Steam pressure is one of the important indicators of boiler safety and economic operation. Generally it is required that the deviation of  pressure and rated valve shall not exceed ±（0.05～0.1）MPa. 

During operation, the steam pressure exceeding the specified value will threaten personal and equipment safety and affect the service life of the unit; on the other hand, the too high steam pressure will make the safe valve to act, which not only will causes large amount of exhaust steam loss, but also will give rise to water level fluctuation and will affect the steam quality, make the safety valve frequently act and will also affect its tightness. 

The steam pressure lower than the specified value reduces the power capability of steam in steam turbine and makes the thermal efficiency of the generating unit decrease; it may also affect the axial thrust of steam turbine, which is bad for security. 

Frequently fluctuation of steam pressure makes the metal of the pressure-containing members of the unit often under the effect of alternating stress, which may make the pressure-containing members fatigue and damage.