The refrigerant leaves the evaporator of a refrigeration system as a low pressure （）.

单项选择题When operating with a negative suction head, which of the following types of pumps will require priming?（）

A.Reciprocating
B.Centrifugal
C.Rotary
D.Gear

单项选择题The discharge rate or capacity of a centrifugal pump will vary directly as the （）.

A.change in the impeller diameter
B.square of the impeller radius
C.cube of the impeller diameter
D.impeller efficiency for large changes in its size

单项选择题Which of the following best describes the thermodynamic effect on the pressure and volume relationship with regards to saturated gases?（）

A.As pressure decreases, volume increases
B.As volume increases, pressure increases
C.As volume decreases, pressure decreases
D.As pressure increases, volume increases

单项选择题To operate a centrifugal fire pump at reduced capacity, you should （）.

A.readjust the relief valve
B.throttle the suction line
C.throttle the discharge valve
D.open the priming line

单项选择题An AC synchronous transmission type remote steering control system consists of a （）.

A.transmitter at the steering station and a receiver at the steering engine
B.reversible motor at the steering station geared to the steering pumps
C.small induction motor on the bridge which controls the redder through pulleys
D.variable displacement hydraulic pump driven by a reversible DC motor