Chapter 7 Pressure control valves 1 Pressure relief

Chapter 7 Pressure control valves

1. Pressure relief valves direct-acting P. R. V. compound pilot drained P. R. V. (or pilot-operated P. R. V. ) 2. Pressure reducing valves direct-acting P. Red. V. pilot-operated P. Red. V. 3. Sequence valves 4. unloading valves 5. Counterbalance valves § Pressure relief valves — used to limit the pressure in a system and protect the components from overload and the danger of bursting. ‧Cracking pressure: The pressure at which the valve opens (打開) ‧full-flow pressure: The pressure at which the rated flow 相當於“全開”時之壓力 passes through the valve. ‧closing pressure: The pressure at which the valve ceases to pass fluid after being opened.

§static performance of direct-acting P. R. V. ‧flow force on poppet :

‧flow force compensated direct-acting P. R. V. § dynamic performance of direct-acting P. R. V. consider the poppet-type:

Schematic layout

‧Appling Newton’s 2 nd law to poppet (together) with damping plunger: where m: mass of the poppet(together with damping plunger) d : damping coeff. where a(x): open cross section area a(x) d xsin Linearization of eq(3) about a operating point gives：

Thus eq(1) becomes:

直動型洩壓閥(direct-acting)

‧if P．A > F = PC ．A then the valve opens Where： PC: cracking pressure A: Area of the measuring surface F: spring force (pre-compressed)

引導作動型(pilot-operated)洩壓閥

減壓閥(pressure reducing valve) (1)直動型：

順序閥(sequence valve)

卸壓閥(unloading valve)

抗衡閥(counterbalance valve)