Do not exert any sideways force on the purge-restrictor when you clamp it into place. If you do, you can damage
the seal between the O-ring (Figure 28, item 2) and the body of the purge-restrictor. If the seal is damaged, gas
may leak through the seal and you will not be able to properly control gas flow into the pump.
Note: If you will use a purge gas other than nitrogen, you must calibrate the purge-restrictor (refer to
Section 7.4.2) before you connect your purge gas supply.
1. Switch off the pump, isolate the pump controller from the electrical supply (on an EXT DX pump, isolate the
podule from the electrical supply), and wait until the pump has stopped rotating.
2. Remove the blank and clamp from the purge-port on the pump.
3. Attach your purge gas supply pipeline (which must be terminated with an NW10 flange) to the purge-port with
the PRX10 purge-restrictor in place of the normal NW10 centring-ring.
4. Carefully secure the connection with the NW10 clamp.
7.4 Operation
7.4.1 General
The PRX10 purge-restrictor, as supplied, is adjusted to restrict the flow rate of dry nitrogen, at a supply pressure
of 0 bar gauge (1 x 10
5
Pa), to 25 sccm (0.42 mbar l s
-1
, 42 Pa l s
-1
). You can increase the supply pressure to increase
the flow rate; see Table 7.
For most applications, you can use a nitrogen flow rate of 25 sccm (0.42 mbar l s
-1
, 42 Pa l s
-1
) to 30 sccm
(0.5 mbar l s
-1
, 50 Pa l s
-1
). To do this, your nitrogen supply pressure must be 0.1 to 0.2 bar gauge (1.1 x 10
5
to 1.2 x 10
5
Pa). Do not exceed the maximum purge gas supply pressure given in the instruction manual supplied with
your pump.
7.4.2 Calibration of the PRX10 for different purge gases
The purge gas flow rate at a particular supply pressure will change if you use a different purge gas.
If you want to use a different purge gas, use the procedure below to adjust the flow rate.
1. Fit the PRX10 purge-restrictor to the pump as described in Section 7.3.2. Fit a calibrated mass flowmeter
between your purge gas supply and the PRX10 purge-restrictor.
2. Switch on the backing-pump to evacuate the EXT pump, then turn on your purge gas supply.
3. Monitor the indicated purge gas flow rate while you adjust the purge gas supply pressure. If you can achieve the
required flow rate, you do not need to adjust the purge-restrictor; in this case, continue at Step 5 below.
4. Refer to Figure 28. If you cannot achieve the required flow rate, undo the locknut (3) on the purge-restrictor and
use a small screwdriver to turn the adjustment screw (4) clockwise to decrease the flow rate or anticlockwise to
increase the flow rate. Tighten the locknut.
5. Turn off your purge gas supply, remove the mass flow meter and connect your purge gas supply to the
purge-restrictor.
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