Pressure accumulator

A pressure accumulator having a shell with the upper portion forming a dome having an axial gas opening, the shell having an axial oil port opposed to said gas opening, a holder in said shell supporting a bladder, a movable convex structure positioned in the shell between the holder and the gas opening, said convex structure having an annular ring elastic sealing material positioned on the exterior of said convex structure and adapted to engage the inner surface of said shell.

The present design concerns an improvement to the accumulator. To describe 
it more specifically, the design offers an improved sealing structure for 
the opening of the accumulator which confines the gases. 
Well-known designs for conventional accumulators, such as disclosed in 
Japanese U.M. application No. 56/24321, filed Feb. 23, 1981, are shown in 
FIGS. 1 and 2 and are characterized by the fact that an amply elastic 
rubber bladder (b) placed in the interior space (a) seals nitrogen gas 
within. The elasticity of this bladder serves to maintain the pressure of 
the fluid body. In such structures, the nitrogen gas entering through 
gas-sealing opening (d) created at the top of the shell (c) is contained 
by a sealing structure (FIG. 1) in which said gas-sealing opening (d) is 
composed of two stages--a section with a large diameter (d.sub.1) and 
another with a smaller diameter (d.sub.2)--, a steel ball (e) being 
inserted inside the section with a large diameter (d.sub.1) and a bolt (f) 
being screwed in place to secure the structure. In another sealing design 
(FIG. 2), a bolt (h) and nut (i), having a washer (g) inserted between 
them, are screwed in place at the center of the gas-sealing opening (d). 
According to such technology, however, the above-described sealing 
structure are used at the gas-dealing opening (d) and when said opening 
(d) is accidentally released or damaged, the nitrogen gas contained within 
the inside chamber (a) in condensed form may be released with great force 
thereby increasing the operative risk. Fixation of the gas-sealing opening 
(d) by electric welding to prevent such an occurrence resulted in the 
burning or deformation of the sealing structures such as the 
above-mentioned bolt (f), leaving many unsolved problems in the design of 
the sealing structure. 
In view of such a situation, the present design for an improved accumulator 
is proposed to solve all the problems described above. Specifically, the 
present accumulator forms a dome-like structure for the upper half of the 
shell with a gas-sealing opening near the apex which corresponds to the 
upper edge of the axial direction. It is equipped with a projecting holder 
to affix the bladder lining the inner lateral surface of said shell. In 
such an accumulator, a slightly convex structure with an opposing surface 
having a curvature roughly identical to that of the inner surface of the 
upper half of the said shell is placed above said holder in a manner such 
that said structure is slightly mobile in the axial direction. In 
addition, a rubber-like elastic sealing material is attached in the area 
between said slightly convex structure and the upper half of the shell. 
Thus, with pressure changes within the internal chamber, the 
aforementioned convex structure moves slightly along the axial direction 
(and travels up with a rise in the pressure) to seal the nitrogen gas 
contained by the above-described sealing material.

The application of the accumulator of the present design is further 
described with the aid of FIG. 3. The figure shows a metal shell (1) which 
is approximately spherical in shape. It forms a dome-like inner wall (1a) 
for the upper half in the upper section in the axial direction (the upper 
section of the figure) as well as a ring-like stepped portion (1b) at the 
lower section which projects outward at the periphery. At the apex of said 
shell (1) which corresponds to the uppermost area in the axial direction, 
gas-sealing opening (2) is created and is fitted with screw (3). At the 
base, the lowest section of said shell (1), oil port (4) is welded. A 
holder (5) with a hook-shaped cross section serves to hold rubber bladder 
(6). Said holder is positioned at the stepped portion (1b) of the 
aforementioned shell (1) and is affixed to inner lateral wall (1c) of 
shell (1). A slightly convex metallic structure (7) has an opposing 
surface (7a) with a curvature roughly identical to that of inner wall (1a) 
of the upper half of the aforementioned shell (1). The outer diameter of 
theperipheal section (7b) is made slightly smaller than the inner diameter 
of the area formed by inner lateral wall (1c) of shell (1) so that the 
metallic convex structure may be inserted above holder (5). A small space 
(8) is formed between the peripheral section (7b) of the convex structure 
and holder (5) so that said convex structure (7) may move slightly along 
the axial direction when it is inserted above holder (5) within shell (1). 
Furthermore, an annular grove (7c) is formed in the midsection of said 
convex structure (7) and an O-ring (9), made of a rubber-like elastic seal 
material, is attached to said ring-like concave section (7c) in such a 
manner that it projects from the opposing surface (7a). In the figure, a 
vulcanized metal poppet (10) is attached to bladder (6) and serves to 
close hole (4a) created in oil port (4). 
The accumulator constructed in the manner described above is explained 
next. The internal chamber of shell (1) is divided by bladder (6) into an 
upper section (11) and a lower section (not indicated in the figure). An 
appropriate quantity of nitrogen gas is sealed inside after it enters 
upper section (11) through gas-sealing opening (2). Nitrogen gas then 
travels between inner wall surface (1a) of the upper half of shell (1) and 
opposing surface (7a) of slightly convex structure (7), after which the 
gas-sealing opening (2) is fastened with screw (3) and the accumulator is 
ready for use. When fluid flows from oil port (4) into the lower section, 
pushing bladder (6) up and raising the nitrogen gas pressure, such 
pressure forces convex structure (7) upward, and washer (9) attached to 
the ring-like concave part (7c) of the convex structure (7) into contact 
with the inner wall surface (1a) of the upper half of shell (1), thus 
sealing nitrogen gas in that section. In such a condition, therefore, 
nitrogen gas is unlikely to be released at a great force and the structure 
is safe even when screw (3) is accidentally loosened or gas-sealing 
opening (2) is damaged. 
The accumulator having the above described structure is produced in the 
following manner: first, shell (1), as shown in FIG. 4, is produced, and 
the slightly convex structure (7) with washer (9), holder (5) meshed with 
bladder (6), and oil port (4) are inserted in it; the lower half of shell 
(1) is then subjected to a drawing process; and oil port (4) and the base 
of shell (1) are welded together. If gas-sealing (2) is to undergo 
electrical welding after it is fitted with screw (3), it is desirable that 
ring-like convex section (7c) of slightly concave structure (7), where 
washer (9) is attached, be formed at a certain distance from gas-sealing 
opening (2) so that said washer (9), a rubber-like elastic material that 
has already been installed in shell (1), is not exposed to the thermal 
effect of the electrical welding process. Washer (9) may be attached on 
inner wall surface (1a) of the upper half of shell (1), or else the 
ring-like concave section (7c) is set at both inner wall surface (1a) of 
the upper half of shell (1) and slightly convex structure (7) while washer 
(9) is inserted between the two. Besides threading, screw (3) may be 
pressure-fitted in gas-sealing opening (2). 
The accumulator of the present design has the above-described structure. In 
such an accumulator, a slightly convex structure is inserted in the upper 
half of the shell which has a gas-sealing opening. Nitrogen gas is sealed 
in by adjoining the rubber-like elastic sealing material attached to said 
convex structure and the inner wall surface of the shell. Such a design 
effectively prevents an accidental overflow of nitrogen gas from the 
gas-sealing opening and greatly increases the safety level of the 
operation. Therefore such a design has a significant practical value.