單項(xiàng)選擇題

When the refrigeration demand is small,（）

A.the expansion valve will move toward the wide open position
B.the expansion valve will move toward the closing position
C.the feeler bulb will conveys the high temperature
D.the superheat degree will raise

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單項(xiàng)選擇題

When the heat load begins to increase, the needle valve of an expansion valve will（）

A.move in an opening direction
B.move in a closing direction
C.either open or close
D.not move at all

單項(xiàng)選擇題

One of the main purposes of refractories in a boiler furnace is to（）

A.help preheat the air for the furnaces
B.help preheat the feedwater
C.protect economizer from excessive heat
D.prevent excessive furnace heat losses