Cameron Barton 752 - DPU below Tank with Reference Leg: Hot or Cool Liquids

A-8
Appendix A Model 752 and 752A Differential Pressure Transmitters
DPU Below Tank with Reference Leg: Hot or Cool Liquids
The use of a reference leg cancels out the "dead leg" (piping from the tank
bottom to center line of meter body). Seal uid in the reference leg must not
volatilize. Process media can be used as a reference leg seal uid if it will
condense in the reference leg under all conditions. Otherwise, special, immis-
cible seal uid must be used. Differences in densities of process media and
seal uid must be considered when computing the differential pressure range
of a DPU.
1. Partially ll the reference leg by opening the bottom block valve, both
shutoff valves, and the bypass valve.
2. Crack the drain valves on the DPU housing and vent the DPU. Close
when clear, bubble-free liquid ows.
3. Close the bypass and shutoff valve on the reference leg.
4. Remove the plug from the top port in the 2-inch pipe cross connection,
and ll the reference leg manually.
5. Open the reference leg shutoff valve and crack the vent valve until
bubbles are expelled. Leave the reference leg full.
6. Replace the plug in the pipe cross and close the vent valve.
7. Slowly open the upper block valve.
HIGH-PRESSURE
SHUT-OFF
VALVE
REFERENCE
LEG
2" CROSS
BYPASS
VALVE
VENT
VALVE
BLOCK
VALVE
BLOCK
VALVE
DPU
SHUT-OFF
VALVE
DRAIN VALVE
Figure A.7—DPU Below Tank with Reference Leg