Fluid under pressure flows from port 1 to chamber 2. Due to the hydraulic loss through slit 3, the pressure in chamber 2 is lower than in port 1. Due to the provision of channels 4 and 5, the pressure established in chamber 8 and behind ball 6 is the same as in chamber 2. When the pressure increases, ball 6 is pushed off its seat and fluid from chamber 2 flows through channels 4, 5 and 7 to the tank. Owing to the pressure drop across metering orifice 9, the pressure in chamber 8 is lower than that in chamber 2. This forces piston 10 upward and reduces slit 3, increasing the pressure drop across the slit and thereby reducing the pressure in chamber 2. The pressure in chamber 2 and the outlet port is regulated by adjusting spring 12 with screw 11.
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