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The valve usually just slides passed the recess which stops the valve wearing a ridge in the port face. You also find teh equivalent of that groove running around all four sides of the portface as it also made machining easier particularly when teh valve chest was an integral part of teh cylinder eg you did not have to plane the surface right into a corner.J
Wipers may just be there to help keep the valve pushed down against the port face you do see various spring arrangements to do this. Given that the engine was likely to be on rough ground they may have thought it helpful if the valve puck did not bounce off on evey bump in the trail.J
Chris, on your labelled picture of the valve it appears as if you can see through it to the port face. Is it 'hollow'? To me the 'wipers' look like sealing strips similar to those found on 'balanced' slide valves, relatively common in locomotive practice. Jason mentions they may be to keep the valve against the port face but I would have thought the steam pressure would have been sufficient for this? Paul Gough.
The valve usually just slides passed the recess which stops the valve wearing a ridge in the port face. You also find teh equivalent of that groove running around all four sides of the portface as it also made machining easier particularly when teh valve chest was an integral part of teh cylinder eg you did not have to plane the surface right into a corner.JEditThis is a good example of the port faces being raised from the surrounding area.
I can't help you Chris.But then, that's not my job.I'm the distractor.How am I doing?