A shallow dish positioned at the normal water level is connected to the（）This enables the blowing down or removal of scum and impurities from the water surface.

The（）enables water to be blow down or emptied from the ...

单项选择题The（）enables water to be blow down or emptied from the boilerIt may be used when partially or completely emptying the boiler.

The（） is fitted in pair one is the main valve, the othe...

单项选择题The（） is fitted in pair one is the main valve, the other the auxiliary or standby.

The（） is a smaller valve fitted in the auxiliary steam ...

单项选择题The（） is a smaller valve fitted in the auxiliary steam supply line, and is usually of the non-return type.