Pressure vessels having end closures and retainers

A fluid-pressure operated actuator has a body and an end cap which when telescoped in the body provides confronting grooves which receive a circlip in the form of a flexible length of wire spring. The end cap carries an O-ring seal axially only outwards of the circlip. Relative rotation between the body and end cap draws the circlip into position. A threaded plug, which may be secured to the outer end of the circlip, sealingly connects the body and end cap and may permit relative axial and angular movement.

This invention relates to pressure vessels. 
Many pressure vessels consist of a hollow cylinder to which end caps are 
fitted. The end cap may be connected to the cylinder by a circlip. One 
example is in British Patent specification 2123517 or U.S. patent 
specification No. 4,496,071 in which the end cap carries two O-ring seals 
on axially opposite sides of a peripheral groove. When tim end cap is 
assembled to the cylinder, the groove confronts a groove in the cylinder 
and a flexible circlip is inserted into the passage defined by the grooves 
through a passage in the end cap which is sealed by a threaded plug. The 
axially inner O-ring acts as a pressure seal. Although such an arrangement 
is satisfactory, the present invention seeks to provide an improvement. 
Other arrangements are shown in U.S. patent specification Nos. 3,494,652, 
3,986,635 which has a locking device axially outwardly of a seal; 3437230; 
2839218; 2952480. 
According to one aspect of this invention a pressure vessel comprises a 
hollow member, an end closure tn telescope relationship with the hollow 
member, flexible continuous means extending around the end closure and 
operatively connecting the closure and the hollow member, a passage in the 
hollow member for insertion and withdrawal of the flexible continuous 
means, an annular pressure seal between the closure and the hollow member, 
the continuous means at its outer end being secured to a threaded plug 
sealingly receivable in a bore in the passage. 
According to another aspect of this invention a pressure vessel comprises a 
hollow member, an end closure in telescopic relationship with the hollow 
member flexible continuous means extending around the end closure and 
operatively connecting the closure and the hollow member, a passage in the 
hollow member for insertion and withdrawal of the flexible continuous 
means an annular pressure seal between the closure and the hollow member 
only axially outwards of and between the continuous means and the 
environment external of the hollow member. 
There may be a threaded member received in the passage and threadedly 
connected to the closure, and seal means between the threaded member and 
the hollow member for sealing the passage, said passage being shaped to 
permit relative axial movement between the threaded member and the hollow 
member. 
The passage may be shaped to permit also relative angular movement between 
the threaded member and the hollow member. 
The passage may define a radially outwardly facing surface, said seal means 
being engaged between said surface and a head on the threaded member. 
The flexible continuous means may at its outer end be secured to a threaded 
plug sealingly receivable in an aperture In the hollow member. 
The invention may be performed in various ways and two specific embodiments 
with possible modifications will now be described by way of example with 
reference to the accompanying drawings, in which: 
FIG. 1 is an axial section through a pressure vessel; 
FIG. 2 is a scrap view showing end cap and cylinder in one relative 
position; 
FIG. 3 is a side view of FIG. 2; 
FIG. 4 is a view showing the cap and cylinder in another position; 
FIG. 5 is a scrap view showing end cap and piston in one position; 
FIG. 6 is a section of another arrangement; and 
FIG. 7 is a section on the line 7--7 of FIG. 6.

Referring to the drawings, a wall 10 of a hollow pressure vessel or 
cylinder 11 has an inner annular groove 13 of semi-circular cross-section 
towards the end of its bore 12. A passage 14 leading into the groove 13 is 
formed in the wall 10. An end cap or end fitting 19 has an axial extension 
20 of an external diameter which is close fit when telescoped in the bore 
12. A further semi-circular cross-section annular groove 21 is provided on 
the external surface of the extension 20 of the same dimensions as the 
groove 13 so that on assembly of the end cap to the cylinder the grooves 
are aligned to provide a substantially circular section annular groove 22. 
A flexible member in the form of a circlip 26, for example a length of 
close-coiled wire spring cut to an appropriate length, is inserted into 
the groove 22. 
As shown in FIG. 2, the passage 14 has a stepped bore providing radially 
outwardly facing annular shoulders 27, 28. The end cap 19 has a radial 
bore 29 FIG. 3 for receiving the inner end 30 of the flexible continuous 
circlip 26 and an angularly spaced internally threaded radial passage 31 
FIG. 2 in the same transverse plane. 
Axially outwardly of the groove 21 is a peripheral groove 32 receiving an 
O-ring seal 33 which acts both as a pressure seal to prevent escape of 
internal pressure and as a seal which prevents the possibly noxious or 
corrosive exterior atmosphere reaching the circlip and interior of the 
vessel. 
To assemble the vessel, the end cap with O-ring 33 is inserted into the end 
of the cylinder with the passage 14 angularly aligned with the bore 29. 
Tile inner end of the circlip 26 is inserted into the bore 29 and the end 
cap is then rotated relative to the body 10 to draw the circlip 26 into 
the groove 22 until the passage 14 is radially aligned with the passage 31 
(FIG. 4). 
A threaded bolt 40 is then screwed into the passage 31. An O-ring seal 41 
is engaged between the shoulder 27 and tile flat underface 42 of the head 
43 of the bolt 40 to prevent ingress of the external atmosphere to the 
groove 22. 
Because the internal pressure acts on the flexible circlip 26 there may be 
relative axial movement between the body 10 and tile end cap 19. The stem 
44 of the bolt 40 has an axial clearance 45 FIG. 3 in the passage 14 to 
permit such movement and avoid undue strain on the bolt. There is also an 
angular clearance 46 FIG. 4. Preferably the bolt head 43 is wholly 
received in the passage 14 and the head 43 may have an external formation 
requiring a special tool to rotate the bolt. 
In some cases the pressure vessel may be in the form of an actuator 
including opposed pistons 60 with axial racks 61 engaging a pinion on a 
shaft 62 extending to the exterior of the body 10 for operating a valve 
for example. A control unit 50 may alternately supply compressed air to 
the interior of the body 10 between the pistons 60 through line 51 and to 
the interior of the body 10 axially outwardly of the pistons on lines 52, 
53 thus to reciprocate the pistons and oscillate the shaft 62. In such a 
case the line 53 may be in the wall 10 in the form of a passage 54 FIG. 5 
communicating with the interior of the vessel by passage 55 in the wall 10 
and a cut-out 56 in the extension 20 (piston 60 shown in an end position). 
It is important to keep the passages 55 and cut-outs 56 in radial 
alignment and this is achieved by bolt stem 44 engaging in passage 31, the 
clearance 46 being insufficient to permit loss of communication between 
the passage 55 and the cut-out 56. 
Such an arrangement with a pressure seal 33 axially outwards of the circlip 
26 enables a simpler end cap with reduced components, the bolt 40 permits 
axial floating of the end cap within acceptable limits whilst maintaining 
adequate sealing and gives radial alignment of the end cap within 
acceptable limits. 
The end cap may be formed with two cut-outs 56 angularly spaced so that the 
same design of end cap can be used at both ends of the vessel. 
In another arrangement shown in FIGS. 6 & 7 the flexible means, circlip 26, 
may at its outer end be secured to a threaded plug 70 receivable in a 
threaded bore 75 of a stepped bore 71 in the hollow member wall 10 which 
bore is tangential to the peripheral groove 22. This affords means of 
direct access for the flexible member into the peripheral groove. The plug 
has an enlarged head 72 which engages an O-ring seal 73 abutting shoulder 
76. 
The flexible member rotates with the threaded plug on assembly and 
disassembly but locks the plug against inadvertent removal when pressure 
is applied to the interior of the pressure vessel. 
The threaded plug 70 is sealed against internal pressure and also affords 
protection against external environments. 
The threaded bore 75 may be made to intersect the passage 54 so that the 
intersection lies below the threaded plug. Compressed air may then feed 
into the interior of the vessel through the bore 71 into the peripheral 
groove and via clearances provided between the body 10 and the closure 19 
into the cylinder 10. 
The coils of the circlip allow free passage of air. 
This arrangement provides a visual confirmation that the circlip is in 
position.