System Manual Oxford Instruments Plasma Technology All OIPT Systems
Rotameter Data
Printed: 5-Jun-09, 9:58 Page R 3 of 6 Issue 2: October 04
The flow-set
ting knob can be on the upstream or downstream side of the tube.
- If it is upstream (below the tube), the pressure in the tube is close to the exit pressure,
which should be close to 1 bar absolute for pump or exhaust pipe purging.
- If the knob is downstream (above the tube) the pressure in the tube is close to the supply
pressure of the gas. This method is normally used if the exit pressure is below
atmospheric pressure, which is often the case in turbomolecular pump purging.
If in doubt, control downstream is always safe, because the ball float will operate normally and the
purge flow will be slightly higher than given in the table.
1.2 Setting the required purge flow rate
Note that the following procedure is for setting N
2
purge flow rates for pumps; a similar procedure
can be used for other applications, e.g. etch cleaning, glove box purging, etc.
To set the required flow rate, use the following procedure:
1) Refer to the pump manufacturer’s literature or to the relevant OIPT Installation Data document
to obtain the required N
2
flow rate.
2) Check the Tube number (marked on the Rotameter tube) and then refer to the relevant
rotameter’s graph on page 4 and note the required scale reading.
3) Ensure that the N
2
supply meets the Mandatory Requirements for Nitrogen Supplies as stated
in the OIPT Services Specifications document sub-section 5.1.
4) Adjust the rotameter flow-setting knob so that the centre of the ball float is aligned with the
required scale reading. (Rotate knob anti-clockwise to increase flow, clockwise to reduce
flow.)
CAUTION
The rotameter scale is graduated with values of 0 to 6. These
graduations do not represent flow rates in sccm or slpm.
To set the required flow rate, use the following procedure.
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