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WHAT IS IT?
 This is a single-stage, direct-acting proportional SERVOID® valve. The valve design provides linear proportional area control of the main port. With a regulated pressure drop, the valve yields linear proportional flow control. Since it is not pilot operated, the valve will operate at extremely low supply pressures, but will allow larger porting (approximately 0.10 in. dia. equivalent orifice in this case) than typical of other single-stage proportional valves. This particular design will operate from a few inches of water column up to approximately 60 PSIG. It has a flow capacity of 100 standard liters of air per minute at 25 PSID, for example. Pre-loading the poppet against the seat with the integral high rate spring system provides for internal air leak rates below 100 cc's per minute. The valve weighs 1.2 lb.. |
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HOW DOES IT WORK?
 The valve utilizes a SERVOID® operator to generate a linear proportional stroke of the poppet (a ball in this model) and is pressure aided to open. The moving poppet is positioned by a SERVOID® spring cartridge which has a rate of 275 pounds per inch. The total combined moving mass is 5 grams, providing a very stiff yet responsive system. An encapsulated coil is used in this "wet coil" design. With the moving element supported on the spring cartridge, there are no dynamic seals, guides or rubbing surfaces to create friction or wear, resulting in extremely low hysteresis, extraordinarily high repeatability and virtually limitless service life. As with all our SERVOID® valves, flow gain is externally adjustable while the unit is pressurized and operating with no performance penalties. |
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| HOW IS IT USED? |
In open or closed loop control systems, this valve can be used to provide infinitely variable proportional flow control. It may be driven by an analog signal or digital PWM signal (1,000 Hz minimum). The drive wave form and resulting flow condition can be virtually any shape, depending upon the application requirements. Repeatability characteristics make this valve a good candidate where different discrete flow values must be selected on each cycle from a zero flow condition. This design can offer turn down ratios as high as 400 to 1 providing flow accuracy from as low as 250 ml per minute up to 100 liters per minute. The valve can be used to meter virtually any gas including air, oxygen, propane and nitrogen, limited only by the availability of compatible static seal materials. The valve may also be used to accurately meter liquid media such as jet and diesel fuel.
Calibration of flow gain and lift off point are factory pre-set, but gain can be externally adjusted by the user to meet specific application needs. Beyond the calibration range, modifications to the basic design can result in significantly higher or lower flow ranges, depending on application requirements. High accuracy can be maintained in this flow ranges as well.
Please see PV-222 at the following link: |
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