Slide valve question

[kvom]

My current project uses double-acting slide valves.

My question is how the slide is held against the cylinder in the steam chest. Does the steam/air pressure hold it down, or does the cover need to push on the top of the valve?

 

[Quickj]

In theory, the valve floats, and steam pressure holds it against the valve face.
Jim

 

[mklotz]

The valve is always over the exhaust port so its bottom is always exposed to atmospheric pressure. Its top is always exposed to the steam pressure (which, naturally, is higher than atmospheric). So there's always a net force pushing the valve against the valve plate/cylinder. It's really very ingenious, isn't it?

 

[d.bick]

The steam pressure should keep the valve on its face. There are slide valve designs that have a spring between the valve and valve chest cover.
The good thing about slide valves is if you get condensate (water) in the cylinder it will pust the slide valve off the face allowing the water to escape, without damaging the cylinder covers or bending something.
Dave Bick

 

[kvom]

Thanks for confirming what I thought. Getting a sliding fit with the cover would be a PITA.

 

[gbritnell]

In all actuality on a full sized engine there was so much pressure on the slide valve and it's attendant wear on the port face that different types of balancing was employed. The simplest means was to extend the slide valve up to the valve chest cover (with clearance) and this would reduce the pressure on the valve.
gbritnell