Fluid handling – Processes – Cleaning – repairing – or assembling
Patent
1998-09-30
2000-08-22
Walton, George L.
Fluid handling
Processes
Cleaning, repairing, or assembling
137 1518, 251214, 277308, 277346, 277510, 277536, 277539, 277540, F16K 4104, F16J 1522, F16J 1524
Patent
active
061055964
DESCRIPTION:
BRIEF SUMMARY
This invention relates to fluid sealing and is in particular concerned with sealing against leakage along rotating and/or rotatable shafts, or reciprocating and/or reciprocable shafts.
Fluid control valves present a significant sealing problem due to conflicting requirements. The fluid seal on the valve actuator shaft must be effective, but not so physically tight as to make operation of the valve excessively difficult. Furthermore, because of the indeterminate frequency of operation, the shaft seal must be capable of maintaining a satisfactory seal both during operation and before and afterwards in periods of protracted idleness.
Of course, packings and/or seals for such applications have been in common use for many years. Traditional gland seals for valve stems and sliding/rotating shafts have used essentially textile materials such as ropes and braids, usually impregnated with a lubricant/sealing composition. For example, braided packings having a generally square cross-section and impregnated with a material such as PTFE or a graphite composition are widely used. A measured length of the braid is formed into a ring and a number of these rings are packed into an open-topped chamber encircling the shaft which is to be sealed. The chamber, or "stuffing box" is then closed, sometimes by means of a screw-threaded adaptor but more usually by means of a gland follower which is retained by a stud follower which is retained by stud bolts and nuts, the tightening of which applies pressure to the rings of braid in the chamber.
Some of the axial pressure is converted into radial pressure on the shaft and it is this radial pressure which creates a seal. Unfortunately, because of the geometry inherent in such a simple system, the actual amount of radial pressure developed is suitable only for use in relatively low pressure applications, or where the mobility of the fluid being sealed is not that great. But for gases under high pressure, the simple traditional stuffing box technique is unsatisfactory, because there are obvious limits to the axial pressure which can be employed without making it extremely difficult to rotate and or axially slide the shaft.
For these reasons, stuffing box designs have become much more complicated. Thus it has been proposed to replace conventional, impregnated braided packings with a set of rings moulded from graphite or a similar relatively conformable material. In order to increase the radial sealing pressure on the shaft, it has also been proposed to shape or contour the interface regions of abutting rings so that axial pressure is more efficiently converted to radial pressure. The use of wedge shaped rings has become popular in order to achieve this, as illustrated in numerous patents; see for example WO/81/02454.
However, whilst such wedge shaped rings are successful, they do not lend themselves to ease of manufacture, or ease of use, since it is possible to install them incorrectly, the angles between the mating faces of the individual rings being not the same. It is therefore an object of the present invention to provide a relatively simple packing assembly which is easy to manufacture/install.
According to the present invention, a rotary and/or sliding shaft seal adapted for use in a stuffing box comprises a first moulded graphite ring of generally triangular cross-section, one side of which is in use generally perpendicular to the longitudinal axis of a rotatable and/or slidable shaft the surface of which is to be sealed in an axial direction against fluid leakage therealong, and a second side which is in use disposed generally parallel to said shaft to engage the inner wall of a housing surrounding said shaft, a second moulded graphite ring of generally triangular cross-section and of generally similar dimensions to the first moulded ring, said second ring being in use installed in inverted relation to the first ring to define therebetween an axially extending void around said shaft together with a third moulded graphite ring having a triangular cross-section and installed bet
REFERENCES:
patent: 3126207 (1964-03-01), Eikelberner
patent: 4328974 (1982-05-01), White et al.
Hoyes John R.
Thorpe Liam C
Flexitallic Investments, Inc.
Shaddox Robert C.
Walton George L.
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