Detection and indication device

A device for indicating the presence of electrically conducting particles, such as metal detritus, in a liquid such as hydraulic oil passing through a filter in which a gap is provided adjacent the filter into which metal particles are swept by the liquid flow to form a conducting bridge in an electrical circuit. In a preferred embodiment, an annular gap closed to through flow is provided between an insulated metal ring around a filter element and the wall of the flow passage surrounding the filter, and the ring and the wall are connected to an electrical circuit for actuating a warning light or audible alarm when the gap is bridged.

BACKGROUND OF THE INVENTION 
This invention relates to a device for the detection and indication of the 
presence of electrically conductive particles in a stream of fluid, 
particularly in an oil supply line. 
Indicators for detecting blockage of filter pores by fine particles are 
known in which the pressure difference between supply and discharge flows 
is indicated by a pressure difference valve. Significant pressure 
differences are produced only when a certain proportion of the filter 
pores are blocked by particles, usually fine particles, and where large 
particles are involved which do not necessarily enter the pores of the 
filter, this type of indicator is not sufficiently effective. 
In an installation such as a hydraulic system, in which oil is passed 
through pumps and other components with moving parts, defects or heavy 
wear usually result in the production of metal detritus or particles which 
enter the oil stream. These particles, which may be either fine or large 
according to the nature of the defect in the component are removed by the 
normal filtration device in the oil line. Unless there is produced a 
quantity of fine metallic particles sufficient to cause substantial 
blockage of filter pores, known indicators dependent on pressure 
differences are not sufficiently sensitive to provide early warning of the 
presence of material resulting from excessive wear or drainage to 
components such as pumps. 
The present invention seeks to provide a device which will give an early 
warning of the presence of electrically conductive particles, such as 
metal detritus in an oil or other fluid stream. 
SUMMARY OF THE INVENTION 
According to the present invention, an indicating device for detecting 
electrically conductive particles in a non-conductive fluid, comprising a 
first electrical pole member constituted by means defining at least a 
portion of a flow-passage for the fluid having an inlet and an outlet, a 
filter element arranged in the flow-passage to intercept flow between 
inlet and outlet and having an entry surface exposed to the flow, a second 
electrical pole member located adjacent the entry surface and electrically 
insulated from the first pole member, a gap between first and second pole 
members dimensioned and located so as to permit bridging of the gap by 
accumulation in the gap of conducting particles, and an electrical circuit 
connecting first and second pole members to an electrically operated 
warning device, the circuit being closed when the gap is bridged by 
conductive particles. Preferably the means defining at least a portion of 
the flow passage is a housing assembly in which is located means for 
supporting a filter element. The means for supporting a filter element is 
preferably a support member made from an electrically insulating material, 
such as rubber or plastics material, which is sufficiently resilient to 
grip the filter element firmly and also to grip a portion of the housing 
assembly and thereby hold the filter in the desired position. 
Conveniently, the support member, which can be a moulded ring, is also 
adapted to carry a metal detector ring mounted on the periphery of the 
mounted ring. The detector ring is thus electrically insulated from the 
housing assembly, which is connected to the electrical circuit of the 
warning device to form the first pole. 
Preferably the housing assembly includes a gland in the wall through which 
passes an insulated conductor terminating within the housing in a contact 
which presses against the detector ring thus connecting the detector ring 
to the electrical circuit to form the second pole. 
The detector ring may be located in the housing assembly more or less 
co-axially with the bore thereof and may be of an outside diameter smaller 
than this bore so as to leave between the outer surface of the detector 
ring and the inner surface of the bore of the housing assembly a gap for 
permitting accumulation of particles when in service. 
Preferably the housing assembly is so constructed as to permit removal of 
the support member, detector ring and filter element. Thus the housing 
assembly may comprise an annular body member, and a detachable locating 
member, the locating member including means for mounting the support 
member thereon and locating the support member in a pre-determined 
position within the housing assembly. 
The locating member is preferably a ring including a bore co-axial with the 
outlet pipe and having tubular extension of the bore which extends into 
the housing body. 
The support member is preferably provided with a tubular extension which 
fits firmly into the extension of the locating member and is preferably 
provided with an annular groove into which a tubular filter element can be 
fitted. The support member also may serve to provide a seal between the 
inlet pipe and outlet pipe whereby all the fluid in the flow passage is 
constrained to pass through the filter element. 
The size of the gap depends upon the size and number of conductive 
particles which enter the fluid and are transportable thereby. This is a 
matter which can be determined readily by those skilled in the art. 
The invention can also be utilised in a modified construction in which the 
second pole member is associated with the filter element e.g., a detector 
ring located on this filter, which acts as an electrical insulator, other 
arrangements being made for mounting and seating the filter in this 
housing. 
In another construction the second pole member may be a pin or stud in an 
insulating mounting in the wall of the housing and provided with an 
electrical conductor, the insulating mounting also being arranged to act 
as a gap which can be bridged by the particles. A pin may also be arranged 
by suitable mounting to provide a gap between it and the housing. 
The invention is not restricted to a tubular form of filter element and a 
disc type of filter element can be used with a detector member such as a 
ring, plate or pin located at a suitable distance from the filter surface 
to provide a gap. 
The gap can be located at a position where gravity assists in the 
accumulation of detritus.

DESCRIPTION OF A PREFERRED EMBODIMENT 
A pipe 1 for conveying oil from a source of supply is welded to a housing 2 
and an outlet pipe 3 is releasably secured to a locating ring 4 by means 
of a collar 5 bearing on the flange 6 and screws 7. 
Locating ring 4 is releasably secured to the housing 2 by screws 8. Sealing 
rings 9 and 10 maintain oil tightness. 
Co-axially in the pipe 1 is located a tubular filter member 11 having one 
end (not shown) closed. An annular flow passage 12 is thus formed between 
the pipe 1 and the filter member 11 and terminates within the housing 2. 
The end portion 13 extends into the housing 2 and is there received in and 
supported by an electrically insulating support ring 14 sealingly engaging 
locating ring 4. Access for cleaning or replacing the filter member 11 is 
by releasing locating ring 4. 
The support ring 14, which is of an oil resistant rubber or plastics 
material, is provided with a wide bore 15 so as to avoid unduly 
restricting oil flow, an axial extension 16 firmly engaging the bore of 
the locating ring 4, and an annular channel position 17 sealingly engaging 
the end portion 13 of the filter element 11. The locating ring 4 and the 
support ring 14 form a closure for the flow passage 12 so that oil is 
forced to pass through the filter element 11. 
On the outer circumference of the support ring 14 is a metal detector ring 
18 which is thus electrically insulated from the housing 2 and the 
locating ring 4 and is adjacent the outer or entry surface of the filter 
element 11. Between the detector ring 18 and wall of the housing 2 is a 
gap 19 which is sufficiently narrow to permit a build up of particles to 
bridge this gap in at least one small area. 
A gland 20 is provided in the wall of the housing 2 having a gland nut 27 
carrying an insulated contact 21 which engages the detector ring 18, and 
which is connected to an insulated electrical lead 22. A warning lamp 23 
is connected to an electrical supply line 24 and through a resistance 25 
to earth, and the lead 22 is connected between the lamp 23 and the 
resistance 25. The housing 2 is connected to earth through the oil pipe as 
a whole but a direct connection 26 to earth can be made if desired. 
In use, oil flows through flow passage 12 and passes through the filter 
member 11, the bore 15, and thus into the outlet pipe 3. Particles are 
trapped in the passage 12, the finer ones in the filter material, and the 
larger, heavier, electrically conductive particles are swept into the gap 
19 which is dimensioned so as to be bridged by a small accumulation of 
such particles. These particles are derived from wear or abrasion of 
machine parts, and are predominantly metallic. 
In normal operation, current is supplied to the lamp 23 which is connected 
to earth through the resistor 25 so that the filament glows only faintly, 
thus indicating that the electrical circuit is alive. When the gap 19 has 
been bridged by one or more metallic particles, electrical current is able 
to flow between the detector ring 18 and the housing 2 which is connected 
to earth, thus short circuiting the resistor 25. The lamp 23 then glows 
brightly thereby giving warning that metallic particles, indicative of 
damage to working parts of the hydraulic system, are present in the oil 
supply. 
Instead of a lamp 23, a warning device which is audible, such as a bell, or 
a combination of both lamp and bell can be used. The resistor connection 
to earth 25 can be omitted, in which case the lamp will be illuminated 
only when the gap 19 has been bridged. 
The arrangement of a suitably dimensioned gap 19 at the end of the flow 
passage 12 provides an environment in which, due to a locally reduced rate 
of oil flow, accumulation of heavier particles can occur, particularly at 
the lowest point. This is an important consideration in giving warning 
early enough to enable action to be taken to prevent a major breakdown in 
a faulty component. A gap which is too wide, will, obviously, require a 
considerable time to become bridged, and this will give insufficient 
warning. 
The filter element 11 can be removed and the gap 19 cleaned by releasing 
screws 8 and withdrawing the locating ring 4 together with the support 
ring 14, detector ring 18 and filter element 11 gripped in the annular 
channel portion from the housing 2. If necessary, the screws 7, collar 5 
and pipe 3 may also be removed. 
Whilst the invention has been described with particular reference to 
liquids, it is also applicable to gaseous fluids in which have entrained 
therein conducting particles, for example, fine metal powders or possibly 
carbon dust. 
The detection of metal particles in an oil system at a sufficiently early 
stage may enable timely remedial action to be taken in respect of defects 
or premature wear in mechanical components of the system, and thereby 
avoid an unexpected breakdown.