelred » Sun Dec 11, 2016 11:52 am

I think you're right Wesley, it does look like the cranks are at 180*
It still seems like a good idea though, and the stopping on the centres is no more a problem than it is on a single or steeple, and all those folk running them seem to cope. In fact historically it appears most small launches were supplied with a single. Sure you can't use a simpling valve but in reality I've observed folk tend to apply boot to flywheel.
Rob Lemon
User avatar
TahoeSteam
Full Steam Ahead
Full Steam Ahead
Posts: 813
Joined: Fri Mar 07, 2014 5:38 am
Boat Name: Wayward Belle
Location: South Lake Tahoe, CA, USA
Contact:

Re: Single valve compounds

Post by TahoeSteam » Mon Dec 12, 2016 3:45 am

The 180* opposed would, in theory, make balancing much easier and more effective, especially if one took the time and care to make sure all reciprocating parts were equal in weight.
Post Reply