A primary function of sequence valve is to direct flow to different components of the circuit in a predetermined sequence. It is a pressure actuated valve which senses a certain change in pressure from the set value.
It then takes the actions to direct the fluid in a definite predetermined order. It also maintains the requisite minimum pressure in the primary line while the secondary operations occur.
Figure shows operating principle of a direct acting, normally closed sequence valve. In this position, fluid passes through the valve from the inlet port P to primary outlet port A at system pressure. When the first step in the sequence is completed, the system pressure increases to act against the exposed area of the piston.
Continued increase in pressure causes the piston to compress the spring and unseat the valve, thereby directing the flow of fluid at high pressure through secondary outlet port B.
Fluid pressure is maintained in both branches of the circuit so long as the sequence valve is open. Adjustment of the sequence valve is accomplished by compressing or extending the piston with the cap screw.