GB2310468A

GB2310468A - Seal assembly for a rotary shaft

Info

Publication number: GB2310468A
Application number: GB9603544A
Authority: GB
Inventors: Thomas Wilson Ramsay
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-02-20
Filing date: 1996-02-20
Publication date: 1997-08-27
Also published as: GB9603544D0

Abstract

A high pressure seal for a rotary shaft 23 is of the tapered-sleeve-with-spiral-groove configuration. The male rotor sleeve 20 has a spiral groove 43 and engages in a female stator sleeve 27. The stator sleeve has a clearance "c" with pump housing 29 to cater for alignment problems between the shaft 23 and the housing. Fluid is pumped via port 48 to pass along the spiral during rotation and past diaphragm 30. The diaphragm prevents flow of process fluid to the sleeves when rotation of the shaft is halted. In a modification Fig 3, the stator is a thin sleeve and fits in a rubber block (52).

Description

Title: SEAL ASSEMBLY FOR ROTARY SHAFT This invention relates to a seal assembly of the type as shown in intemational patent publication number WO-95/35457, published 28 december 1995.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS By way of further explanation of the invention, exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig 1 is a cross-section of the stuffing-box area of a shaft-driven pump; Fig 2 is the same cross-section as Fig 1, with the pump in a different stage of operation; Fig 3 is a cross-section of the corresponding area of a modified pump; Fig 4 is an exploded cross-sectional view of some of the components of Fig 3.

The apparatuses shown in the accompanying drawings and described below are examples which embody the invention. It should be noted that the scope of the invention is defined by the accompanying claims, and not necessarily by specific features of exemplary embodiments.

In Fig 1, a pair of complementary tapered sleeves are arranged with the male rotor sleeve 20 fixed to the rotary drive shaft 23 of a pump by means of grub screws 25, and the female stator sleeve 27 mounted in the housing 29 of the pump. The stator sleeve 27 is attached directly to a diaphragm 30, by means of bolts 32. The diaphragm is made of suitable elastomeric material, such as rubber. Bolts 34 secure a clamping ring 36 around the edge of the diaphragm 30.

The diaphragm 30 is physically, and sealingly, secured to both the sleeve 27 and the housing 29. The diaphragm is able to flex whereby the female stator sleeve 27 is able to float (slightly) in the axial and radial directions. Also, the axis of the female sleeve (and therefore of the male sleeve 20, and in tum the axis of the shaft 23) is permitted to lie at a slight angle relative to the axis of the bore 38 in the housing. In fact, the outside surface 40 of the stator sleeve 27 is made rather smaller than the bore 38, by a clearance C; which may be, for example, 1 or 2 mm on the diameter.

The clearance C permits the axis of the sleeve 27 to lie slightly displaced and misaligned relative to the axis of the bore 38, as is also permitted by the flexibility of the diaphragm 30.

When the shaft is not rotating, the diaphragm lies flat against the right end or nose of the male sleeve 20. Thus, any back-pressure in the process fluid which might be remaining when the shaft has stopped, serves to press the diaphragm more closely and more sealingly into the nose of the male sleeve, whereby the process fluid cannot leak through to the atmosphere.

When the shaft is rotating, barrier liquid is supplied at ambient pressure via an inlet port 48. The barrier liquid enters the left end of a spiral groove 43 cut in the surface of the male sleeve 20, and is driven thereby to the right, as shown by the arrow 45 (Fig 2). The barrier liquid emerges from the right end of the groove 43, under pressure, and exerts a force on the diaphragm, tending to push the diaphragm to the right. The diaphragm moves slightly away from the nose of the rotor sleeve 20, allowing the barrier liquid to escape through the diaphragm, and into the process fluid. Of course, this can only be allowed if leakage of the barrier liquid into the process fluid can be tolerated.

The designer may arrange that the barrier liquid be under constant supply, e.g from a reservoir. Or, it may be possible, in some cases, for the barrier liquid to be derived, or partially derived, from the process fluid, as is shown in Fig 2.

The provision of the elastomeric diaphragm permits the shaft to be misaligned linearly, and especially angularly, relative to the housing. In order for the two sleeves 20,27 to create a proper sealing effect, in which the barrier liquid is pumped to the right, the two sleeves must fit very intimately, and indeed the two sleeves are lapped together during manufacture. Because the flexible diaphragm is provided, the two sleeves can remain in this intimate barrier-liquid-pumping relationship, even when the shaft and housing are misaligned.

The two sleeves can also be expected to remain in the intimate pumping relationship even when the shaft is running out, i.e when the shaft is undergoing a lateral displacement cyclically per revolution of the shaft. Normally, the amount of runsut that can be permitted on the shaft of a pump, with normal stuffing box seal, is less than about a thou (0.001"). Because of the flexible diaphragm, at least double that magnitude of run-out can be tolerated. The extra run-out can be tolerated at the same time as the angular and linear misalignments.

Fig 3 shows another manner of providing flexibility to accommodate misalignments and run-out. Here, the female stator sleeve is formed from a cone 50 of relatively thin sheet metal. The metal cone 50 is moulded directly into a rubber block 52. The block 52 is moulded also with a flange 54 for securement of the stator sleeve into the housing. The outer surface of the block 52 again is 1 or 2 mm clear of the bore in the housing.

A lip seal 56 is moulded into the block 52. This serves to prevent process fluid from leaking to the left, but allows barrier-liquid to pass to the right.

The structure of the combined sleeve/block/lip-seal is shown in Fig 4.

Claims

Claims.

1. Seal assembly as shown in, and as described in relation to, Figs 1 and 2 of the accompanying disclosure.

2. Seal assembly as shown in, and as described in relation to, Figs 3 and 4 of the accompanying disclosure.