COMPONENT OPERATION / Control Valve OVERLOAD RELIEF VALVE (WITH MAKE-UP FUNCTION) The overload relief valves are provided with the circuits in the bottom and the rod sides of the bucket and in the bottom and the rod sides of the coupler (auxiliary). The overload relief valve controls pressure in each front attachment circuit in order not to rise abnormally when each front attachment is operated by external load. It also makes make-up operation by drawing oil from the hydraulic oil tank in order to prevent cavitation when pressure in the front attachment circuit decreases.
Make-Up Operation 1. When pressure in port HP (front attachment circuit) decreases lower than pressure in port LP (hydraulic oil tank), the sleeve moves to the right. 2. Hydraulic oil in port LP flows to port HP and cavitation is prevented. 3. When pressure in port HP increases more than the specified level, the sleeve is closed by the force of spring C.
Bottom Side and Rod Side Circuits of Bucket Relief Operation 1. Pressure in port HP (front attachment circuit) acts on the pilot poppet through the orifice in the piston. 2. When pressure in port HP reaches the set force of spring B, the pilot poppet is opened, pressure oil from passage A flows to port LP (hydraulic oil tank) through the outer circumference of the sleeve. 3. At this time, a pressure difference occurs between port HP and the spring chamber due to the orifice. 4. When this pressure difference reaches the set force of spring A, the main poppet is opened and pressure oil from port HP flows to port LP. 5. Consequently, the pressure in Port HP (front attachment circuit) decreases. 6. When pressure in Port HP (front attachment circuit) decreases to the specified level, the piston and the main poppet are closed by the force of spring A. The circuit in the bottom and the rod sides of the coupler (auxiliary) are also relieved in the same way.
T3-2-17
