Quick opening manhole cover assembly

A quick opening manhole cover including a clamping flange (16) which captures the ears (48) of a locking ring (46) upon rotation of the locking ring with respect to a manhole cover (40). The manhole cover has an O.D. less than the I.D. of the manhole for axial movement into the manhole. A gasket (42) about the manhole cover is clamped between the locking ring (46), manhole cover (40) and against the manhole surface upon axial movement of the manhole cover towards the locking ring.

BACKGROUND OF THE INVENTION 
The present invention relates to manhole cover assemblies for glass lined 
steel pressure vessels, and more particularly to a quick opening manhole 
cover assembly for such vessels. 
Glass lined steel pressure vessels are well known in the art and are used, 
for example, by the chemical and food industry to process various 
chemicals and food stuffs. Such vessels can be relatively large, ranging 
in capacity to several thousand gallons, and can be constructed to 
withstand internal pressures of several atmospheres. It is common to 
provide such vessels with manholes to permit entry into the vessel for 
cleaning and inspection. 
Usually, the cover for such a manhole is clamped directly to a flange 
surrounding the manhole opening. The clamps are sized to withstand the 
load necessary to compress a gasket between the manhole cover and the 
flange in order to obtain a leak-free joint. It is not uncommon to use 
many large clamps in order to distribute the load evenly about the manhole 
cover and to use a hand tool, such as a wrench, to individually tighten 
each clamp. Use of a hand tool can result in overtightening that could 
cause distortion of the flange and glass damage. Use of clamps that can be 
removed or left untightened may result in unsafe conditions. For example, 
such clamps or the handtool used to tighten the clamps could drop into the 
vessel and damage the glass lining. 
Moreover, in order to secure the cover in the prior art, each clamp had to 
be individually wrench tightened several times to properly seat the 
gasket. This procedure could take as long as an hour depending upon the 
size of the manhole, the number of clamps used and the pressures expected 
within the vessel. Conversely, to open the manhole cover, each clamp had 
to be loosened and removed. 
The present invention provides a quick opening manhole assembly where the 
manhole cover can be opened or closed within one minute without using hand 
tools. No clamps are used to compress a gasket between the manhole cover 
and the vessel and once an initial seal is made, the pressure within the 
vessel automatically compresses a gasket for a tighter seal. The quick 
opening manhole assembly of the present invention is an integral assembly 
which can be retrofitted to existing glass lined pressure vessels.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings, FIG. 1 shows the quick opening manhole cover 
assembly generally indicated at 10, fixed to a flange 12 about a vessel 
manhole. It should be appreciated that the interior manhole surface 14, as 
well as the interior surface of the pressure vessel (not shown) and the 
surfaces of all elements of the manhole cover assembly 10 exposed to the 
environment of the pressure vessel is provided with a corrosion and 
abrasion resistant glass or ceramic coating as is common in the art. 
One component of the quick opening manhole cover assembly 10 is a collar 
16. Collar 16 is placed about the manhole flange 12 and is fixed to the 
manhole flange by any suitable means such as clamps 18 and bolts 20 
located at spaced intervals about the manhole. 
Upstanding from collar 16 at one side of the manhole opening is a bracket 
22. Pivoted to this bracket at 24 is one end of a bridge structure 26 
which spans the manhole opening. The other end 28 of the bridge rests on 
collar 16 opposite bracket 22. Also attached to the bracket 22 and to 
bridge 26 is a counter balance mechanism 30, the details of which form no 
part of the present invention. 
Bridge structure 26 includes a housing 32. Within the housing is a drive 
nut 34 and drive screw 36. One end of the drive nut extends through the 
housing for attachment to a handwheel 38. Rotation of the handwheel 
rotates nut 34 which in turn causes axial movement of screw 36. The screw 
extends down through the housing for attachment to a manhole cover 40. 
As best seen in FIG. 1 the outside diameter of the manhole cover is less 
than the inside diameter of the manhole so that the cover can move easily 
into and out of the manhole. To this end, turning the handwheel 38 rotates 
screw 36 for moving the manhole cover axially into and out of the manhole 
opening. 
Disposed about the outer periphery of manhole cover 40 is an annular seal 
member 42. Seal 42 may be on O-ring of suitable corrosion resistant 
material or an appropriately clad gasket or the like as is well known in 
the art. As shown in FIGS. 1-3, the outer peripheral surface of manhole 
cover 40 is contoured so that a portion 44 of the manhole cover underlies 
seal member 42 to help retain the seal member on the manhole cover. 
Carried by and supported on manhole cover 40 is a locking ring 46. This 
ring 46 has three ears 48 spaced at 120.degree. intervals about the 
locking ring. These ears are adapted to engage corresponding vertical 
slots and horizontal grooves 50, 52 respectively in collar 16 for purposes 
set out hereinbelow. 
Locking ring 46 is held captive to manhole cover 40 at three points, each 
including a cam lock, one of which is shown in each of FIGS. 1-3. One 
element of each cam lock is a bolt 54 which is threaded to manhole cover 
40 and extends upwardly through a elongated opening 56 in locking ring 46. 
The elongated opening allows for limited rotational movement of the 
locking ring with respect to the manhole cover. Bolt 54 continues 
upwardly, passing through a cam bearing block 58 for attachment to one end 
of a cam lock handle 60. This handle includes a cam surface 62 which bears 
against cam bearing block 58 when the cam handle is rotated for raising or 
lowering manhole cover 40 with respect to the locking ring 46. It should 
be appreciated that in order for operation of the cam lock to raise and 
lower manhole cover 40, there must be some allowance for vertical movement 
of screw 36, drive nut 34 and handwheel 38. To this end, the construction 
of housing 32 is such that drive nut 34 can move vertically within the 
housing until a shoulder 64 on the drive nut engages an end wall 66 of the 
housing (FIG. 1). 
About each bolt 54 is a plug or nut 68 on the manhole cover. This nut is 
adapted to be received in a corresponding recess 70 formed in the bottom 
of locking ring 46 (FIG. 2). Thus, when the nut is not in alignment with 
recess 70 (FIGS. 3 and 4), the manhole cover is prevented from moving 
axially with respect to the locking ring. Recess 70 is brought into 
alignment with plug 68 by rotating the locking ring with respect to the 
manhole cover. Once this alignment is achieved (FIGS. 1 and 2), operation 
of the cam locks can move the manhole cover vertically with respect to the 
locking ring. 
Extending downwardly from about the outer periphery of the locking ring 46 
is a lip 72. When the manhole cover is in a closed position (FIGS. 1 and 
2) this lip extends generally into the space between the outer periphery 
of the manhole cover and manhole surface 14 to provide a seat for the 
O-ring seal 42 as set out hereinbelow. 
For purposes of describing the operation of quick opening manhole cover 
assembly 10, assume the manhole cover 40 is in the full closed position as 
shown in FIGS. 1 and 2. In this full closed position, ears 48 of locking 
ring 46 are fully engaged beneath collar 16 in horizontal grooves 52. In 
addition, manhole cover 40 is positioned so that seal member 42 is 
captured between lip 72 on the locking ring and the underlying portion 44 
of the manhole cover and is seated against manhole wall surface 14. In 
this position the seal member 42 is in intimate, fluid tight engagement 
with each of these components. In addition, if the vessel is pressurized, 
the internal pressure acting on the seal member will force it upward and 
against each of these three components to further enhance the sealing 
engagement. 
In order to open the manhole cover, the vessel is first depressurized. Cam 
lock handles 60 are then rotated so as to disengage the cam locks. This 
rotation moves manhole cover 40 downwardly with respect to locking ring 46 
so that each plug 68 may clear from its corresponding recess 70. If need 
be, handwheel 38 can be rotated to drop the manhole cover an amount 
sufficient to permit the clearance of the plugs from the recesses. With 
plug 68 clear, locking ring 46 may now be rotated to the position shown in 
FIG. 4. This brings ears 48 into alignment with vertical slot 50 and out 
from beneath collar 16. Now the handwheel can be rotated to raise the 
manhole cover until the level of seal member 42 is at the approximate 
level of collar 16. Thereafter, the bridge 26 and the entire manhole cover 
assembly can be pivoted about bracket 22 to clear the manhole opening. 
In order to close the manhole, the procedure is reversed. First the bridge 
26 is pivoted downwardly until its end 28 rests against collar 16. Ears 48 
are then aligned with vertical slot 50 and handwheel rotated to lower 
manhole cover 40 into the manhole opening. This also drops locking ring 46 
to the level of horizontal groove 52. In this position, as shown in FIG. 
3, seal member 42 is clear of both lip 72 on the locking ring and manhole 
surface 14. In order to effect an initial seal, cam lock handles 60 are 
operated to draw manhole cover 40 upwardly toward the locking ring. 
However, in the position shown in FIGS. 3 and 4, this upward movement 
cannot occur because plug 68 is not in alignment with recess 70. Such 
alignment occurs only after locking ring 46 has been rotated with respect 
to the manhole cover so as to carry ears 48 into horizontal groove 52 and 
beneath collar 16. Thus, plug 68 provides a safety feature preventing the 
operation of the cam locks when locking ring 46 is not in a proper 
position. 
After proper rotation of the locking ring (clockwise as viewed in FIG. 4) 
recess 70 is positioned over plug 68 so that the cam locks can be 
operated. Operation of the cam lock draws manhole 40 upward. This carries 
seal member 42 into engagement with lip 72 and squeezes the seal between 
this lip and the underlying portion 44 of the manhole cover. Squeezing the 
seal in this fashion distorts the seal towards the manhole surface 14 to 
effect a preliminary seal between the manhole surface, locking ring 46 and 
manhole cover 40. Thereafter, handwheel 38 is rotated to draw up the 
manhole cover 40 by an amount sufficient to further compress seal member 
42 and fully seat it as shown, for example, in FIGS. 1 and 2. Thereafter, 
when the vessel is pressurized the internal pressure acting on the manhole 
cover and the seal compresses the seal still further between the manhole 
cover and the manhole surface making a tighter seal as pressure increases. 
The quick opening manhole cover assembly of the present invention is 
designed so that the structure used to lift and raise the manhole cover, 
such as bridge 26, screw 36 and the bracket 22 does not support any of the 
load due to internal vessel pressures. The total load from the pressure 
within the vessel is transmitted to the three locking ears 48 and collar 
16. 
While not shown, it should be appreciated that the connection between screw 
36 and manhole cover 40 allows for the slight tipping of the manhole 
cover. This permits the cover to adjust slightly to the configuration of 
locking ring 46 when the cam lock handles 60 are operated so as to permit 
a uniform engagement of seal member 42 between the locking ring and the 
manhole cover. 
As mentioned above, all surfaces of the manhole cover assembly and vessel 
which are exposed to the environment within the vessel is provided with a 
glass or ceramic coating. On the manhole cover 40, this coating 74 extends 
around the manhole cover portion 44 and behind seal member 42. Likewise 
the coating on the vessel interior extends over the manhole surface and 
above the level of seal 42. 
The depending lip 72 on the locking ring need not be ceramic or glass 
coated because it is fully insulated from the vessel interior by the 
sealing engagement of the seal member between manhole surface 14 and 
manhole cover 40. 
Thus, it should be appreciated that our invention provides a manhole cover 
assembly which is quick opening as contrasted to manhole covers for 
pressure vessels of the prior art. In this respect the present invention 
eliminates the need for a plurality of individually operated clamps about 
the periphery of the manhole cover and instead allows quick operation 
without special tools. Also the assembly has a suitable safety feature as 
provided by nuts 68 and recesses 70 to prevent pressurization of the 
vessel without first properly closing the manhole cover.