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8.1 Pressure Hold Test (PDT)
In addition to a permeate water quality monitoring system, the Asahi Kasei membrane systems are
designed with capability for conducting both pressure hold test and air leak tests in order to
establish the integrity of the membranes. See below test protocol flow chart.
Figure 15
Leak Test Flow
Pressure hold tests may also be performed automatically or manually by an operator as required.
The small membrane pores will not allow air to pass through the membrane due to the surface
tension of the water being held in the membrane pores. This results in the air pressure in the
system to remain almost constant when the membranes have integrity. The pressure will decay if
there is a defect (such as broken fibers) as air can pass through such defects.
Leak judgment criterion
Item
Pressure Decay Rate
Amount of Pressure Decay (after 3 min)
No Leak
Slower than 5 kPa/min
Less than 15 kPa
Leak Present
5kPa/min or faster
15 kPa or more
Pressure Decay Test (PDT)
Pressure decay (kPa/min) measurement
Start air leak test
Decay rate < Expected rate?
Air Leak Test
Observe the joint's transparent
section for air bubble occurrence.
NO
YES
Continuous air
bubbles?
YES
Fix leakage
Replace modules
NO
End of Leak Test