Abstract: A screw compressor employs a piston unloader disposed in a bore remote from the compressor's working chamber. Flow communication between the bore and working chamber is through a series of unloader ports. The unloader piston has an end portion of uniform geometry which causes the physically non-overlapping unloader ports to, in effect, overlap in operation and is such that the unloader piston need not be maintained in any specific orientation within the bore in which it resides in order to unload the compressor in a continuous fashion.

Abstract: A shut-off cylinder for use in a hydraulic braking system comprising a cylindrical housing, an inlet end cap and an outlet end cap received and secured in the open ends of the housing, the inlet end cap having an inlet port in fluid communication with the interior of the housing and connected to an inflow source of hydraulic fluid from a hydraulic reservoir of the braking system, the outlet end cap having an outlet port in fluid communication with the interior of the housing and connected at its output end to an outflow source of hydraulic fluid to the braking system, a piston slidably received in the interior of the housing between the inlet end cap and the outlet end cap, a coil spring received in the space between the piston and the outlet end cap biasing the movement of the piston under normal operating conditions against the pressure of the inflow source, a by-pass tube communicating with the inlet and outlet ports of the housing, a valve for opening and closing communication between the by-pass tube and