Boilers are divided into four grades according to pressure.

Generally divided into low-pressure boilers, medium-pressure boilers, high-pressure boilers and ultra-high-pressure boilers.

According to the working pressure of steam, it is generally divided into four grades: low pressure boiler, medium pressure boiler, high pressure boiler and ultra-high pressure boiler. Among them, the steam working pressure of low-pressure boiler is generally between 0. 1-2.5MPa, medium-pressure boiler is generally between 2.5-6.0MPa, high-pressure boiler is generally between 6.0- 13.0MPa, and ultra-high-pressure boiler is generally higher than 13.0MPa.

According to the internal pressure of boiler, it can be divided into positive pressure boiler and negative pressure boiler. Positive pressure boiler refers to a boiler with internal pressure higher than atmospheric pressure, and negative pressure boiler refers to a boiler with internal pressure lower than atmospheric pressure.