单选题In its simplest form the pressure reducing valve is opened or closed by （） which is balanced by the downstream pressure acting on a diaphragm.Aadjusting a nutBa pre-tensioned springCany springDupstream pressure
单选题
In its simplest form the pressure reducing valve is opened or closed by （） which is balanced by the downstream pressure acting on a diaphragm.
A
adjusting a nut
B
a pre-tensioned spring
C
any spring
D
upstream pressure
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