An improved magnetostrictive valve for remotely controlling a flow of liquid helium has been developed. Heretofore, flows of liquid helium have been controlled by use of valves with mechanical or gas connections to actuators in warmer locations. The connections act as heat-leak paths. In contrast, the design of the present valve is optimized for operation at liquid-helium temperature (below 4.2 K), so that the entire valve can be maintained at or slightly above liquid-helium temperature to minimize leakage of heat into the liquid helium.
A valve with some similarities to the present one was described in "Magnetostrictive Valve for Use at Low Temperature" (NPO-19480), NASA Tech Briefs, Vol. 21, No. 2 (February 1997), page 14b. The poppet in this valve, as in the previous one, is a ball contained in a passage between an inlet and an outlet. In this case, the ball is made of 440C and is of high sphericity [root-mean-square deviation< 5 µin. (0.127 µm)]. The valve seat is made of superclean, fine-grained 316L steel and is initially lapped to optical flatness. In a later stage of fabrication, the ball is used to "coin" the seat.
As in the previous valve, the actuator in this valve is a magnetostrictive device comprising a rod of terbium/dysprosium alloy surrounded by a solenoidal drive coil that generates the magnetic field needed for actuation. The Tb/Dy alloy was chosen because it exhibits a large magnetostriction in the intended cryogenic operational temperature range. The Tb/Dy rod is mounted in such a way as to provide for removal and installation of different drive coils. To minimize generation of heat in the cryogenic environment, a superconductive drive coil can be used. For temperatures up to 77 K, one can use high-temperature superconductor; for liquid-helium temperature, one can use a superconductive Nb/Ti alloy.
Stainless filters containing submicron pores are inserted in the inlet and outlet ports of the valve to prevent particulate contamination and thereby prolong the operational life of the valve. The "dead" volume in this valve is only 6 µL on the outlet side. In tests at a temperature of 77 K, the valve withstood 300 actuations, with no sign of helium leakage. The valve was also tested at 4.2 K for several actuations with no sign of helium leakage.
This work was done by Robert Chave, Christian Lindensmith, Jennifer Dooley, Brent Fultz, and Marius Birsan of Caltech for NASA's Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
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Refer to NPO-20271