2-43
Relief valve operation
First stage
At the start of operation, the shockless piston moves to maintain the spring chamber at a low
pressure. Thus, the pressure receiving area of the poppet becomes the poppet seat area (S1), a
considerably larger area than the pressure receiving area (S1-S2) at the specified relief setting.
For this reason, the relief operating pressure is kept at a low pressure until the shockless piston
completes its movement.
The low pressure holding time depends on the poppet orifice diameter, the free piston pressure
receiving area and the free piston stroke.
S2
S1
Shockless piston
R35Z72SM06
Η
Second stage
When the shockless piston completes its movement, the pressure inside the spring chamber
increases to make the pressures before and after the poppet equal. Then the relief valve operates
at the specified set pressure.
Poppet
Shockless piston
R35Z72SM07
Θ
Θ
(2)