Nowadays, water treatment plants are equipped with an ultrafiltration system as standard, with membranes as the central component. If they start to leak, contaminants will get into the filtrate. You need to closely monitor the differential pressure between the inlet and the outlet in order to identify leakages as early as possible. Festo recommends automated, decentralised pressure control and pressure monitoring for this function.
Automated testing and control
Ultrafiltration systems and membrane filtration can be found in both water treatment and industrial water treatment 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. In 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 leakage in the membranes.
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 simply be connected to the central controller using standard fieldbus protocols. In addition, this does away with almost all the cabling. Continuous process monitoring, even remotely, is possible, as is the protection of the pressure regulator against operational error and tampering.
Next, we will show you the benefits over manual or semi-manual testing. Otherwise, you can go directly to the Festo solution.
Comparison of the efficiency of filter integrity tests
Disadvantages of the manual process
The conventional solution is to carry out a pressure retention test manually. That is the way it's still often done: by manually opening and closing all the valves. 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 is difficult to integrate into the control system.
Intermediate solution: semi-automated process
Some water treatment plants are already semi-automated. In this case, all the various steps of the pressure retention test no longer have to be triggered and executed manually. The pressure values are 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 the cabling of 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.
Semi-automated pressure retention testing
Integrated solution CPX/MPA from Festo
Festo offers 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 system is installed directly in the decentralised system and listens to the standard fieldbus protocols, making it easy to integrate it into the higher-order centralised control system. Alternatively, a local autonomous PLC controller can also be created decentrally using the control module that is integrated into the CPX/MPA. In any case, the cabling effort is minimal. The system guarantees continuous process monitoring, even remotely, and protects the pressure regulator from operational error and tampering.
Pressure sensing is carried out using an analogue input card CPX-4AE-P-xx, which you can use to measure the pressure in the tubing through a direct supply port. The setting defined in the PLC directly resets a proportional pressure regulator that is integrated on the CPX/MPA, This means you don’t need a separate regulator or a pressure sensor in the field. The solution also controls solenoid shut-off valves that prevent the ingress of raw water into the pneumatic parts through integrated digital output cards on the CPX.
The CPX/MPA can even take on other functions from your system. These include pilot valves for shut-off process valves, analogue output cards for control process valves, digital input cards for position feedback from the process valves or analogue input cards for process sensors.
Fully automated solution for pressure retention testing
Benefits of automation with CPX/MPA
Festo is able to offer an innovative solution for ongoing ultrafiltration integrity tests by combining electrics and pneumatics in one I/O system. This solution offers benefits to both operators and design engineers of water treatment systems.
- Integration: The direct connection of the pressure regulator, the pressure sensing and the digital outputs via a backplane bus minimise the cabling effort. Tubing and an electrical signal cable are only needed for the shut-off valve.
- Safety: The pressure level is defined using the PLC. In comparison to manual pressure settings, this protects the system against operational errors by system staff. Safety is further increased if the CPX/MPA is installed in a closed control cabinet.
- Efficiency: The correct pressure setting is optimally reproducible.
- The pressure of the individual membrane modules can be sensed trouble-free via terminals.
- Autonomy: CEC as the decentralised PLC function facilitates an autonomous system that works reliably, even in the case of fieldbus errors.
- Management: Data can simply be gathered and evaluated using the higher-order PLC or decentrally via Festo SCADA on the CPDX. That also applies to remote access via the Internet or the mobile phone network.
And, as has already been said, the CPX/MPA can integrate additional solutions.
Valve terminal MPA-S with CPX terminal
Incredibly modular and versatile! The CPX interface on the valve terminal MPA is based on the bus system of the CPX and uses this serial communication system for all the solenoid coils and electrical input and output functions.
Proportional pressure regulator VPPM
The new dimension in proportional pressure regulators. The right parameters for each application – simply choose the suitable control characteristic from 3 presets at the press of a button. Reliable control – thanks to the two-stage control loop with multi-sensor control