Thermo Scientific XBF40-MD Series Installation, Operation And Service Manual page 44

Appendix
40 Installation, Operation and Service Manual
CHECK FOR LEAKS
1. After all the components and tubing has been brazed closed, pressurize
the system with nitrogen to 150 psig and check all the joints using a leak
soap mixture, if no leaks are detected, purge the nitrogen from the
system and wipe the joints to remove the soap film. You now can now
start the triple evacuation procedure as explained in the next steps.
EVACUATION
2. The gauge manifold should be still attached to the process tubes; remove
the center hose from the nitrogen tank manifold and install an
electronic micron meter in line with the center hose from the manifold
gauge and the vacuum pump.
TRIPLE EVACUATION PROCEDURE
3. Perform a triple evacuation procedure as described; evacuating the
system until the electronic vacuum gauge read 1500 microns, then break
the micron level with about 5 psig of dry nitrogen and let it set for 5
minutes. Purge the 5 pisg of nitrogen back to 1 psig and then start the
vacuum pump again allow the system to evacuate until the electronic
micron gauge reads 500 microns, follow the same procedure of breaking
the evacuation with nitrogen back to 5 psig. Bleed the nitrogen back to
1 psig and turn on the vacuum pump again until the electronic vacuum
gauge reads 50 microns or lower.
4. Close the vacuum pump inlet valve, leaving the pump running and
watch the electronic micron gauge carefully.
Note The vacuum gauge must be installed between the compressor and the
pump shut-off valve to perform this check. The electronic vacuum gauge should
not rise above 200 microns within a 20 minute blank off.
Evacuate the system following the above procedure; vacuum now should
hold or meet the 200 micron level discussed earlier. If not, then this
indicates either moisture in the system or a leak in the tubing or
components. Check the system again for a leak, by as described above and
then repeat this process as many times as necessary to obtain the required
vacuum and holding time.
Thermo Scientific XBF40-MD Series Blast Freezers