CA1224659A

CA1224659A - Safety manhole cover

Info

Publication number: CA1224659A
Application number: CA000459161A
Authority: CA
Inventors: Jack W. Mckinley; John E. Shore; Cornelious P. Smythe
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-07-18
Filing date: 1984-07-18
Publication date: 1987-07-28

Abstract

ABSTRACT OF THE DISCLOSURE
A safety manhole cover includes a solid circular plate for closing a manhole, a sleeve extending downwardly from the plate for insertion into the manhole, a plurality of square openings with bottom shoulders in the plate, and flexible, plastic plugs for closing the openings, the area of the plugs being slightly greater than the area of the openings so that the plugs can be jammed into the openings, but are free to escape when subjected to pressure substantially below the pressure required to lift the cover.

Description

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This invention relates to a manhole cover, and in particular to a safety manhole cover~
Conventional manhole covers are constructed of solid materials. Unless such manhole covers are vented, there is a tendancy for the cover to be blown into the alr when subjected to pressure from below which can result in injuries to anyone in the area of the manhole, or damage to vehicles. To applicant's knowledge the only attempts to solve the problem of venting man-hole covers are disclosed by Canadian Patents Nos. 978,785 and 959,691, both issued to B.J. Campagna on December 2~, 1974 and December 2, 1975 t respectively, and Canadian Patent No. 1,0~7,817 issued to S.A. Campagna Jr., et al on February 6, 1979. The Campagna structures are relatively complicated, since each o~
them contains some form of pressure relief valve, Thus, a need exists for a simple inexpensive pressure release for a manhole cover.
The object of the present invention is to meet the above-identified need by providing a manhole cover incorporatina a relatively simple pressure release device.
Accordingly, the present invention relates to a manhole cover comprising solid plate means for closing a manhole; at least one opening in said plate means for releasing pressure from the manhole; flexible plug means normally closing said opening, -the area of said plug means being slightly greater than the area of said opening wherebv the plug means is normally retained - 1 - ~æ, ~Z~2~L6~ ~

in said opening by friction, and permitted to escape from said opening when acted on by a predetermined manhole pressure, which is less than the pressure required to lift the cover.
The invention will now be described in greater detail with reference to the accompanying drawings, which illustrate preferred embodiments of the invention, and wherein:
Figure 1 is a plan view of a manhole cover in accordance with the present invention;
Figure 2 is a bottom view of the cover of Fig. l;
Figure 3 is a side elevation view of the cover of Figs, 1 and 2;
Figure 4 is a cross section of a portion of the cover of Figs. 1 to 3;
Figure S is a side elevation view of a second embodiment of the manhole cover of the present invention; and Figure 6 is a partly exploded, cross-sectional view of a portion of the cover of Fig. 5.
With reference to Figs. 1 to 4 of the drawings, a man-hole cover in accordance with the present invention generally indicated at 1 includes a circular plate 2 with a cylindrical sleeve 3 extending downwardly therefrom. The plate 2 has a larger diameter than the sleeve 3 for defining a shoulder 4 for resting on the ledge normally provided in a manhole opening frame (not shown). A plurality of openings 6 are provided in the plate 2. The sides of the openings 6 are defined by ~he inner ~a2;~6s9, periphery of the sleeve 3, an~ by a plurality of parallel partitions 7 and 8 at right angles to each other. As best shown in Figs. 3 and 4, the partitions 7 and 8 inc:Lude downwardly tapering bottom portions 9, and upwardly tapering top portions 10, with a shoulder 12 therebetween. The bottom end 13 of each partition 7 and 8 is rounded.
The second embodiment of the invention (Eigs~ 5 and 6) has the same appearance from above as the cover of Figs. 1 to 4, The cover of Flgs. 5 and 6 includes a top plate 2, a sleeve 3, and partitions 15 and 16 similar to partitions 7 and 8, respectively.
The partitions 15 and 16 include bodies 17 which taper upwardly throughout their lengths from rectangular bottom portions 18, with shoulders 20 between the bodies and bottom portions.
The openings 6 in each embodiment of the invention are intended to receive downwardly tapering hollow plastic plugs generally indicated at 21 (Fig. 6). Each plug 21 has the same shape as the hole 6, i.e. square. Each of the plugs 21 is defined by a top wall 22 and side walls 23. The plugs are slightly larger in area than the holes 6, so that the plugs can be jammed into the holes to a position in which the bottom surface of the plugs rest on the shoulders 12 or 20, and the top surfaces 25 are flush with the top edges of the partitions 7 and 8 or 15 and 16.
The dimensions and Elexibility of the plugs 21 are such that the plugs are normally retained in the holes 6 by friction. However, when the pressure in the manhole reaches a level substantially ~L2~ 9 below the pressure necessary to lift the cover from the manhole, the plugs 21 are discharged from the holes 6 to release such a pressure. Thus, the danger of the manhole being suddenly launched into the air is substantially reduced or eliminated.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A manhole cover comprising solid plate means for closing a manhole; at least one opening in said plate means for releasing pressure from the manhole; flexible plug means normally closing said opening, the area of said plug means being slightly greater than the area of said opening whereby the plug means is normally retained in said opening by friction, and is permitted to escape from said opening when acted on by a predetermined manhole pressure which is less than the pressure required to lift the cover.

2. A manhole cover according to claim 1, wherein said opening and plug means taper downwardly.

3. A manhole cover according to claim 1 or 2 including shoulder means in said opening for limiting movement of said plug means downwardly into the opening.

4. A manhole cover according to claim 1 or 2, including a plurality of openings, and a plurality of plug means for closing said openings.