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 WHAT IS IT?
This is a Linear Proportional 2-way SERVOID® Metering Valve suitable for use with either liquidous or gaseous media. It contains a rare earth (Samarium Cobalt) permanent magnet which establishes a level of energy and readiness to react linearly with the application of an external electrical (current) signal.
The design features a dry coil and all "wetted" surfaces are wither stainless steel or nickel plated. Hardened steel poppets and seats are used to ensure durability, increase insensitivity to contamination and prevent calibration drift due to seat deformation typically associated with high cycle life applications using "soft" seats or poppets.
The unit can be adjusted for gain and seat pre-load (lift-off point/leakage control) with common tools, while pressurized and running. Ordinarily, these adjustments are pre-set at the factory but can be made available to the end user.
The valve can be configured with a variety of coil resistances, current levels and voltage drops to accommodate the user's driver circuitry. |
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 HOW DOES IT WORK?
The SERVOID® Driver is a linear D.C. solenoid; a current to displacement transducer. It has a nominal working stroke of .008 inch and a spring rate of 300 lb./inch. Irrespective of maximum current draw and voltage drop, the driver requires 5 watts of power at full stroke.
It is designed primarily as an analog device but will function normally when driven by a pulse width modulating signal of between 500 and 5000 Hz or higher.
When coupled to to this valve, the driver will open and close an effective sharp edge orifice of .053 inch diameter in proportion to the input current. If pressure drop across that is maintained nearly constant, the resulting flow rate will be proportional to the input signal.
There are no dynamic seals or friction-producing surface contacts. Hence, the valve exhibits no dead band whatsoever and what performance hysteresis there is arises from magnetic material hysteresis. Also, hysteresis is in proportion to stroke. Small excursions exhibit almost no hysteresis.
The unit has a fluid-damped natural frequency near 100 Hz and a frequency response of greater than 10 Hz full stroke. |
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| HOW IS IT USED? |
 This valve concept has had the widest range of applications of our SERVOID® Valves to date. These include propeller feathering using hydraulic fluid at 100 PSI, a proportional thruster for research satellites with argon at 75 PSI and two small turbine engine control systems; a primary fuel metering valve at 35 PSI on one and a secondary fuel adjustment device at 250 PSI on the other. In each case the physical configuration of the valve is the same but the gain and lift-off points are adjusted to fit the specific need.
Generally, the valve has application in any metering system (gas or liquid) or, when used in parallel, in any mixing and metering system, requiring relatively low flow (.053 inch dia. orifice).
This design can be scaled upward to approximately four times the flow. Other similar, single stage valves will control, for example, up to 200 LPM at 10 PSID.
This design is the face-mounted style. It can be re-configured for a manifold mount as well. |
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