GB789671A - Improvements in and relating to fluid seals - Google Patents

Abstract

789,671. Stuffing-box substitutes. MURRAY, W. Oct. 19, 1955 [Oct. 21, 1954; Nov. 5, 1954], Nos. 30367/54 and 32100/54. Class 122(5). A seal for preventing leakage of fluid between relatively-rotatable parts 33, 36, Fig. 1, comprises an annular liquid-retaining channel 35 sub-divided by an axially-movable wall 48 into a sealing chamber 45 and communicating pressure chamber 55, the arrangement being such that the centrifugal pressure generated in the sealing chamber 45 upon relative rotation of the parts 33, 36 results in a lowering of the pressure in this chamber acting upon the wall 48 relatively to the pressure exerted on the opposite side of the wall (i.e. in the chamber 55) and therefore axial movement of the wall for the purpose of reducing or eliminating the contact pressure between the two members 49, 50 of a sliding-contact seal. As applied to the sealing of the impeller shaft 33 of a centrifugal pump, as shown in Fig. 1, the annular channel 35 is formed between the body 36 of the pump casing and the shaft, the axially-movable wall 48 is a stiff annular disc, and the outer wall 51 of the chamber 55 is an annular diaphragm clamped peripherally in the casing and at its inner margin sealed in a recess in the wall 48; the sealing member 50 is a collar fixed to the wall 48 and the member 49 a collar on the shaft 33. Under static conditions, full liquid pressure acts on both sides of the wall 48, the liquid passing from the chamber 45 to the chamber 55 around the periphery of the wall or through notches or apertures therein; the greater area of the wall surface in the chamber 45 results in the member 50 being pressed into sealing contact with the member 49 and the resilience of the diaphragm may be used to assist this action if desired. When the pump is running, an impeller 44 on the shaft 33 in the chamber 45 provides the necessary centrifugal pressure of the liquid to effect a seal and results in a diminution of the liquid pressure on the wall inside this chamber so that the wall moves axially until it engages a stop-face 58 and the sealing pressure between the members 49, 50 is reduced or eliminated ; if desired, rotation of the liquid in the chamber may be effected by rotating the wall of the chamber instead of or in addition to employing the impeller 44. The wall 48 may be guided axially by having peripheral tongues engaging recesses in the pump casing, and helical springs may co-operate with these tongues to assist in making the contact seal. In the modification shown in Fig. 5, the wall 80 dividing the annular channel into two chambers 83, 84 is connected to the outer cover 72 of the channel by a fluid-tight bellows 81 encircling the shaft 75 and carries a seal member 79 for making a contact seal with a member 77 on the shaft; the bellows and/or one or more springs tend to urge the members 77, 79 into contact. During static conditions, the liquid pressure on the surface 85 of the wall 80 being greater than that on the opposite surface 86, results in the member 79 being pressed into sealing contact with the member 77, and, when the pump is operated, the reduced pressure on the surface 85 caused by the action of the impeller 76 results in the wall being forced to move towards the impeller until it engages the stop-face 74a; notches in the periphery of the wall maintain communication between the two chambers. In the further modification shown in Fig. 6, the movable wall 80a is guided by pins 90 and urged by springs 89 in a direction to cause the members 77a, 79a to make a contact seal, an apertured cylindrical shroud 91 on either the wall 80a or pump casing surrounds the impeller 76a to prevent turbulence of liquid around the impeller, and short blades 93 are provided on the impeller 76a on the side remote from the wall 80a. In the case of pumps the liquid pumped is used as the sealing liquid, and, in other cases, oil or water may be fed to the annular channel. Specification 757,486 is referred to in the first Provisional Specification.