There are two main tasks for the periodic discharge of Instrument Valves. One is sewage, and the other is regular purge. This work should be tailored to local conditions. Not all valves in the Process Instrument Manifold Systems require regular blowdown.
Blowing is a method of using a blow or a liquid to make the measured medium not in direct contact with the meter component or the measuring line to protect the measuring instrument and perform the measurement. The blowing is to continuously and quantitatively inject gas into the measuring object through the measuring line. The flushing is to continuously and quantitatively flush the liquid into the measuring object through the measuring line. Purging is carried out when the corrosive, viscous, crystalline, fusible, and precipitating media are measured and the isolation method is difficult to meet the requirements.
The precautions for purging should be as follows:
1 The purge gas or liquid must be the flow medium allowed by the object to be tested. Generally, it should meet the following requirements:
a. No chemical reaction with the tested process medium;
b. Clean, free of solid particles;
c. No phase change occurs after throttling and decompression;
d. non-corrosive;
e. Good liquidity.
2 The purge liquid supply is sufficiently reliable and unaffected by process operations.
3 The pressure of the purge fluid should be higher than the highest pressure that the process can reach at the measurement point, ensuring that the purge fluid is continuously and steadily purged at the flow rate required by the design.
4 Measure and control the flow of purge liquid or gas using a restrictor orifice or a variable resistance rotor flow meter.
5 The purge fluid entry point should be as close as possible to the meter's source component (or close to the measurement point) to keep the pressure drop created by the purge fluid in the measurement line to a minimum.
6 In order to minimize measurement errors, the flow rate of the purge fluid must be constant. The purge flow rate is determined according to the type of purge fluid, the characteristics of the measured medium, and the measurement requirements.
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