单项选择题
A.absolute humidity B.specific humidity C.effective humidity D.relative humidity
The purpose of an air compressor unloading device is to...
单项选择题The purpose of an air compressor unloading device is to （）
A.drain water from the air receiver B.drain water from the cylinders C.delay the compression process until the motor is up to speed D.check pump alignment
Personnel working with refrigeration systems, and subje...
单项选择题Personnel working with refrigeration systems, and subject to the exposure of refrigerants should wear （）.
A.face shield B.a respirator C.rubber gloves D.an all purpose gas mask
To absorb the wear resulting from impeller rotation and...
单项选择题To absorb the wear resulting from impeller rotation and abrasives in the liquid, a centrifugal pump is usually fitted with （）.
A.lantern rings B.bearings C.easing volutes D.wearing rings
