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WHAT IS IT? This is a linear proportional, three-way blending or diverting SERVOID® Valve. The unit has three ports. In the diverter mode, the Valve will split a supply flow into two flows, the mass ratio of which will be in proportion to the current applied to the SERVOID® Controller. In the blender mode, the Valve will control the mixture ratio of two fluids, again, in direct response and in proportion to the signal to the Controller. Total flow from the valve is a constant at a given pressure drop across the unit.
The design features a dry coil, an externally adjustable gain and stainless steel or nickel-plated wetted surfaces. The poppet and seats are hardened stainless steels which insure long life and avoid calibration shift due to compression deformation associated with "soft" seats.
The SERVOID® Controller can be equipped with a customer-specified electrical connector in place of the pigtail leads shown. A wide variety of coil resistance, current level and voltage drop is available to interface with signal generation devices. However, he SERVOID® Controllers will require between 3 and 6 watts of total power to operate efficiently. |
HOW DOES IT WORK? The Valve is driven by one of a family of linear, proportional D.C. Solenoids which we call SERVOID® Controllers. It is a current-driven device which makes it immune to coil resistance changes with temperature. To achieve immediate and linear motion with the first application of power, the unit contains a permanent magnet. The spring system will have a rate between 300 and 1000 lb./inch, depending on other factors such as required stroke and vibration/acceleration environments. This spring-mass system will have natural frequencies as high as 900 Hz. When coupled with the poppet and shaft in this design, the natural frequency is on the order of 300 Hz. Fluid damping will reduce that somewhat.
Leakage in the de-energized mode, is controlled by pre-loading the SERVOID® spring system, through the poppet shaft, onto the seat. Electrically overdriving the Valve in the energized mode provides the same control on the opposite seat.
To achieve proportional flow, apply current, in milliamps, to the Controller at a level equivalent to the desired ratio of fluid flow. The ball poppet moves to a position between the opposing seats which will give that ratio in accordance with the calibration curve specified on the drawing.
HOW IS IT USED? The Valve can be used with liquid or gaseous media in any system which requires the proportional blending or diverting of fluids. Application for this kind of device will include thermal cooling or heating, chemical blending of gases or liquids, pump bypass control and so on. In a thermal control system, for example, when the temperature at the work place must be maintained with varying heat loads, this valve can be used. It will bypass or feed the returning fluid either through or around the heat exchanger in response to the temperature feed-back from the blended hot and cold fluids returning to the work place. Systems requiring laser or infra-red cooling, crew suit temperature control, lube oil systems or avionics cooling are candidates.
In systems which use flame in the process of manufacture and which blend two gases, (i.e.) oxy-acetylene or oxygen and propane or butane, this device has application. In life or health support systems where air and oxygen or anesthetic gases must be blended in varying ratios to suit the patients' needs, this concept will provide accurate control.
If the system designer requires flow as well as ratio control, S.B.C. can do that as well using two SERVOID® Valves in a common manifold. |
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