piston valve

基本解释

Keep the F. O piston valve open not in excess of 10 seconds max.
保持燃油活塞阀开状态最多不超过10秒。
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Make sure of the pilot burner ignition and open the F. O piston valve for main burner light off.
确认点火燃烧器点火，打开燃油活塞阀停主燃烧器点火。
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To avoid these two kinds of noise, the paper gived some requirements to the internal structure design of shock absorber, such as piston valve system, bottom valve system, piston rod etc.
为降低或消除这两种减振器噪声，提出了对减振器内部结构如活塞阀系统、底阀系统以及活塞杆等的设计要求。

All it means is that the Piston is not the Steam Box that Valve plans to release.
FORBES: Xi3 Is Committed to Piston, While Valve's Steam Box Remains Elusive