Utah-94-721002-System-Manual.pdf - 第217页

System Manual lñÑçêÇ=fåëíêìãÉåíë=mä~ëã~=qÉ ÅÜåçäçÖó== ^ää=lfmq=póëíÉãë The flow-setting knob can be on the upstream or downstream side of the t ube. - If it is upstream (below the tube), the pressure in the tube is close…

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A rotameter is a manually controlled variable valve/indicating tube, used by OIPT to manually set the flow
rate
1
for various gas supplies. For example, purge flow rates for turbomolecular
2
, rotary vane and dry
pumps, glove boxes and etch gas supplies for process chamber cleaning.
Flow control
knob
Graduated
scale
Ball float
Tube type number
is marked on this
side of the tube
Fig 1: Typical rotameter
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The models of rotameter used for setting purge gas flows on OIPT equipment is fitted with a common
scale, reading from 0 to 6 as flow is varied from zero to full scale. The full-scale flow depends on:
• The tube type (marked on the tube itself)
• The ball material
• The gas type
• Temperature
• Pressure
The full-scale flows given in the following table are for 20° C, 1 atmosphere pressure, air or nitrogen gas.
OIPT part Tube number Ball material Normal use Full scale flow
G/GAS/ROT/050 A125-3 Glass Turbo pump purge 53 sccm
G/GAS/ROT/25L A250-4 Carboloy Rotary pump purge, PECVD 27.5 slpm
G/GAS/ROT/40L A250-6 Stainless steel Pump exhaust purge 43.4 slpm
G/GAS/ROT/800 A125-7 Stainless steel CF4/O2 ‘clean gas’ metering 850 sccm
G/GAS/ROT/900 A250-1 Stainless steel Rotary pump purge, etch,
PECVD
4.4 slpm
1
Flow rates are quoted in either standard cubic centimetres per minute (sccm) or standard litres per minute (slpm).
2
In most OIPT systems, turbomolecular pump purge flows are set automatically and monitored by the system software via a flow
meter: these systems do not incorporate a rotameter for the turbo pump purge.
Rotameter Data
Issue 1: August 03 Page 2 of 4 Printed: 2-Jul-05, 11:43
System Manual lñÑçêÇ=fåëíêìãÉåíë=mä~ëã~=qÉÅÜåçäçÖó== ^ää=lfmq=póëíÉãë
The flow-setting 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.
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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.
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.)
Rotameter Data
Printed: 2-Jul-05, 11:43 Page 3 of 4 Issue 1: August 03
^ää=lfmq=póëíÉãë lñÑçêÇ=fåëíêìãÉåíë=mä~ëã~=qÉÅÜåçäçÖó== System Manual
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G/GAS/ROT/050 (Tube No: A125-3)
0
0
123456
10
20
30
40
50
60
Scale Reading
Flow
(sccm)
A125-
3
G/GAS/ROT/25L (Tube No: A250-4)
0
0
123456
5
10
15
20
25
30
Scale Reading
Flow
(slpm)
A
250-4
G/GAS/ROT/40L (Tube No: A250-6)
0
0
123456
10
20
30
40
50
Scale Reading
Flow
(slpm)
A250-
6
G/GAS/ROT/900 (Tube No: A250-1)
0
0
123456
1
2
3
4
5
Scale Reading
Flow
(slpm)
A
250-
1
G/GAS/ROT/800 (Tube No: A125-7)
0
0
123456
100
200
300
400
500
Scale Reading
Flow
(sccm)
A
125-7
600
700
800
900
Rotameter Data
Issue 1: August 03 Page 4 of 4 Printed: 2-Jul-05, 11:43