Selection of pressure gauges under normal conditions
Thread Content
I would like to ask the teachers: when installing pressure gauges on equipment, how do you determine which type of pressure gauge to use? For example, in the case of a heat network heater, the design pressure on the tube side is 2.5 MPa.a with a design temperature of 130°C, while the design pressure on the shell side is 1.0 MPa.a with a design temperature of 270°C. How should you choose the gauge for this situation? Should a gauge with a capacity of 4.0 MPa be used for the tube side, or one with a capacity of 6.3 MPa based on the required measurement range? The same goes for the shell side – is 1.6 MPa used, or 2.5 MPa?
Since the requirement is 1.5 to 3 times the design pressure, values of 4.0 MPa and 6.3 MPa for the tube side, and 1.6 MPa and 2.5 MPa for the shell side are all within a reasonable range and can be used.
In cases where all conditions are met, it is better to choose a lower range, as this will result in higher accuracy
Selection of measurement range: ⑴ When measuring a stable pressure, the normal operating pressure value should be between 2/3 and 1/3 of the upper limit of the instrument’s range. ⑵When measuring pulsating pressure (such as the pressure at the outlet of pumps, compressors, fans, etc.), the normal operating pressure value should be between 1/2 and 1/3 of the upper limit of the instrument’s measurement range. ⑶When measuring high and medium pressures (greater than 4 Mpa), the maximum operating pressure should not exceed 3/5 of the upper limit of the instrument’s measurement range. ⑷After the upper and lower limits of the gauge are calculated based on the pressure to be measured, these values cannot be used directly as the gauge’s range. In China, pressure gauges manufactured come with standard ranges: 1 KPa, 1.6 KPa, 2.5 KPa, 4.0 KPa, 6.0 KPa, along with their multiples of 10 (where n is an integer). Therefore, when selecting a gauge range, it is necessary to use the values specified in relevant standards or regulations.
Are there any books or standards regarding the selection of instruments?
For details, please refer to the fixed capacity regulations; I’ve forgotten the exact page number – it should be in the attachments
Thank you to all the teachers for their helpful answers. On page 176 of the standards, it is stated that the maximum scale value on a pressure gauge should be 1.5 to 3.0 times the maximum allowable operating pressure, and the diameter of the gauge face must be no less than 100 mm. The technician here advised me to choose based on a scale value of 3.0 times, but I think there’s no need to stick to the highest scale value within the range of 1.5 to 3.0 times; as the person who posted above mentioned, choosing a lower range results in relatively higher measurement accuracy. What do you think?
6.3 MPa for the tube side and 2.5 for the shell side, I guess. Refer to Clause 8.4.1 of the Fixed Volume Code: The scale limits of the pressure gauge should be between 1.5 and 3 times the design pressure.
Comply with Article 8.4.1 of the Safety Technical Inspection Regulations for Fixed Pressure Vessels.
The design pressure of the pipe train is 2.5 MPa, with the normal operating pressure being lower than this value. Calculated at 2 times the design pressure, it is 5 MPa; therefore, a pressure gauge with a rating of 4 MPa is selected.
Most of the time, I see the pointer on the pressure gauge at 1/2 when it is in use.