BACKGROUND

Field of the Invention

The invention herein relates to a process and apparatus for preventing corrosion, and more particularly microbiologically influenced corrosion, as well as galvanic and water influenced corrosion, of a hydraulic elevator cylinder.

Background of the Invention

A hydraulic elevator shaft cylinder is normally constructed of steel and installed underground, thus exposing the cylinder to soil and ground water. As a result, corrosion of various types may occur. Because the cylinder is installed beneath the elevator car frame and platform, and typically beneath the building, any repair or replacement of a corroded cylinder necessarily involves substantial difficulties in gaining access to the cylinder. Leakage of hydraulic fluid from a corroded or defective cylinder may create an environmentally hazardous situation.

While corrosion of various types, including water influenced and galvanic corrosion, are known to occur, of particular concern is microbiologically influenced corrosion caused by bacteria such as sulfate reducing bacteria and acid producing bacteria. This type of corrosion will

occur when microbiologically rich ground water comes in contact with the cylinder and occurs substantially more rapidly than many other types of corrosion. Therefore, it is a particularly serious problem.

Examples of corrosion causing sulphate-reducing bacteria are those of the genus Desulfovibrio. Bacteria of the genus Gallionella are examples of acid producing bacteria also known to cause corrosion. Corrosion of simple metal pipes caused by these bacteria has been recognized and documented. However, no one has ^' previously described any method for prevention of corrosion of hydraulic elevator cylinders caused by microorganisms.

A number of methods and devices, such as protective coatings and casings, have been utilized to deal with the problem of corrosion to hydraulic cylinders caused by the effects of salts, sulphur, stray currents and other causes. Typical examples are shown in U.S. Patents Nos. 4,983,072; 5,076,146 and 5,226,751. However, these methods and devices are subject to failure as a result of damage occurring during transportation or installation or due to ground movement after the installation, when the casing may leak or the coating may become damaged, thus breaking the seal and exposing the cylinder to the underground environment of soil, water and bacteria. Additionally, these methods and devices have not addressed the problem of microbiologically influenced corrosion.

Techniques exist for detection and removal of fluid within a casing, such as sensing for the presence of a fluid by the use of pressure. However, such sensing means are located below ground and under cement so that failure of this system cannot be checked. Furthermore, this system does not prevent the growth of bacteria and the resulting damage to the cylinder and further does not prevent damage to the protective casing, caused by earth movement or other movement of the cylinder.

There is clearly a need for an efficient method and device to prevent corrosion, especially microbiologically influenced corrosion, of a cylinder of a hydraulic elevator and to detect the leakage of water into the casing surrounding the cylinder. Furthermore, there is a need for an efficient method to detect the leakage of hydraulic fluid from a corroded or defective cylinder into the casing surrounding the cylinder.

SUMMARY OF THE INVENTION The present invention is directed to a process and apparatus that addresses the needs identified above and comprises protecting a hydraulic cylinder having a surface exposed to the underground environment against bacteriogenic, aqueous and galvanic corrosion.

The exposed cylinder surface is enclosed within a cylindrical casing with an annular space between the cylinder surface and the casing. The space is filled with a fluid, preferably a thixotropic, dielectric and

hydrophobic fluid which retains a gel structure when static, has a specific gravity greater than water and inhibits the bacteriogenic, aqueous and galvanic corrosion referred to above.

The invention further provides a fluid conduit between the annular space and a reservoir for the thixotropic hydrophobic fluid. The space and reservoir are filled with the fluid to a predetermined level. The presence of water or hydraulic fluid in the annular space can then be detected by observing the fluid reaching a level in the reservoir above the predetermined level. The water can be removed from the space and reservoir by drawing off water floating on top of the fluid in the reservoir.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of the invention with parts cut away; FIG. 2 is a side elevation view of the casing and the compression clamp;

FIG. 3 is a longitudinal section, rotated 90°, of casing and clamp, taken along line 3-3 of Figure 2; and

FIG. 4 is a cross-section taken along line 4-4, showing the clamp, the seal, the casing, the fluid filled space and the cylinder.

DETAILED DESCRIPTION OF THE BEST MODE

Referring to the drawings, Figure 1 illustrates an embodiment of an invention for prevention of corrosion, including microbiologically influenced corrosion, of a hydraulic cylinder 2, normally constructed of steel, and positioned underground beneath the elevator car frame and platform (not shown) and the steel support for the cylinder 18. The cylinder, having a surface 6, has a closed end 20 (shown in Figure 3) and an open end 22. The cylinder is supported by brackets 26 and 27 opposedly located on either side of the cylinder above the steel support for the cylinder 18. Ram 29 is a smaller diameter than that of cylinder 2. Pressurized hydraulic fluid 31 is supplied to cylinder 2 to force the ram up so as to raise the elevator car (not shown). Alternatively, hydraulic fluid 31 is released to allow the elevator car to lower. A stop ring 33 prevents the ram from extending above or below a desired level in cylinder. The cylinder extends downward within a drill hole 28 that is backfilled with dirt or sand 30.

A cylindrical casing 8 surrounds the cylinder along its length that is exposed to the underground environment. The casing may be constructed of one or more portions of tubing, 32 and 34, as shown in Figure 2, joined using a socket or coupling 36 and having an end cap 38 as illustrated in Figure 2. The casing is spaced apart from the cylinder along the axial length of both, forming an annular space 7 between the inner surface of the casing and the outer surface of the cylinder. The

width of the annular space 7 is preferably about 0.50 to 0.75 in., but may be any convenient distance sufficiently great to permit the fluid to flow into and throughout the entire annular space.

The aforedescribed casing and fittings may be of any rigid material, but preferably will be made of a non-electrically-conductive inert material such as polyvinyl chloride (PVC). PVC tubing is readily available commercially in many diameters and is reasonably priced, and therefore is preferred in the present invention. Other types of non-conductive tubing, such as acrylonitrile-butadiene-styrene (ABS) and glass fiber reinforced polymeric tubing, may also conveniently be used. A number of suitable materials are described in Seymour, Engineering Polymer Sourcebook (McGraw-Hill: 1990) and Rubin, (ed.), Handbook of Plastic Materials and Technology (Wiley-lnterscience: 1990).

Returning to Figure 1 , a compression clamp 10 and a seal 1 1 (described in more detail below) surround the cylinder and secure the top of the casing to cylinder. Below the clamp and seal an airbleed plug 12 caps nipple 14, with the nipple being inserted through the casing into the space between the casing and the cylinder 2, providing a space for air bleed. A PVC cement may be used to provide a better seal around said nipple.

Directly opposite but along the same plane as the aforesaid airbleed plug, a second nipple 16 is also inserted through the casing to provide a conduit between the annular space and a socket 40 which is further

joined to flexible tubing 42 by a a nipple 44 and hose clamp 46. At the opposite end the tube or hose 42 is attached to elbow 50 by another hose clamp 48. Elbow 50 is attached at fitting 52 to reservoir 54.

A fluid 56 pumped into reservoir 54 fills the annular space between the shaft cylinder and the casing, filling said reservoir to a predetermined level 58, (the level being within a range to allow for thermal expansion 60 of the fluid). The fluid 56 is a thixotropic, hydrophobic fluid which forms a stable gel when static and which has a specific gravity greater than that of water. This fluid functions to fill the entire volume of the annular space between the outer surface of the shaft cylinder and the inner surface of the casing. Since the fluid when in the annular space is essentially static, its thixotropic character prevents it from flowing out of the casing through any minor penetration of the casing. Its hydrophobicity further inhibits the incursion of water from the surrounding soil even if the casing is subject to such minor penetration. In addition, the hydrophobicity and the specific gravity of the fluid, as well as the minor motion within the fluid (as from. thermal expansion and contraction or vibration from elevator and/or earth movements), serve to force any water or hydraulic fluid which does get into the space 7 up through the space 7 and hose or tube 42 to the reservoir 54, where the water or hydraulic fluid appears as a separate layer on top of the surface of the hydrophobic fluid 56. That aqueous layer can easily be removed, as by use of a suction tube, thus keeping the space between the casing

and the cylinder substantially free of water. In addition, any leakage of hydraulic fluid into space 7 will also be detected by a rise in the level of fluid in reservoir 54 and the presence of said hydraulic fluid on top of fluid 56 in reservoir. Since the space 7 between the cylinder and the casing will be filled with the thixotropic, hydrophobic fluid and essentially free of water, nothing will support the presence corrosion-causing microorganisms, which need water to survive, so that corrosion of the cylinder's surface will be essentially eliminated. It will also be desirable for the fluid 56 to have a biocidal character, to enhance the fluids ability to keep microorganisms from becoming established within the annular space, and further for the fluid to be electrically insulating or di-electric, in order to inhibit galvanic corrosion of the cylinder. Also, of course, the fluid itself must not be corrosive to either the cylinder or the casing and preferably the fluid should be environmentally safe.

There are numerous polymeric fluids and fluid suspensions which can suitably be used in this invention. Typical examples are described in Barnes et al., An Introduction to Rheology (Elsevier: 1989), Ferguson et al., Fluid Rheology (Elsevier: 1991 ) and Walters (ed.), Rheometry:

Industrial Applications (Research Studies Press: 1980). Typical of the useful fluids are the clay- and/or oil-based aqueous emulsions and suspensions, such as those described in Walters, supra, Chs. 3 and 7,

and Ferguson et al., supra, Ch. 6, especially Section 6.5. A particularly preferred material is a proprietary thixotropic dielectric liquid product formed of a non-phytotoxic paraffin base petroleum oil, organophilic clay, and water (and including minor amounts of poly-fatty-acid esters and derivatives, calcium carbonate and lime), which is commercially available under the trade name "Union-Gard 160" from Pacific Standard Chemical Co. This product has a pH of 9 (slightly alkaline), a boiling point of 169°F (76°C), a specific gravity of 1 .1 , and has a light gray, opaque appearance. Figure 4 shows a ring seal 1 1 surrounding the upper end 68 of cylinder 2 and filling the width of that portion of the space 7 between the cylinder 2 and the casing 8. On the outside of casing 8 and aligned with ring seal 1 1 is compression clamp 10, which is a two-piece adjustibie clamp containing two adjusting bolts 64 and 66. The clamp 10 is tightened to compress the top of casing 8 and ring seal 10 against the top portion 68 of the cylinder 2 to seal the top of the space 7 against loss of the fluid.

It will be evident that there are numerous additional embodiments which are clearly within the scope and spirit of this invention but which have not been expressly described. Therefore the above description should be considered to be exemplary only, and the scope of the invention is to be detemined by reference to the appended claims. What is claimed is: