LEFM 3xxCi User Manual
IB1406 Rev 12
Section 10
Page 67
February 2017
Secondary Seals and Seal Failure Indication
Secondary Seals
Some versions of the 3xxCi LEFM flowmeter have been designed to comply with the requirements of ISA
standard 12.27.01, “Requirements for Process Sealing between Electrical Systems and Flammable or
Combustible Process Fluids”. Specifically, the meter has an indication when an O-ring fails to meet its
specifications.
All transducer housings have been designed and built with 2 sets of seals. The first and primary seal set
retains the process gas. If the first seal set were to fail, the secondary seal exists to prevent gas from
entering into the electrical compartments and to redirect that gas out through a vent.
For meters built to comply with ISA 12.27.01, a special vent has been designed to vent gas if all seals were
to fail – this provides a visual indication of a seal failure. If a seal were to fail, the vent has a plunger that
deploys at the location of the failure. Refer to Figure 10.1 below.
Figure 10.1 Primary Seal Failure Indication