单项选择题
A.a pressure reducing valve B.a pilot valve C.an operating piston D.downstream pressure
In its simplest form the pressure reducing valve is ope...
单项选择题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
Most marine biological sewage treatment plants consist ...
单项选择题Most marine biological sewage treatment plants consist of all the following statements except （）.
A.aeration tanks B.settling tanks C.disinfection agent D.anaerobic bacteria
To prevent accidents from occurring, special valve ches...
单项选择题To prevent accidents from occurring, special valve chests are used in such cases in which interchangeable blanks and connecting passages are incorporatedThe bold and italic word “which” means （）.
A.accidents B.special valve chests C.interchangeable blanks D.connecting passages
