Marine tilt and trim systems conventionally use a check valve and a relief valve in connecting a top and a bottom of a hydraulic cylinder to a reservoir tank. A hydraulic conduit connecting the top of the hydraulic cylinder to the reservoir communicates with the check valve. The check valve allows for fluid to be drawn from the reservoir to the top of the cylinder, but prevents fluid from flowing from the top of the cylinder to the reservoir. A hydraulic conduit connecting the bottom of the hydraulic cylinder to the reservoir communicates with the relief valve. The relief valve is necessary for circumstances requiring tilt (or trim) relief, or a quick removal of fluid from the bottom of the cylinder. Examples where fluid removal or relief from the bottom of the cylinder is required include: 1) relief from thermal expansion if the fluid within the cylinder expands; and 2) relief from impulses from the propeller.
Conventionally, two separate valves are used for the above system. The check valve conduit is separate from the conduit involving the relief valve. As a result, an excessive amount of hydraulic conduits are used. Also, both check valves and relief valves can be quite expensive. For relief valves in particular, there is a significant cost associated with manufacturing relief valves which are correctly and accurately made to consistently open at target, set pressures.
Accordingly, there is a need for a relief valve which can be consistently set to a desired relief pressure in a more economically advantageous manner. In the context of marine tilt and trim systems, there is a further need to reduce the number of parts and costs required in providing a check valve and relief valve system.