Trick passsage for sliding valve steam engines

I'm looking for some information on a sliding valve assembly for steam engines that contains a "trick passage" or "trick valve". It may have something to do with conterbalancing the pressure on the working face of the valve, or something to do with counteracting the forces involved in reversing the direction of motion of the piston at the end of each stroke.

If anyone has any information on such a device, or knows where it can be found, it would be appreciated if you could get a message to me at

Many thanks.

Reply to
Domingo Chavez
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