There are two main tasks of regular discharge of the Instrumentation Valves, one is the sewage, and the other is the regular purging. This work should be adapted to local conditions, not all process testing instruments need to regularly discharge.
1. Instrumentation Valves discharge
The discharge of the Instrumentation Valves is mainly for differential pressure transmitter, pressure transmitter, float level gauge and other instruments, because the measurement medium containing dust, grease, tiny particles in the pressure tube deposition (or in the pressure valve deposition) Directly or indirectly affect the measurement. The discharge cycle can be determined by the instrument workers according to their own practice.
The periodic discharge of the Instrumentation Valves should be noted as follows:
① before the sewage, must contact with the technical staff, to obtain technical personnel to carry out;
② flow or pressure adjustment system before the sewage should be automatically switched to manual, to ensure that the opening of the control valve unchanged;
③ for the differential pressure transmitter, before the first three valve sets of positive and negative pressure valve closed to death;
④ place the container under the discharge valve, slowly open the positive and negative pressure pipe sewage valve, so that the material and dirt into the container to prevent the material directly into the trench, otherwise, one to pollute the environment, and second to cause waste;
⑤ due to the poor quality of the valve, the valve after a few times the switch will appear unhappy condolences, emergency measures is to add blind plate to ensure that the sewage valve is not leaked, so as not to affect the measurement accuracy.
⑥ open the three valve group positive and negative pressure valve, loosen the differential pressure transmitter body on the sewage (exhaust) screw to sewage, sewage tightening screws;
⑦ observe the field instructions instrument, until the output is normal, if the adjustment system, will manually switch and automatic.
2. Instrumentation Valves purge
Blowing is a method in which the measuring medium is not in direct contact with the meter part or the measuring line by means of blowing or flushing to protect the measuring instrument and to carry out the measurement. Blowing is through the measurement of the pipeline to the measurement object to continuously quantitatively blow the gas. The flushing fluid is continuously and quantitatively flowing into the measuring object through the measuring line.
For the corrosive, viscous, crystalline, melt, sedimentation medium to measure, and the use of isolation is difficult to meet the requirements, the use of purging.
Instrumentation Valves purge should be noted as follows:
① purge gas or liquid must be measured by the process of allowing the flow of media, usually it should meet the following requirements:
A. With the measured process medium does not occur chemical reaction;
B. Clean, free of solid particles;
C. Does not undergo phase change after throttling and decompression;
E. Good liquidity.
② purge liquid supply is reliable enough, not affected by the operation of the process.
③ The pressure of the purge fluid should be higher than the maximum pressure that the process may achieve at the measuring point to ensure that the purge fluid is continuously and steadily purged with the flow required by the design.
④ the use of restrictive orifice or adjustable resistance of the rotor flow meter to measure and control the flow of liquid or gas flow.
⑤ The purge fluid inlet point should be as close as possible to the instrument source (or near the measuring point) so that the pressure drop generated by the purge fluid in the measuring line is kept to a minimum.