'Shuttle' type valve control

[SignalFailure]

Does anyone have experience of, or an opinion on, using the shuttle-type arrangement for controlling the valve on Stuart pumps but on an ordinary engine (i.e. not a pump and with a flywheel)?

Here's a picture in case my description isn't clear enough...
http://www.stationroadsteam.co.uk/Stuart/steam%20pump.jpg

Thanks in advance

Paul

 

[SignalFailure]

Bump: No takers?

 

[Blogwitch]

Paul,

The only reason for using what you call a 'shuttle' arrangement is because there is no rotary movement on that pump, being completely linear in action.

To use it on a normal engine I think would introduce uneccessary complexity over the generally accepted method of using an eccentric driven from the crank.

The method could be used by using a spring loaded rod from the valve chest with a cam follower on the bottom, and a cam mounted onto the crank, but that is almost the same as using an eccentric and strap.

The method must have been tried out over the centuries, but usually the easiest method comes to the top of the pile and takes over.

It would certainly be worth chasing if you wanted to make something out of the ordinary.


Bogs

Pat got in first

 

[Maryak]

Paul-

2. If you did use an eccentric, you would normally cut off the steam before the piston completes it full travel. For a pump, cutting off steam before the end of stroke would just cause the pump to stop in mid travel.

Pat J

Sorry Pat J but the Weirs Shuttle and Glissard valves can be adjusted to cut off the steam at around 0.75 of stroke, (with the rest of the stroke carried out by expansion of the steam), or supply steam for the full pump stroke. This can be done whilst in operation. These pumps are normally started with full admission and cut off is applied after they have warmed up and settled down. Mind you it's one hell of a complicated way to get a pump to go up and down and a right royal pain in the posterior to refit and adjust for wear in the "D" valve and shuttle valve combination. The savings achieved are probably not all that significant with the possible exception of a large air pump.

Paul,

If you don't want to use an eccentric then have a look at "Joy" valve gear.

Best Regards
Bob

 

[cfellows]

Paul, there used to be a company which offered several different model steam engine kits that used a shuttle valve arrangement rather than an eccentric. I know they were offered on ebay and I may have seen ads for them in some magazines. They weren't very expensive and they were somewhat non-traditional in their design. Haven't seen them now for a number of years. Here's a picture I saved from some years ago:

Chuck

 

[arnoldb]

Paul, a couple of months ago I pondered the same question.

Like already stated it will definitely work, and is fairly easy to implement.

For compressed air engines requiring air for the full stroke, it will work very well, but if you want to use steam expansion, the mechanism will be difficult to design and adjust like Bob said.

One thing that put me off using this type of valve gear was the noise it would kick up in operation; a constant Click-Click because of the impact each time the valve gear gets engaged to be switched, as well as the associated wear on the components; I actually thought of using some rubber padding to eliminate this additional noise and wear. I like to just hear the engines chuf-chuf
The other was trying to reverse the engine. The gear would work well if you started the engine by a turn of the flywheel in the direction you wanted it to go, but switching while running will be precarious.

Bogs is spot-on, as always; if you want something unique, go for it!

Bob's suggestion of using Joy gear to get away from using an eccentric is also good.

If you get Charles Dockstader's "Valve Gear" program, there's a myriad of valve gears in there - I happen to like the Hackworth because of it's simplicity - though slightly faulted.

Pat, you were posting while I was getting some facts straight ;D

Regards, Arnold

 

[SignalFailure]

Thanks everyone for the very detailed replies - some very useful information in there, lots to ponder on and some great ideas for yet more projects....arrrgghhhhh! :big:

Cheers

Paul