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WHAT IS IT?
 This is a SERVOID® Pilot-operated, two stage, linear proportional fuel metering valve with a built-in Large Scale Integrated (LSI) solid state microcircuit. The SERVIOD® Controller on this valve is a linear proportional DC Solenoid which is used to position a button over the pilot orifice in the follower piston. This system provides maximum stability, minimum transient effects due to vibration and extraordinary repeatability. The coil is dry, electrically isolated and epoxy encapsulated.
All wetted surfaces are either stainless steel, anodized aluminum or nickel-plated ferro-magnetic alloys. The dynamic seal on the follower piston is a modified unfilled virgin TFE with excellent wear and extrusion resistance. The piston rides in a chrome-plated, polished bore providing further wear resistance and low-friction operating characteristics. All static seals are florosilicone. The LSI micro-chip is housed in a laser-welded, hermetically sealed container.
The piston functions as a poppet which engages a fixed metal seat when at zero voltage. The SERVIOD® driver can be supplied with a variety of coil resistance and voltage drop options. However, the maximum power required will always be in the 12 to 14 watt range. The electrical connector shown conforms to MIL-38999. |
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HOW DIES IT WORK?
 The supply pressure is ported to the back side of he piston through a restricting orifice and unrestricted to the poppet end. When voltage is applied to the Controller, its resulting motion opens the pilot orifice (piston orifice), allowing servo pressure to flow through the piston orifice to the outlet port. The supply pressure at the poppet end of the piston then moves the piston toward the retracted pilot until it closes the pilot orifice sufficient to regain pressure equilibrium. In the closing mode, the button moves toward and closes the pilot orifice causing the servo pressure to build toward supply pressure. With the effective area at the back of the piston being larger than the poppet, rising pressure causes the piston to move toward the seat. Pre-loading the Controller button against the pilot orifice insures that pressure forces always act to load the piston/poppet against the main metering orifice providing excellent leakage control across both main and servo orifices.
Given the low moving mass and high spring rate, the damped natural frequency of the system is 300 Hz. The frequency response is 10 Hz, square wave and 50% stroke. |
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