GB2049110A - Fluid control apparatus - Google Patents

Abstract

A fluid operated actuator for a valve includes a sensing piston (22), a fluid-tight seal (30) between the piston and a duct (34) for connection to a source of fluid, and a cantilevered spring rod (40, 46) that acts on the piston to resist movement of the piston. The seal and the piston may be mounted within a removable plate (14) beneath a support plate (10) carrying the spring. A lever mechanism (70, 74) is provided for amplifying the effect of the piston movement at the valve (not shown). <IMAGE>

Description

SPECIFICATION Fluid control apparatus This invention relates to fluid control apparatus which may include a control pilot valve for use in, for example, conduits carrying a fluid and which may sense a change of press sure in the fluid to shift an operating valve from one position to another position.

There are many pilot assemblies- available for use in safety systems for monitoring a flow line pressure and sending a signal to or removing a signal from an end device, such as a safety valve, or a control console.

The most common pilot assembly employed is known as a spool pilot that employs a spool valve and a sensing piston opposed by an adjustable coil spring. For example, when the pressure of the fluid being sensed by the piston overcomes the force of the associated spring, the flow of control fluid through the spool valve is altered to control flow within a conduit. It will be appreciated that in such systems, the coil spring assembly generally must be guided to minimise friction. The systems are typically only 88 to 90% accurate with respect to repeatability of the trip point of the associated valving arrangements. Presently, government regulations require such systems to be much more accurate in their sensing properties, particularly with respect to repeatability.

There are spool pilot assemblies which are able to meet the present higher accuracy requirements, but are deemed to be commercially very expensive.

Bourdon tube assemblies are also used for sensing flow line pressures and monitoring the same. However, these assemblies have limited over-pressure capacities. If the Bourdon tube assemblies are used to sense systems at a pressure of 1 500 psi, the maximum limiting pressure may be 2,000 psi. This is not very satisfactory when the system is employed in connection with sensing a flowing well which typically operates at a pressure of 2,000 psi, and then when the well is shut in the pressure may rise to 5,000 psi, considerably above the capacity of the monitoring system.

In the invention a fluid pressure activated pilot broadly comprises connecting means for connecting the pilot to a source of fluid, a sensing piston, a spring that acts on the piston to resist movement of the piston, control means operable in response to movement of the piston, and a fluid tight seal between the connection means and the piston, and in this pilot the seal and the piston are movable upon a change in the pressure of the fluid.

Thus in this pilot the control means is actuated by the movement of the piston when the pressure of the fluid being sensed causes the piston to move in opposition to the force generated by the spring. The change in pres sure may be an increase or a decrease in the pressure.

The spring is generally a cantilevered spring having a static end portion and a dynamic end portion with the dynamic end portion resisting movement of the piston away from the con necting means.

In general the spring comprises at least one elongated rod having a static end portion and a fixed end portion and more usually com prises a pair of parallel elongated rods, the pair having a static end portion and a dy namic end portion. Preferably there are means for reducing transverse movement of any elongated spring rod. For instance when there are a pair of rods the dynamic end portions of these rods may be joined together in a mount ing. Preferably there are means for adjusting the force of the spring. For example the force applied by a cantilever spring may be adjusted by applying an adjustable load to the cantilevered spring at a point distant from the dynamic end portion.

The seal is generally a diaphragm, prefera bly a rolling diaphragm. It may be formed of an elastomer, preferably a reinforced elas tomer.

The piston is generally located within a passage having a diameter larger than the piston, and the combination of this with the fact that movement of the piston is preferably caused by variations in the pressure applied to the diaphragm means that the effect of friction in the apparatus is minimised.

The pilot generally includes a support plate on one side of which the spring is mounted and on the other side of which the piston, seal and connection means are located and there is an aperture through the plate permit ting the spring to act on the piston.

The pilot generally also comprises, on the side of the support plate distant from the spring, a mounting plate having a second aperture aligned with the first aperture and this mounting plate generally carries the seal, or means for mounting the seal, across the second aperture and the piston is within the second aperture, this second aperture thus serving as the above-mentioned passage within which the piston is located. Preferably the mounting plate is removable. Normally the piston is located within the second aperture and a member extends from the piston up through the first aperture to contact the spring means.

The pilot may also comprise a cover plate secured to the mounting plate on the side distant from the support plate, the cover plate including the connector means and defining a passage leading from the connector means to the second aperture.

When, as is preferred, the spring means comprise at least one rod there may be bracket means on the support plate for mount ing the static end of the rod or rods and there may be clamp means at the other end of the rod or rods in alignment with the first aperture.

The pilot preferably includes also pivotally mounted lever means operating between the piston and the control means, in order that movement of the piston may be amplified at the control means. The control means may merely be, for instance, one end of the lever but generally the pilot apparatus includes a valve or other apparatus that is to be controlled in response to variations in fluid pressure.

One fluid pressure actuated pilot according to the invention comprises a sensing piston, means providing a fluid-tight seal between a source of fluid pressure to be sensed and the piston, the seal and the piston being movable upon changes in the pressure of the sensed fluid, the means including a removable member containing a cavity for the piston and means for mounting the seal, and spring means normally for resisting movement of the piston in one direction, whereby a control means is actuated by the movement of the piston when the pressure of the fluid being sensed causes the piston to move in opposition to the force of the spring.

Another fluid pressure actuated pilot according to the invention comprises a sensing piston, means providing a fluid-tight seal between a source of fluid pressure to be sensed and said piston, the seal and the piston being movable upon changes in the pressure of the sensed fluid, and a cantilevered spring means having a static and a dynamic end portion, the dynamic end portion of the spring means normally resisting movement of the piston in one direction whereby a control means is actuated by the movement of the piston when the pressure of the fluid being sensed causes the piston to move in opposition to the force of the spring means. In a modification of either of these pilots, the means providing a fluid-tight seal between a source of fluid pressure to be sensed and the piston may be movable towards and away from the piston.

The invention will now be described in more detail with reference to the accompanying drawings in which: Figure 1 is an elevational view of a fluid pressure pilot assembly incorporating the features of the invention.

Figure 2 is a top planar view of the assembly illustrated in Fig. 1.

Figure 3 is an end elevational view of the assembly illustrated in Fig. 1 as viewed from the right-hand side thereof.

Figure 4 is an end elevational view of the assembly illustrated in Fig. 1 as viewed from the left-hand side thereof.

Figure 5 is a fragmentary sectional view of a portion of the assembly illustrated in Fig. 1 taken along line 5-5 thereof.

Figure 6 is a fragmentary exploded view of the internal configuration of diaphragm mounting plate and the associated diaphragm cover plate.

Figure 7 is a fragmentary sectional view of a modified form of a sensing piston and associated cooperating solid elastomer diaphragm element.

Figure 8 is a fragmentary sectional view of another modified form of the sensing piston and associated sealing means.

Figure 9 is an elevational view similar to Fig. 1 showing a modified form of a fluid pressure pilot assembly wherein the motion amplification system has been eliminted.

Referring to Figs. 1 through 5, inclusive, there is shown a fluid pressure pilot assembly incorporating a motion amplification mechanism. More specifically, there is provided an elongate rigid support plate 10 having an aperture 1 2 formed adjacent one end thereof.

A diaphragm mounting plate 14 and an associated diaphragm cover plate 1 6 are secured in relation to the under-surface of the plate 10 by a plurality of threaded fasteners 38 adapted to extend through aligned apertures formed in the mounting plate 14 and the cover plate 1 6 and threadably received within suitably positioned internally threaded apertures in the plate 10.

The diaphragm mounting plate 14 is provided with a central chamber 20 adapted to receive the main body portion 22 of a piston 24. The piston 24 has an upwardly extending extension 26 which is adapted to be received within the aperture 1 2 of the plate 10.

A diaphragm member 30 is positioned to completely cover the lower open end of the chamber 20 of the mounting plate 14. The diaphragm member 30 is of the rolling diaphragm type and is typically comprised of a fabric material with an elastomeric coating.

The diaphragm cover plate 1 6 has an internal sensing chamber 32 generally in alignment with the diaphragm 30 and the chamber 20 of the diaphragm mounting plate 1 4. The sensing chamber 32 communicates with the source of fluid pressure being sensed through a threaded aperture provided with a fitting 34. Also, an alternative threaded aperture is formed in the wall of the sensing chamber 32 of a large diameter and is shown as being closed by an externally threaded plug 36. With the illustrated structure, a separate line could be coupled between the fitting 34 and the source of fluid pressure, such as a flow line of a gas well, for example; or alternately, plugging the fitting 34, removing the plug 36, and attaching the assembly directly to the flow line at that point.

The plurality of threaded fasteners 38 is employed to couple the diaphragm mounting plate 14 and the diaphragm cover plates 1 6 to the underside of the plate 1 0. Typically, the threaded fasteners 38 are adapted to extend through suitably positioned and aligned holes in the diaphragm cover plate 1 6 and the diaphragm mounting plate 14 and are thence threadably received within suitably tapped internally threaded holes in the mounting plate 10.

In the assembled form, the diaphragm member 30 functions to provide a fluid-tight seal between the fluid pressure being sensed in the sensing chamber 32 of the diaphragm cover plate 16, and atmospheric pressure of the remainder of the assembly. It will be appreciated that pressure in the sensing chamber 32 acts on the under surface of the diaphragm member 30 which is exposed to the interior of the sensing chamber 32. The force produced by the sensed fluid pressure is then transmitted through the diaphragm member 30 to the piston 24. As the pressure of the fluid within the sensing chamber 32 increases, a proportional increase will occur in the force applied to the piston 24 by the diaphragm member 30. One of the advantages in the use of the type of diaphragm illustrated is that virtually no sliding friction is involved during the operation thereof.

Further, it will be noted that the diameter of the sensing elements may be changed without affecting any other portion of the assembly by merely removing the threaded fasteners 38 and the diaphragm cover plate 16, and then substituting a new diaphragm mounting plate 14 having a different diameter diaphragm member 30 and central chamber 20 for the cooperating sensing piston 24. Such modification will result in the assembly having different (higher or lower) sensing ranges without the necessity of changing the spring force.

A pair of cantilevered spring rods 40 are mounted in horizontally extending spaced relation within a pilot valve mounting plate 42.

The mounting plate 42 is secured to the upper surface of the mounting plate 10 by a threaded fastener 44 which is adapted to extend through an aperture formed in the plate 10 and thence into an internally threaded aperture in the base of the mounting plate 42. One end of each of the spring rods 40 is inserted into and snuggly retained within spaced apart holes drilled in the mounting plate 42. The opposite or dynamic ends of the spring rods 40 are retained in spaced relation with respect to one another by a spring clamp 46 provided with a pair of spaced apart apertures for receiving the ends of the spring rods 40. The spring clamp 46 is securely fastened to the spring rods 40 by set screws 48, as illustrated in dotted lines in Figs. 1 and 2, and is positioned over the extension 26 of the sensing piston 24. The spring clamp 46 provides side-to-side stability for the spring rods 40.The spring clamp 46 receives a levelling pad 47 which is defined at the lower end of the nut assembly 78.

An adjustable spring clamp 50, having spaced apart horizontally extending apertures for receiving the spring rods 40, is securely attached thereto by respective set screws 52.

The adjustable spring clamp 50 is adjustably secured to the plate 10 by means of an adjustable threaded shank 54 which extends through an aperture in the plate 10 and thence into an internally threaded aperture extending upwardly from the base of the clamp 50 intermediate to the location of the spring rods 40. When the threaded shank 54 is tightened by turning the head portion thereof in a clockwise direction, the spring rods 40 are put under load. The tighter the threaded shank 54 is adjusted, the more preload force is applied to the associated spring clamp 46 on the reaction ends of the spring rods 40 to the extension 26 of the sensing piston 24.

Accordingly, it will be seen that the piston 24 may be moved by the force transmitted thereto from the sensed fluid pressure through the movement of the diaphragm member 30, only after the applied force overcomes the oppositely applied force of the spring rods 40 acting through the spring clamp 46.

As the sensed pressure becomes higher and higher, the spring rods 40 deflect and the forces of the spring rods 40 become correspondingly increased. The amount of deflection that the spring rods 40 traverse will, of course, be very small.

A pilot valve assembly 60 is mounted to the side wall of the pilot valve mounting plate 42 by means of spaced apart threaded fasteners 62. The pilot valve assembly 60 may be typically a three-way, two position poppet valve having no sliding seals. In order to shift the valve assembly 60, a force must be applied. The force required to shift the valve is a function of pilot valve supply pressure and not a friction characteristic. It is a very repeatable force if the supply pressure is regulated carefully. The pilot valve assembly 60 is effective to control a fluid which is allowed to flow therethrough from the inlet fitting 64 to the outlet fitting 66 and the above referred to force is typically required to shift the valve assembly from an open to a closed condition.

Typically, the stroke required to actuate the pilot valve 60 is comparatively small. As pressure increases, the sensing piston 24 is moved against the force of the spring rods 40 a distance of approximately 10% of the pilot valve 60 stroke for each 1 % change in sensed pressure. This means that if the pilot valve assembly 60 were mounted directly to the spring clamp 46 of the spring rods 40 for tripping and resetting purposes, the trip point to resetbpoint, or dead-band, would vary 10% or more. To reduce this dead-band and probability of non-repeatable functions, a motion amplification system is provided as illustrated in Figs. 1, 2, 3 and 4.

The motion amplification system includes a transfer bar 70 having one end pivotally mounted in a U-shaped mounting bracket 72, by a threaded fastener 74. The mounting bracket 72 is typically secured to the mounting bar 10 by suitable threaded fasting means 76. A threaded nut assembly 78 is mounted on the transfer bar 70 and includes a depending threaded shank portion 80, the end of which has an integral levelling pad 47 which is aligned to contact the spring clamp 46.

The transfer bar 70 is normally urged about the pivot point of the threaded fastener 74 by a coil spring 82 so that the levelling pad 47 of the depending shank portion 80 remains in contact with the spring clamp 46, thereby assuring no undesired sloppiness or misalignment in the respective contacting elements.

One end of the coil spring 82 is secured to the transfer bar 70 by a threaded fastener 84, while the opposite end is secured to the mounting plate 10 by a threaded fastener 86.

The opposite end of the transfer bar 70 is provided with an adjustable nut assembly 88 having a depending threaded shank portion 90 adapted to contact the operating element of the pilot valve assembly 60.

The transfer bar 70 is guided, during movement thereof, by a milled slot 92 in the upper portion of the pilot valve mounting plate 42 and is retained therein by a plate 94 secured to the plate 42 by a pair of threaded fasteners 96.

Accordingly, in operation, as the sensing piston 24 is moved upwardly by the pressure of the fluid being sensed against the opposing force of the spring rods 40, the spring clamp 46 urges the transfer bar 70 upwardly about the pivot axis of the threaded fastener 74.

Since the distance from the longitudinal axis of the adjustable nut assembly 78 to the pivot axis of the threaded fastener 74 is of the order of one-eighth the distance from the axis of the nut assembly 78 to the corresponding axis of the adjustable nut assembly 88, the upward movement of the sensing piston will be in effect amplified eight times at the pilot valve assembly 60.

While in the illustrated preferred embodiment of the invention upward movement of the sensing piston 24 causes upward movement of the reaction end of the transfer bar 70, the arrangement may be readily changed to reverse the above action. In the event such change is desired, the mounting bracket 72 is mounted at the location on the mounting plate 10 where the threaded fastener 86 is used to normally maintain the bottom portion of the coil spring 82. The transfer bar 70 is then pivotally mounted to the mounting bracket 72 at the aperture in the bar 70 which is employed to receive the threaded fastener 86. The coil spring 82 is attached to the end of the transfer bar 70 where it had been pivotally mounted to the mounting bracket 72, as illustrated.

Fig. 7 shows a modified form of the diaphragm and sensing piston arrangement.

While the rolling type diaphragm illustrated in Figs. 5 and 6 may be made to accommodate pressures above 2,000 psi, the normal usage of such diaphragm 30 is in a range below about 2,000 psi. The modification illustrated in Fig. 7 is designed for higher pressure ranges and utilises a flat disc elastomer sensing element 100. In this embodiment, the cooperating sensing piston 24 fits relatively closely into the cooperating chamber 20. This embodiment is useful when the system is used to sense high pressures, and utilises very small piston configurations.

The embodiment illustrated in Fig. 8 is a modified form of the sensing arrangement and includes a piston 102, in lieu of a diaphragm, which employs a seal member 104 to maintain a sealing relation between the sensing piston 24 and the pressure fluid being sensed in the sensing chamber 32.

In all instances, it is an important objective of the mechanism comprising the assembly to utilise moving elements which exhibit a minimum amount of frictional contact.

Fig. 9 illustrates another embodiment of the invention wherein the pilot assembly is in most all structural aspects similar to the assembly illustrated in Figs. 1, 2, 3, 4, 5 and 6 with the exception of the elimination of the motion amplification system and the relocation of the pilot valve assembly. More specifically, spring rods 40 are mounted in a mounting bracket 42' secured to the plate 10 by a threaded fastener 44 in the same manner as the pilot valve mounting plate 42 of the earlier described embodiment is mounted.

However, the pilot valve assembly 60 is mounted at the opposite end of the plate 10 to co-act directly with sensing piston 24 of the associated spring clamp 46. The lower end of the mounting bracket 106 is secured to the mounting plate 10 by threaded fastener 108, while the upper end supports the pilot valve assembly 60. In operation, it will be seen that an adjustable nut assembly 88' is mounted at the top of the spring clamp 46 and employed to physically contact and shift the poppet valve mechanism of the pilot valve assembly 60 upon movement of the sensing piston 24. As discussed above, this arrangement typically would exhibit a trip point to reset point, or dead-band, of 10% or more.

However, in certain applications, this may be acceptable and the mechanism would be simplified. By careful selection of the size, or spring rate of the spring rods 40 relative to the size of the sensing element and in consideration of the required sensing pressure range, this configuration might well be designed to provide less than 10% dead-band.

While the illustrated embodiments show the diaphragm cover plate assembly as being cou pled to a single pilot valve assembly, it is within the invention to couple a plurality of pilot valve assemblies to the diaphragm cover plate.

Claims (16)

1. A fluid pressure actuated pilot comprising connecting means for connecting the pilot to a source of fluid, a sensing piston, a spring that acts on the piston to resist movement of the piston, control means operable in response to movement of the piston and a fluidtight seal between the connection means and the piston and in which the seal and the piston are movable upon a change in the pressure of the fluid.

2. A pilot according to claim 1 in which the spring comprises a cantilevered spring having a static end portion and a dynamic end portion and in which the dynamic end portion normally resists movement of the piston.

3. A pilot according to claim 1 or claim 2 in which the spring comprises at least one elongated rod having a static end portion and a dynamic end portion and in which the dynamic end portion normally resists movement of the piston.

4. A pilot according to claim 3 in which the spring comprises a pair of the elongated spring rods.

5. A pilot according to any of claims 2 to 4 including means for reducing transverse movement of the spring.

6. A pilot according to any preceding claim including means for adjusting the force applied by the spring on the piston.

7. A pilot according to any preceding claim in which the seal comprses a diaphragm.

8. A pilot according to claim 7 in which the diaphragm is a rolling diaphragm.

9. A pilot according to any preceding claim in which the seal is formed of a solid elastomer.

10. A pilot according to claim 9 in which the elastomer is a reinforced elastomer.

11. A pilot according to any preceding claim comprising a support plate on one side of which the spring is mounted and on the other side of which the piston, seal and connecting means are located, and in which there is a first aperture through the support plate permitting the spring to act on the piston.

1 2. A pilot according to claim 11 also comprising, on the side of the support plate distant from the spring, a mounting plate having a second aperture aligned with the first aperture and in which this mounting plate carries the seal, or means for mounting the seal, across the second aperture and the piston is within the second aperture.

1 3. A pilot according to claim 1 2 in which the mounting plate is removable.

1 4. A pilot according to claim 1 2 or claim 1 3 also comprising a cover plate on the side of the mounting plate distant from the support plate, the cover plate including the connecting means and defining a passage leading from the connecting means to the second aperture.

1 5. A pilot according to any of claims 11 to 14 in which the spring comprises at least one elongated rod and there are bracket means on the support plate for mounting one end of the rod and there are clamp means on the other end of the rod in alignment with the first aperture.

16. A pilot according to any preceding claim in which the piston is located within a passage having a diameter sufficiently greater than the diameter of the piston that the piston moves freely within the passage.

1 7. A pilot according to any preceding claim including also lever means operating between the piston and the control means whereby movement of the piston is amplified at the control means.

1 8. A pilot according to any preceding claim substantially as herein described with reference to any of the accompanying drawings.

CLAIMS (8 July 1980) 1 8. A fluid pressure activated pilot according to claim 1 comprising connecting means for connecting the pilot to a source of fluid, a sensing piston, a cantilevered spring having a static end portion and a dynamic end portion and in which the dynamic end portion normally resists movement of the piston, means for adjusting the force applied by the cantilevered spring on the piston, control means operable in response to movement of the piston and a fluid tight seal between the connection means and the piston and in which the seal and the piston are movable upon a change in the pressure of the fluid.