Electrostatic fluid filter and system

The invention is to an electrostatic fluid filter that includes a housing, a removable array of filter elements and alternately electrically charged plates positioned parallel to the fluid flow. The charged plates are mounted between spacers each of which includes a mesh made of an insulating material and further includes a plurality of parallel guide tracks positioned on the mesh for holding the charge plates, and where each guide track is adjacent to a conductive strip which is in electrical contact with the plate in that guide track so that the plates are in electrical contact with alternately either a positive or negative electrical terminal.

FIELD OF THE INVENTION 
This invention relates to fluid filters, and more particularly to an 
electrostatic filter for removing micron and sub-micron size particles 
from fluids. 
BACKGROUND OF THE INVENTION 
The filtering of fluids has been done by both mechanical and electrostatic 
methods. In mechanical filtering, it is difficult to filter out particles 
having dimensions of less than 5 to 10 microns because of the small size 
of the particles. 
Electrostatic filtering has been accomplished as defined in U.S. Pat. No. 
4,594,138, issued Jun. 10, 1986. The filter described in this patent 
filters the fluid through a mechanical filter media, and also passing the 
fluid through perforated electrodes which are oppositely polarized by 
positive and negative charges. Because of the mechanical structure of the 
filter apparatus, it is not practical to change out and/or clean the 
mechanical filter media. 
SUMMARY OF THE INVENTION 
The invention is to an electrostatic fluid filter that includes a housing, 
a removable array of filter elements and alternately oppositely 
electrically charged plates positioned parallel to the fluid flow. The 
charged plates are mounted between spacers in which the charged plates 
alternately mounted in slots that are in electrical contact with either a 
positive or negative electrical terminal. The fluid inlet and outlet are 
on opposite ends of the housing such that the fluid to be filtered flows 
along the length of a plurality of mechanical filtering media and parallel 
to and in between the alternately charged plates. 
The technical advance represented by the invention, as well as the objects 
thereof, will become apparent from the following description of a 
preferred embodiment of the invention when considered in conjunction with 
the accompanying drawings, and the novel features set forth in the 
appended claims.

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 shows an exploded view of the components of the fluid filter 10 of 
the present invention. Housing 11 has top 12 and bottom 13 sides. Top side 
12 has an opening 14 which serves as the fluid outlet for the filter. 
Bottom side 13 has opening 15 which serves as the fluid inlet for the 
filter. There are two rows of electrical contacts on bottom side 13. A 
first row includes contacts 16 and a second row includes contacts 17. 
Contacts 16 and 17 are spaced so that each contact makes electrical 
contact with alternate charge plates 19. Charge plates 19 are spaced apart 
with filter elements 18 in between the plates. A charge plate filter 
element assembly 28, made up of a combination of charge plates 19, filter 
elements 18, and two holder/spacers 30a and 30b is placed inside of 
housing 11. A cover 20 encloses housing 11 after the assembly 28 is placed 
housing 11. Assembly 28 is placed between two holder/spacers 30 (FIGS. 
5-7) described below making assembly 29 which is placed inside of housing 
11. 
FIGS. 2, 3 and 4 are front view, bottom and side views of housing 11. In 
the front view, the two rows of contacts 16 and 17 are shown. The contacts 
16 and 17 alternate so that alternate charges, positive and negative may 
be placed on the charged plates 19. The two rows of contact are connected 
to positive and negative terminals as shown in FIG. 3. Positive terminal 
21 on strip 23 provides the positive charge placed on contacts 16, and 
negative terminal 22, on strip 24 provides the negative charge to contacts 
17. Fluid inlet 15 is shown on the bottom side in FIG. 3. 
In the side view shown in FIG. 4, it may be observed that the positive 
terminal 21 on strip 23 is located on the front side of housing 11 and 
negative terminal 22 on strip 24 is located at the back of housing 11. 
FIGS. 5, 6 and 7 are front, edge and side views, respectively, of 
holder/spacer 30. Two holder/spacers 30 are used in conjunction with 
charge plate 19 and filter elements 18 to form the filter cartridge 28. 
Holder/spacer 30 includes a plurality of guides 31 with tracks 32 into 
which the charge plates are placed. Holder/spacer 30 has a non-conductive 
grid 33 upon which the guides 31 are placed. There is one guide 31 for 
each charge plate 19 that is to be used in the filter cartridge. Beneath 
each guide 31 is a conductive strip 34 which is electrically connected to 
a charge plate 19 when a charge plate 19 is placed in a track 32. When a 
cartridge is assembled with the charge plates 19 and filter elements 18 
and a holder/spacer on two sides, and the cartridge is placed in housing 
11, each of conductive strips 34, on holder/spacer on the bottom of the 
cartridge contacts one of contacts 16 or 17 in the bottom of housing 11. 
FIG. 8a shows an assembled filter cartridge 28 with a holder/spacer 30a and 
30b on the top and bottom, and the charge plate 19-filter element 18 
assembly. Each charge plate 19 is in a track 32 in a guide 31. Conductive 
strips 34 are on both the top and bottom of cartridge, but only the bottom 
one makes contact with the contacts 16 and 17 in housing 11. With contacts 
34 on both top and bottom holder/spacer 30, the cartridge can be placed in 
housing 11 with either end up, or down. Since cartridge 29 simply is 
placed in housing 11 and enclosed with cover 20. It is only necessary to 
remove cover 20 to remove filter cartridge 29 to clean or replace the 
filter elements 18. When cartridge element is in housing 11, the fluid 
flow through cartridge 29 is as shown by arrow F. 
FIGS. 8b and 8c are isometric illustrations of the top and bottom 
space/holders 30a and 30b. 
FIG. 9 shows a filter system which is used in conjunction with the filter 
of the present invention. A pump 49 pumps liquid to be filtered from a 
tank or reservoir (not illustrated), the fluid enters the pump at the 
arrow labeled "IN". The pumped fluid first flows, as indicated by the 
arrows, to a water separator which includes a filter cartridge 51 through 
which the fluid to be filtered flows, separating it from any water in the 
fluid. An air bleed valve 52 is on the top of water separator 50, and a 
water drain valve 53 is on the bottom of water separator 50. The fluid 
then flows out of water separator 50 into the electrostatic filter 54. 
After being filtered, the fluid then flows as indicated by the "Out" arrow 
and is returned to a container, or may be recycled through the system for 
additional filtering. 
The system is powered by power from an A.C. input line. The A.C. voltage 
powers pump 49 and a high voltage power supply 56. Switch 57 is used to 
turn the system ON or OFF. High voltage power supply 56 provides the high 
voltage source in the range of 1000 to 20,000 volts, for inputs at 
terminal 22 of electrostatic filter 21. 
The fluid may be optionally prefiltered using a mechanical filter to remove 
large particle contaminants prior to using the filter of the present 
invention. 
As the fluid flows through the filter assembly, the particulate matter will 
be attracted to the eclectically charged filter foam elements between the 
oppositely charged plates. The particles will adhere to the foam and 
plates as the fluid passes through the electrostatic filter. 
FIG. 10 shows the efficiency of the filter of the present invention, as 
compared with a standard specification. This specification NAS 1638 shows 
the number of particles allowable for each series of particle sizes. For 
example, the NAS 1638 standard allows up to 8000 particles of sizes 
between 5 and 15 microns per 100 milliliters of fluid. In the test sample, 
which was 100 ml of an fluid, the particle count is shown for the five 
ranges of particle sizes. This is labeled as "Original Fluid". Hydraulic 
fluid was filtered in four passes. The particle count for each of the five 
ranges of particle sizes is shown for each of the four passes of the fluid 
through the filter. It should be noted, for example, in the 5 to 15 micron 
particle range, the original fluid contained 47,563 particles. The 
particle count was reduced to 2,111, 723, 564 and 466 in each of the four 
passes through the filter. The particle count in each of the five particle 
ranges was below the NAS 1638 specification after Pass 1, and after each 
subsequent filter pass. This shows the technical advance of the present 
invention.