WO1998017930A1

WO1998017930A1 - Piston and cylinder device with resilient seal

Info

Publication number: WO1998017930A1
Application number: PCT/GB1997/002865
Authority: WO
Inventors: James Brian Wilson
Original assignee: Abb Offshore Systems Limited
Priority date: 1996-10-18
Filing date: 1997-10-17
Publication date: 1998-04-30
Also published as: AU4712797A; BR9711938A; GB9722056D0; NO991804L; NO991804D0; GB2318403A; GB9621769D0

Abstract

A metal piston (15, 16) has a skirt (17, 18) which engages a resilient seal (19, 20) mounted within a bore (13, 14) of a metal cylinder (11, 12). The skirt (17, 18) has a thin walled portion (34, 35) which is resiliently flexible and is dimensioned relative to the bore (13, 14) such that, whenever fluid pressure acting on the piston (15, 16) exceeds a predetermined value, the thin walled portion (34, 35) will be deformed to provide a secondary metal-to-metal seal (36, 37) protecting the resilient seal (19, 20) from the external ambient environment. In this manner the clearance space between the piston skirt (17, 18) and the cylinder (11, 12) is closed by the outward deformation of the thin walled portion (34, 35) due to the increasing fluid pressure. This inhibits corrosion of the engaged metal surfaces and denies space for the accretion of marine growth or sediment.

Description

PISTON AND CYLINDER DEVICE WITH RESILIENT SEAL

The invention relates to a piston and cylinder device for use in harsh

environments which may cause deterioration of the conventional resilient seal between

the skirt of the piston and the bore of the cylinder.

One particular harsh environment is the ocean floor where subsea oil field apparatus are typically exposed externally to high water pressures and internally to high

oil pressures. A piston and cylinder device used in this environment typically has high water pressure applied to one face of its resilient seal and a high oil pressure applied to

the opposite face of the resilient seal. Such conditions can cause progressive

deterioration of the material from which the resilient seal is formed. Furthermore the face of the resilient seal exposed to the sea water is positioned within the clearance space

between the piston skirt and the cylinder bore which can be affected by corrosion and

by the accretion of marine growth and can cause the piston to jam or may otherwise

damage the resilient seal during piston movement.

Other harsh environment exist in many industrial processes such as chemical

plants and foundries.

It is known to provide a device comprising a metal cylinder defining a bore which has a resilient seal mounted within the bore and a metal piston arranged to fit

within the bore.

It is an object of the present invention to provide a piston and cylinder device in

which the resilient piston seal can be protected from such a harsh environment.

According to the invention the piston comprises a resiliently flexible skirt which

extends from the piston, the skirt being arranged to fit within the bore and to engage the

resilient seal, the cylinder and piston are arranged to define a fluid connection to admit pressurised fluid between the piston and cylinder so as to generate an axial movement

of the piston and the skirt is dimensioned relative to the bore such that whenever pressure of the fluid exceeds a predetermined value the skirt will deform to provide a

metal-to-metal seal with the bore. In this manner, after a predetermined load has been applied to the piston, the clearance space between the skirt and the cylinder is closed by

the outward deformation of the skirt due to the increasing fluid pressure. This prevents

corrosion of the engaged metal surfaces, provided that they are the same material, and

denies space for the accretion of marsh growth or sediment.

Preferably the skirt is dimensioned to form the metal-to-metal seal in a region

lying between the resilient seal and a head of the piston. In this manner the metal-to-

metal seal forms a barrier protecting the resilient seal from the environment outside the

cylinder and also protects that part of the skirt which will slide through the resilient seal

when the piston is eventually relocated into the cylinder. Preferably an outer surface of the skirt is formed with a thin walled portion

which distorts into an external land to form the metal-to-metal seal with the bore. The

use of this land defines the exact position of where the metal-to-metal seal will be

formed and limits the amount of the skirt that need to be machined to a fine tolerance

relative to the cylinder bore.

Desirably axial movement of the piston out of the bore is limited by a stop to

prevent the piston being ejected from the cylinder. This is particularly useful where

the piston only requires a slight travel and provides a reaction point for the axial piston

load as the pressure of the fluid is increased to cause the skirt to expand and grip the cylinder bore. Preferably, the stop is provided by an external cylindrical flange of the

piston and a retaining ring secured within the bore.

Both the piston and the cylinder are formed preferably from the same metal

which would normally be chosen to be highly resistant to corrosion by the ambient

environment.

The invention will now be described, by way of example only, with reference

to the accompanying drawings, in which: -

Figure 1 is a transverse section through a two-part connector for pressurised fluid

illustrating their disengaged position; Figure 2 illustrates the engaged position of the two-part connector shown in

Figure 1;

Figures 1 and 2 illustrate a two part connector 10 as described in our co-pending

British Applications GB 9621770.8A and GB 9621768.2A, the whole contents of each

Application being incorporated herein by reference.

Referring to Figure 1, as described in our co-pending Applications, each part of

the connector 10 comprises a metal cylinder 11, 12 which defines a bore 13, 14 and a metal piston 15, 16 having a skirt 17, 18 engaging a resilient seal 19, 20 mounted within

the bore 13, 14. Each cylinder 11, 12 has a mating surface 21, 22 located at a head of

the piston 15, 16 which is arranged to engage the mating surface 21, 22 of the other part

of the connector 10.

Movement of each piston 15, 16 axially out of its bore 13, 14 is limited by a stop

comprising an external cylindrical flange 23, 24 arranged to abut the inner end of a

retaining ring 25, 26 that is secured within the bore 13, 14 by a threaded connection 27,

28. A pre-loaded compression coil spring 29, 30 reacts between each piston 15, 16 and

cylinder 11, 12 to bias the position of the piston 15, 16 towards its retaining ring 25, 26

such that the flange 23, 24 is held against its respective retaining ring 25, 26.

The mating surfaces 21, 22 when in a engaged position, as illustrated in Figure 2, allow fluid pressure to be communicated between respective lines 31, 32 defined

within the cylinders 11, 12 and pistons 15, 16. The fluid pressure acts on the effective

areas of each piston 15, 16 to press their mating surfaces 21, 22 firmly together to

provide metal-to-metal seal 33.

The resilient seals 19 and 20 provide secondary seals which are superseded by

secondary metal-to-metal seals in the following manner. Each piston skirt 17 and 18 is

formed with a respective thin walled portion 34 and 35 which is resiliently flexible and

dimensioned relative to the respective bore 13 and 14 such that, whenever the fluid pressure exceeds a predetermined value, the thin walled portions 34 and 35 of the skirts

17 and 18 will be deformed to provide secondary metal-to-metal seals 36, 37 protecting

the resilient seals 19 and 20 from the external ambient environment. The dimensions of each thin walled portion 34 and 35 are preferably controlled by the position of

external cylindrical lands 38 and 39, thereby limiting the fine tolerances to a very small

portion of each piston 15, 16 and determining precisely where each secondary metal-to-

metal seal 36, 37 is positioned. In this manner the two-part connector 10 is completely

sealed against the external environment by metal-to-metal seals 33, 36 and 37.

Claims

1. A device (10), comprising

a metal cylinder (11, 12) defining a bore (13, 14) and having a resilient seal (19,

20) mounted within the bore (13, 14),

a metal piston (15, 16) arranged to fit within the bore (13, 14),

characterised in that,

the piston (15, 16) comprises a resiliently flexible skirt (17, 18) which extends

from the piston (15, 16), the skirt being arranged to fit within the bore (13, 14) and to engage the resilient seal (19, 20),

the cylinder (11, 12) and piston (15, 16) are arranged to define a fluid connection

to admit pressurised fluid between the piston (15, 16) and cylinder (11, 12) so

as to generate an axial movement of the piston (15, 16), and

the skirt (17, 18) is dimensioned relative to the bore (13, 14) such that whenever

pressure of the fluid exceeds a predetermined value the skirt (17, 18) will deform

to provide a metal-to-metal seal (36, 37) with the bore (13, 14).

2. A device, according to Claim 1, characterised in that the skirt (17, 18) is

dimensioned to form the metal-to-metal seal (36, 37) in a region lying between

the resilient seal (19, 20) and a head of the piston (15, 16).

3. A device, according to Claim 1 or 2, characterised in that an outer surface of the

skirt (17, 18) is formed with a thin walled portion (34, 35) which distorts into an external cylindrical land (38, 39) to form the metal-to-metal seal (36, 37) with

the bore (13, 14).

4. A device, according to any of Claims 1 to 3, characterised in that axial

movement of the piston (15, 16) out of the bore (13, 14) is limited by a stop.

5. A device, according to Claim 4, characterised in that the stop is provided by an

external cylindrical flange (23, 24) of the piston (15, 16) and a retaining ring

(25, 26) secured within the bore (13, 14).