Check valve are disclosed having a primary seal and a secondary seal, where the primary and secondary seals resist movement of a fluid through the check valve, and the secondary seal can provide a backup seal in an instance where the check valve does not function as intended. The primary and secondary seals can be formed by first and second sealing ridges, respectively, and a valve body can be positioned within the check valve, between a valve support, the first sealing ridge, and a second sealing ridge. The valve body is configured to move relative to the first and second sealing ridges, and can have a position wherein a portion of the valve body is engaged against any of the first and second sealing ridges.

A check seat assembly includes a check valve seat with a by-pass passage in parallel with a check valve passage of the check seat assembly to meter flow and maintain stability of a hydraulic system, such as a hydraulic cylinder. The check valve may include an o-ring seated in a V-shaped groove. The check seat assembly may allow flow from a pump to a hydraulic cylinder to freely pass through the check valve to pressurize one side of a piston of the hydraulic cylinder, such as a front side of the piston to retract a corresponding rod connected to the piston.

A dynamic seal assembly is disclosed for use in a valve having an upstream pressure side and a downstream pressure side, the dynamic seal assembly including an annular seal member having a generally C-shaped cross-section and including opposed upstream and downstream legs defining an internal cavity with an opening facing toward the upstream pressure side of the valve, wherein the upstream leg has a radial length that is greater than a radial length of the downstream leg and includes a retaining foot that extends angularly away from the upstream leg in an upstream direction at an angle of between about 0 and 90, and a metallic spring is disposed within the internal cavity of the seal member for providing a constant sealing force to the seal member.

A bypass valve having an adjustable flow resistance for a device through which a fluid medium flows. The valve includes a seat and a body which is biased closed, and which is movable in the opening direction by a fluid medium pressure difference between the inflow and the outflow side of the valve when the pressure difference exceeds a threshold. A bypass flow path connects the inflow side to the outflow side through the seat. The bypass valve includes a screen disposed in the bypass flow path. The valve body has two different open positions that depend on the fluid medium pressure difference. The entire cross-section of the bypass flow path is covered by the screen in a first valve body open position with a lower pressure difference, and a screen-free bypass flow path cross-section is exposed in a second valve body open position with a greater pressure difference.