Abstract:
A solenoid valve wherein a conical tip of a cylindrical plunger armature seals a flow-limiting orifice in an elastic valve-seat annulus, enabling minimum armature travel per unit of flow. The resulting short-gap, combined with a thin-walled armature housing and an efficient unitary exterior magnetic yoke yields a low reluctance magnetic circuit, and a high impedance solenoid. Wattage demand is reduced in both inrush and steady-state conditions. Choice of gap dimension and annulus design enables a low wattage demand, substantially free from variable fluid pressure effects. The use in combination of a unitary dual-path exterior magnetic loop, with a ferrous armature housing, and a novel phase-splitting core enable operation at still further reduced wattage values. Size, copper usage, temperature rise and cost are held to low values previously unattainable.

Description:
BACKGROUND OF THE INVENTION 
     This is a continuation of co-pending application Ser. No. 215,052 For Alternating Current Solenoids, filed Jan. 3, 1972, now abandoned, which is a continuation in-part of prior co-pending application Ser. No. 830,342 for Alternating Current Solenoids filed June 4, 1969, now U.S. Pat. No. 3,647,177, which in its turn contains subject matter in common with application co-pending therewith Ser. No. 783,035 for Phase Splitting Core for Electromagnetic Devices filed Dec. 11, 1968, now U.S. Pat. No. 3,553,618. Additionally thereto, this application and sequential parents hereof Ser. No. 783,035, and Ser. No. 830,342 now U.S. Pat. No. 364,177 contain subject matter in common with application co-pending therewith Ser. No. 103,429 for Alternating current Relays filed Jan. 4, 1971, now U.S. Pat. No. 3,735,301. 
    
    
     This invention relates to alternating current electromagnets useful in solenoid devices such as relays, actuators, and particularly in magnetic flow control valves of the type used to control the flow of gases or liquids under pressure in a closed system, and for convenience of illustration is shown and described herein as applied thereto. 
     In the design of solenoid fluid control valves it has been common practice to provide a cylindrical plunger guide or cup member of non-magnetic material to serve as a housing for the movable valve plunger and a normalizing bias spring. The housing with appropriate gasketed assembly to the valve body, confines within the cup whatever fluid is controlled by the valve. Such constructions are often referred to as &#34;wet armature&#34; valves. The exciting coil is provided with a magnetic yoke or shell and cylindrical or tubular pole pieces designed to conduct the flux to the vicinity of the plunger housing with a minimum of gaps or magnetic discontinuities, to thereby attain a relatively high magnetic efficiency. The coil is commonly assembled about the housing such that when energized the flux path is through the wall of the non-magnetic housing and the plunger-armature. 
     The foregoing non-magnetic material interposed between the plunger and pole members precludes attainment of a truly closed magnetic circuit. The housing wall-thickness forms plural gaps across which the flux must pass, on entering and leaving the armature. It is necessary that the housing be of appreciable wall thickness to withstand the fluid or hydraulic forces often encountered, a typical brass or bronze housing being 0.026 inch thick for a fluid pressure of 125 P.S.I. 
     Any such interruption of an otherwise closed magnetic circuit has the twofold effect of causing major reduction of solenoid impedance, and in total flux flowing in the system. Thus for a given applied voltage, high current will flow, coupled with a major weakening of the mechanical pull-force attained by the armature. Ringshaded poles are ineffective across an interposed gap, which has caused wide usage of long-stroke solenoids having tubular poles, thus adding further to the foregoing power loss difficulties. High input wattage, rapid temperature rise, and the frequent need for resort to intermittent-duty ratings have been commonly accepted as unavoidable incidences of wet-armature valve constructions heretofore available. 
     Efforts to overcome those limitations have included the use of high strength non-magnetic materials such as 18-8 stainless steel for thinner housing wall constructions, and also at increased manufacturing cost, the use of immersed magnetic poles provided with annular shading rings. But these methods along have provided only slight gains in electro-magnetic efficiency. The problem is clearly one of reducing or eliminating the armature series gap; of providing a short-stroke armature characteristic; and of reducing the susceptibility of the solenoid structure to the power-loss and heating effects of induced circulating or eddy currents. 
     SUMMARY OF THE INVENTION 
     In accordance with this invention I have found that in fluid control valves of the present type, the cup or guide housing the armature may be constructed of thin ferro-magnetic material such as A.I.S.I. type 430 stainless steel, chosen from the group known as &#34;straight chrome ferritic.&#34; This material enables design of thin wall housings with adequate strength to withstand fluid pressures of the order of ten atmospheres or more. The use of a magnetic material virtually eliminates the magnetic series gap invariably present in previous wet-armature valve constructions. Moreover, the thin-walled housing in combination with a piston-like armature and a highly efficient unitary exterior magnetic shell, yields a solenoid structure of low reluctance with a consequent high flux value flowing in the core and armature. Exciting magnetomotive force and input wattage requirements are therefore diminished, for a given initial `unporting` or steady state holding load. 
     An axial valve stem integral with the armature has a conical tip arranged for sealing engagement with a fluid orifice in a resilient valve-seat annulus. The orifice and associated fluid duct serve a flow limiting function, the diameters thereof varying in accordance with the intended fluid pressure and flow rate. The conical tip cooperates with the small orifice diameter thereby provided to place upon the armature a minimum of fluid load or &#34;unporting&#34; pull force. It further enables a short-stroke or small-gap solenoid having a relatively high electrical impedance value. Open gap inrush current, and steady-state energized input wattage are correspondingly reduced for a given fluid pressure and flow rate. 
     A secondary benefit in magnetic efficiency is provided by the use of a unitary formed box rectangular shell, external to the exciting coil, and formed from a strip of ferro-magnetic material. The ends of the strip are in retained abutting engagement at the point of attachment of the internal stationary core member. This arrangement breaks a common eddy-current path around the core end, and enables a significant reduction in eddy-current heating in that area. 
     The foregoing elements of novelty taken separately or in combination, have the effect of reducing or elimination of the magnetic gaps or reluctances invariably encountered in previous wet-armature valves, with the resultant large increase in total flux, and in flux linking the armature. Eddy current heat losses are reduced, and fluid loads on the armature are greatly reduced, for a given value of fluid pressure, and fluid flow. The attainable decrease in current values, input wattage, and temperature rise enable major savings in the weight, size, and cost of the copper winding and solenoid structure required for a given fluid load and flow rate. 
     It is accordingly an important object of the present invention to provide for a fluid control valve of the immersed armature type, a solenoid construction having an essentially &#34;gapless&#34; or closed magnetic circuit with resulting improvement, at reduced cost, in electro-magnetic efficiency and mechanical force attained by the armature, for a given electrical input. 
     Another object is to provide for a magnetic fluid valve of the above type, a construction wherein for a given fluid load on the armature, the required electrical power is reduced whereby the usage of copper in the solenoid winding may be greatly reduced. 
     A further object is to provide for a magnetic fluid valve of the above type, a solenoid and magnetic circuit construction of new and novel character such that the required electrical input power per unit of fluid pressure or of fluid flow is decreased, whereby the heat dissipation and time rate of temperature rise of said solenoid is reduced over prior constructions. 
     Another object is to provide for a magnetic fluid valve of the immersed armature type, a solenoid and magnetic circuit of new and novel character enabling increased armature force, and increased fluid loads, pressures, and flow rates, for a given value of electrical input power. 
     A still further object is to provide for a magnetic fluid control valve, an armature housing constructed of ferro-magnetic material having the property of hysteresis, to coact with a phasesplitting core of the type described in my prior application Ser. No. 783,035, Filed Dec. 11, 1968, now U.S. Pat. No. 3,553,618, issued Jan. 5, 1971. In this combination, phase shifting effectiveness is enhanced with resulting further improvement of the solenoid magnetic efficiency. 
     Another important object is to provide an electro-magnetic construction of high efficiency for use in hermetically sealed devices commonly used in vacuum or explosion-proof systems wherein complete isolation by an impermeable barrier is requisite between the electrical energizing and magnetically actuated elements of said devices. 
     An additional object is to provide a solenoid construction wherein a housing or guide for the armature is constructed of ferro-magnetic material whereby the distribution of magnetic flux in and around the armature is modified to yield an improved force-versus-distance characteristic, to thereby increase the wide-gap pull value attained by said solenoid. 
     Yet another object is the provision in a flow control valve of an armature and a closely fitting housing which is characterized by a motion inhibiting piston dash-pot effect, which serves to reduce the tendency of the valve to produce hydraulic noise or water-hammer effects. When the valve is utilized for liquid flow control, the damping effect reduces the need for magnetic phase-splitting means to avoid magnetic noise or &#34;buzz&#34;. 
     Another important object is to provide in a fluid flow control valve a combination construction wherein an axially movable valve member cooperates with a small diameter fluid orifice having flow-limiting properties, thereby enabling a short-stroke solenoid structure having a high electrical impedance characteristic, thus enabling operation at low current and wattage levels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The foregoing and other objects and advantages of the invention will become apparent from the following description, and the accompanying drawings of a preferred embodiment, in which: 
     FIG. 1 is a median sectioned view of a fluid valve embodying solenoid and flow-controlling elements according to this invention. 
     FIG. 2 is a median sectioned view of an alternative solenoid construction according to my prior application Ser. No. 783,035, now U.S. Pat. No. 3,553,618 for &#34;Phase Splitting Core,&#34; in combination herewith. 
     FIG. 3 is an enlarged partially sectioned view showing key details of the core assembly of FIG. 2. 
    
    
     PRINCIPLES OF OPERATION 
     Wet armature valve constructions heretofore available were presumably based on the premise that the use of magnetic material as an armature or plunger housing would act adversely as a magnetic shunt, bypassing a large portion of the available flux, thus reducing the tractive force exerted by the plunger. 
     A basis of this invention is my discovery that a valve solenoid having an armature housing constructed of ferromagnetic material of relatively thin wall section behaves in an unexpectedly opposite manner to that previously postulated. The magnetic pulling force per unit of input power is greatly increased over the values obtainable with the use of non-magnetic prior art armature housings. 
     This apparently anomalous behavior is explainable; first by the virtual elimination of the dual magnetic gaps, with a major increase in flux flowing in the magnetic circuit due to decrease in the reluctance thereof; and secondly by the fact that pole-to-pole shunting of flux by the housing wall has a limited adverse effect because the thin ferro-magnetic housing wall becomes saturated at relatively low values of flux. As a result of the above saturation effect, the predominant balance of the available flux therefore flows through the best alternate magnetic path which in the present case is represented by the plunger armature, as will be hereafter described. 
     I have ascertained that the relatively small loss of flux due to parallel shunting by the housing wall is more than compensated by the large increase in total magnetic circuit flux due to the above mentioned elimination of the housing-wall gaps. The resulting tradeoff yields a substantial net gain in armature force available per unit of electrical input power. I have observed gains in excess of 100% during tests of the present invention. 
     The combination of an armature and a closely fitted ferromagnetic housing yields a substantial further benefit whereby the armature stroke vs. force characteristic is modified in a manner favoring the initial, or wide-gap pull value. This is a desirable characteristic in fluid valve usage, and in some other applications. This effect is believed explainable as a modification of flux distribution in and around the armature by the close proximity of my ferromagnetic housing, with said flux distribution varying progressively from the initial or open-gap armature position, to the sealed or closed gap position. 
     The above described combination of a piston-like armature operating in a closely fitting housing, whether of magnetic or non-magnetic material, provides a useful damping or motion inhibiting effect, when immersed in a liquid medium. Magnetic &#34;buzz&#34; is reduced, and the velocity of movement of the armature is restricted, a material aid in reducing liquid line-surge, and other undersirable valving transient effects. 
     A widely recognized principle of magnetic circuit design where minimum magnetic reluctance is sought, is the iron-torus core. It is a simple iron ring of generous cross-section, the exciting coil being wrapped around an arcuate portion thereof. The ring has no joints or iron-to-iron junctions transverse to the flux path. Any such junctions introduce an inherent cumulative reluctance or demagnetizing force offsetting a portion of the available exciting m.m.f. Such junctions should be held to a practical minimum. 
     In A.C. service, such a torus is subject to undesirable heatrise and watt loss caused by induced eddy-currents flowing througout it&#39;s cross-section. This effect may be largely overcome by lamination, the torus being sub-divided into a stacked series of laminar iron rings totalling the cross-sectional area of the original. A useful first-approximation of the foregoing is to divide the torus into two rings arranged in a &#34;figure eight&#34; manner, with the exciting coil wrapped through the two toroids in the area of tangency. This establishes two separate magnetically parallel flux paths of reduced eddy-current susceptibility, having a common exciting coil, the flux being confluent therethrough. My magnetic circuit including the outer unitary magnetic shell as disclosed herein embodys the substance of the foregoing two paragraphs in a novel form which is simple, low in cost, and of relatively high magnetic efficiency suitable for A.C. service. In order to avoid flux restrictions and maintain a uniform crosssection throughout the divided magnetic circuit, the flat ferrous strip forming the outer shell is of a thickness approximating one quarter of the diameter of the cylindrical core. Similarly, the width of said strip is at least 1.8 times the core diameter. 
     The above ferrous strip is formed into a closed rectangular loop having it&#39;s abutting ends coinciding with the axis of the stationary cylindrical core at it&#39;s point of attachment to the outer loop. This arrangement interrupts a major eddy-current path otherwise existing in the outer shell, in an area of high flux concentration surrounding the attached end of the cylindrical core. Heat loss is thereby minimized in that area. 
     The flow controlling or valving arrangement as disclosed herein has an important relationship to the electrical and magnetic performance of the solenoid portion of the device. The resilient valve-seat member has a flow passage therethrough of the smallest diameter appropriate to the desired fluid pressure and flow rate, thus serving a flow-limiting function. The conical valve member seals the small orifice thus provided with a minimum depth of entry thereinto, for a given flow capacity. The deenergized armature polar gap may thus be held to the smallest axial dimension consistent with a given or chosen flow rate, enabling a high reactance or high impedance solenoid characteristic. Opengap inrush current values are thereby reduced, enabling construction of the exciting coils with copper wire of reduced gauge, and with a reduced number of convolutions for a given flow capacity and exciting line voltage. Major economies in copper wire usage are enabled by this element of novelty. 
     The small orifice arrangement above described has a major effect on solenoid size, input wattage, and pull force required. The maximum open gap or initial pull force required is the sum of the bias spring force, and the fluid pressure load operating on the valve plunger in a sealing direction. This fluid &#34;unporting&#34; force is numerically the product of the orifice area, and the net unit differential fluid pressure operating on that area. It follows that for a given fluid pressure, the unporting force varies linearly with orifice area, or proportional to the square of orifice diameter. It is thus apparent that the use of a minimum orifice size consistent with a given flow requirement, enables avoidance of excessive armature pull, and solenoid input wattage requirements. 
     The foregoing relationship is valid for a resilient valve seat annulus arranged for a fixed orifice size as shown, or as arranged for a pressure-distortable variable orifice flow control function commonly applied in valves of the present type. 
     U.S. Pat. No. 2,454,929 issued Nov. 30, 1948, illustrates a typical prior art arrangement for obtaining the variable orifice function by simple modification of the cavity wherein the resilient annulus is seated. 
     It will be apparent to those skilled in the art that many changes may be made in the arrangement of parts and details of construction of the solenoid devices described herein without departing from the spirit of the invention as expressed in the appended claims. Moreover, it will be understood that the applications shown as applied to flow controlling fluid valves are by way of illustration only, and that the several advantages of the invention are applicable to other solenoid devices such as relays and clutches, as well as to hermetically sealed and explosion-proof solenoid actuated devices requiring a vapor or fluid barrier. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring more particularly to the drawings wherein similar reference characters designate corresponding parts throughout the various views; FIG. 1 is a median sectional view of a solenoid flow control valve according to the present invention in which cylindrical armature 1, and bias spring 2, are enclosed by armature housing 3, said housing being optionally constructed of ferro-magnetic or non-magnetic material, and so dimensioned as to permit free axially slidable motion therein by plunger armature 1. Armature 1 is formed with a projecting &#34;pintle&#34; or valve stem portion 4, having at it&#39;s lower end an integrally formed conical valve portion 5 designed to enter and seal fluid orifice 6, under the influence of bias spring 2, when the valve is deenergized or closed. Bias spring 2 is of the conical compression type having it&#39;s large diameter upper end supported by annular shoulder 11 formed in housing member 3, and having it&#39;s small diameter lower end engaged with valve stem 4, by snap-ring 7, or other suitable means. Compression spring 2 thus biases armature 1 in a downward direction to seal fluid orifice 6 when the solenoid is deenergized. When so biased the upper surface of armature 1 is separated from the inner abutting surface of housing guide cup 3, thus forming working gap 8 which allows upward motion of armature 1, when the solenoid is energized. 
     Valve body 9, formed of plastic or metal is provided with inlet pipe fitting 14, and outlet tubular duct 22, which are connected by integrally formed internal fluid passages with the appropriate sides of the valving means. Inlet 14 is provided with an annular recess 16 adapted to receive wire mesh inlet strainer 15 which serves to prevent fluid borne particulate matter from entering the valve. Inlet 14 is connected by fluid duct 17 to annular fluid channel 18, whereby the incoming fluid is conducted to the pressure chamber formed by the inside of the conical portion 12 of plunger housing 3. The peripheral flange portion 13 of housing 3 is pressed into sealing contact with elastic sealing ring 20 by the downward force exerted on annular pressure plate 19 by a number of appropriately spaced assembly screws, not shown. Fluid seal ring 20 formed of an elastomer is seated in annular channel 21 formed in valve body 9. Elastic ring 20 thus forms a compressibly deformed seal which confines the pressurized incoming fluid to the inside of said pressure chamber. 
     Outlet fitting 22 is formed by a downward projecting portion of valve body 9, generally tubular in form and positioned coaxial with armature plunger 1. Outlet fluid duct 23 extends upward to connect with fluid passage 24 which passes vertically through annular valve seat member 25. Valve member 25 is molded of elastomeric material and is dimensioned to fit snugly in annular recess 26 formed in valve body 9 coaxial with fluid duct 23, and forming the upper extremity thereof. Fluid orifice 6 forms the valve-seat proper, being normally sealed by the engagement thereagainst of valve cone 5, when the valve is deenergized. Fluid passage 24 forms a flow limiting restriction, the diameter being appropriate to the fluid pressure, viscosity, and flow rate desired. 
     The magnetic solenoid is assembled over the cylindrical cup portion of housing 3, coaxial therewith. The solenoid is comprised of copper winding 27 on insulating spool 28, and is connected to the external power source by terminals or leads 29. The winding encloses soft iron core piece 30, and is enclosed by mild steel magnetic outer shell 31 to which core piece 30 is attached at top center 32. Outer shell 31 is formed from an elongated rectangular strip of mild steel formed into a closed box-like rectangular loop having the line of abutment of the strip ends at top center, substantially at the axis of core piece 30, as described elsewhere herein. The abutting engagement may be mechanically retained by suitable means such as interlocking dovetail, or spot welding at the corners, but should preferably not be through welded the full length of the abutment. Magnetic shell 31 has in its lower surface a bore or hole dimensioned to fit snugly over the cylindrical cup portion of housing 3 which extends into the winding spool 26 to abut the lower end of core 30, thus completing the magnetic circuit linking solenoid 27 in an effectively closed manner. A dimensional length of core 30 equal to 75% of the length of solenoid winding 27 has yielded favorable results in tests of the present invention. 
     FIG. 1 depicts the valve in the deenergized state with armature 1 in the downward position thus forming axial gap 8 separating armature 1 from the diaphragm portion 33 of housing 3. When housing 3 is constructed of ferro-magnetic material such as A.I.S.I. 430 stainless steel, a high value of performance is obtained, the mode of operation being postulated as follows: Upon energization, the magnetomotive force deriving from the current flowing in solenoid 27 gives rise to a concentration of flux flowing axially in the thin cylindrical wall of housing 3, with a resulting saturation of the wall in the area surrounding gap 8. The excess of available flux beyond the saturation level is thus diverted radially through the wall of housing 3, thence axially through armature 1, across gap 8 and through diaphragm 33 to core 30. The armature thus develops a pulling force which causes it to rise, compressing spring 2 and opening passage 24 to allow the flow of fluid therethrough. 
     It can be noted that the upward travel of armature 1 causes working gap 8 to vanish, with the previous gap space then becoming occupied by the upper portion of armature 1. This completes a low reluctance link in the solenoid magnetic circuit of relatively large cross-section and low susceptibility to saturation, with the solenoid reactance rising to a relatively high value. A result is a re-distribution of flux whereby the greater part of the total flux passes axially through armature 1, with the lesser remainder flowing axially in the thin wall of housing 3 in the area around gap 8. A preponderance of the available flux will thus flow through armature 1 under both open-gap and closed-gap conditions. 
     It is therefore postulated that the housing wall operates in two differing sequential magnetic states, varied by the motion or position of armature 1, acting as a magnetic switch. The housing wall becomes saturated by the high inrush current at energization followed by transition into a less saturated state as armature 1 reaches the full stroke or zero gap position, with flux re-distributing and with coil current dropping to the lower steady-state value. Both states result in the flow of major values of flux into and through the armature thereby causing it to develop usefully high values of mechanical pulling force. 
     The arrangement of armature 1 with a closely fitted housing 3, as disclosed in FIG. 1 provides further functional benefits resulting from an inherent dash-pot liquid damping effect. Said damping serves to reduce the tendency of A.C. solenoids to produce intermittent pull-forces, and buzzing sounds, when phase-splitting means are not employed, as in FIG. 1 wherein core piece 30 is of the simple cylindrical type. The diametral clearance between armature 1 and housing 3 may be varied to control the damping and rate of movement of armature 1, as the controlled fluid enters and leaves gap space 8. 
     The force and rate of bias spring 2 is an important design factor, since spring force and the above mentioned armature diametral clearance are basic in determining the rate at which armature 1 moves downward after de-energization of solenoid 27. The above damping effect may be further modified for fluids of varying viscosity by providing an axially aligned fluid passage through armature 1, or by providing axially aligned leakage grooves in the periphery of said armature. The fluid damping serves beneficially to reduce the tendency of the valve to produce hydraulic hammer or other fluid surge and transient effects arising from rapid armature motion. 
     FIG. 2 depicts a solenoid construction in which a phase-splitting core of a self-shading class disclosed in my U.S. Pat. No. 3,553,618 is employed in lieu of the plain cylindrical core 30, of FIG. 1. This combination yields a further major improvement in magnetic efficiency and attainable pull-force per watt over the values attainable with said cylindrical core. The solenoid construction of FIG. 2 has structural and magnetic features in common with FIG. 1, and is directly usable therewith, the related valve description thus being applicable to FIG. 2. 
     The two-piece core 34 and 35 makes use of the discovered fact that hysteresis and eddy-currents in flux carrying core members may be economically and efficiently used to obtain phase retardation and resultant phase-splitting in A.C. devices in lieu of shading rings heretofore used for that purpose. The core assembly including soft iron outer sleeve 34, and mild steel inner cylindrical member 35 is shown in section in FIG. 2, and also in enlarged section in FIG. 3 which discloses the annular and peripheral gap means which contribute to the phase-splitting function, and high magnetic efficiency characteristic of the core assembly. 
     Outer cylindrical core member 34 is the leading phase flux path, being designed to introduce a minimum of phase retardation of the flux wave flowing therein. To that end it is constructed of a low hysteresis material such as silicon steel or annealed ingot iron. It is further provided with longitudinal slot 36 which extends the full length of said sleeve thus interrupting the phase retarding circumferential circulating current which would otherwise flow therein. The flux wave flowing in sleeve 34 is thus substantially in phase with the alternating magnetomotive force established by the current flowing in exciting coil 27. 
     Inner cylindrical core member 35 is the lagging phase or retardant flux path, being designed to obtain a substantial value of flux wave retardation by the combined effects of hysteresis and internal circulating currents. Inner member 35 is constructed of a mild steel such as A.I.S.I. C-1117 which is characterized by a moderate degree of inherent hysteresis or remanence, such as to cause an effective value of phase retardation of the flux wave flowing therethrough. Moreover, member 35 is designed as an unbroken cylindrical body, subject to the flow of circular induced eddy-currents throughout its length. Said eddy-currents operate magnetically to oppose changes in the instantaneous flux value flowing in said member 35, thus retarding the phase of the resultant flux wave, in addition to the hysteresis phase retardation aforesaid. The resultant angular phase shift is thus a composite value which may be considered as the vector sum of the two phase lag angles obtained separately from the retarding effects of magnetic hysteresis and eddy-current flow. 
     An annular gap 37 provides a magnetic separation of the two members 34 and 35, to avoid inter-phase shunting or commingling due to close proximity. In FIG. 3, gap 37 is produced by forming member 35 with a step or shoulder 38, thus slightly reducing the diameter of the lower portion of member 35. A shoulder radial dimension of 21/2% of the outside diameter of sleeve 34 has yielded satisfactory phase separation. The axial length of gap 37 is relatively uncritical, optimum length appearing to be between 70% and 90% of the length of sleeve 34. The gap space thus formed may be filled with a plastic or solid insulsting material if desired. 
     During the development of the present invention, a non-magnetic housing 3 was constructed for comparison purposes. It was in all dimensions identical with the foregoing ferro-magnetic housing but was in accordance with prior art valve practice, being constructed of 18-8 stainless steel. Tests performed with this nonmagnetic housing in the valve construction of FIG. 1 disclosed a substantial performance advantage in terms of pull-force per watt, over a commercial prior art water valve. The test values are disclosed in a comparative performance table which follows below. This starting improvement is believed to derive from the novel structure and elements as disclosed in combination including the short-gap solenoid; the split-path magnetic circuit having low reluctance and eddy-current susceptibility; and the above described liquid motion-damping effect. The foregoing is an initial improvement which should be taken into account in evaluating the further advantages contributed by my ferro-magnetic armature housing, and phase-splitting core. 
     In the absence of mathematical expressions reliably applicable to the present invention, an experimental test program was undertaken to provide a basis for mathematical definition, and to establish optimum or near-optimum dimensions, materials, and size ratios for a water valve application similar to FIGS. 1 and 2. A flow rate of 1.0 g.p.m. was chosen at a water gauge pressure of 60 p.s.i. with operation on 115V. 60H. A.C. Diameter of fluid passage 24 was established as 0.072 inch, and an armature travel of 0.063 inch was chosen, thus setting the axial dimension of armature gap 8 at 0.063 inch. An armature open-gap (inrush) pull requirement of 10 oz. was established to allow a reserve over the maximum load values to be met. 
     The following dimensions and size ratios were established: 
     Coil spool 28, length o.a. 0.820 inch, winding length 0.760 inch. 
     Coil 27, 3900 t. -39 or 40 B&amp;S ga. copper, weight 11 or 8 gms. 
     Core 30, 0.600 inch long, 0.437 inch dia., magnetic ingot iron. 
     Core sleeve 34, 0.600 inch long, 0.437 inch dia., 0.062 inch wall, ingot iron. 
     Core 35, 0.600 inch long, dia&#39;s. 0.296 inch &amp; 0.316 inch, C-1117 c.r.s. 
     Housing 3, cup 0.437 inch o.d., 0.405 inch i.d., 430 magn.s.s. &amp; 18-8 s.s. 
     Magn. shell 31, 12 ga. × 0.812 inch w. 1012 h.r.s. Butt at top center. 
     Armature 1, dia. 0.395 inch to 0.400 inch, plunger length 0.325 inch, 430 s.s. 
     For evaluation purposes a numerical performance factor of merit &#34;P&#34; was devised as an expression of open-gap pull in ounces attainable, per watt of steady-state electrical input. For the present examples &#34;P&#34; becomes 10 (oz) divided by the measured input watts (w.) for the closed gap steady-state condition. A commercial prior art water valve of similar capacity was included in the test series as a comparison base, with the supply voltage adjusted to obtain 10 oz. of armature pull at inrush. At that voltage it consumed 16 watts steady-state, for a value P = 0.625. 
     Values obtained for the present invention were: 
     Assembly of FIG. 1, non-magnetic housing 3, w. = 9.50, P = 1.05. 
     Assembly of FIG. 2, non-magnetic housing 3, w. = 7.80, P = 1.28. 
     Assembly of FIG. 1 with magnetic housing 3, w. = 5.85, P = 1.71. 
     Assembly of FIG. 2 with magnetic housing 3, w. =3.10, P = 3.22. 
     The use in this invention of hysteretic materials has been found not to cause difficulties with &#34;sticking armature&#34; due to remanence or residual flux. Annealing of outer shell 31 after forming is desirable, however, attention to the force and rate of spring 2 has provided freedom from residual flux problems. It thus appears that magnetic housing 3 serves beneficially as a saturable magnetic shunt, bypassing around armature 1 a major portion of the residual flux arising in parts such as core 30, shell 31, or core 35. This is a further benefit accruing to the present invention. 
     From the foregoing it will be apparent that I have provided novel, simple, and economical means of attaining the objects and advantages recited.