Statement of problem:

For many years, machine builders and plant maintenance managers have complained about issues with traditional needle valve flow controls used to adjust the speed of pneumatic actuators. There are three key areas of concern that can be generalized as technical, operational, and economical. From a technical perspective, many flow controls have issues with accuracy. The adjustment range of most flow controls, much like electrical pots, lacks linearity across the full span of adjustment. This fact combined with the requirement for manual adjustment by the machine operator can spell disaster. As the manufacturing world has evolved from mass production to mass customization, the need for “on the fly” adjustments to minimize down time has exacerbated the flow control issue. Machine operators are frequently asked to adjust flow controls on a cylinder to meet recipe requirements for a specific product run. Improper adjustment or simply failure to make the adjustment can reduce productivity and cost companies thousands of dollars.

The technology to solve this problem is not new, however the third issue – economics, has previously prevented the solution from becoming viable. Recent innovations and manufacturing efficiencies have resulted in products that can solve this problem without breaking the bank.

Solution:

A proportional speed control circuit to eliminate the need for manual adjustment of traditional pneumatic flow controls.

Through the precise control of air pressure at a fixed orifice and thus flow through that orifice, it is possible to obtain control of a cylinder’s piston speed. Furthermore, a linear relationship exists between the pressure supplied to the cylinder and the resulting piston speed, or as shown in the following diagram, flow through a nozzle.

Livingston & Haven is pleased to present an innovative solution to this problem utilizing two key products that will facilitate an economical proportional speed control circuit for applications where frequent speed control adjustment is required.

The circuit merges the economic precision found in the new ED02 series Electro-Pneumatic Pressure Control Valve from Bosch Rexroth with the Airpel Anti-Stiction air cylinder to provide manufacturers and machine builders alike a viable solution to the manual flow control issue for less than $500.

While some skeptics may bring up the fact that a traditional flow controls can be obtained for about $15, we must consider the ROI. For the plant manager, the confidence that the system will automatically adjust through the recipe in the machine’s controls simply by a touch of the HMI, is certainly justification for a better night’s rest. And consider the OEM service man that has flown half way across the country only to find that the cause of the machine malfunction was nothing more than an improperly adjusted needle valve.

If you would like to learn more about this application, please contact your local Livingston & Haven representative. We will be happy to assist you and provide a demonstration of this technology.

Additional Technical Data:

A 4-20 mAmp or 0-10 Volt signal must be supplied to the ED02 valve to vary the output pressure. The valve is available with various pressure ranges to suit the application requirements. Calibration of pressure and input signal will allow for very precise control of output pressure supplied to the directional control valve and eventually the cylinder.

While the ED02 can achieve similar results with a standard cylinder, the use of the Airpel Anti-Stiction air cylinder will greatly enhance the performance of the circuit due to the lack of break-away friction and fast response. This cylinder utilizes a glass lining and a graphite or stainless steel piston. It rides on an air bearing rather than dynamic seals which essentially eliminates stiction and yields extremely low friction during actuation.

A fixed orifice located near the cylinder port as shown in the diagram is required to achieve the desired results.

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