Abstract: A pressure regulator for a pump aspirating a working fluid from a tank comprises a throttle valve at a junction between an inlet pipe extending from the tank and an outlet pipe terminating at the intake port of the pump. The discharge port of the pump is connected to a control port of the regulator housing in line with the inlet pipe, this control port being separated by a partition with a narrow passage from a chamber containing the shiftable valve body. The passage accommodates a small-diameter rod which has a flat tail penetrating that passage only when the discharge pressure of the pump has reached a certain threshold above a point at which that pressure has caused the rod to move the valve body into a blocking position against a countervailing spring pressure. This establishes a connection between the discharge and intake ports of the pump preventing further rises in the pump's delivery pressure.