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4.4
Liquid Circulation System Design Recommendations
In typical semiconductor wet process liquids, a catalyst such as H
liquid. The subsequent reaction generates heat and produces extreme gassing of the liquid. Measures
should be taken to reduce the amount of gas laden liquid which can enter the pump chambers. Excessive
gas can cause an air lock condition for the pump which may increase the pump stroke rate to excessive
levels.
For safe and efficient circulation and feeding of liquid, it is necessary to carry out air elimination and take
proper safety measures.
Air elimination technique
When air enters the bellows and the pump becomes air locked, the pump stroke rate increases. If the
increase is excessive, that is, higher than the specified pump stroke rate, stop the pump or carry out air
elimination.
Plan A (Bubbles are blocked by means of a baffle plate)
1. In case of flooded suction system (Figure 5)
A baffle plate is set in the overflow tank to separate bubbles
from the liquid, thus limiting the air content.
2. In case of suction lift system (Figure 6)
A baffle plate is set in the lower level in the reaction tank. The
top of the suction port tube is positioned under the baffle so that
bubbles are not drawn into the suction piping with the liquid.
Plan B (Automatic air elimination with auto valve
installed)
1. Regardless of the occurrence of air locking, continuous
automatic air elimination is executed in the entire system. For
example, the air elimination process is activated every 2
minutes after the start-up of the pump by opening the auto
valve for 10 seconds. (Figure 7)
Note 1: Some filters have diameters too small for air
elimination. Take the diameter into consideration when selecting a
filter.
Note 2: Determine the open period of the auto valve on the basis of
the system performance.
2. If the conditions under which bubbles are created remain the
same, an air elimination technique which fits well with such
conditions may be applicable. For example, if bubbles are
generated only when feeding H
air elimination only when H
0
, open the auto valve to carry out
2
2
0
is fed.
2
2
10
O, O
or H
O
is added to the process
2
3
2
2
Reaction tank
Figure 5
RECOMMENDED
P
Reaction
tank
Figure 6
Baffle plate
H 0 , 0 , H 0
2
2
3
2
Reaction
tank
Heater
Figure 7
Baffle
plate
Overflow
tank
P
NOT RECOMMENDED
P
Bubbles are
drawn up.
Air elimination line
Auto valve
Filter
P
Pump
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