Hydraulic fluid compositions

Claim 2

A hydraulic fluid capable of withstanding applied torques of at least 2000 foot pounds before galling or seizing as measured by the Timken test comprising an aqueous solution containing at least one zwitterion having a amine group separated from a carboxylate group by a carbon chain having from 1 to 3 carbon atoms, said zwitterion comprising an unbranched alkyl group having from 10 to 30 carbon atoms attached to the amine nitrogen.

Claim 3

A hydraulic fluid as claimed in claim 1 wherein at least a portion of the zwitterions contain a functional group selected from the group consisting of polyethylene groups containing from 3 to 40 ethylene oxide units and polypropylene oxide groups having from 1 to 10 propylene oxide units attached to the amine nitrogen.

Claim 4

A hydraulic fluid as claimed in claim 1 wherein at least a portion of the zwitterions contain at least one alkyl substitution on the carbon chain between the amino group and the carboxylate group.

Claim 5

A hydraulic fluid as claimed in claim 1 wherein the zwitterion is present in a concentration from about 0.01 percent to about 0.15 percent by volume.

Claim 6

A hydraulic fluid as claimed in claim 1 further comprising at least one polyethoxylated fatty amine containing an unbranched alkyl group having from 10 to 30 carbon atoms and a polyethylene oxide group containing from 3 to 40 ethylene oxide units.

Claim 7

A hydraulic fluid comprising: a. at least one first compound selected from compounds having the formula ##STR7## wherein R 1 comprises an unbranched alkyl group containing from 15 to 25 carbon atoms, R 2 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups containing from 3 to 40 ethylene oxide units and polypropylene oxide groups containing from 1 to 10 propylene oxide units; and b. at least one second compound selected from compounds having the formula R 4 -NH-R 5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from 15 to 25 carbon atoms and R 5 comprises an alkyl group having from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon.

Claim 8

A hydraulic fluid comprising: a. at least one first compound selected from compounds having the formula ##STR7## wherein R 1 comprises an unbranched alkyl group containing from 15 to 25 carbon atoms, R 2 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups containing from 3 to 40 ethylene oxide units and polypropylene oxide groups containing from 1 to 10 propylene oxide units; and b. at least one second compound selected from compounds having the formula R 4 -NH-R 5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from 15 to 25 carbon atoms and R 5 comprises an alkyl group having from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon.

Claim 9

A hydraulic fluid as claimed in claim 6 wherein R 1 and R 4 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms.

Claim 10

A hydraulic fluid as claimed in claim 6 wherein either or both of R 2 and R 5 comprises an alkyl group having a carbon chain containing from 1 to 2 carbon atoms between the nitrogen and carboxylate carbon.

Claim 11

A hydraulic fluid as claimed in claim 6 wherein R 5 contains at least one alkyl substitution on the carbon chain between the nitrogen and carboxylate carbon.

Claim 12

A hydraulic fluid as claimed in claim 6 wherein the first compound and the second compound are each present in a concentration of from about 0.01 percent to about 0.15 percent by volume.

Claim 13

A hydraulic fluid as claimed in claim 6 further comprising a polyethoxylated fatty amine having the formula ##STR8## wherein R 6 comprises an unbranched alkyl group containing from 15 to 25 carbon atoms, R 7 comprises a polyethylene oxide group containing from 3 to 40 ethylene oxide units and R 8 is selected from the group consisting of hydrogen and polyethylene oxide groups having from 3 to 40 ethylene oxide units.

Claim 14

A hydraulic fluid as claimed in claim 11 wherein the polyethoxylated fatty amine is present in a concentration of about 0.005 percent to about 0.05 percent by volume.

Claim 15

A hydraulic fluid comprising: a. at least one first compound selected from compounds having the formula ##STR9## wherein R 1 comprises an unbranched alkyl group containing from 15 to 25 carbon atoms,-R 2 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups having from 3 to 40 ethylene oxide units and polypropylene groups having from 1 to 10 propylene oxide units, said first compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; b. at least one second compound selected from compounds having the formula R 4 -NH-R 5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from between 15 to 25 carbon atoms and R 5 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon, said second compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; and c. at least one third compound selected from compounds having the formula ##STR10## wherein R 6 comprises an unbranched alkyl group containing from 15 to 25 carbon atoms, R 7 comprises a polyethylene oxide group containing from 3 to 40 ethylene oxide units and R 8 is selected from the group consisting of hydrogen and polyethylene oxide groups having from 3 to 40 ethylene oxide units, in a concentration from about 0.005 percent to about 0.05 percent by volume.

Claim 16

A hydraulic fluid comprising: a. at least one first compound selected from compounds having the formula ##STR9## wherein R 1 comprises an unbranched alkyl group containing from 15 to 25 carbon atoms,-R 2 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups having from 3 to 40 ethylene oxide units and polypropylene groups having from 1 to 10 propylene oxide units, said first compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; b. at least one second compound selected from compounds having the formula R 4 -NH-R 5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from between 15 to 25 carbon atoms and R 5 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon, said second compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; and c. at least one third compound selected from compounds having the formula ##STR10## wherein R 6 comprises an unbranched alkyl group containing from 15 to 25 carbon atoms, R 7 comprises a polyethylene oxide group containing from 3 to 40 ethylene oxide units and R 8 is selected from the group consisting of hydrogen and polyethylene oxide groups having from 3 to 40 ethylene oxide units, in a concentration from about 0.005 percent to about 0.05 percent by volume.

Claim 17

A hydraulic fluid as claimed in claim 13 wherein any or all of R 1 , R 4 and R 6 comprise an unbranched alkyl group containing from 18 to 22 carbon atoms.

Claim 18

A hydraulic fluid as claimed in claim 13 wherein R 3 is selected from the group consisting of polyethylene oxide groups containing from 10 to 15 ethylene oxide units and polypropylene oxide groups containing from 3 to 5 propylene oxide units.

Claim 19

A hydraulic fluid as claimed in claim 13 wherein either or both of R 2 and R 5 comprise an alkyl group having a carbon chain containing from 1 to 2 carbon atoms between the nitrogen and carboxylate carbon.

Claim 20

A hydraulic fluid as claimed in claim 13 wherein the first compound is present in a concentration of about 0.05 percent to about 0.10 percent by volume.

Claim 21

A hydraulic fluid as claimed in claim 13 wherein the second compound is present in a concentration of about 0.03 percent to about 0.07 percent by volume.

Claim 22

A hydraulic fluid as claimed in claim 13 where the third compound is present in a concentration of about 0.015 percent to about 0.035 percent by volume.

Claim 23

A hydraulic fluid as claimed in claim 13 further comprising a biocide capable of preventing the growth of bacteria in the hydraulic fluid.

Claim 24

A hydraulic fluid as claimed in claim 20 wherein the biocide comprises at least one compound selected from the group consisting of fatty acid quaternary ammonium salts having a cation formula R.sub.9 -N(CH.sub.3).sub.3.sup.+ wherein R 9 comprises an unbranched alkyl group containing from 15 to 25 carbon atoms.

Claim 25

A hydraulic fluid as claimed in claim 13 further comprising a freezing-point depressant containing at least one polyhydroxide compound having from 2 to 4 carbon atoms in a concentration sufficient to reduce the freezing point of the hydraulic fluid to below -30° F.

Claim 26

A hydraulic fluid as claimed in claim 22 wherein the polyhydroxide compound is selected from the group consisting of ethylene glycol, propylene glycol and 2-butene-1,4-diol.

Claim 27

A hydraulic fluid as claimed in claim 22 wherein the polyhydroxide compound is present in a concentration from about 0.6 percent to about 1.4 percent by volume.

Claim 28

A hydraulic fluid as claimed in claim 13 further comprising a polyhydroxide compound having from 2 to 6 carbon atoms in a concentration from about 0.04 percent to about 0.3 percent by volume.

Claim 29

A hydraulic fluid comprising: a. at least one first compound selected from compounds having the formula ##STR11## wherein R 1 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, R 2 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups having from 3 to 40 ethylene oxide units and polypropylene groups having from 1 to 10 propylene oxide units, said first compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; b. at least one second compound selected from compounds having the formula R.sub.4 -NH-R.sub.5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from between 18 to 22 carbon atoms and R 5 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon, said second compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; c. at least one third compound selected from compounds having the formula ##STR12## wherein R 6 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, R 7 is a polyethylene oxide group containing from 3 to 40 ethylene oxide units and R 8 is selected from the group consisting of hydrogen and polyethylene oxide groups having from 3 to 40 ethylene oxide units, said third compound being in a concentration from about 0.005 percent to about 0.05 percent by volume; d. a biocide comprising at least one compound selected from the group consisting of fatty acid quaternary ammonium salts having a cation formula R.sub.9 -N(CH.sub.3).sub.3.sup.+ wherein R 9 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, said biocide being in a concentration of from about 0.01 percent to about 0.1 percent by volume; e. a corrosion inhibitor selected from the group consisting of polyethoxylated fatty amines containing a polyethylene oxide group having from 3 to 40 ethylene oxide units and polyethoxylated fatty diamines containing a polyethylene oxide group having from 3 to 40 ethylene oxide units in an amount sufficient to substantially prevent corrosion of metal in contact with the hydraulic fluid; and f. a freezing-point depressant comprising at least one polyhydroxide compound having from 2 to 4 carbon atoms in a concentration sufficient to reduce the freezing point of the hydraulic fluid to below -30° F.

Claim 30

A hydraulic fluid comprising: a. at least one first compound selected from compounds having the formula ##STR11## wherein R 1 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, R 2 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups having from 3 to 40 ethylene oxide units and polypropylene groups having from 1 to 10 propylene oxide units, said first compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; b. at least one second compound selected from compounds having the formula R.sub.4 -NH-R.sub.5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from between 18 to 22 carbon atoms and R 5 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon, said second compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; c. at least one third compound selected from compounds having the formula ##STR12## wherein R 6 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, R 7 is a polyethylene oxide group containing from 3 to 40 ethylene oxide units and R 8 is selected from the group consisting of hydrogen and polyethylene oxide groups having from 3 to 40 ethylene oxide units, said third compound being in a concentration from about 0.005 percent to about 0.05 percent by volume; d. a biocide comprising at least one compound selected from the group consisting of fatty acid quaternary ammonium salts having a cation formula R.sub.9 -N(CH.sub.3).sub.3.sup.+ wherein R 9 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, said biocide being in a concentration of from about 0.01 percent to about 0.1 percent by volume; e. a corrosion inhibitor selected from the group consisting of polyethoxylated fatty amines containing a polyethylene oxide group having from 3 to 40 ethylene oxide units and polyethoxylated fatty diamines containing a polyethylene oxide group having from 3 to 40 ethylene oxide units in an amount sufficient to substantially prevent corrosion of metal in contact with the hydraulic fluid; and f. a freezing-point depressant comprising at least one polyhydroxide compound having from 2 to 4 carbon atoms in a concentration sufficient to reduce the freezing point of the hydraulic fluid to below -30° F.

Claim 31

A hydraulic fluid as claimed in claim 26 wherein R 9 is selected from the group consisting of coco, tallo and soya.

Claim 32

A hydraulic fluid as claimed in claim 26 wherein the biocide is soya quaternary ammonium chloride.

Claim 33

A hydraulic fluid as claimed in claim 26 wherein the corrosion inhibitor is a polyethoxylated fatty diamine.

Claim 34

A hydraulic fluid as claimed in claim 26 wherein the corrosion inhibitor is present in a concentration of from about 0.01 percent to about 0.1 percent by volume.

Claim 35

A hydraulic fluid as claimed in claim 26 wherein the freezing-point depressant comprises ethylene glycol.

Claim 36

A hydraulic fluid as claimed in claim 31 wherein the concentration of ethylene glycol is from about 0.6 percent to about 1.4 percent by volume.

Claim 37

A hydraulic fluid as claimed in claim 26 further comprising hexylene glycol in a concentration of from about 0.04 percent to about 0.3 percent by volume.

Claim 38

A hydraulic fluid concentrate capable of being diluted with water in an amount of up to 80 parts water for each part concentrate to thereby yield a working hydraulic fluid as described in claim 26.

Claim 39

A process for the preparation of a hydraulic fluid concentrate as described in claim 34 comprising: a. blending the first, second and third compounds with sufficient water to substantially prevent reaction of the first, second or third compounds with a subsequently added component wherein blending is performed by a substantially non-foaming means for a time sufficient to achieve a substantially homogeneous first mixture; b. adding to the mixture the freezing-point depressant and the corrosion inhibitor and blending the mixture to thereby form a second substantially homogeneous mixture; c. adding the biocide to the second mixture and blending the mixture to thereby form a substantially homegeneous third mixture; and d. adding sufficient water to the third mixture and blending the mixture to provide a concentrate requiring a select dilution of up to 80 parts water for each part concentrate to achieve a working hydraulic fluid.

Claim 40

In a process for transmitting power from a power source to a load through the use of a hydraulic fluid, the improvement comprising using as the hydraulic fluid an aqueous solution containing at least one zwitterion having an amine group separated from a carboxylate group by a carbon chain having at least one carbon atom, said zwitterion comprising an unbranched alkyl group having from 10 to 30 carbon atoms attached to the amine nitrogen.

Claim 41

In a process for transmitting power from a power source to a load through the use of a hydraulic fluid, the improvement comprising using as the hydraulic fluid an aqueous solution containing at least one zwitterion having an amine group separated from a carboxylate group by a carbon chain having at least one carbon atom, said zwitterion comprising an unbranched alkyl group having from 10 to 30 carbon atoms attached to the amine nitrogen.

Claim 42

The process as claimed in claim 36 wherein at least a portion of the zwitterions contain a functional group selected from the group consisting of polyethylene groups containing from 3 to 40 ethylene oxide units and polypropylene oxide groups having from 1 to 10 propylene oxide units attached to the amine nitrogen.

Claim 43

The process as claimed in claim 36 wherein at least a portion of the zwitterions contain at least one alkyl substitution on the carbon chain between the amino group and the carboxylate group.

Claim 44

The process as claimed in claim 36 wherein the zwitterion is present in the hydraulic fluid in a concentration from about 0.01 percent to about 0.15 percent by volume.

Claim 45

The process as claimed in claim 36 wherein the hydraulic fluid further comprises at least one polyethoxylated fatty amine containing an unbranched alkyl group having from 10 to 30 carbon atoms and a polyethylene oxide group containing from 3 to 40 ethylene oxide units.

Claim 46

In a process for transmitting power from a power source to a load through the use of a hydraulic fluid, the improvement comprising using as the hydraulic fluid an aqueous solution comprising: a. at least one first compound selected from compounds having the formula ##STR13## wherein R 1 comprises an unbranced alkyle group containing from 15 to 25 carbon atoms, R 2 comprises an alkyl group having a carbon chain containing at least 1 atom between the nitrogen and the carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups containing from 3 to 40 ethylene oxide units and polypropylene oxide groups containing from 1 to 10 propylene oxide units; and b. at least one second compound selected from compounds having the formula R.sub.4 -NH-R.sub.5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from 15 to 25 carbon atoms and R 5 comprises an alkyl group having at least 1 carbon atom between the nitrogen and the carboxylate carbon.

Claim 47

In a process for transmitting power from a power source to a load through the use of a hydraulic fluid, the improvement comprising using as the hydraulic fluid an aqueous solution comprising: a. at least one first compound selected from compounds having the formula ##STR13## wherein R 1 comprises an unbranced alkyle group containing from 15 to 25 carbon atoms, R 2 comprises an alkyl group having a carbon chain containing at least 1 atom between the nitrogen and the carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups containing from 3 to 40 ethylene oxide units and polypropylene oxide groups containing from 1 to 10 propylene oxide units; and b. at least one second compound selected from compounds having the formula R.sub.4 -NH-R.sub.5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from 15 to 25 carbon atoms and R 5 comprises an alkyl group having at least 1 carbon atom between the nitrogen and the carboxylate carbon.

Claim 48

In a process for transmitting power from a power source to a load through the use of a hydraulic fluid, the improvement comprising using as the hydraulic fluid an aqueous solution comprising: a. at least one first compound selected from compounds having the formula ##STR14## wherein R 1 comprises an unbranched alkyl group containing from 15 to 25 carbon atoms, R 2 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups having from 3 to 40 ethylene oxide units and polypropylene groups having from 1 to 10 propylene oxide units, said first compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; b. at least one second compound selected from compounds having the formula R.sub.4 -NH-R.sub.5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from between 15 to 25 carbon atoms and R 5 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon, said second compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; and c. at least one third compound selected from compounds having the formula ##STR15## wherein R 6 comprises an unbranched alkyl group containing from 15 to 25 carbon atons, R 7 comprises a polyethylene oxide group containing from 3 to 40 ethylene oxide units and R 8 is selected from the group consisting of hydrogen and polyethylene oxide groups having from 3 to 40 ethylene oxide units, in a concentration from about 0.005 percent to about 0.05 percent by volume.

Claim 49

In a process for transmitting power from a power source to a load through the use of a hydraulic fluid, the improvement comprising using as the hydraulic fluid an aqueous solution comprising: a. at least one first compound selected from compounds having the formula ##STR14## wherein R 1 comprises an unbranched alkyl group containing from 15 to 25 carbon atoms, R 2 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups having from 3 to 40 ethylene oxide units and polypropylene groups having from 1 to 10 propylene oxide units, said first compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; b. at least one second compound selected from compounds having the formula R.sub.4 -NH-R.sub.5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from between 15 to 25 carbon atoms and R 5 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon, said second compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; and c. at least one third compound selected from compounds having the formula ##STR15## wherein R 6 comprises an unbranched alkyl group containing from 15 to 25 carbon atons, R 7 comprises a polyethylene oxide group containing from 3 to 40 ethylene oxide units and R 8 is selected from the group consisting of hydrogen and polyethylene oxide groups having from 3 to 40 ethylene oxide units, in a concentration from about 0.005 percent to about 0.05 percent by volume.

Claim 50

In a process for transmitting power from a power source to a load through the use of a hydraulic fluid, the improvement comprising using as the hydraulic fluid an aqueous solution comprising: a. at least one first compound selected from compounds having the formula ##STR16## wherein R 1 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, R 2 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups having from 3 to 40 ethylene oxide units and polypropylene groups having from 1 to 10 propylene oxide units, said first compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; b. at least one second compound selected from compounds having the formula R 4 -NH-R 5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from between 18 to 22 carbon atoms and R 5 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon, said second compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; c. at least one third compound selected from compounds having the formula ##STR17## wherein R 6 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, R 7 is a polyethylene oxide group containing from 3 to 40 ethylene oxide units and R 8 is selected from the group consisting of hydrogen and polyethylene oxide groups having from 3 to 40 ethylene oxide units, said third compound being in a concentration from about 0.005 percent to about 0.05 percent by volume; d. a biocide comprising at least one compound selected from the group consisting of fatty acid quaternary ammonium salts having a cation formula R.sub.9 -N(CH.sub.3).sub.3.sup.+ wherein R 9 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, said biocide being in a concentration of from about 0.01 percent to about 0.1 percent by volume; e. a corrosion inhibitor selected from the group consisting of polyethoxylated fatty amines containing a polyethylene oxide group having from 3 to 40 ethylene oxide units and polyethoxalated fatty diamines containing a polyethylene oxide group having from 3 to 40 ethylene oxide units in an amount sufficient to substantially prevent corrosion of metal in contact with the hydraulic fluid; and f. a freezing-point depressant comprising at least one polyhydroxide compound having from 2 to 4 carbon atoms in a concentration sufficient to reduce the freezing point of the hydraulic fluid to below -30° F.

Claim 51

In a process for transmitting power from a power source to a load through the use of a hydraulic fluid, the improvement comprising using as the hydraulic fluid an aqueous solution comprising: a. at least one first compound selected from compounds having the formula ##STR16## wherein R 1 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, R 2 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and carboxylate carbon and R 3 is selected from the group consisting of polyethylene oxide groups having from 3 to 40 ethylene oxide units and polypropylene groups having from 1 to 10 propylene oxide units, said first compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; b. at least one second compound selected from compounds having the formula R 4 -NH-R 5 -COOH and salts thereof wherein R 4 comprises an unbranched alkyl group having from between 18 to 22 carbon atoms and R 5 comprises an alkyl group having a carbon chain containing from 1 to 3 carbon atoms between the nitrogen and the carboxylate carbon, said second compound being in a concentration of from about 0.01 percent to about 0.15 percent by volume; c. at least one third compound selected from compounds having the formula ##STR17## wherein R 6 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, R 7 is a polyethylene oxide group containing from 3 to 40 ethylene oxide units and R 8 is selected from the group consisting of hydrogen and polyethylene oxide groups having from 3 to 40 ethylene oxide units, said third compound being in a concentration from about 0.005 percent to about 0.05 percent by volume; d. a biocide comprising at least one compound selected from the group consisting of fatty acid quaternary ammonium salts having a cation formula R.sub.9 -N(CH.sub.3).sub.3.sup.+ wherein R 9 comprises an unbranched alkyl group containing from 18 to 22 carbon atoms, said biocide being in a concentration of from about 0.01 percent to about 0.1 percent by volume; e. a corrosion inhibitor selected from the group consisting of polyethoxylated fatty amines containing a polyethylene oxide group having from 3 to 40 ethylene oxide units and polyethoxalated fatty diamines containing a polyethylene oxide group having from 3 to 40 ethylene oxide units in an amount sufficient to substantially prevent corrosion of metal in contact with the hydraulic fluid; and f. a freezing-point depressant comprising at least one polyhydroxide compound having from 2 to 4 carbon atoms in a concentration sufficient to reduce the freezing point of the hydraulic fluid to below -30° F.