Abstract: A valve arrangement is disclosed for controlling the supply of an operating fluid, having a casing with an inlet port, a main flow path provided with a non-return valve extending from the inlet port to an operating outlet port and a secondary flow path extending from the inlet port to a by-pass outlet port, the secondary flow path containing a ball applied to a valve seat under spring prestressing to close said secondary flow path, there being provided a piston including a tappet operable to displace the ball from the seat, a spring for biasing the piston away from the ball, a flow path including a restrictor communicating pressure from the main flow path to said piston to displace the piston against the spring following an excessive rise in pressure in the main flow path, the structure permitting a predetermined stroke of the piston against the force of the spring prior to displacing the ball from its seat via the tappet.