Isolation of the Separator Floor YokogawaEXJ110A DP Cell,
Step 1 – Secure all trips and let an operator know to put the controller in manual – we are about to take a process variable transmitter out of service.
Step 2 – Close the High and Low process line valves. The instrument is now isolated from the process impulse pressure lines
Step 3 – Open the equalising valve. Pressures are now equal on both sides of the measuring diaphragms resulting in nil differential pressure.
Step 4 – Open the bleed valves on the transmitter. No pressure remains in the instrument.
De-Isolation is not a reverse procedure, closing the equalising valve and opening the process line valves with even the slightest difference in time can cause unequal pressurisation of the measurement diaphragms.
Instead we use this procedure.
Step 1 – Close the Bleed Valves
Step 2 – Confirm the equalisation valve is open.
Step 3 – Open the High process line valve. Equal High process line pressure is now present across the High and Low measuring diaphragms resulting in a nil differential pressure.
Step 4 – Close the Equalising Valve.
Step 5 – Open the Low process line valve. The instrument is now measuring differential pressure across the High and Low process impulse line connections. Instrument can be placed back in service.