Liquid filter with chip detecting means

A device using intentionally introduced centrifugal force to direct particles suspended in a liquid to peripherally arranged contact members and to detain them there through the static pressure caused by the peripherally moving liquid. The device separates the ferrous, magnetizable, from the nonferrous, not magnetizable, particles by providing a magnetic capturing unit having a diameter smaller than that of the aforementioned contact member arrangement, so that ferrous particles will be retained by magnetism and so indicated, while nonferrous ones will be detained by the radially more outwardly located contact members and indicated accordingly. Individual indications of, especially nonferrous particle accumulations, are provided for at least two particle magnitude ranges.

BACKGROUND 
Various patents of prior art teach methods and devices for the detection of 
electrically conductive particles suspended in a moving, electrically 
nonconductive liquid. Especially important is the detection of particles 
in lubrication systems resulting from the wear and tear of mating 
mechanical moving parts, such as in internal combustion engines, turbines 
and comparable ground support and airborne power plants and accessories. 
Because particles of the described nature may, firstly, be of either 
ferrous or nonferrous substances, different methods must be employed to 
capture all those particles; secondly, considering the possible presence 
of physically large particles of either composition, a separate and 
additional detection element appears to be required. 
These teachings, which do not cover the entire domain of the particle 
detection practice, include, but may not be limited to, the following 
examples and references, presenting at least one typical antecedent for 
each individual function of possible relevance: 
______________________________________ 
Bowser 1,176,732 March 28, 1916 
(none) 
Matheson 2,010,435 Aug. 6, 1935 (210-43) 
Lincoln 2,016,642 Oct. 8, 1935 (183-2.7) 
Schrader 2,349,992 May 30, 1944 (175-183) 
Scott 2,375,826 May 15, 1945 (92-28) 
Bourne, Jr. 
2,429,920 Oct. 28, 1947 
(177-311) 
Bourne, Jr. 
2,450,630 Oct. 5, 1948 (200-52) 
Vokes 2,544,244 March 6, 1951 
(210-166) 
Botstiber 2,704,156 March 15, 1955 
(210-1.5) 
Botstiber 2,936,890 May 17, 1960 (183-86) 
Winslow 2,952,330 Sept. 13, 1960 
(183-2.5) 
Botstiber 2,983,385 May 9, 1961 (210-222) 
Hurby 3,067,876 Dec. 11, 1962 
(210-65) 
Winslow 3,127,255 Mar. 31, 1964 
(55-178) 
Botstiber 3,317,042 May 2, 1967 (210-86) 
Botstiber 3,432,750 Mar. 11, 1969 
(324-41) 
Kudlaty 3,628,662 Dec, 21, 1971 
(210/136) 
Miller 3,686,926 Aug. 29, 1972 
(73/61R) 
Miller 3,878,103 Apr. 15, 1975 
(210/243) 
Tauber 4,199,443 Apr. 22, 1980 
(210/85) 
Tauber 4,282,016 Aug. 4, 1981 (55/204) 
______________________________________ 
The foregoing enumeration of prior art indicates that, while specific 
significant features are present in various teachings, the operationally 
required wide performance characteristics of the subject invention can not 
be observed in that prior art. 
Reviewing the prior art more selectively, in U.S. Pat. No. 3,317,042 both a 
method and a device are described for the detection of electrically 
conductive particles in a moving liquid. In that invention, a screen, or 
filter is used to guide the particles towards electrical contacts which, 
when bridged by one or more conductive particles, will close an electric 
circuit. Other patents, such as U.S. Pat. Nos. 3,686,926 and 3,878,103 use 
a screen in which the fibers are of conductive materials, alternatingly 
connected to electrical lines of different polarities and separated from 
each other by insulating members. All these devices have the deficiency of 
insufficient contact pressure of the particles on the electrically 
conductive members of the detecting device; the particles are small and 
light in weight; buoyancy in the liquid acts to aggravate this condition 
and as a result, the contact pressure is too low to produce a reliable 
electric circuit. For ferrous, i.e., magnetizable particles, this 
deficiency can be alleviated by combining the detector contacts with a 
magnet, as in U.S. Pat. Nos. 2,936,890 and 3,432,750. Of these, the former 
applies to ferrous particles only, the latter uses the magnetic effect to 
attract ferrous particles, while nonferrous particles are still subject to 
the above-mentioned deficiency in detection. The devices based on 
alternatingly connected screens do not offer the contact pressure 
increasing effect of magnetism; they detect ferrous as well as nonferrous 
particles indiscriminately, with the above-mentioned shortcoming in 
contact conductive effect. Also, they have the disadvantage of requiring 
large areas of such alternatingly connected, separately insulated grids or 
weaves, with the resulting high manufacturing cost, unstable construction 
and difficulty in identifying and removing particles that have become 
lodged in the grid, or weave. 
Most applications for this type of device relate to fluid systems, such as 
the lubrication oil circuits of engines and mechanical power 
transmissions, or the liquid systems of hydraulic power and control units. 
In these, it is desirable to ignore the very small particles produced by 
normal wear of moving parts, while capturing and indicating the presence 
of larger particles which are either of alien nature to the system, or are 
indicative of incipient gradual deterioration and eventual failure of such 
moving parts. The screens used in the above-mentioned patents may be 
selected to pass fine and harmless wear particles, while retaining for 
indication the larger particles. These, however, will then be subject to 
the above-mentioned problem of insufficient electrical contact pressure 
and conductivity. 
In U.S. Pat. No. 4,282,016 a device is described, which separates particles 
and air from a flowing liquid by subjecting both substances to a 
centrifugal force of rotation of the liquid. In this system, the 
separating effect for small, normal wear particles is absent. A particle 
sensor introduced into a device according to that patent will not indicate 
nonferrous particles, but will have to rely on the magnetic effect for 
ferrous particles only, such as in U.S. Pat. No. 2,936,890. It would be 
possible to equip such devices with self-closing particle sensors, such as 
described in U.S. Pat. Nos. 2,704,156 and 2,983,385. The above-mentioned 
particle detectors of the screen type, namely, U.S. Pat. Nos. 3,686,926 
and 3,878,103, do not offer the advantageous use of such self-closing 
sensor arrangements, which make them impractical for removal and 
inspection of captured particles, a feature which is of utmost importance 
in all systems which do not permit shut-down and drainage of the fluid 
system during operation. 
SUMMARY OF INVENTION 
This invention extends to a liquid filter with chip or particle detection 
means for stationary, mobile and airborne use in crank cases, gear cases, 
transmissions, oil sumps, tanks, in conjunction with lubrication systems 
for mechanical equipment which utilize a fluid such as oil. 
It is the objective of this invention to effect improved contact pressure 
for conductive particles on the detector contacts, in order to obtain 
reliable electrical circuit action for the operation of an indicating 
system. 
It is a further objective of this invention to obtain separate electrical 
signals for ferrous and for nonferrous particles. 
It is another object of this invention to capture excessively large 
particles and to indicate their presence accordingly and separately. 
It is yet a further objective of this invention to make possible a 
structurally strong and compact construction of the device in its 
entirety. 
It is another objective of this invention to make possible the removal of 
the captured ferrous and nonferrous particles without spillage or drainage 
of the fluid system and without interrupting the movement of the liquid. 
Still another objective of this invention is to provide additional, 
desirable features such as the removal of air entrained in the liquid and 
the prevention of obstruction of flow in case the system becomes 
excessively saturated with solid particles. 
Additional advantages of the subject improvement--per se--and over prior 
art will become more apparent from the following description and the 
accompanying drawing.

DETAILED DESCRIPTION 
Referring now to the drawing, wherein like reference numerals designate 
like or corresponding parts, and more particularly to FIGS. 1, 2 and 3, 
illustrating the method with which the first listed objective of this 
invention is accomplished, the filter 20 has an upper opening 22 in its 
substantially cylindrical metal housing 24, which is closed at its lower 
end by a bottom piece 26 of, in this example, an electrically 
nonconductive material having various annular grooves formed therein and 
equipped at its upper end with an annular top member 28 of, in this case, 
an electrically nonconductive material having various annular grooves and 
holes formed therein. A cylindrical inlet unit 30 having a cylindrical 
center piece 32 mounted in its center hole is, in turn, mounted in the 
center hole of said annular top member 28. The center piece 32 is held in 
place through a plurality of helically-shaped vanes 34 positioned radially 
between said inlet unit 30 and said center piece 32, so that the liquid 
entering at the upper opening 22 and flowing through the housing 24 will 
be imparted a rotary centrifugally and helically downward motion as 
indicated by the flow path symbol and arrow "A", tending to drive the 
liquid towards the cylindrical filter or strainer 36, through which the 
liquid, together with particles smaller than the strainer openings may 
pass into the space between strainer 36 and housing 24, the latter 
extending into an outlet opening 38. In its rotation within the 
cylindrical strainer 36, the liquid drives solid particles towards that 
strainer, where they will move in a helical path inside the strainer 36. 
At one position within that strainer, near its inner circumference, a pair 
of rods 40 and 40A of electrically conductive material is placed 
essentially parallel to the strainer axis whereby, for example, the rod 40 
is the one radially near the strainer 36 and the rod 40A radially near the 
rod 40. The distance between the rods 40 and 40A is selected to be of a 
magnitude to conform to the smallest size of particles to be detected. The 
rods 40 and 40A are supported and held in place by a number of spacer 
rings 42, which consist of an electrically nonconductive material, and 
lodged in the through-holes 41 formed at appropriate locations in said 
spacer rings 42, in recesses 44 in the bottom piece 26 and through-holes 
46 formed in the top member 28. The strainer 36 is arrested in groove 48 
of the bottom piece 26 and in the groove 50 of the top member 28. The 
tangential component of the essentially circular movement of the liquid 
pushes particles against the rods 40 and 40A, effecting a contact pressure 
which depends on the aspect area of the particles and the tangential 
velocity of the liquid. The particles will come to rest on the spacer 
rings 42 and remain there, being pressed against the conductive rods 40 
and 40A. As they bridge the space between the rods, as shown for one 
particle aggregation 52 in FIG. 3, they close the electric circuit 54 
energized by the source 56, causing the indicator lamp 58 to light or to 
effect another alarm or signal. 
In principle, one such pair of rods 40 and 40A would suffice for the basic 
effect described above, but design considerations may indicate the 
desirability of more than one set of rods within the circumference of the 
strainer, or more than two rods in one set; for example, FIG. 3 shows four 
sets of rods within the circumference. 
Another modification and possible simplification is the mounting of only 
one rod 40 at each position along the stack of spacer rings 42, each such 
rod being spaced apart radially and inwardly from the strainer 36 for a 
distance suitable for the capturing of a predetermined minimum particle 
size; to indicate an accumulation of electrically conductive particles for 
this arrangement, each single rod 40 has to be connected with one pole of 
an electric alarm circuit, whereas the strainer 36 will be connected with 
the other electric pole of the alarm system (not shown), to indicate the 
collection of particles between a rod 40 and the strainer 36. 
The sets of rods 40 and 40A may be electrically connected in parallel, the 
effect of which will be that one particle bridging one gap of any one rod 
sets will close the electric signal circuit. This will be the desired 
function for certain systems, that are considered sensitive to even the 
smallest amount of metal contamination. However, in some systems, it is 
desired to get a signal only after more than one particle has been 
retained. Such an effect can be obtained with great probability by 
connecting two or more of the rod sets in series. The electric circuit 
will then be activated only after each of these two or more rod sets have 
been bridged by particles. 
If more than one pair of rods 40, 40A is employed, other than just straight 
rods parallel with each other and the strainer and in electrical 
connections varying from those described in the foregoing may be selected, 
without requiring additional guidelines. 
The principle is, in any such arrangement, the use of alternately connected 
rods, or wires, or conductive, protruding members to obstruct the free 
movement of particles driven by the rotating motion of the liquid. 
Obviously, the foregoing method and equipment does not differentiate 
between the capturing of ferrous and nonferrous particles. 
It is sometimes desired and required to indicate the presence of ferrous 
and nonferrous particles separately. For such a requirement, the principle 
of this invention may be extended to provide for one sensing arrangement 
to attract ferrous particles, while nonferrous particles are detected by 
the above-mentioned circulation of the liquid and its effect of holding 
particles against a gap formed by two conductors connected to alternate 
electric polarities. Such an arrangement is shown in FIG. 4. The liquid 
enters in the same manner as in FIG. 1, through the upper inlet 22 of the 
filter 20A having a rotation-inducing system of guide vanes 34. The center 
support 32A is extended downward towards the outlet 38. Near the lower end 
of the center support 32A, its diameter increases to match the diameter of 
a first disc 60 of magnetizable material, which extends in its center with 
a downwardly directed pin 62. The disc 60 abuts with a magnet 66 which, in 
this case, is shown as an electrically insulating, ceramic, permanent 
magnet, as used in my U.S. Pat. No. 2,936,890. At a lower surface, a 
second disc 64 of a magnetizable, ferrous, material is arranged. The 
magnetic axis of the magnet 66 is oriented axially, i.e., through the 
thickness of the magnet 66, so that the discs 60 and 64 will form pole 
pieces of opposite magnetic polarity, producing a magnetic field over the 
cylindrical surface of the magnet 66. This magnetic field attracts ferrous 
particles in the liquid, making them adhere to the pole pieces formed by 
the discs 60 and 64 and close the gap between them, thus activating a 
signal circuit 68F, indicating the presence of ferrous particles. 
The nonferrous particles will remain unaffected by the magnetic field 
provided by the above-described component parts; they will circulate with 
the liquid and descend into the cup-shaped cavity 70 below the magnet 66. 
In this cavity is located a conductive member 72 consisting of a hub 74 
with a downward extension 76 and one or more vanes 78, appearing more 
clearly in FIG. 5. As the particles move in a circular path with the 
liquid, they tend to move towards the larger radius of the cavity 70, 
where they will be guided by the vanes 78 towards the inner circumference 
of the outer cup-shaped part of the cavity 70 to be pushed against the gap 
80 between the outer end of a vane 78 and the lateral surface 82 of the 
essentially, upwardly open, cup-shaped part 84, thus closing an electric 
circuit consisting of the parts 84, 78, 74 and 76, together with the 
coacting source of electric voltage 86 and its respective signal 68N. 
Both the top member 28A and the bottom member 26A in FIG. 4 are made of an 
electrically nonconductive material, like the examples for the filter 
construction in FIG. 1. Insulating members 87A, 87B and 87C are positioned 
between conductive parts of disassociated electrical polarities. 
The previously described effect of obtaining approximate quantitative 
indication of nonferrous particles by using more than one set of contacts 
and connecting them in series may be had by making the two basic contacts 
of the nonferrous indicator, namely, the inner cup surface 82 and the 
inner member 74, 76 and 78 in several sectors which may be separated by 
radial gaps in the conductive parts. This provision would not change the 
basic arrangement shown in FIG. 4, but it is not indicated in the drawing, 
FIG. 4, in order not to introduce unnecessary intricacies. 
It should be noted that all structural parts of the filter 20A are 
identical with those of the filter 20 shown in FIG. 1. and not necessarily 
completely repeated in FIG. 4 not to impair the clarity of the significant 
factors of this illustration. 
In the above-described arrangements, particles caught by the electric 
strainer set, or sets, can be removed and inspected only by disassembling 
the filter unit, which necessitates stopping the flow of the liquid and 
draining the system. In another version shown for a chip detecting liquid 
filter or strainer based on the principles of this invention, this 
inconvenience can be avoided, the particle carrying member can be removed 
without draining the liquid from the system and additional advantages may 
be realized, as shown and described in the following. 
Such a device 20B is illustrated, in cross-section, in FIG. 8. The liquid 
enters at the upper opening 22 of the substantially cylindrical housing 
24. Helical vanes 34 impart the rotating motion on the liquid which 
rotates inside of the cylindrical strainer 36. The essentially cylindrical 
center support 32B for the vanes 34 further supports a center piece 
extension 88 in which there is arranged an axially movable rod 90, which 
extends downward onto a poppet-shaped valve member 92. This poppet 92 is 
biased against a downward movement by an expansion spring 94, which, in 
the version shown here, urges against the upper flange surface of the 
poppet 92. The latter may be shaped to effect an improved downward 
movement of the rotating liquid. On its largest diameter, the poppet 
carries a chamfer, or rounded edge 96 which, when downward movement of the 
poppet is made possible, will seat on a matching ring surface 98 of the 
bottom piece 26B, which is removable from the strainer housing 24 by 
conventional fastening means, such as a flange 101 with threaded bolts 100 
and binding nuts 102, of which only one each is shown in FIG. 8. A 
customary "O"-ring 103 is lodged between the bottom piece 26B and the 
bottom opening of the housing 24. 
It should be noted that the following details can be observed in both FIG. 
8 and in the enlarged particle detecting subassembly in FIG. 12. The lower 
end surface of the poppet 92 abuts with the top surface of a first disc 60 
having a downwardly extending pin 62. The disc 60 is of a magnetizable 
material such as steel. Underneath the disc 60 is located an annular 
permanent magnet 66, which, in this example, is shown as an electrically 
insulating, ceramic magnet as used in my U.S. Pat. No. 2,936,890. At the 
underside of that magnet 66 is a second disc 64, also of a magnetizable 
material, forming the counterpart to said first disc 60, so that parts 60 
and 64 will act as the two pole pieces of a magnet system consisting of 
the parts 60,66 and 64. Ferrous particles in the liquid will be attracted 
to this magnet system and tend to bridge the gap between parts 60 and 64, 
occupied by the magnet 66. Disregarding possible combinations of parts to 
simplify the capture of ferrous vs nonferrous parts and the respective 
indication signals, the following arrangement will be described as a 
system attaining an optimum differentiation between ferrous and nonferrous 
particle capture and indication. Under the ferrous second disc 64 is a 
substantially cylindrical insulating member 105 having the cross-section 
of an inverted "L". Underneath this insulating member 105 is arranged a 
conductive, but not magnetizable contact 104 having a star-shaped top 
surface and a cylindrical center sleeve. Its operation can be seen in FIG. 
9. The radial spokes 106 extend from the cylindrical sleeve of part 105 to 
the cavity of the cup-shaped part 84 at the circular bottom of which 
spokes 108 are mounted interposed in depth with the spokes 106 of part 
104. The axial distance between the radial spokes 106 of part 104 and 
those of part 108 is smaller than the circumferential distance between the 
radial spokes 106 of part 104 and those of 108 is smaller than the 
circumferential distance between the spokes of either one of these, so 
that particles circling around in the circular cavity 84 will fall through 
the spokes 106 of part 104 and be caught between the spokes 106 of part 
104 and part 108, thus bridging the electrical gap and activating the 
nonferrous alarm 68N. Particles even larger than the circular distance 
between the spokes 106 of part 104 will stay on top of these spokes and 
touch the inner rim of the circular cavity of part 108 and thus bridge the 
contact gap to also cause the closing of the alarm circuit for the 
indicator 68N. In this example, the electrically conductive housing 24 is 
"grounded", requiring the following insulating members placed between the 
parts 24, 84, 104, 64 and 62 and in the same sequence: 109A, 109B 105 and 
109D, readily so identified in FIG. 12. 
The above-mentioned arrangement of radial extensions for effecting a 
nonferrous particle bridge may also be accomplished by giving the radial 
spokes 110 of the nonmagnetizable detector contact 104A an essentially 
slanted shape, which, due to the basically circular nature of this 
component will form helical vanes 110, as shown in FIGS. 6 and 7 in axial 
and radial view, respectively. The spokes or protrusions 108 on the outer 
part 84 in FIG. 9 may then be omitted as the spaces under the spokes 110 
of part 104A will form wedge-shaped openings over the flat bottom of the 
cavity of part 84. In these wedge-shaped spaces, the particles to be 
detected will be caught and their rotating movement stopped, while the 
further rotating liquid will apply pressure to improve the conductive 
contact. 
By making the cylindrical filter support 112 at the top of the screen 36, 
FIG. 8, which also supports the rotating-inducing guide vanes 34, of an 
electrically insulating material, the inner section consisting of support 
88, spring 94 rod 90 and poppet 92 will be insulated from the screen 36 
and the filter housing 24. If the screen is made of a conductive material, 
such as a perforated or woven metal or wire screen, then the annular 
radial gap 114 between the poppet 92 and the screen 36 will act as a 
retaining restriction for particles of larger size than expected to 
proceed to the particle detecting area below the poppet. By introducing a 
signal into the circuit formed by the above-mentioned poppet center unit 
92 and the screen 36, or any parts electrically connected to it, a signal 
for large particles will be activated from a common source of electric 
power 86. This will then act as an indicator 68L of particles of unusually 
large sizes. 
Where large quantities of contamination are expected in the liquid, the 
filter or strainer may become clogged with solid particles, resulting in 
reduced open filter area and correspondingly increased pressure drop in 
the fluid system. The current approach to this effect, which may become 
critical to the functioning of the equipment served by the fluid system, 
is to indicate the increased pressure drop by a warning signal, operated 
by the difference between inlet pressure and outlet pressure. Where 
interruption of fluid flow can not be tolerated, a check valve under 
spring pressure may be interposed between inlet and outlet, so that 
clogging of the filter will cause the liquid to bypass the filter. In the 
filter arrangement according to this invention, the circular and downward 
direction of the liquid flow is used to obtain the desired bypass effect 
upon filter clogging. The filter support 112 is extended into a shroud 
118, which is oriented downward in the direction of fluid flow and shields 
the liquid from flowing to the overflow openings 120 formed in the ring 
member 116, so that during normal filter operation there will be no flow, 
or only an insignificant amount of liquid flow through these openings 120. 
Upon increased pressure difference between inlet and outlet, the liquid 
will be forced to partly overcome the circular and downwardly directed 
effect of the guide vane unit 34 as shown in FIGS. 1, 2, 4 and 8 and will 
reverse its flow direction to upwards and bypass the filter through the 
overflow openings 120. 
The circular-downward flow of the liquid, which is effected as shown in 
FIGS. 1, 2, 4 and 8 by a circular arrangement of guide vanes 34, can also 
be obtained by using a circular shape of the entry chamber 22 in FIGS. 10 
and 11. By introducing the liquid at an angle to the axis of the filter 
at, approximately, 90 degrees and at a slightly downward direction and 
causing the liquid to be deflected into a circular path, such a 
circular-downward flow may be obtained. It is enhanced, as shown for 
filter 200 in FIG. 10, by giving the top chamber an angular top surface 
122. A conical shape of the entry chamber, as shown by item 124 in FIG. 
10, further directs the liquid flow in the desired circular-downward 
direction. 
The entire interior parts assembly is mounted on the gland 140 for filter 
20B, FIG. 8, or on the equivalent member for the filter 20C, FIG. 10. 
Describing these component parts for only the filter 20B, FIG. 8, an 
insulating washer 142, a pressure-distributing metal washer 144, a wiring 
lug 146 and a binding nut 148 applied to the pin 62 constitute this 
subassembly. A customary "O"-ring 103A is inserted between the bottom 
piece 26B and said gland 140 for either filter version. 
A conventional, in this case, four-pin male receptacle 150 of an electrical 
connector is mounted by crimping over its edge 152 in said gland 140 so as 
to accommodate the corresponding female plug of an electrical connector 
(not shown). Wires leading from the, in this case, grounded gland 140, the 
cup-shaped part 84, the second disc 64 and the wiring terminal lug 146 of 
the pin 62, respectively, are connected with a corresponding pin of said 
four-pin receptacle 150. The external connections and accessories, namely, 
the voltage source 86 and the signal indicators 86F, 86N and 68L are shown 
schematically, all in FIG. 8. 
To accomplish one of the listed additional objectives, shown of FIG. 10, 
consists in the specific form given the support for the center member 
which carries the spring-loaded poppet valve 92, namely, by extending said 
support upwardly through the housing as a hollow cylinder 126. As the 
liquid circulates, centrifugal forces impart an accelerating effect, which 
imposes pressure on entrained air, vapor or gases in the liquid. The 
effect is that such lighter media are driven toward the center, where they 
enter the hollow cylindrical center of member 126, from where they may be 
ducted into a desired location, such as a reservoir of the fluid system, 
which is usually vented to atmosphere. It should be noted that in this 
manner the effect endeavored by U.S. Pat. No. 4,282,016 is obtained 
without the extensive means described in that patent. 
By providing the filter housing 130 with a radial bottom opening 132 which 
connects to an axially-parallel chamber 134, shown in FIGS. 10 and 11, the 
outgoing flow may then be directed to an outlet port 136, which is in line 
with the inlet port 138. This in-line arrangement is desirable for 
purposes of installing the unit in a horizontal duct, thus obviating the 
changes of direction necessitated by the arrangements described in U.S. 
Pat. Nos. 4,199,443 and 4,282,016. 
It should be noted that various component parts shown and described in the 
foregoing for filters in accordance with this invention may be substituted 
for parts made of materials other than originally specified, without 
departing from the operational intent and the spirit of this concept. More 
specifically, electrically nonconductive materials may be replaced by 
electrically conductive ones, provided another insulating member is added 
at the appropriate position. Comparable situations may exist at the 
magnetic subassemblies throughout this specification, whereby the herein 
shown, but illustrative, electrically nonconductive ceramic permanent 
magnets may readily be substituted through permanent magnets of an 
electrically conductive material, a substance containing rare earths and 
through electromagnets, selectively, in combination with insulating 
members as operationally required. 
It is further understood that the herein shown and described embodiments of 
the subject invention are but illustrative and that variations, 
modifications and alterations are feasible within the spirit of these 
teachings.