Manway cover balancing mechanism

A manway is defined by a cylindrical portion of a vessel wall and is closed by a cover pivotally movable between open and closed positions by means of a hinge mechanism including external brackets on the cover and the wall portion interconnected by a hinge pin. The opposite ends of the hinge pin carry bushings, on which are respectively disposed two torsion springs. Each spring has a vessel wall end portion disposed parallel to the hinge pin, the vessel wall end portions being respectively received in the opposite ends of a coupling sleeve engageable with bearing surfaces on one of the brackets. The other ends of the two torsion springs are respectively disposed generally perpendicular to the hinge pin and are received slidably through eyebolts fixed to the cover bracket.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a cover for a manhole or manway which provides 
access to an enclosed space, such as a tank, or other type of storage 
vessel. In particular, the invention relates to mechanisms for balancing 
the weight of the cover to assist in manual movement of same between open 
and closed positions. 
2. Description of the Prior Art 
Operating procedures for tank cars and other types of tank vessels commonly 
require that operating personnel not be required to lift in excess of a 
predetermined weight, e.g., 50 pounds. Hinged manway covers for such 
vessels typically weigh in excess of 100 pounds. Thus, the lifting force 
required at the handle to open the manway cover typically exceeds the 
allowable maximum lifting weight. Accordingly, it is known to provide such 
manway covers with balancing or lifting assisting mechanisms to provide a 
spring-biased assist to the operating personnel. 
One such arrangement is made and sold by Midland Manufacturing Corp. and 
includes a pair of torsion springs mounted on opposite ends of the cover 
hinge pin. Each torsion spring has one end thereof received through an 
opening in the portion of the vessel wall defining the manway, and the 
other end thereof disposed through an eyebolt which is fixed through an 
opening in the manway cover. While this arrangement works well, it cannot 
be used with pressurized vessels because of the proscription against 
drilling holes in the cover or in the vessel wall which defines the 
manway. Standard operating procedures typically prohibit forming holes 
through or welding directly to a pressurized vessel wall. 
Balancing mechanisms which are mounted entirely externally of the manway 
and the cover have been provided and are disclosed, for example, in U.S. 
Pat. Nos. 4,137,669 and 4,038,520. But both of these mechanisms are quite 
complex and consume a considerable amount of space, projecting a 
substantial distance radially from the manway. 
SUMMARY OF THE INVENTION 
It is a general object of the invention to provide an improved balancing 
mechanism for a manway cover which avoids the disadvantages of prior 
balancing mechanisms while affording additional structural and operating 
advantages. 
An important feature of the invention is the provision of a balancing 
mechanism for a manway cover which is mounted entirely externally of the 
manway and the cover and does not require the formation of holes in or the 
welding directly to either the cover or the manhole-defining wall or 
manway. 
In connection with the foregoing feature, another feature of the invention 
is the provision of a balancing mechanism of the type set forth which can 
readily be retrofitted to existing pressurized vessel manway covers. 
Still another feature of the invention is the provision of a balancing 
mechanism of the type set forth which is of simple and economical 
construction. 
Yet another feature of the invention is the provision of a balancing 
mechanism of the type set forth which is compact and does not extend 
substantially beyond the outlines of the existing manway and cover. 
These and other features of the invention are attained by providing a 
balancing mechanism for a cover for a manway defined by a portion of a 
pressurized vessel wall, wherein the cover is pivotally mounted for 
movement between open and closed positions relative to the manway by 
externally mounted hinge structure which includes a hinge pin coupling 
external first and second hinge brackets respectively on the cover and the 
wall portion, the balancing mechanism comprising: torsion spring mechanism 
carried the hinge structure and having first and second end structures, 
first coupling mechanism disposed externally of the manway and the cover 
and cooperating with one of the end structures and with the first hinge 
bracket to cause the one end structure and the cover to move together, and 
second coupling mechanism disposed externally of the manway and the cover 
and cooperating with the other of the end structures and with the second 
hinge bracket effectively to prevent movement of the other end structure 
in response to movement of the cover, the torsion spring mechanism being 
oriented so as to resiliently urge the cover toward the open position 
thereof. 
The invention consists of certain novel features and a combination of parts 
hereinafter fully described, illustrated in the accompanying drawings, and 
particularly pointed out in the appended claims, it being understood that 
various changes in the details may be made without departing from the 
spirit, or sacrificing any of the advantages of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIGS. 1-3, there is illustrated a portion of a storage vessel 
10 defined by a wall 11. The vessel 10 may be of any of a number of 
different types of tanks, such as that used in a railway tank car, and is 
preferably of the pressurized type designed for storing the contents 
thereof under superatmospheric pressure. The vessel 10 is provided with a 
manway structure 12 which includes a saddle 13 fixedly secured to the 
vessel wall 11, as by welding, and including an upstanding cylindrical 
wall 14 which cooperates with an aligned opening in the vessel wall 11 to 
define a manway 15 (see FIG. 3) in a known manner. The cylindrical wall 14 
may be provided with a radially outwardly extending annular flange 16 
midway between the upper and lower ends thereof. Fixedly secured to the 
outer surface of the cylindrical wall 14 at equiangularly spaced apart 
locations thereon and just above the flange 16 are a plurality of inverted 
U-shaped hold-down brackets 17, each having aligned bores 18 through the 
legs thereof. 
The manway 15 is provided with a cover 20 which includes a circular, 
slightly domed wall 21 provided with a radially outwardly projecting 
handle 22 extending from the wall 21. Coaxially therewith is a cylindrical 
flange 23 having a plurality of spaced-apart axially extending projections 
24, the flange 23 having an inner diameter very slightly greater than the 
outer diameter of the cylindrical wall 14 of the manway structure 12 and 
adapted to be telescopically received thereover. The cover wall 21 has a 
plurality of equiangularly spaced-apart and radially outwardly extending 
lobes 25, each having a slot 26 formed therein. The lobes 25 are arranged 
so as to be respectively vertically aligned with the hold-down brackets 
17. Mountable in the hold-down brackets 17 are a plurality of hold-down 
lugs 27 in-the form of eyebolts, each having one end fixed to a pivot pin 
28 extending through the aligned bores 18 in the associated bracket 17 and 
being externally threaded at the other end. Each of the lugs 27 has a 
length such that, when it is pivoted to an upright position, it extends 
through the associated slot 26 in the cover 20. Nuts 29 are respectively 
threadedly engageable with the hold-down lugs 27 firmly to clamp the cover 
20 in its closed position, illustrated in the drawings. 
The cover 20 is adapted to be pivotally moved between the illustrated 
closed position and an open position (not shown) by a hinge assembly 30, 
which includes a manway bracket 31 mounted on the manway structure 12 and 
a cover bracket 40 mounted on the cover 20, the brackets 31 and 40 being 
hingedly interconnected by a pivot pin in the nature of a hinge bolt 49. 
More particularly, the manway bracket 31 includes a base wall 32 having 
the outer end thereof upturned to define an upstanding lip 33, and a pair 
of substantially parallel side walls 34 respectively fixed to the base 
wall 32 and the lip 33 at the opposite sides thereof. Each of the side 
walls 34 is provided with an upstanding pivot ear 35, the ears 35 having 
aligned pivot bores (not shown) formed therethrough. The side walls 34 
have vertical end edges 36 which are fixed to the outer surface of the 
manway cylindrical wall 14, as by welding, and the base wall 32 has an end 
edge 37 which is arcuately concave so as to fit matingly against the 
manway cylindrical wall 14 and is also fixed thereto as by welding. The 
upper edges of the side walls 34 inboard of the ears 35 define 
substantially coplanar bearing surfaces 38 (FIG. 2). 
The cover bracket 40 also includes a pair of substantially parallel side 
walls 41 which are dimensioned to be disposed in use, respectively just 
inboard of the manway bracket side walls 34. Each of the side walls 41 has 
a pivot ear 42 with aligned pivot bores (not shown) therethrough. Each of 
the side walls 41 is fixed to the cover 20, as by welding, or is cast 
unitary therewith and extends along the outer surface of the cover wall 21 
to define elongated, tapered flanges 43 upstanding from the cover wall 21. 
The cover bracket 40 also includes a base wall 44 interconnecting the side 
walls 41 at their distal ends, the base wall 44 having a stepped 
configuration, including an upper portion 45, a step portion 46 and a 
lower portion 47. A stiffening web 48 extends from a location along the 
underside of the cover wall 21 radially outwardly of the flange 23 to the 
base wall 44 intermediate the side walls 41. 
In use, the cover bracket 40 is adapted to fit inside the manway bracket 31 
when the cover 20 is disposed in its closed position, with the bores 
through the pivot ears 35 and 42 being coaxially aligned for receiving 
therethrough the hinge bolt 49, hingedly to interconnect the cover 20 and 
the manway structure 12 for pivotal movement of the cover 20 between its 
open and closed positions about the axis of the hinge bolt 49, all in a 
known manner. Preferably, the hinge bolt 49 has an enlarged head 49a at 
one end and is externally threaded at its opposite end. 
The hinge assembly 30 also includes a balancing mechanism 50, constructed 
in accordance with the present invention. The balancing mechanism 50 
includes a pair of bushings 51 and 51A which are constructed as mirror 
images of each other. Each of the bushings 51 includes a cylindrical solid 
body 52 provided at one end thereof with a radially outwardly extending 
annular flange 53 and having a cylindrical axial bore 54 therethrough 
provided at the flanged end thereof with an enlarged-diameter counterbore 
55. The bore 54 is dimensioned to freely receive therethrough the hinge 
bolt 49. The balancing mechanism 50 also includes a pair of washers 56 
which are fitted over the hinge bolt 49 and respectively abut the outer 
surfaces of the pivot ears 35 of the manway bracket 31. In assembly, the 
hinge bolt 49 is received through the bushing 51A, with its head 49a 
seated against the bottom of the counterbore 55. The hinge bolt 49 is then 
received through one washer 56, the pivot ears 35 and 42 and then through 
the other washer 56 and the bushing 51, until the bushings 51 and 51A abut 
the associated washers 56. Then a nut 58 is threadedly engaged with the 
distal end of the hinge bolt 49 until it abuts the base of the counterbore 
55 to hold the assembly together. A cotter pin 59 is received through a 
radial bore through the threaded end of the hinge bolt 49 to prevent 
accidental removal of the nut 58. 
The balancing mechanism 50 also includes a pair of torsion springs 60 and 
60A which are arranged as mirror images of each other. Each of the torsion 
springs 60 and 60A has a plurality of coils or turns dimensioned to fit 
coaxially over an associated one of the bushings 51 and 51A. Each of the 
springs 60 has a manway end 61 which is bent inwardly back along the 
outside of the coil, substantially parallel to the axis of the coils, the 
ends 61 having a length such that, when the springs 60 and 60A are 
respectively disposed on the bushings 51 and 51A, as illustrated in FIG. 
3, the ends 61 respectively extend inwardly to a point where they nearly 
touch each other. The manway ends 61 are respectively received in opposite 
ends of a tubular sleeve 62, which has a length sufficient to extend 
outboard of the side walls 34 of the manway bracket 31. Each of the 
torsion springs 60 also has a cover end 63 which projects tangentially 
from the spring coils generally orthogonal to the manway ends 61, the ends 
63 respectively extending along the outside of the cover bracket flanges 
43. The ends 63 respectively have sleeves 64 fitted thereover and are 
retained in eyebolts 65. More specifically, two eyebolts 65 are 
respectively received through complementary bores in the cover bracket 
flanges 43, with washers 66 being respectively disposed on each side of 
each flange 43. Each eyebolt 65 has an enlarged eye 67 at one end which 
freely slidably receives therethrough the associated torsion spring end 63 
and its associated sleeve 64. The inner ends of the eyebolts 65 are 
externally threaded for engagement with associated nuts 68 to securely 
mount the eyebolts 65 in place. Cotter pins 69 may be received in radial 
bores in the threaded ends of the eyebolts 65 to prevent accidental 
removal of the nuts 68. 
In assembly, it will be appreciated that the torsion springs 60 and 60A 
are, respectively, fitted over the bushings 51 and 51A prior to their 
assembly with the hinge bolt 49. When the balancing mechanism 50 is 
assembled, the bushing flanges 53 prevent the torsion springs 60 and 60A 
from moving axially off the ends of the bushings 51 and 51A. The torsion 
springs 60 and 60A are arranged and configured so that they resiliently 
urge the cover 20 toward its open position with a predetermined force, 
which is insufficient in itself to move the cover 20, but which serves to 
reduce the manual force which must be exerted by an operator in lifting 
the cover 20 to its open position. In this regard, it will be appreciated 
that the eyebolts 65 cooperate to anchor the cover ends 63 of the torsion 
springs to the cover bracket 40, effectively preventing any pivotal 
movement of the torsion spring ends 63 relative to the cover bracket 40 
while accommodating a slight reciprocating sliding movement thereof in the 
eyes of the eyebolts 65 as the cover 20 is moved between its open and 
closed positions. The sleeve 62 cooperates with the manway ends 61 of the 
torsion springs 60 and 60A to anchor them to the manway bracket 31. More 
specifically, the sleeve 62 spans and engages the bearing surfaces 38 of 
the manway bracket 31 beneath the stiffening web 48 of the cover bracket 
40. This effectively prevents pivotal movement of the manway ends 61 
relative to the manway bracket 31, since the manway ends 61 are 
resiliently urged toward the bearing surfaces 38. 
It is a significant aspect of the invention that the balancing mechanism 50 
does not require that any openings be formed in the pressure vessel 10 or 
that any additional weldments be made thereto. More specifically, no such 
openings need be formed in or weldments need be made to the pressure wall 
21 of the cover 20 or the cylindrical wall 14 of the manway structure 12. 
The balancing mechanism 50 is disposed entirely externally of the manway 
structure 12 and the cover 20. Furthermore, it will be appreciated that 
the balancing mechanism is of simple and economical construction and can 
readily be retrofitted to an existing hinge assembly by simply 
substituting the elongated hinge bolt 49 for the standard hinge bolt. The 
upper portion 45 of the cover bracket base wall 44 is disposed so as to 
bear against the upper edge of the manway bracket lip 33 to limit the 
opening movement of the cover 20 and support the cover 20 in its open 
position, all in a known manner. 
When the cover 20 is in its open position, the balancing mechanism 50 will 
continue to urge it toward that position, although with a lesser force 
than it exerts when the cover 20 is in the closed position. The force 
exerted by the balancing mechanism 50 increases as the cover 20 is lowered 
back to its closed position, serving to counterbalance the weight of the 
cover 20 and thereby assist in both closing and opening thereof. In a 
constructional model of the invention, the torsion springs 60 and 60A are 
such that they will exert a force sufficient to reduce the overall manual 
lifting force required to lift the cover 20 to a value less than the 
maximum permitted by applicable operating procedures which, in typical 
applications, is approximately 50 pounds. 
From the foregoing, it can be seen that there has been provided an improved 
balancing mechanism for a vessel manway cover which is mounted entirely 
externally and requires neither holes to be formed in nor welds to be 
applied directly to the pressurized walls of a vessel, the balancing 
mechanism being of simple, compact and economical construction and being 
adapted for easy retrofitting to existing hinge structures.