Dual Valve Actuator With Two Piezo Benders

Solenoid technology did not meet the customer's requirements for performance or form factor. Piezoelectrics met the requirements, however raw piezoelectric actuators were unreliable and labor intensive. A packaged piezoelectric actuator custom designed for their application.

For over 20 years we have been producing and delivering this custom actuator.  There have been over 1 million units fielded globally with zero reported field failures.

The Challenge

In the late 1990s a Fortune 500 multi-national industrial company recognized they needed a better pneumatic valve solution for their HVAC system. Their current application used old solenoid valve technology that was too loud, too large, drew too much power, and most importantly, was not accurate enough.

This company also recognized the potential benefits of piezoelectric valves in overcoming these challenges. However, raw piezoelectric materials presented a different set of challenges.

Piezos can be brittle and difficult to integrate into high volume systems. The company found this out the hard way when they first worked with a competing supplier of raw piezoelectric actuators. After many development failures, the customer thought a piezo solution with all of its benefits might be “too good to be true.”

ACX (now Piezo.com) worked hand in hand with this customer to design and provide a packaged piezoelectric valve solution that met all of their needs and requirements.

Challenges of Solenoids 

Typical pneumatic valves utilize a dual solenoid design, but solenoids have a number of shortcomings. Our customer knew a piezoelectric solution would meet all of their critical needs, because;

• Piezos have no audible noise
• Piezos have a much faster response time, less than 10 ms
• Piezos require much less power and are capable of holding a position with virtually no additional power consumption
• Piezos require less space with a thinner form factor
• Piezos are an order of magnitude lighter
• Piezos can be proportionally controlled, not just the binary on/off characteristics of solenoids

Challenges of Raw Piezos

The competing supplier’s raw piezos didn’t have the unique benefits that Piezo.com's piezoelectric packaging provided. Most significantly the raw piezo design had three important shortcomings in the words of their engineer:

1. One of the piezos is used in a sealed chamber maintained at a 20 psi supply pressure. Sealing the flying leads of that piezo without leakage was difficult.
2. Soldering the flying leads (4) of the piezos to our controller PCA was a costly factory operation.
3. Compressed air inherently has moisture in it. We are driving the piezos at ± 160 Vdc. Our testing showed that the presence of moisture allowed a shorting path around the edge of the raw piezos causing unacceptable failures

The Solution

Like most applications, the company needed a custom design solution that could meet their specific needs. Over the course of 6 weeks, Piezo.com worked closely with engineers at the client company to design the packaged piezo valve configuration. Many reciprocal trips were made between the client and Piezo.com so that all parties involved had an intimate understanding of each other’s design and manufacturing processes.

Our final design delivered a proprietary packaged piezo pneumatic valve that included a packaged resistor for electrically protecting both the drive circuit and the piezo.  This was achieved by encapsulating the raw piezoelectric ceramic between layers of flexible circuits, enabling;

• A hermetical seal around the wafers - eliminating the moisture issue
• An electrical connection to the wafers - eliminating the need for solder
• The design to include features to ease mechanical integration
• Flat & flexible circuits - making sealing easy and repeatable

Results

The result was a design that has stood the test of time, and has not required a change for over 20 years. What’s more, the manufacturing and quality assurances processes developed in that initial development have ensured reliability and very low failure rates. Piezo.com routinely is ranked among the best suppliers due to the consistently high quality of these actuators. In the words of the engineering customer:

“The piezos are silent, low power and very accurate. Our stated pneumatic output accuracy is ± .25 psi which is, at a minimum, two times more accurate than the solenoid solution. The results have been excellent. Very low factory reject and field return rates over the 20 years that the product has been in our line.”

- Guy C., Engineer