Calculating the Air Pressure Required to Latch and Unlatch the SDSS Instrument Latches

Sloan Digital Sky Survey Telescope Technical Note 19970725
Larry Bartoszek

The sketch below shows the forces acting on the latch hook at the moment of unlatching when all the forces are concentrated at the edge of the detent.

Summing moments about the latch hook axle,

From the point of view of the air cylinder, at the moment of unlatching, Fr is broken into 2 components, the load the cylinder needs to exert and the load transmitted to the walls of the latch housing.

The force required to be exerted to unlatch is

We have a 2" bore cylinder. When it is unlatching, the effective area of the piston is 2.7 in2. The latching effective area is 3 in2. The pressure required to exert the unlatching load comes from:

This should be considered a bore minimum unlatch pressure. I would like to see 90 psi or better. (Latching requires more pressure. We discovered this experimentally. LB 8/20/97) BR>

Questions regarding this note should be addressed to Larry Bartoszek by phone at (630) 844-0248 or by e-mail at

Last modified 04/28/99