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