[cknuth]

Richard, yes - room extended shown. Your explanation is helping to clear this up. The microswitch makes the connection that tells the pump control panel that the room is out. But there is no similar switch that I have been able to find that tells the panel when the room is in; the other end (not shown) of the channel just has the adjustable stop for the sliding block to land. I gather from the manual that the pump stops when hydraulic pressure reaches 3000 psi. But how do the locking pins know when to engage?
Thanks again!