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 WHAT IS IT?
This is a single-stage direct-acting proportional SERVOID® valve. The valve design provides linear proportional flow control. Since it is not pilot operated, the valve will operate at extremely low supply pressures, but allow rather large porting (.25 inches diameter) not typical of other single stage proportional valves. This particular design will operate from a few inches of water column up to approximately 30 psig and has a flow capacity of 200 standard liters per minute (7 SCFM) at a 10 psid pressure drop.
Pre-loading the poppet against the seat with a high rate spring system, provides for internal leak rates below 25 cc/min. |
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HOW DOES IT WORK?
 The valve utilizes a SERVOID® operator to generate a linear proportional stroke of the poppet. This moving poppet is supported on the SERVOID spring cartridge which has a spring rate of 600 pounds per inch and the total combined moving mass is approximately 20 grams. The upper and lower elastomer diaphragms provide pressure balancing of the valving elements, and isolation of the fluid path from the SERVOID® operator. Therefore, the coil and all other internal moving parts are dry. With the moving elements supported on the spring cartridge, there are no guides or rubbing surfaces to create friction or wear. Therefore, hysteresis is extremely low, repeatability is extraordinarily high and service life is virtually limitless.
As with all our SERVOID® valves, flow gain and lift off point are 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 provide proportional modulation of downstream flow conditions. The driving wave form and resulting flow condition can be of virtually any shape, such as saw-toothed, sine wave or square wave, as well as a normal ramp. Due to the extremely long cycle life and fast response, the valve can be pulse modulated directly from a digital signal. With this valve element design, turn down ratios as high as 1000 to 1 allow accurate metering from as low as 200 cc/minute up to 200 liters/minute. The valve can meter virtually any gas such as air, oxygen, propane or nitrogen; the only limitation being the availability of compatible elastomer seals.
In closed loop control systems where valve position feed-back would enhance the system performance, an LVDT can easily be added to the valve to provide position or flow feedback (flow, when constant delta-P is maintained.)
Modifications of the basic design can result in reduced flow capacities and better flow resolution, while maintaining the high turn down ratios. Systems requiring proportional "needle valve" metering would be good applications. |
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