New Types of Pressure Valves:The ‘Soft Relief’ and the ‘Soft Start’ Valves

This paper describes a new principle for pilot-operated hydraulic relief valves. The new, patented feature enables pressure relief valves to not only limit a pressure differential, but also to limit the rate of pressure rise. The principle is to use the pilot flow to build up pressure in the pilot chamber of a relief valve. This pressure then drives a sleeve that further loads the pilot spring thus increasing the setting of the valve.

This paper specifically describes two new valves that use this principle. The first one, referred to as the soft relief valve, uses a simple internal relief valve and two orifices to control the pressure in the pilot chamber. The second valve, called a soft start valve, uses an internal priority flow control valve to control the pressure build up in the pilot section. Each unique internal control mechanism produces a controlled pressure rise rate in the system with subtle but important differences.