3.3　Pressure

3.3.1　The selection of pressure measuring point position shall meet the following requirements：

1　The measuring points for measuring the pipeline pressure shall be set at the straight pipe section with stable flow speed but not at the position with vortex flow.

2　The distance of pressure sampling element with the regulating valve on pipeline：shall be larger than 2 times of the inside diameter of process pipeline at the upstream side and shall be larger than 5 times of the inside diameter of process pipeline at the downstream side.

3　Where measuring the pressure less than 0.1MPa，the additional deviation caused by liquid column of the temperature measuring element shall be reduced.

4　Where measuring the micropressure or negative pressure of relatively big vessels，the multi-point sampling mode should be adopted and then the averaging should be implemented.

5　The positions of the sampling elements for furnace pressure shall meet the requirements of boiler works and the sampling elements should be set above the flame center of combustion chamber.

6　The pressure measuring point for the primary air duct of boiler shall be selected at the position where is in front of the burner and is able to correctly reflect the pressure of primary air；and the pressure measuring point for secondary air duct shall be selected between the air preheater and burner，and its distance from the said two devices shall be equal distance as far as possible.

7　As for the bin storage pulverizing system，the air pressure sampling element before the coal mill shall be installed at the inlet neck of coal mill；the air pressure sampling element after the coal mill shall be installed on the gas-powder mixture pipeline nearby the tailing classifier.

8　The measuring points for lubricating oil pressure of steam turbine generator shall be selected at the places with low pressure at the end section of oil pipeline.

3.3.2　The installation orientation of the pressure measuring points on horizontal or inclined pipeline shall meet the following requirements：

1　Where measuring the gas pressure，the measuring points shall be installed at the upper half part of pipeline.

2　Where measuring the liquid pressure，the measuring points shall be installed within the scope of 45° included angle between the lower half part and the horizontal center line of pipeline.

3　Where measuring the steam pressure，the measuring points shall be installed at the upper half part of pipeline or within the scope of 45° included angle between the lower half part and the horizontal center line of pipeline.

3.3.3　When measuring the pressure of such medium containing dust or gas-powder mixture，the pressure measuring device with anti-clogging structure and purging structure shall be adopted.The installation direction of pressure measuring pipe shall meet the following requirements：

1　On the vertical pipeline，boiler wall or flue，the pressure measuring pipe shall be installed by upward inclination，its included angle with the horizontal line shall be larger than 30°.

2　On the horizontal pipeline，the pressure measuring pipe shall be installed above the pipeline and should be vertically installed.

3.3.4　The diameter of the air pressure hole shall conform to the outside diameter of pressure measuring device so as to avoid blocking.The pressure measuring device shall be provided with plug and dismountable pipe joint for purging purpose.

3.3.5　The end of pressure sampling element shall not exceed the inner wall of measured equipment or pipeline，both the pressure hole and the sampling element shall be free from burrs.