GB2478613A

GB2478613A - Pressure sensor with a chamber surface profiled to conform to diaphragm corrugations

Info

Publication number: GB2478613A
Application number: GB201014356A
Authority: GB
Inventors: David Webster
Original assignee: T-3 ENERGY SERVICES Inc; T3 Energy Services Inc
Current assignee: T-3 ENERGY SERVICES Inc; T3 Energy Services Inc
Priority date: 2009-08-28
Filing date: 2010-08-31
Publication date: 2011-09-14
Also published as: GB201014356D0; GB0915056D0

Abstract

A pressure sensor 1 comprises metal diaphragm (or membrane) 4 mounted within chamber 3 to provide a cavity 5,6 on either side of the chamber, the diaphragm having a profiled form and the upper surface of the chamber having a matching profile. The sensor may include an actuator (e.g. a piston (111, Fig. 2) or actuator 8 extending through bore 9) connected to the diaphragm so as to move with it and also connected to a pressure indicator such as lever 10. Cavity 7 may contain a compressible fluid (e.g. air). The diaphragm may comprise stainless steel and/or have a thickness of 0.002 — 0.005 inches (i.e. 0.0508 - 0.127 mm). The piston may have a range of travel of around 6mm. A second cavity (320, Figure 6) may be included to provide an indication of rupture or failure of the diaphragm.

Description

PRESSURE SENSOR

This invention relates to a pressure sensor and more particularly to a pressure sensor which is sensitive to low changes in pressure whilst accommodating high pressure differentials.

Instruments, devices and other apparatus are often required to be exposed to conditions within a pipeline. This allows pipeline conditions to be monitored for integrity purposes and to effect certain actions if the conditions within the pipeline are beyond acceptable limits.

A typical pressure sensor comprises a body with a cylinder and a piston slidably mounted within the cylinder. A diaphragm is connected between the piston and the side wall of the cylinder to create two sealed cavities on either side of the diaphragm. One of the cavities is filled with a fluid and the other is exposed to the pressure source to be monitored. Whilst the pressures in each cavity are equal the diaphragm is held in a relaxed condition however in the event of an increase in pressure from the source being monitored, the piston moves within the cylinder and the diaphragm is placed under tension.

The burst rating of the diaphragm must be selected to match the typical operating pressures of the source being monitored otherwise an increase in pressure in the source can burst the diaphragm and lead to a failure of the sensor.

The present invention aims to provide a sensor which is sensitive to low pressure changes whilst being adapted to accommodate large pressure differentials across the diaphragm without compromising the integrity of the diaphragm.

It is a further object of the present invention to provide a sensor which can provide a simple and effective indication of the presence of a pressure within a tool or environment.

According to one aspect of the present invention there is provided a pressure sensor comprising a metal diaphragm mounted within a chamber to provide a cavity on either side of the chamber, the diaphragm having a profiled form and the upper surface of the chamber having a matching profile Conveniently an actuator is connected to the diaphragm such that movement of the diaphragm within the chamber moves the actuator.

Preferably the actuator is a piston.

Advantageously the diaphragm is connected between the outer surface of the piston and the inner surface of the chamber.

Preferably the diaphragm is connected to the piston towards the upper end of the piston.

Advantageously the diaphragm comprises stainless steel.

Conveniently a compressible fluid is present in the cavity between the upper surface of the diaphragm and the upper surface of the chamber.

Preferably the chamber is a cylinder.

Advantageously the fluid is air.

Preferably the diaphragm is between 2/1 000ths and 5/1 000ths of an inch thick and preferably 3/l000ths of an inch thick.

Advantageously the travel of the piston is around 6mm.

Embodiments of the present invention will now be described with reference to the accompanying drawings in which:-Fig. 1 is a schematic view of a pressure sensor according to one embodiment of the present invention Fig. 2 is a schematic view of a further pressure sensor according to one embodiment of the present invention with no pressure differential across the diaphragm; Fig. 3 is a schematic view of the pressure sensor of Fig. 2 with a low pressure differential across the diaphragm, Fig. 4 is a schematic view of a further embodiment of a pressure sensor according to the present invention in a no pressure differential condition; Fig, 5 is a schematic view of the pressure sensor of Fig. 4 in a pressure condition; Fig. 6 is a schematic view of a further embodiment of a pressure sensor according to the present invention in a no pressure differential condition; Fig. 7 is a schematic view of the pressure sensor of Fig. 6 in a pressure condition, and Fig. 8 is a schematic view of the pressure sensor of Fig. 6 in a ruptured diaphragm condition.

Turning now to the Figures, there is shown in Fig. 1 a pressure sensor 1 according to one aspect of the present invention. The pressure sensor comprises a body 2 which in the illustration is a cylinder with a chamber 3 formed in the cylinder.

A stainless steel diaphragm 4 is mounted within the chamber to form a first sealed cavity 5 between the bottom surface of the chamber and the diaphragm and a second sealed cavity 6 between the diaphragm and the top surface 7 of the chamber.

The diaphragm is profiled and in the illustrated embodiment has a sinusoidal cross-sectional form although the profile may comprise regular or irregular undulations, corrugations or projections. The top surface 7 of the chamber has a matching profiled form as will be described further below.

The diaphragm is preferably around 3/1 000ths of an inch thick and has a burst rating of between 40 to 6Opsi and preferably around 50 psi.

An actuator rod 8 is mounted on the upper surface of the diaphragm and extends through a bore 9 in the upper surface of the chamber. The bore extends through the body 2 of the sensor and a lever 10 is pivotally mounted on the top of the body extending over the bore.

The operating range of the monitor is preferably between 0 and 2 psi.

In use of the monitor, the second cavity 6 between the diaphragm and the top surface of the chamber is filled with a compressible fluid and preferably air and the first cavity 5 is exposed to pressure from the source which is being monitored. In the illustrated embodiment this is a pipeline pressure. The pressure in the second cavity may be set to match that of the normal operating pressure of the source being monitored.

During normal operating conditions, the diaphragm 4 is in a relaxed condition with equal pressure in the cavities above and below the diaphragm, i.e. there is no pressure differential across the diaphragm In the event of even a small increase in pressure from the source being monitored, within the 0 to 2 psi range, the higher pressure fluid enters the first cavity and the diaphragm 4 is pushed upwards within the cylinder. As the diaphragm moves towards the upper surface of the cylinder the actuator rod 9 is pushed into the bore 10 in the chamber.

As the diaphragm makes contact with the profiled surface 7 of the top of the cylinder the surface of the diaphragm and the surface of the chamber are in full contact with no voids between them. At this point in mechanical terms the diaphragm is no longer accommodating any differential pressure as a dynamic component within the monitor but is being compressed against the upper surface of the cylinder. Any further increase in pressure in the monitored source merely increases the compressive force on the diaphragm against the upper surface of the chamber which restrains the diaphragm from further upward movement.

In the illustrated embodiment the movement of the diaphragm between the at rest condition and the actuated condition in which the diaphragm is compressed against the upper surface of the chamber is only about 6mm.

As the diaphragm 4 moves into compression against the upper surface 7 of the cylinder, the free end of the actuator 9 extends through the bore and contacts the under surface of the lever 10 raising the lever to indicate a pressure situation within the sensor.

In the event that the pressure in the source falls, the diaphragm 4 returns to the relaxed condition. As the free end of the actuator 9 falls back into the bore, the lever 10 is returned to the no pressure condition as illustrated in Fig. 1.

The pressure monitor as described indicates the presence or not of a pressure in the source which is above a preset limit without measuring the specific pressure. Whilst the pressure from the source remains above the preset pressure, the diaphragm 4 will remain in the compressed condition against the upper profiled surface of the chamber. In the event that the pressure from the source drops below the preset pressure, the piston will move downwards within the chamber and the diaphragm will return to the relaxed condition.

A further embodiment is illustrated in Figs. 2 and 3. In this embodiment a piston 111 is slidably mounted within the chamber and the diaphragm 104 is connected between the outer surface of the piston and the inner surface of the chamber. An actuator rod 109 is mounted on the piston and extends through a bore 110 in the cylinder.

In the Figs. 2 and 3 seals 112 are provided between the lower end of the piston and side walls of the cylinder and a third cavity 113 is defined between the lower end of the piston and the cylinder which is exposed to pressure from the device being monitored. However in some embodiments such as shown in Figs. 4 and 5, the lower end of the piston will be within the first cavity 105 as described above and the under side of the diaphragm will be exposed to pressure from the device being monitored.

As with the other embodiments, the sensor therefore detects very low changes in pressure which are converted to a short travel distance of the piston whilst accommodating very high changes in pressure without risk of rupture of the diaphragm.

The embodiment illustrated in Figs. 5 and 6 is modified by connecting the diaphragm to an upper edge of the piston 211 and providing a lever 210 on the top of the outer surface of the sensor. In this embodiment the piston extends through a bore in the upper surface of the sensor and when in the raised position the upper end of the piston extends out of the bore.

The lever is mounted over the bore in the sensor.

In this embodiment the piston 211 and the lower surface of the diaphragm 204 are exposed to pressure from the source being monitored. In the event of an increase in pressure from the source which creates a pressure differential across the diaphragm, the piston moves up through the chamber and the profiled diaphragm moves into compression against the profiled upper surface of the cylinder.

As the piston rises in the cylinder, the free end of the piston extends through the bore and contacts the under surface of the lever raising the lever to indicate a pressure situation within the sensor.

In the event that the pressure in the source falls, the piston drops within the cylinder and the diaphragm returns to the relaxed condition. As the free end of the piston falls back into the bore, the lever is returned to the no pressure condition as illustrated in Fig. 5.

A further embodiment is illustrated in Figs. 6-8 which show a pressure sensor similar to that shown in Figs. 4 and 5 but with means for indicating a rupture or failure of the diaphragm 304. In this embodiment a secondary chamber 320 is formed in the body of the sensor which is in fluid communication with the second cavity 306 of the main chamber of the sensor.

A piston 321 is slidably mounted in the secondary chamber and a free end 322 of the piston extends through a bore 323 in the body of the sensor and can extend from the bore if the piston is raised within the secondary chamber. A second lever 324 is mounted on the top of the sensor and is contacted by the free end of the piston of the secondary chamber as the piston is actuated.

As with the previous embodiment, a positive pressure differential across the diaphragm 304 will result in the primary piston 311 rising within the primary chamber thereby raising the diaphragm to the upper surface of the primary chamber where it is held against the profiled surface 307 under compression.

In the event of a failure of the diaphragm fluid will pass through the diaphragm 304 and into the second cavity 306 between the diaphragm and the top surface of the chamber. Fluid then passes between the primary piston 311 and the wall of the chamber and enters the secondary chamber 320 thus raising the secondary piston 321. This raises the additional lever 324 on the top surface of the sensor to alert an operator to the failure condition within the sensor and allowing remedial work to be undertaken to address the problem.

Modifications and improvements can be made without departing from the scope of the invention for example the visible signal which indicates a pressure condition or failure of the diaphragm described above could be replaced by an audible signal to attract the attention of an operator to the sensor.

Claims

CLAIMS1. A pressure sensor comprising a metal diaphragm mounted within a chamber to provide a cavity on either side of the chamber, the diaphragm having a profiled form and the upper surface of the chamber having a matching profile.
2. A pressure sensor according to claim 1, wherein an actuator is connected to the diaphragm such that movement of the diaphragm within the chamber moves the actuator.
3. A pressure sensor according to claim 1 or 2, wherein the actuator is a piston.
4. A pressure sensor according to claim 3 wherein the diaphragm is connected between the outer surface of the piston and the inner surface of the chamber.
5. A pressure sensor according to claim 4, wherein the diaphragm is connected to the piston towards the upper end of the piston.
6. A pressure sensor according to any of the preceding claims, wherein the diaphragm comprises stainless steel.
7. A pressure sensor according to any of the preceding claims, wherein a compressible fluid is present in the cavity between the upper surface of the diaphragm and the upper surface of the chamber.
8. A pressure sensor according to any of the preceding claims, wherein the chamber is a cylinder.
9. A pressure sensor according to claim 7 or claim 8 when dependent upon claims 7, wherein the fluid is air.
10. A pressure sensor according to any of the preceding claims, wherein the diaphragm is between 2/1 000ths and 5/1 000ths of an inch thick.
11. A pressure sensor according to any of the preceding claims, wherein the travel of the piston is around 6mm.
12. A pressure sensor substantially as hereinbefore described with reference to and as shown in figures 1-3, 4-5 or 6-8 of the accompanying drawings.