Brooks Instrument 5851i - Manual (Page 33)

4-5
Installation and Operation Manual
X-TMF-5851i-MFC-eng
Part Number: 541B109AAG
September, 2009
Brooks ® Model 5851 i
Section 4 Maintenance
& Troubleshooting
Table 4-2 Sensor Troubleshooting
An alternate method for flushing out the sensor is to replace the restrictor
element with a low flow plug restrictor. This plug forces all the flow through
the sensor and may dislodge any obstructions. With the valve orifice
removed, subject the flow controller to a high differential pressure.
Pressurizing the outlet of the MFC higher than the inlet may help force the
obstruction upstream and out of the sensor tube.
4. Inspect the orifice for clogging by holding it in front of a light source and
looking for light through the bore. Clean by soaking in a suitable non-
residuous solvent and directing a stream of compressed dry nitrogen
through the bore.
5. Deposits of silicon dioxide may be removed by soaking the internal parts
in a solution of 5 parts hydrofluoric acid (HF) and 95 parts water (H
2
O)
followed by a non-residuous solvent or DI water.
6. Restrictor elements can be cleaned in an ultrasonic bath or replaced.
Refer to Section 4-7 for the correct restrictor to use.
7. Blow all parts dry with dry nitrogen and reassemble. Refer to Section
4-4b (assembly).