SAFETY MANHOLE COVER

TAMPON DE SURETE POUR PUITS DE VISITE

English 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.

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.

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
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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
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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
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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.