MNA0010, Revision B October 2014
21
forces the purge gas to enter a confined area around the seam to be welded. Dams are
available for various size tubes and feature quick connect fittings for easy coupling to the
shield gas source. To position the dam around the seam, a chain or rope is connected at
either end of the dam, and the assembly is pulled through the tube until in place. The dam
features soft elastomer gasketing to ensure a gas tight seal . See figure 22. Purge dams are
available from Neutronics . Contact our Applications department for more information.
2.1.2.1
Install the Plumbing:
Plumbing connections for the standard Model 7100P Portable
analyzer are made at the back of the chassis at the sample tube. Choose the right
prefiltering required for your application and install the sample tube and accessories
as shown in the figures above. Do not overtighten fittings . The threads of the
fittings should be wrapped with Teflon tape to prevent gas leakage. For best results,
make sure the sample pressure is regulated so that you have approximately 0.8 to 1
SCFH flow rate as indicated on the flow meter.. Do not exceed 5 psig at the sample
input port. To prevent back pressure on the sensor, the sample exhaust should be
vented to atmospheric pressure.
Purge Gas Exhast
Neutronics Oxygen Analyzer
Purge Dams
Weld Seam
Purge
Input
Tubes to be orbitally welded
Figure 22
Using a Purge Dam