Seal for a joint or juncture – Seal between relatively movable parts – Relatively rotatable radially extending sealing face member
Patent
1994-09-01
1996-08-06
DePumpo, Daniel G.
Seal for a joint or juncture
Seal between relatively movable parts
Relatively rotatable radially extending sealing face member
251174, 251176, 251177, F16K 1114
Patent
active
055426840
DESCRIPTION:
BRIEF SUMMARY
This invention relates to seals for gas isolators, and in particular to high expansion tolerance seals for large gas isolators where large amounts of differential expansion have to be accommodated between certain components of the isolator, namely, the movable closure member (the blade) and the fixed frame (the casing).
The increasing size of gas turbines is creating a need for larger isolating equipment. One of the main problems which confronts the designer of such equipment is that of the differential expansion which occurs between the fixed frame and the moving blade member. The amount of expansion depends on the size, the maximum temperature differential and the materials of construction. For example, on a diverter valve 5.5 m square the differential expansion can be as much as 65 mm.
In addition, modern gas turbines have very high exhaust velocities, mean values of 80-100 m/s being common. Unless the design of the exhaust ducting has been executed using good aerodynamic design principles, flow separation and high fluctuating dynamic pressures can result. The frequencies of the fluctuating pressures can exist over a wide range of values up to as much as 50 hz. Seals for gas isolators located in these systems must be designed so that they will not be excited by forcing frequencies in the system up to say 60 hz. Attention to resistance to flutter is therefore of paramount importance.
In the prior art (GB-1308801 & GB-2060824) the amount of differential expansion which can be accommodated is limited by the width of the clamping/support bar under the seal. This bar has the dual function of clamping the seal to the blade or frame member and to prevent flutter of the seal when it is in the non-sealing position.
GB-1308801 describes a seal for a gas isolator which comprises a cantilever leaf spring to be attached to a fixed frame or a movable member of the isolator, and a bias spring acting on the leaf spring to tension the leaf spring so as to curve the latter when the seal is not in the sealing position, the bias spring being itself tensioned to press the leaf spring flat against a seating when the seal is in the sealing position.
An alternative form of seal is described in GB-2060824 which provides a seal for a gas isolator which comprises a cantilever leaf spring to be attached to a fixed frame or a movable member of the isolator, and a bias spring acting on the leaf spring, wherein the leaf spring is bent or curved when unstressed and wherein in the non-sealing position of the seal the bias spring makes only touch contact with the leaf spring, so that the leaf spring is unstressed in the said non-sealing position, whereby in the sealing position of the seal the stress induced in the bias spring will be the same as that induced in the leaf spring where the leaf spring and the bias spring have the same section modulus per unit length of seal.
A yet further alternative form of seal for a gas isolator is described in PCT patent application no. PCT/GB89/01382 (publication no. WO 90/06460), which provides a seal for a gas isolator which comprises a cantilever leaf spring to be attached to a fixed frame or a movable member of the isolator, and a bias spring acting on the leaf spring, wherein the seal is given an initial curvature corresponding to an initial deflection of 10% to 90% of the final free deflection, preferably 25% to 75% thereof, more preferably 40% to 60% thereof.
The present invention is particularly concerned with an improvement in or modification of a seal of the type according to GB-2060824, but is also applicable to a seal of the type according to GB-1308801 or PCT/GB89/01382.
The present invention provides a seal for a gas isolator which comprises a cantilever leaf spring to be attached to a component of the isolator selected from a fixed frame or a movable member of the isolator, and a bias spring acting on the leaf spring, and a bar disposed below the seal for clamping and supporting the latter, characterized by at least one additional damping element which will usually comprise a further l
REFERENCES:
patent: 3698429 (1972-10-01), Lowe et al.
patent: 4325411 (1982-04-01), Squirrell
patent: 4383693 (1983-05-01), Heller
patent: 4575099 (1986-03-01), Nash
patent: 4823836 (1989-04-01), Bachmann et al.
patent: 5099886 (1992-03-01), Squirrell
patent: 5120021 (1992-06-01), Squirrell et al.
DePumpo Daniel G.
Holler Norbert P.
WES Technology Inc.
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