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I think I understand what you are asking. The problem is, the steam valve must be set, or moved, according to the position of the steam piston. There must be some sort of connection between the steam piston and the steam valve so the valve can be set, or moved, correctly in relation to where the steam piston is. I cannot think of any steam engine that has a mechanism other than mechanical, to move the steam valve.
Is there a different way to sense the position of a steam piston and then correctly position or move the steam valve ? Electrical, pneumatic, magic?
Most steam engines have a part that rotates, so a simple eccentric, or return crank (which really an eccentric) is most often used to position the valve. When there is no rotating part, like in a reciprocating feed water pump, the only simple way to move the steam valve is by a mechanism connected to the reciprocating part, such as the piston rod, or, even through the piston itself.