# US 4,396,436 A · Method and flushing for removing hydraulic fluid from hydraulic systems

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- Number: US 4,396,436 A
- Document ID: US4396436A
- Status: Granted
- Kind: A
- Application number: 06/284,731
- Filed: 1981-07-20
- Granted: 1983-08-02
- Earliest claimed: 1981-07-20
- Assignees: Aluminum Company of America
- Inventors: Joseph T. Laemmle; William E. Boren
- Web page: https://patentgrep.com/patent/US4396436A

## CPC

- B08B 3/08: the liquid having chemical or dissolving effect
- C11D 7/5018: {Halogenated solvents}
- Y10T 137/0419: Fluid cleaning or flushing
- B08B: CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL
- C11D: DETERGENT COMPOSITIONS; USE OF SINGLE SUBSTANCES AS DETERGENTS; SOAP OR SOAP-MAKING; RESIN SOAPS; RECOVERY OF GLYCEROL
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

A method for removing residual hydraulic fluid from hydraulic systems employing a flushing fluid comprising a thickening agent dissolved in an organic solvent having a boiling point below about 125.degree. C. After draining fluid from a hydraulic system, flushing fluid is injected into the system and circulated to dissolve residual fluid. The flushing fluid, containing dissolved residual fluid, is then drained from the system. In a preferred embodiment, the flushing fluid comprises about one to three percent by weight ethyl cellulose dissolved in 1,1,1-trichloroethane together with about 0.1 to six percent by weight of a friction-reducing antiwear additive.

## Claims

### Claim 1

A method for flushing residual hydraulic fluid from a hydraulic system, comprising the steps of
(a) draining hydraulic fluid from the system;
(b) injecting into the system an organic solution comprising a thickening agent of ethyl cellulose dissolved in an organic solvent of chlorinated hydrocarbon having a boiling point below about 125.degree. C., said hydraulic fluid being soluble in said organic solution;
(c) circulating the organic solution through the system under an elevated pressure above atmospheric by pumping to dissolve any residual hydraulic fluid contained therein; and
(d) draining the organic solution from the system.

### Claim 2 (depends on 1)

The method of claim 1 further comprising
(e) evaporating the organic solvent from the organic solution recovered in step (d).

### Claim 3 (depends on 2)

The method of claim 2 further comprising
(f) recycling to step (b) organic solvent recovered in step (e).

### Claim 4 (depends on 1)

The method of claim 1 wherein said thickening agent consists essentially of ethyl cellulose having an ethoxyl content greater than about 49% by weight.

### Claim 5 (depends on 1)

The method of claim 1 wherein said thickening agent is present in an amount less than about 10% by weight.

### Claim 6 (depends on 5)

The method of claim 5 wherein said thickening agent is present in an amount of about one to three percent by weight.

### Claim 7 (depends on 1)

The method of claim 1 wherein said organic solvent has a boiling point of about 40.degree. to 100.degree. C.

### Claim 8 (depends on 1)

The method of claim 1 wherein said organic solvent is selected from the group consisting of 1,1,1-trichloroethane, tetrachloroethene and trichloromethane.

### Claim 9 (depends on 8)

The method of claim 8 wherein said organic solvent is 1,1,1-trichloroethane.

### Claim 10 (depends on 1)

The method of claim 1 wherein said organic solution further comprises about 0.1 to 6% by weight of a friction-reducing additive.

### Claim 11

A solution useful, as a flushing fluid for hydraulic systems, said solution comprising
(a) a chlorinated hydrocarbon solvent having a boiling point below about 125.degree. C. for hydraulic fluid;
(b) an organic polymeric thickening agent of ethyl cellulose dissolved in said solvent in an amount less than about 10% by weight of said solution; and
(c) about 0.1 to 6% by weight of a friction-reducing additive soluble in said solvent.

### Claim 12 (depends on 11)

The solution of claim 11 wherein said organic solvent is 1,1,1-trichloroethane.

### Claim 13 (depends on 11)

The solution of claim 11 wherein said thickening agent is ethyl cellulose having an ethoxyl content greater than 49% by weight.

### Claim 14 (depends on 9, 12)

Claim 9 or claim 12 wherein said hydraulic fluid comprises polychlorinated biphenyl.

### Claim 15 (depends on 10, 13)

Claim 10 or claim 13 wherein said friction-reducing additive comprises zinc dithiophosphate.