Liquid Storage Tank

Abstract

A liquid storage tank having inner and outer parallel spaced walls of substantially U-shaped vertical transverse cross-section, the outer wall being of metal and the inner wall being of a liquid resistant plastic material. The outer wall is closed at the top by a horizontal plate and the interior of the inner wall is in fluid communication with the space between the inner and outer wall. A drainage may be provided at the bottom of the outer wall for removing liquid from the inner wall.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a double-walled storage tank for liquids, such as fuel oil, the inner wall of which consists of a plastics material and the outer wall of sheet steel. The storage tank has the shape of a trough; its upper side being the largest cross-section of the tank, is closed by a substantially flat cover. A space several millimeters wide may be provided between the inner and outer wall of the storage tank. The cover may be designed as a flat trough.

2. Description of the Prior Art

With storage tanks for organic liquids, for example for fuel oil, of the conventional sheet steel construction, there is always the risk of internal corrosion as a result of water penetration. In order to obviate this corrosion risk, plastics materials were used in various ways, which plastics materials should of course be sufficiently resistant to the liquid to be stored. Thus, it was suggested to line sheet steel storage tanks with a plastics material. To this end, use is made of a curable plastics material such as epoxy resins which is sprayed on to the inner surface as a two-component system. In order to obtain a pore-free layer, spraying must be effected with special care so that tanks of this type become relatively expensive. It is nevertheless essential to inspect the emptied tanks over longer periods since porous spots in the coating can possibly only be detected after prolonged use. In practice this is a considerable disadvantage. Storage tanks of plastics material such as polyolefins are already known which are easier to inspect. However, they are difficult to produce and are consequently expensive, at any rate in the sizes of 1 cubic meter and larger which are required for domestic use. The main disadvantage is that in case of fire they form a great additional risk. Arrangement in residential buildings, for example near heating installations in basements, is therefore not advisable.

Storage tanks are also known which consist of a sheet steel outer wall and a plastics inner tank, and which form in a certain sense double-walled tanks. In this case the inner tank is made of a plastics film and adapted to the shape of the sheet steel outer tank; it is introduced through the dome-shaped opening and secured to the edge of the latter. Although the above drawbacks are thus obviated, the flexible, loosely inserted inner tank is exposed to mechanical stresses as a result of wrinkling and rubbing when being filled and emptied. Damage cannot be detected from the outside; the contents then flow into the outer sheet steel tank which is again exposed to corrosion.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a liquid storage tank which is a double-walled tank in the real sense and in which the outer wall is made of sheet steel and the inner wall is made of plastics material, e.g., polyolefin, so that the walls retain their position relative to each other independent of the fact whether the tank is emptied or filled. The inner wall is therefore not subjected to any mechanical stresses. As with the known double-walled sheet steel tanks, the space between the inner wall and the outer wall can be used for inspecting the inner tank for possible leakages. In case of damage, the inner tank can be exchanged as readily as the known flexible inner tank made of plastics film.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a vertical cross-sectional view of the storage tank of the invention; and

FIG. 2 is a modification of a portion of the storage tank of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 of the drawing, the storage tank includes a elongate outer tank 1 of substantially U-shaped vertical transverse cross-section, shown, its upper side being the largest cross-section of the tank. The bottom side is suitably rounded and provided at its lowest point with a collecting gutter 2. The tank is preferably provided at its bottom with legs 3 or a similar support so that it is free-standing. The end faces may be flat so that the tank has a rectangular cross-section in top-plan view. The depth is preferably approximately twice the width or more so that good use is made of the floor space required for mounting the tank. Tank 1 is of metal, preferably sheet steel or the like.

The wall thickness of the outer tank 1 is so selected that when the tank is filled to capacity, it is still reliably stable. The thickness is therefore smaller than that of a comparable steel tank of the usual type, the wall thickness of which is usually selected 50 percent greater because of the risk of corrosion.

The shape of the plastics inner tank 4 corresponds to that of the outer tank but the inner tank has no collecting gutter. Its wall thickness is optional since, as a result of the trough shape, any flexible plastics tank suspended in the outer tank 1 will retain its shape at any degree of filling. However, the wall thickness of the inner tank 4 is advantageously so selected that, when empty, the inner tank 4 will retain its shape even without the supporting outer tank 1. In this case, a firm connection with the outer tank 1 is not essential. The outer surfaces of the inner tank 4 are preferably provided with a plurality of ribs or burls which are several millimeters thick and serve as spacing elements, as for example, spacing elements 4a.

A cover 5 is provided which is substantially flat. Cover 5 preferably has an upturned edge so that a flat trough is formed which is disposed in the opening of the inner tank 4. The cover 5 may be made of a metal such as steel, or more preferably of a plastics material.

The cover 5 must be in adequate sealing engagement with the inner tank 4 so as to prevent nuisance from odors given off by the contents. This object may be achieved by passing a number of bolts 6 through corresponding openings arranged in the vertical part of the cover edge of the inner tank 4 and the outer tank 1 as shown in FIG. 1. A flexible plastics strip 7 of appropriate width is preferably arranged between the upper edges of the inner 4 and the outer tank 1, into which the spacing elements 4a of the inner wall press, so that the space between the tanks 1 and 4 is filled up. If the cover 5 is made of a plastic material, proper sealing is provided by merely pressing it against the plastics material of the inner tank 4. In this instance, steel strip 8 may be advantageously arranged on the inside of the vertical cover edge which distributes the pressure exerted by the bolts 6 more uniformly over the plastics cover. If cover 5 is of steel, this additional steel strip is of course unnecessary, although in this case strip 8 may be a flexible plastics sealing strip.

Referring now to FIG. 2, the seal between the outer edge of the cover 5 and the inner tank 4 may be provided by bending the cover 5 outwardly and horizontally mating with a horizontal edge 9 of the outer tank 1. Pressing on is preferably again ensured by a series of bolts 6. Sealing is preferably obtained by arranging a flexible plastics strip 10 between the cover edge and the edge 9 (or a steel strip 10 as discussed hereinabove). In both embodiments, tension lever fasteners (not shown) may be used instead of the bolts 6.

A tubular connection 11 (FIG. 1) for connecting to filling and discharge lines (not shown) is preferably arranged on the cover 5 so that the strength of the inner tank is not impaired by additional welds. This arrangement has the additional advantage that when the tank is slightly overfilled, for example by negligence, the oil overflow is collected on the cover 5, from which it can be easily removed.

Connections at the lower part of the tank are, however, necessary when several tanks are to be combined into a so-called tank battery. In this case, the lower parts of the end faces of the inner tank 4 may be provided with a plastics connecting piece (not shown) which is enclosed by an additional steel connecting piece welded on to the outer tank 1. The interconnection of two tanks thus equipped to form a battery is effected by a plastics tube which is enclosed by another flexible metal tube or corrugated tube. The metal tube is welded or soldered on to the sheet steel connection of the outer tank at both ends, so that the double-wall arrangement with the associated interspace is retained at the connecting piece (all not shown).

The end faces of the outer tank 1 are suitably provided with a connection 12 at the level of the collecting gutter 2, in which connection a liquid trace element of a known type may be arranged as a leakage indicator.

Claims

We claim as our invention:

1. A liquid storage tank comprising:

an elongate outer metal vessel of substantially U-shaped vertical transverse cross-section;

an elongate open-top inner vessel of substantially U-shaped vertical transverse cross-section and formed of a liquid-resistant plastic material adapted to contain a liquid therein, said inner vessel conforming to substantially the shape of said outer vessel;

spacing means associated with both of said vessels for maintaining said vessels in spaced parallel relationship forming an annular space therebetween;

substantially horizontal closure means disposed at the top of said tank closing at least said outer vessel;

said closure means including a shallow flat bottom trough disposed in the open top of the inner vessel and having out turned flanges on the upper edges of the trough side walls sealingly secured to the top edges of the side walls of the outer metal vessel; and

said inner vessel being in fluid communication with said annular space at substantially the top thereof.

2. The tank of claim 1 including a liquid collecting gutter at the bottom of said outer vessel in fluid communication with said annular space.

3. The tank of claim 1 wherein said outer vessel is of sheet steel.

4. The tank of claim 1 wherein said inner vessel is of polyethylene.

5. The tank of claim 1 wherein the lowermost portions of said outer vessel is rounded and including support means associated with said outer vessel for supporting said tank with its side walls in a substantially vertical position.

6. The storage tank of claim 1 wherein the wall of the inner vessel is of a thickness so that, when empty, the inner vessel will retain its shape without being connected to the outer vessel.

7. The storage tank of claim 1 wherein the spacing means includes spacing elements on the outer surfaces of said inner vessel.

8. The storage tank of claim 1 wherein said trough includes an upturned flange extending substantially vertically upwardly from the flat bottom portion disposed in the opening of said inner vessel, then extending outwardly from the top edge of said flange and substantially perpendicular thereto; and

said closure means further including bolt means extending through both the outwardly extending portion of the flange and a horizontal wall portion on said outer vessel for securing said outer vessel to said closure means.

9. The storage tank of claim 1 wherein said trough includes an upturned side wall extending substantially vertically upwardly from the flat bottom portion disposed in the opening of said inner vessel, and a portion extending outwardly from the top of said trough side wall and substantially perpendicular thereto;

said outer vessel having an outwardly extending substantially horizontal portion extending substantially parallel to said outwardly extending portion of said trough; and

said closure means further including bolt means extending through both said trough outwardly extending portion and said horizontal portion on said outer vessel for securing said outer vessel to said closure means.

10. The storage tank of claim 1 including a substantially vertically extending tubular connection arranged on said trough bottom and opening into the interior of said inner vessel for introducing liquid into the interior of said inner vessel.