Wikipedia says:
a) Regarding point (2) on "piston valves" - How does lubrication fair on balanced slide valves?The D slide valve, or more specifically Long D slide valve, is a form of slide valve, invented by William Murdoch and patented in 1799
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The balanced slide valve was invented by the Scottish engineer Alexander Allan. It was not much used in the UK but, at one time, had great popularity in the United States. It gave some of the advantages of a piston valve to a slide valve by relieving the pressure on the back of the valve, thus reducing friction and wear.
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In the 20th century, slide valves were gradually superseded by piston valves, particularly in engines using superheated steam. There were two reasons for this:
- With piston valves, the steam passages can be made shorter. This reduces resistance to the flow of steam and improves efficiency.
- It is difficult to lubricate slide valves adequately in the presence of superheated steam.
b) How does the wear on the o-ring seal I see in some photos of balanced slide valves between the valve and the steam chest compare to piston valve wear?
c) Feel free to correct, augment, share your opinions
I'm totally not biased in any way....
-CB