Double relief valve is installed in the pipelines of the hydraulic steering system (close to the cylinder). It protects the system from overload.

If the pressure in the system increases (more than permitted), the relief valve starts to let the oil into the return pipe until the pressure decreases to permitted level.

Pressure Increase can occur due to increased activity of manual or electric hydraulic pump or due to resistance of sea water on the rudder blade (at higher angle deflection of rudder blade or higher speed of the boat, or driving astern).

The installation of double relief valve in the hydraulic steering systems is recommended on larger ships and in case of installed electro-hydraulic power unit.