# US 6,881,330 B2 · Multi-stage EDM filter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,881,330 B2 - Document ID: US6881330B2 - Status: Granted - Kind: B2 - Application number: 10/101,780 - Filed: 2002-03-19 - Published: 2003-09-25 - Granted: 2005-04-19 - Earliest claimed: 2002-03-19 - Assignees: Hoff Engineering Company, Inc. - Inventors: E. Michael Doyle; Edward M. Doyle - Web page: https://patentgrep.com/patent/US6881330B2 ## CPC - B01D 35/147: Bypass or safety valves - B01D 29/232: {with corrugated, folded or wound sheets} - B01D 29/58: arranged concentrically or coaxially - B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28) ## Abstract A two-stage, retrofit filter is adapted for use with an electrical discharge machine (EDM) includes nested inner and outer filtering elements that may be placed as a unit in the same tank and over the apertured standpipe used for a one-stage filter, such that the fluid to be filtered now flows through each of the multiple filter elements. The retrofit EDM filter may be configured for flow in either direction, though the usual arrangement is one whereby the fluid being filtered flows up through the bottom of the tank, out the apertured standpipe, and into the inner filter element. Preferably, the filter elements are cylindrical, pleated elements composed of a technical grade filter paper. In the preferred embodiment, a pressure-operated release valve is provided in conjunction with the inner filter, such that when a predetermined pressure is reached due to the entrapment of contaminants by the inner filter, the valve opens to allow the fluid to be filtered to flow through the outer filter. ## Claims ### Claim 1 A two-stage retrofit filter adapted for use with an electrical discharge machine (EDM) of the type wherein a one-stage filter is placed in a tank over an apertured standpipe such that a fluid being filtered flows through the apertured standpipe and filter, the retrofit EDM filter comprising: a plurality of nested filter elements, including an inner element and an outer element, the physical configuration of the elements being such that the retrofit filter may be placed in the same tank and over the apertured standpipe used for the one-stage filter, so that the fluid to be filtered flows through the apertured standpipe and each of the filter elements; an aperture extending through the inner filter from an upstream side to a downstream side of the inner filter; and a reproducibly rupturable diaphragm covering the aperture, the diaphragm being designed to rupture when subjected to a predetermined pressure. ### Claim 2 (depends on 1) The retrofit EDM filter of claim 1, wherein the fluid being filtered flows from the EDM work table tank to the apertured standpipe, and into the inner filter element. ### Claim 3 (depends on 1) The retrofit EDM filter of claim 1, wherein the filter elements are cylindrical. ### Claim 4 (depends on 1) The retrofit EDM filter of claim 1, wherein the filter elements are pleated. ### Claim 5 (depends on 1) The retrofit EDM filter of claim 1, wherein the filter elements are composed of filter paper. ### Claim 6 (depends on 1) The retrofit EDM filter of claim 1, wherein: at least the inner filter element is pleated; and the pleatings are reinforced at least in the vicinity of the pressure-operated release valve to ensure that the pleatings do not interfere with the opening or flow through the valve. ### Claim 7 A two-stage retrofit filter adapted for use with an electrical discharge machine (EDM) of the type wherein a one-stage filter is placed in a tank over an central, apertured standpipe, such that a fluid to be filtered flows up through the bottom of the tank, out the apertured standpipe, and into the filter, the retrofit EDM filter comprising: a plurality of nested cylindrical pleated filter elements, including an inner element and an outer element, the physical configuration of the elements being such that the retrofit filter may be placed in the same tank and over the apertured standpipe used for the one-stage filter, so that the fluid to be filtered now flows through the apertured standpipe and each of the filter elements; an aperture extending through the inner filter from an upstream side to a downstream side of the inner filter; and a reproducibly rupturable diaphragm covering the aperture, the diaphragm being designed to rupture when subjected to a predetermined pressure. ### Claim 8 (depends on 7) The retrofit EDM filter of claim 7, wherein the filter elements are composed of filter paper. ### Claim 9 (depends on 7) The retrofit EDM filter of claim 7, wherein: the pleatings are reinforced at least in the vicinity of the pressure-operated release valve to ensure that the pleatings do not interfere with the opening or flow through the valve.