The 3-point hydraulic circuit has a relief valve to restrict the maximum pressure in its circuit.
This is a guide piston relief valve with damper, a direct acting relief valve suitable for relatively high pressure and capacity, and constructed so as to prevent chattering and other unstableness associated with direct acting relief valves. As shown in the figure, the poppet (5) has a guide, and there is a valve chamber called a damping chamber (6) in the base of this guide piston.
The valve inlet is connected to this chamber through the clearance between the guide surface and the seat so that the chamber provides a damping effect, controlling valve vibration.
When the pressure in the circuit rises, the pressure in the damping chamber also rises, and when it exceeds the relief pressure setting the spring is compressed, making a clearance between the poppet and the seat.
The hydraulic oil can escape to the transmission case through this clearance, controlling the pressure rise.
