Integrity test of an ultrafiltration membrane

Integrity test in ultrafiltration

It is highly likely that ultrafiltration is already a key part of your water treatment system, with membranes as the main component. If they start to leak, contaminants will get into the filtrate. You therefore need to closely monitor the differential pressure between the inlet and outlet in order to identify leakages as early as possible. Festo recommends automated, decentralised pressure control and pressure monitoring to help you with this.

Automated testing and control

Ultrafiltration systems and membrane filtration are used in both water treatment and industrial water plants. The pressure retention test is a proven method to test the filter integrity. It is important to carry it out regularly to prevent contamination of the filtrate. During this test, the individual membrane modules are supplied with controlled compressed air for two to three minutes and the pressure drop is measured. If this deviates from the reference value, it indicates that there is a leak in the membrane.

The integrity test can be automated in such a way that it is as reliable as the pressure retention test itself. The key to this is the system CPX/MPA from Festo as a remote I/O with integrated pneumatics. It allows you to record the pressure in the tubing using an analogue input card with a direct supply port, giving you an accurate leak test.

The CPX/MPA is installed directly in the field and can be easily connected to the central controller using common fieldbus protocols. In addition, this eliminates almost all of the cabling. Continuous process monitoring, even remotely, is possible, as is protecting the pressure regulator against operating errors and tampering.

Next, we will show you the benefits over manual or semi-automated testing. Or click here to go directly to the Festo solution.

Comparison of the efficiency of filter integrity tests

Disadvantages of manual testing

In many cases, the pressure retention test is still carried out manually. That is the conventional way of doing it: opening and closing all the valves by hand. The applied pressure also has to be set manually. Recording, evaluating and monitoring are also done by hand. However, this approach has considerable disadvantages. Other than the personal effort required, recording the data is a laborious process. On top of that, the process is prone to errors and difficult to integrate into the control system.

The semi-automated process as an intermediate solution

Some water treatment systems are already semi-automated. This means that many of the steps in the pressure retention test no longer have to be started off and carried out manually. The pressure values are also measured automatically using a PLC. However, adjusting and regulating the pressure generally still have to be done by hand.

Benefits of an automated solution

Complete automation, as offered by Festo with the CPX/MPA, is easy to integrate at the PLC level by cabling the field devices to I/O cards. This means that all process steps are automated. The pressure is regulated and measured directly in the field thanks to integrated functions.

Integrated solution CPX/MPA from Festo

Festo offers you a solution for ultrafiltration systems that integrates the pressure retention test as a function on the I/O system: the CPX/MPA, a modular electrical terminal (CPX) with integrated pneumatics (MPA). The compact system is installed decentrally in the system and can be used with all common fieldbus protocols, making it easy to integrate into the higher-order centralised control system. Alternatively, a local, autonomous PLC controller can also be installed decentrally via the control module CEC that can be integrated into the CPX/MPA. This also means that cabling is kept to a minimum. The system guarantees continuous process monitoring, even remotely, and protects the pressure regulation from operating errors and tampering.

Pressure sensing is carried out via an analogue input card CPX-4AE-P-xx with which you can measure the pressure in the tubing via a direct supply port. The setting defined in the PLC directly resets a proportional pressure regulator that is integrated on the CPX/MPA, As a result, you don’t need a separate regulator or a pressure sensor in the field. Solenoid shut-off valves, which prevent raw water from entering the pneumatic part, are also controlled via the digital output cards integrated into the CPX.

The CPX/MPA can even take on other system functions. These include pilot valves for shut-off process valves, analogue output cards for control valves, digital input cards for position feedback of the process valves or analogue input cards for process sensors.

Fully automated solution for pressure retention testing

Fully automated solution for pressure retention testing

Benefits of automation with CPX/MPA

By combining electric and pneumatic components into one I/O system, Festo is able to offer an innovative solution for ongoing ultrafiltration integrity tests. This solution offers benefits to both operators and design engineers of water treatment systems:

  • Integration: By directly connecting the pressure regulator, pressure sensing and the digital outputs via a backplane bus, cabling is kept to a minimum. Tubing and an electrical signal cable are only needed for the shut-off valve.
  • Safety: The pressure level is defined using the PLC. Compared to manually adjusting the pressure, this protects the system against operating errors by system personnel. Safety is further increased if the CPX/MPA is installed in a closed control cabinet.
  • Efficiency: The correct pressure setting can be reproduced perfectly.
  • Monitoring: The pressure at the individual membrane modules can be easily sensed via terminals.
  • Autonomy: As a decentralised PLC function, CEC provides an autonomous system that functions reliably, even in the event of fieldbus errors.
  • Management: Data can simply be gathered and evaluated using the higher-order PLC or decentrally via Festo SCADA on the CDPX. That also applies to remote access via the Internet or mobile phone network.

And, as already mentioned, the CPX/MPA can also integrate additional solutions.