（） provides the head or pressure to su

1、If the head pressure is too high,（）

If the head pressure is too high,（）Athe relief valve should open before the high-pressure cutoutBthe relief valve should open and let excess ...

2、If the head pressure of a reciprocatin

If the head pressure of a reciprocating refrigeration compressor is excessive, （）.Athe relief valve should open before the high pressure cutout...

3、The pressure head of a pump is given i

The pressure head of a pump is given in the unit of （）.AkgBMPaCmeter fluid columnDNone of the above is true

4、The network layer provides services to

The network layer provides services to the transport layer．It can be based on either (1)．In both cases，its main job is (2) packets from the...

5、（） is provided to alternators, in the

（） is provided to alternators, in the event of prime mover failure to ensure that the alternator does not act as a motor.AReverse current protectionBReverse power protectionCSynchronising deviceDFrequency meter

6、To maintain the down stream pressure w

To maintain the down stream pressure within defined limits over a range of flow and despite any changes in supply pressure, （） is fitted.Aa check valveBa gate valveCa pressure reducing valveDa quick closing valve