Acro pinch valves employ a linear spring-loaded electric or pneumatic actuator to control the engagement of the pinching surfaces. Generally, there are two pinching surfaces: a fixed pinching surface called the pinch ridge and a movable pinching surface called the pinch head. Flexible tubing is loaded between the pinch head and the pinch ridge and flow is normally restricted (normally closed) by a spring mechanism that forces the pinch head against the pinch ridge. The pinch head is mechanically linked to the valve's actuator so that when the actuator is energized with a pressure or current signal, the pinch head is disengaged. The distance between the pinch head and pinch ridge is increased and fluid flows unrestricted through the tubing.

Feedback

The state of a pinch valve can be inferred through knowledge of the position and motion of its pinch head. The purpose of a feedback device is to confirm that a valve is in the state dictated by a control input (a current or pressure signal). Traditionally, pinch valve are equipped with either mechanical or solid state switches in applications where feedback is desired. These traditional solutions have a number of drawbacks that Acro addressed during the development of MPS sensing technology (see next section). MPS enabled pinch valves employ the only sensing technology developed specifically for use in pinch valves.

MPS Technology

MPS (Magnetic Positioning System) Technology consists of two components: (1) a pinch valve designed with a permanent magnet integrated into the actuator which moves in unison with the pinch head and (2) an electronic IDPMC (Integrated Digital Position Management Computer) module that mounts in a recessed pocket in the valve body. The IDPMC is wired to the user's equipment via a 5-lead data cable that provides DC power and digital feedback.

The IDPMC is a miniature (33mmx26mmx11mm, 4.5g) embedded system for pinch valves that uses a moving permanent magnet to track and process the position of the pinch head. The IDPMC embodies seven major components: (1) precision linear Hall element, (2) microprocessor, (3) non-volatile configuration memory, (4) three transistor outputs, (5) red/yellow/green diagnostic LED, (6) bi-directional infrared communications port, (7) factory supplied firmware.

The magnetic field from the integrated magnet drives the Hall element. The Hall element output is then amplified, filtered and digitized. The microprocessor samples the Hall element at approximately 2.7kHz and processes the signal using the preset configuration. The result of this processing is expressed to the user through the three programmable transistor outputs and the multicolor diagnostic LED. The infrared port facilitates initial factory configuration, field reconfiguration and data acquisition.

The IDPMC can be configured for unambiguous detection of the following valve states: (1) POWER OFF; (2) TUBE OUT (valve closed, tubing removed); (3) TUBE IN (valve closed, tubing inserted); (4) PART OPEN (pinch head partially disengaged); (5) FULL OPEN (pinch head fully disengaged). When a MPS enabled pinch valve is delivered to a customer, it is ready to plug directly into their digital interface; user calibration is not required, meaning the pinch valve becomes an interchangeable component.

The IDPMC also has some secondary capabilities. It will track total valve cycles and in-service time, along with serial/lot numbers and service record. The IDPMC also has optional self-diagnostic end-of-life capabilities. It can be configured to error upon power-up if the valve has exceeded its useful life. A field technician can use the infrared interface and a laptop to diagnose the valve in-service and determine if repair or replacement is necessary. This eliminates unnecessary component repairs, which lowers operating costs.

Conclusion

Acro Associates' MPS technology provides a unique "out of the box" solution for critical pinch valve applications. The combined simplicity and flexibility of our MPS sensing technology will provide unparalleled safety and value for your flow control project.