This more complicated construction is required in double-acting engines.
这种非常复杂的结构多用于双向做功的发动机。
2
They are available in either double-acting or spring-return configurations.
他们可以以双作用或弹簧返回配置。
3
AW series of large diameter valves using pneumatic actuator fork-type transmission, reasonable structure, output torque, a double-acting and single acting.