DH Instruments GFS2102, Руководство по эксплуатации и обслуживанию, Страница: 66 / 206

GFS2102™ OPERATION AND MAINTENANCE MANUAL
© 2007 DH Instruments, a Fluke Company Page 50
The cylinder support, connector and regulator assembly can all remain attached to the cylinder
while it is placed in the plastic case. The assembly can be carried to the location of the GFS fill
station, filled and returned to the GFS2102 work area all inside the case.
Do not ship the reference gas cylinder while pressurized or with the regulator assembly
attached. See Section 6.4 for instructions on preparing a cylinder for shipment.
4.3.2 EVACUATING AND RINSING
When the test gas used in the reference gas cylinder will be changed from one test to the next, or
when the cylinder has sat for a long time between tests and may be fully or partially filled with air,
some action is needed to ensure that the cylinder is refilled with a pure gas for further testing. Do
not rely on the quick connect fitting on the regulator assembly to provide a positive shutoff from
gas leaving or entering the cylinder if the quick connector has no stem connected. Stems with
plugs are provided with the GFS2102 system to allow a positive seal to the cylinder to be made
when a filled cylinder sits disconnected from the flow system.
Evacuation
When switching gases, an effective way to produce a pure gas fill with the new gas is to first
evacuate the cylinder using vacuum. If a vacuum pump is used for cylinder evacuation, it is
important that either a dry pump is used, or precautions are taken to avoid any backflow of pump
oil into the cylinder assembly. Under low vacuum conditions with little flow, molecular backflow of
oil vapor from an oil lubricated pump to upstream components is common. It is not necessary to
use a pump that generates a low ultimate vacuum, especially if some “rinsing” of the cylinder is
done.
Rinsing
Whether using vacuum or not, a good way to ensure a pure gas fill is to also do some “rinsing” of
the cylinder during filling. Rinsing refers to partially filling the cylinder with the new gas, then
venting it until close to atmospheric pressure and refilling again. When starting from an
evacuated cylinder, doing this one time up to 700 kPa (100 psi) or more and venting would be
sufficient. When starting from atmospheric pressure with remains of the previous gas in the
cylinder, a filling and draining two to three times to this pressure before filling would ensure
sufficient purity.
4.3.3 CONNECTING TO GFS-FS
Figure 29.
GFS-FS reference gas cylinder fill station connections
1. 4T Swage supply connection 2. 2NPTF exhaust connection 3. DH500 connection to cylinder tube