what is the procedure to isolate flow a transmitter and
flushing it?
Answer Posted / amjad sohail
1. There is no any problem if open the equalizing valve
first. just dp become zero after equalizing valve
opening. so we can open 1st equalizing valve. and
then isolate both process isolation valves at
manifold one by one.
And keep it in your mind at orifice or any other dp
creating device the pressure difference b/w both
sides of transmitter is not high, in fact its a minor
difference b/w both sides.usually minimum 500 ~
2500mmh2o to maximum 10000mmh2o for flow
measurements. and LP side & HP side diaphragms are
designed for bear the same MWP value.(Which is given
at name plate of TX) so there is no matter if high
pressure side process comes to LP side diaphragm. So
if we open equalizing valve 1st then minor difference
of pressure b/w both sides will also become zero.
then we isolate the LP & HP valves one by one.
2. If we 1st isolate high pressure side of tx then pressure will be trapped B/W transmitter and isolation valve of manifold. so there is no any problem if we isolate the high pressure side 1st. (But do not open the drain of HP side. Because its very harmful for TX due to transmitter will come to its maximum & out of range dp value before isolate the LP side and open the equalizing valve.) So do not operate the drain valve and open the equalizing valve & then isolate the low pressure side. Now we can drain the LP & HP side respectively. And usually this practice is adopted by all instrument technician and engineers.
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