Cirrus SP101013.111 – 10 October 2012
MKS Instruments UK Ltd., Spectra Products
7.3 Replacing the Orifice Disk
Before carrying out ANY operations that involve the orifice disk, take precautions to
prevent contact with any hazardous substances that may have been sampled.
Allow all parts of the inlet and oven to cool before commencing.
You may need to replace the orifice if it becomes blocked or, more likely, you wish to fit a different size
orifice in order to monitor an environment operating at a different pressure.
The orifice is a small disc, with a number of holes in it, which is fitted into a holder machined into the
CF flange.
The inlet flange is mounted on the end of the quadrupole vacuum chamber opposite to the analyser
flange. The flange is held in place by eight M8 stainless steel bolts.
The analyser in your Cirrus will almost certainly be fitted with a PVD source, so there will be a ceramic
coupling which mates with the gas inlet tube on the top of the analyser. You may wish to remove this
to get easier access to the orifice holder, although it is not essential.
1. Shut down the Cirrus by following the instructions in Shutting Down then disconnect from the
mains supply. Remove the outer cover.
2. Disconnect the high pressure end of the capillary from the gas source. If there is a shut off valve
remember to close it.
3. Remove the oven lid.
4. In the oven compartment, use a 5/16 inch spanner to undo the nut on the inlet flange and slide it,
and the ferrule, along the fused silica tube towards the front of the oven.
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