Seal for a joint or juncture – Seal between relatively movable parts – Circumferential contact seal for other than piston
Reexamination Certificate
2001-05-23
2003-01-07
Knight, Anthony (Department: 3676)
Seal for a joint or juncture
Seal between relatively movable parts
Circumferential contact seal for other than piston
C377S099000, C377S099000, C377S099000, C377S099000
Reexamination Certificate
active
06502827
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to sealing devices. In particular, although not exclusively, the invention relates to a gland wherein fluid pressure is applied to energise the follower. The invention also relates to repair and replacement of conventional sealing devices.
BACKGROUND TO THE INVENTION
A conventional shaft sealing arrangement is illustrated in FIG.
1
and indicated by numeral
10
. The shaft sealing arrangement
10
is arranged to provide a fluid seal around the shaft
11
where the shaft
11
exists the machine housing through a portion of the machine housing
12
. The portion
12
defines an annular recess adjacent the shaft
11
in which packing
14
is provided. A gland follower
16
operates to compress the packing
14
within the recess. As the packing
14
is compressed axially ie parallel to the axis of the shaft
11
, the packing
14
applies a radial force to the shaft
11
, thereby sealing against the shaft. The gland follower
16
is secured to the portion
12
of the machine housing by bolts
18
and nuts
20
. The nuts and bolts
18
,
20
can also control the compressive force applied by the gland follower
16
to the packing
14
. As shown, the shaft sealing arrangement
10
is conventionally assembled between the portion
12
of the machine housing and the bearing
13
. The bearing
13
is retained in place by bearing bracket
15
secured by fasteners
17
.
A disadvantage of this arrangement is that as the packing
14
wears the compressive force applied to the packing
14
will decrease. Therefore, regular maintenance checks are required. This may involve regular tightening of the nuts
20
. The labour involved in maintaining conventional sealing arrangements
10
in operating order is therefore high.
The illustrated arrangement in
FIG. 1
shows considerable space between the machine housing
12
and the bearing
13
. This is not always the case and where the portion
12
is closely spaced to the bearing
13
, difficulties will be encountered in accessing and tightening nuts
20
. Further difficulties will also be encountered in repacking the packing
14
as required.
It is therefore an object of the present invention to provide a sealing device which overcomes or at least ameliorates some of the above mentioned disadvantages. Additionally, it is an aim of a preferred embodiment of the present invention to replace of the present invention is at least to provide the public with a useful choice.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, there is provided a sealing device for sealing about a rotatable member extending through a machine housing, the sealing device including: primary sealing means disposed in a recess of the machine housing for sealing against the rotatable member; a follower for compressing the primary sealing means; a follower housing connected to the machine housing and of annular form for mounting about the rotatable member with an axial direction of the follower housing aligned with the rotational axis of the rotatable member, wherein the follower housing includes inner and outer annular walls, with the follower having an annular body portion which is slidingly engageable with both the inner and outer annular walls, an annular chamber being defined by the inner and outer annular walls and a pressure face of the follower, the chamber having means to receive fluid; the follower being slidable within the follower housing generally in the axial direction and having sliding interfaces for interfacing with the inner and outer walls of the follower housing, there being further provided, secondary sealing means at the sliding interfaces for sealing against the egress of fluid from the chamber along the sliding interfaces of the follower.
The sealing device defined above may be used in any application where a conventional sealing device is used eg. pumps, augers, valves.
The primary sealing means may be in the form of packing conventionally used in sealing devices although other sealing means such as elastomeric rings are considered within the scope of the present invention.
Preferably the follower is in the form of an annular piston received within the follower housing. In a preferred form of the invention, the piston further includes an annular extension extending beyond the follower housing and into the recess in the machine housing. The follower may come in two or more parts such as two symmetrical halves to aid assembly.
The follower housing may come in two or more parts such as two symmetrical halves to aid assembly.
The secondary sealing means may be of any form although conventional piston rings are the preferred form.
The sealing device may be adapted to utilise any fluid such as air or hydraulic fluid for energising the follower. When the sealing device is used in applications transferring a clean liquid eg. water, oil or stream, a connection may be provided from the discharge of the transferring apparatus to the sealing device. In other applications, an independent fluid supply may be adopted. This might include a source of compressed air or a hydraulic system could be employed.
Additionally, control means may be provided to control the fluid pressure. Preferably the control means provides a constant fluid pressure to the chamber. Thus if the chamber starts to leak, further fluid will be provided to maintain the pressure and the sealing device remains in operation. The control system may be adapted to provide an alarm condition when the amount of further fluid reaches an unacceptable level. The control system may comprise a P.L.C. with feedback. Alternatively, an air cylinder with a regulator may be appropriate.
In another preferred form of the invention, the follower may comprise two parts, a first packing portion and a second piston portion. The first packing portion maybe in the form of an annular body portion with an annular extension. The second piston portion may be in the form of an annular piston. The two portions may be held in spaced configuration by a biasing means urging the two portions apart, such as a spring. Moreover, instead of an open fluid system whereby the chamber is supplied with fluid to a predetermined pressure, the fluid system may be essentially closed. For example, the follower housing may define a forward chamber between the first follower portion and the forward wall of the housing and a rear chamber between the second piston portion and the rear wall of the follower housing. The forward and rear chambers are interconnected for fluid flow therebetween. Furthermore, the pressure face of the first follower portion against which the fluid acts in use may be smaller than the pressure face of the second portion to maintain a greater force against the second portion than the first portion, this difference being balanced by the reaction force acting against the first follower by the packing. As the packing wears with a consequent reduction in the reaction force applied to the first follower portion, the greater force on the second follower portion urges both follower portions forwardly, with the force being transmitted through the spring to the first follower portion. This brings about a consequent reduction in the volume of the forward chamber. With the first and second chambers fluid-filled in use, a reduction in the volume of the forward chamber will cause fluid to flow to the second chamber. As the area of the pressure face of the second follower portion is greater than the first, the second follower portion will not move the same distance as the first follower portion. The spring thus takes up the slack between the two follower portions.
It will be appreciated that the various parts are unlikely to move in step-wise fashion as explained above. Rather, it is expected that the various parts of the device move gradually to retain equilibrium of the various forces acting on the various parts.
In accordance with a second aspect of the present invention, there is provided a kit for sealing about a rotatable member extending through a machine housing
GRM Distributors Limited
Peavey Enoch E
Workman & Nydegger & Seeley
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