GB2433298A

GB2433298A - Diaphragm with rupture detection

Info

Publication number: GB2433298A
Application number: GB0525259A
Authority: GB
Inventors: Joseph Anthony Griffiths
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-12-13
Filing date: 2005-12-13
Publication date: 2007-06-20
Also published as: GB0525259D0

Abstract

A flexible diaphragm 100/200 for use in fluid flow control applications which includes means for detecting when the diaphragm has ruptured, and a method of manufacturing such a diaphragm. The diaphragm comprises an elastic electrically conductive polymer circuit 102/202 formed on a flexible substrate 101/201 with an electrically insulating moulded, flexible rubber body 108/208 encapsulating the substrate and circuit. The substrate may be knitted nylon and the rubber may be formed around the substrate and perneate through the substrate. When the diaphragm ruptures the electrically conductive circuit is broken or its resistance is altered.

Description

Diaphragm with Rupture Detection

Description

The present invention relates to a diaphragm for use in fluid flow control applications and, more particularly, to such a diaphragm incorporating a means to enable a rupture in the diaphragm to be detected and, a method of manufacturing such a diaphragm.

--------w--Vious-tpes-o-f-diah-ragms-are-known-for-use-in-fl id-coniol--devices--such-as---------------diaphragm pumps used for pumping liquids or gases, and are commonly in the form of inoulded rubber diaphragms. En many applications where these diaphragms are used, it is important that the integrity of the diaphragm is not compromised. This can be particularly important in medical applications where a leaking or ruptured diaphragm can have serious consequences, such as contamination of medical or biological fluids. However, it is difficult to tell quickly when a diaphragm has ruptured so that the device incorporating the diaphragm can be switched off and the diaphragm replaced before any serious consequences occur.

An example of a known diaphragm pump 10 is shown schematically in Figure 1 and comprises a chamber 11, through which fluid being pumped flows, having an inlet 12 and an outlet 13. The in.let 12 includes a one-way valve 14 which allows fluid to flow into the chamber 11 though the inlet 12 but not out of the chamber 11 therethrough, and the outlet 13 includes a one-way valve 15 which allows fluid to flow out of the chamber 11 through the outlet 13 but not into the chamber 11 therethrough. A flexible diaphragm 16 is mounted in the wall of the chamber 11 separating the chamber 11 from a cavity 17 filled with a driving fluid, usually oil.

The pressure of the driving fluid in the cavity 17 can be alternated which in turn causes the diaphragm 16 to deform accordingly. When the driving fluid pressure is increased to a positive pressure relative to the fluid pressure in the chamber 11, the diaphragm deforms into the chamber 11 as shown by position I in Figure 1.

Conversely, when the driving fluid pressure is lowered to a negative pressure relative to the pressure within the chamber 11, the diaphragm deforms into the cavity 17 as shown by position II in Figure 1.

The fluid to be transported is caused to flow through the diaphragm pump chamber 11 by cyclically alternating the driving fluid pressure between positive and negative pressure. When the diaphragm 16 extends to position I, the volume of the chamber 11 is reduced and the fluid pressure therein is increased. Therefore, the fluid in the chamber 11, unable to pass through the inlet one-way valve 14, is forced out of the outlet 13 through the outlet one-way valve 15. Then, when the diaphragm 16 fluicL.

pressure therein is reduced. This causes the fluid outside the chamber 11, which is unable to pass into the chamber 11 through the outlet one-way valve 15, to be drawn into the chamber 11 through the inlet 12 through the inlet one-way valve 14.

As this cycle is repeated, the fluid is pumped through the diaphragm pump 10 from the inlet 12, through the chamber 11 and out of the outlet 13.

It will be appreciated that if the diaphragm 16 fails due to rupturing of the diaphragm wall, the fluid-tight seal between the pump chamber 11 and the driving fluid cavity 17 is broken and the driving fluid contaminates the fluid flowing through the diaphragm pump chamber 11. If the pump 10 is being used in a medical application, for example, to pump blood, this contamination could have serious consequences to the patient. Furthermore, a small rupture which is sufficient to allow the driving fluid to leak into the pump cavity 11 may still allow the diaphragm pump 10 to continue to pump fluid, and so the rupture, and the resulting contamination of the pumped fluid may initially go unnoticed, by which time considerable damage may have been done. Such pumps are also used in other applications in which the purity of the transported fluid is critical, such as pharmaceutical, chemical, biological or food applications.

One known solution to this problem is to provide two diaphragms in parallel adjacent one another so that if one diaphragm fails, the other will still function properly and prevent the pump from malfunctioning and the pumped fluid from being contaminated by the driving fluid. Although this back-up' diaphragm type solution protects against a situation where a single diaphragm ruptures, it still suffers the same drawbacks in the event that both diaphragms fail. In addition, use of one diaphragm may go unnoticed because the second diaphragm would keep the device working properly, and so the fluid pump could be allowed to operate with only the second diaphragm intact, which could continue for some time with the increased risk of failure of the second diaphragm the longer the pump is operated.

Another solution proposed in the prior art is to provide a diaphragm comprising two flexible members sandwiching an electrically conductive circuit between them.

i0__Whenihediaphragm is...in.,uae,this circuitcanhe..onnectedto.an.electrical devic.e...

which measures the resistance of the electrically conductive circuit in the diaphragm. If the diaphragm ruptures, the driving fluid would permeate into the space between the two flexible members and contact the electrically conductive circuit or would break the electrically conductive circuit, thereby changing the resistance measured by the electrical device and triggering an alarm to indicate that the diaphragm has failed.

Although effective at detecting a ruptured diaphragm, the above prior art device still suffers a number of drawbacks. Firstly the construction techniques used to make these types of diaphragm means that they are relatively large and can only operate at speeds of about 10 -20 oscillations per minute, whereas it is desirable to produce a smaller diaphragm that can operate at much higher speeds, such as around 1000 oscillations per minute. At these high speeds, conventional diaphragms would quickly fracture and the circuit within the diaphragm would break quickly. Secondly, it is desirable to be able to screen print the electrical circuit used in the diaphragm, but this requires the surface onto which the circuit is printed to be completely flat.

However, many diaphragms need to be contoured for use in their respective applications, such as the diaphragm 20 shown in Figures 2A -2C, which has a raised ridge 21 extending around its upper surface. The contoured diaphragm is preferable to a flat diaphragm for various reasons. One is that a contoured diaphragm is able to deflect much more under the application of driving fluid pressure variations and so the volume of fluid that can be pumped is much greater than if a flat diaphragm was to be used. Secondly, contoured diaphragms are stronger than flat diaphragms and so are much more preferable for the longevity of the device. However, a circuit cannot be screen printed directly onto the surface of a pre-formed contoured diaphragm because it would not form correctly across the contoured surface.

Therefore, it is the object of the present invention to provide a diaphragm and a method of manufacture thereof, that substantially alleviates or overcomes the problems mentioned above.

_W_&ccoidingly,. the...present.invention.pxovidesadiaphragm comprising.a flexible substrate sheet, an electrically conductive circuit formed on the substrate sheet and a flexible moulded body encapsulating the substrate sheet and circuit such that when the flexible moulded body ruptures, the electrically conductive circuit is broken or its resistance to the flow of electric current is altered.

In a preferred embodiment, the electrically conductive circuit is screen-printed onto the substrate, and preferably, the substrate is stretchable in any direction to substantially the same extent. Conveniently, the substrate comprises a knitted material, preferably knitted nylon.

Advantageously, the flexible moulded body is made of an electrically insulating rubber. The rubber may be bonded to both sides of the substrate, or alternatively, the rubber may be formed around the substrate and permeates through the substrate.

In a preferred embodiment, the flexible moulded body is coated in PTFE and preferably, the electrically conductive track is formed of an elastic conductive polymer.

In a preferred embodiment of the invention, the diaphragm comprises two disc-shaped portions connected to each other, the two disc-shaped portions preferably being connected to each other at their respective peripheral edges by a bridging portion of the moulded body. A single electrically conductive circuit may extend through both discs, or alternatively, a separate electrically conductive circuit may extend through each disc.

The present invention also provides a method of manufacturing a diaphragm comprising the steps of forming an electrically conductive circuit on a substrate sheet, placing the substrate into a mould and encapsulating the substrate sheet and electrically conductive circuit in a flexible moulded body.

The step of forming the electrically conductive circuit on the substrate may i0_cmpriae..screen-printing.the. electricallycondictive.circuitoii the substrate. . The step of forming the flexible moulded body preferably involves bonding the rubber to each side of the substrate using a bonding agent, or alternatively, may involve the rubber permeating though the substrate.

Conveniently, the method also includes the step of coating the flexible moulded body of the diaphragm with PTFE.

A preferred embodiment of the present invention will now be described, by way of example only, with reference to Figures 3 -8 of the accompanying drawings, in which: Figure 1 is a simplified schematic view of a known diaphragm pump; Figure 2A is a perspective view of a known diaphragm; Figure 2B is a side view of the diaphragm of Figure 2A; Figure 2C is a cross-sectional side view of the diaphragm of Figures 2A and 2B; Figures 3A is a schematic view of a first step in a production process of a diaphragm of the present invention; Figures 3B is a schematic view of a second step in a production process of a diaphragm of the present invention; Figure 4 is a plan view showing the circuit layout of a first embodiment of a diaphragm of the present invention; Figure 5 is a plan view showing the circuit layout of a second embodiment of a diaphragm of the present invention; Figure 6 is a plan view showing the circuit layout of a third embodiment of a diaphragm of the present invention; Figure 7A is a plan view showing the circuit layout of a fourth embodiment of a diaphragm of the present invention; Figure 7B is a cross-sectional side view of the diaphragm of Figure 6A in an operative position; and Figure 8 is a cross-sectional view of a diaphragm of any of Figures 4 -7B.

_..,--.-., -..,.-.-.-...--..----...-Referring now to Figures 3A and 3B, a method of producing a diaphragm 100 of the present invention is shown, and comprises a first step A (see Figure 3A) of taking a flexible substrate 101 and laying it on a flat surface 105, and screen-printing an electrically conductive circuit 102 on the substrate 101 using a screen printing apparatus 106. The electrically conductive circuit 102 is made of a flexible polymer which also has elastic properties. The circuit 102 is printed in a suitable pattern within a generally circular area on the substrate 101 corresponding to the eventual circular shape of the diaphragm 100, and includes start and end contact points 103, 104 extending outwardly from the edge of the pattern. After the circuit 102 has been printed, the substrate 101 is placed in a moulding tool 107 in a rubber moulding machine and, in a second step B (see Figure 3B), a body 108 of the diaphragm 100 is formed around the substrate 101 and associated electrically conductive circuit 102. The moulding tool 107 is contoured to reflect the desired final shape of the diaphragm and so during the moulding process in step B, it is important that the substrate conforms to the shape of the moulding tool 107 and to the contours of the finished diaphragm. It is important therefore, that the substrate 101 is able to stretch in both directions shown by axes x and y in Figure 3B and able to conform over the contours of the moulding tool 107 so that the substrate is perfectly encapsulated by the rubber during the moulding process. It has been found that a substrate 101 made from a sheet of knitted material, preferably nylon, is most suitable for this application, primarily because it is capable of stretching equally in the x-direction and the y-direction. Conversely, it has been found that woven materials, including woven nylon sheets, do not stretch equally in the x-direction as in the y-direction and consequendy, are unsuitable for use in the apparatus and method of the invention because it does not properly conform to the shape of the mould.

In addition to the above, it is also important that the electrically conductive circuit 102 printed on the substrate 101 is also able to stretch and conform to the contours of the moulding tool 107. Otherwise, the circuit could be damaged or broken during the moulding stage. Therefore, the conductive polymer used for the circuit 102 must have the appropriate elastic physical properties to achieve this.

___.-.---.-.--..---------..---.-. -.--.--.--...--..---,.,----.....V.--------. ____ The diaphragm body-forming step B can comprise an injection moulding process in which rubber flows around the substrate 101 within the moulding tool 107 and permeates through the fibres of the substrate 101 thereby encapsulating it in a single body. In this embodiment, it is important that the substrate 101 is compatible with the rubber so that the rubber adheres to the substrate material. Alternatively, the body-forming step B can comprise bonding a first pre-formed side of the contoured diaphragm body 108 to one side of the substrate 101, and then bonding a second pre-formed side of the contoured diaphragm body 108 to the opposite side of the substrate, thereby encapsulating the substrate 101 by sandwiching it between the two pre-formed diaphragm body parts. An appropriate bonding agent may be used to bond the diaphragm body parts to the substrate 101.

The substrate sheet 101 may be sized so that its entire area is encapsulated within the diaphragm body 108 in step B. Alternatively, the substrate sheet (but not the circuit 102 printed thereon) may be larger in area than the final diaphragm body 108, in which case, a further step (not shown) will be required in which the excess substrate 101 that extends beyond the edge of the diaphragm body 108 is trimmed to size.

In another optional processing step (not shown), the diaphragm 100 is coated with PTFE which is resistant to various chemicals and is inert so as not to affect or be affected by the fluids that it may come into contact with during use. It has been found that coating the diaphragm 100 with PTFE is preferable to constructing the entire diaphragm of PTFE because if the entire diaphragm was made of PTFE, it would be too brittle and would quickly fracture when oscillated at the high speeds.

The configuration of the circuit 102 printed on the substrate can take any number of forms, but it is important that the circuit covers a large proportion of the area of the diaphragm 100 so that, in use, wherever a rupture may occur through the diaphragm, it will cross a part of the circuit and break the circuit so that the rupture can be detected. Exemplary circuit configurations are shown in Figures 4 -6 and include radial, circular or linear layout.

________

In use in a diaphragm pump, the start and end contacts 103, 104 are connected to the contacts of an electrical/electronic device (not shown) that can measure an electric current being passed through the circuit 102 and can therefore detect any break in the circuit 102 by detecting changes in the resistance of the circuit 102. It will be appreciated therefore, that the rubber from which the body 108 of the diaphragm is made must be an electrical insulator otherwise the rubber diaphragm body 108 would continue to conduct the electrical current passing through the circuit, even if the circuit was broken. For the same reason, the material of the substrate must also be an electrical insulator.

A second embodiment of a diaphragm 200 of the invention may be produced by the above-described method and is shown in Figures 7A and 7B. This second embodiment 200 is a double diaphragm comprising a first disc 210 and a second disc 211 joined to one another by a bridging part 212. As with the first embodiment 100 described above, a substrate 201 is printed with an electrically conductive circuit 202 made of a flexible elastic conductive polymer. However, in this embodiment, the circuit is printed in an area corresponding to the two discs 210, 211, with a portion extending across the bridging part 212. The circuit 202 is formed with start and end contact points 203, 204 that, in use, are connected to the contacts of an electrical/electronic current measuring device (not shown). The circuit is printed as a single circuit extending across both discs 210, 211 and so has only one single pair of contact points 203, 204 (as shown in Figure 7A). As with the first embodiment 100 described above, the substrate 201 is then placed on a contoured moulding tool and a contoured body 208 of the diaphragm is moulded around the substrate 201, or is bonded as two parts to either side of the substrate 201 using a bonding agent.

In use, the double diaphragm 200 is intended to be positioned with the first and second discs 210, 211 lying parallel to one another as shown in Figure 7B with the bridging part 212 across the gap between them and perpendicular to each disc 210, 211. In the layout of the circuit 202 illustrated, a single circuit extends around the surface area of both discs 210, 211 meaning that if either diaphragm disc 210, 211 (not shown) could comprise two separate circuits, one on each disc 210, 211, each separate circuit terminating in a separate pair of contacts, each pair individually connectable to an electronic detection device so that a rupture in either disc 210, 211 can be detected separately.

A cross-sectional view of a diaphragm 100/200 of the present invention is shown in Figure 8, which shows the substrate 101/201 with the electrically conductive circuit 102/202 thereon, encapsulated in the moulded body 108/208 of the diaphragm 100/200.

Various other suitable materials may be used in the construction of the diaphragm within the scope of the invention, other than those described above.

Claims

-10 -Claims 1. A diaphragm comprising a flexible substrate sheet, an

electrically conductive circuit formed on the substrate sheet and a flexible moulded body encapsulating the substrate sheet and circuit such that when the flexible moulded body ruptures, the electrically conductive circuit is broken or its resistance to the flow of electric current is altered.

2. A diaphragm according to claim 1 wherein the electrically conductive circuit is screen-printed onto the substrate.

3. A diaphragm according to claim I or claim 2 wherein the substrate is stretchable in any direction to substantially the same extent.

4. A diaphragm according to any of claims I to 3 wherein the substrate comprises a knitted material.

5. A diaphragm according to any of claims I to 3 wherein the substrate is knitted nylon.

6. A diaphragm according to any of claims I -5 wherein the flexible moulded body is made of an electrically insulating rubber.

7. A diaphragm according to claim 6 wherein the rubber is bonded to both sides of the substrate.

8. A diaphragm according to claim 6 wherein the rubber is formed around the substrate and permeates through the substrate.

9. A diaphragm according to any preceding claim wherein the flexible moulded body is coated in PTFE.

-11 - 10. A diaphragm according to any preceding claim wherein the electrically conductive track is formed of an elastic conductive polymer.

11. A diaphragm according to any preceding claim wherein the diaphragm comprises two disc-shaped portions connected to each other.

12. A diaphragm according to claim 11 wherein the two disc-shaped portions are connected to each other at their respective peripheral edges by a bridging portion of the moulded body.

13. A diaphragm according to claim 11 or claim 12 wherein a single electrically conductive circuit extends through both discs.

14. A diaphragm according to claim 11 or claim 12 wherein a separate electrically conductive circuit extends through each disc.

15. A method of manufacturing a diaphragm comprising the steps of forming an electrically conductive circuit on a substrate sheet, placing the substrate into a mould and encapsulating the substrate sheet and electrically conductive circuit in a flexible moulded body.

16. A method according to claim 15 wherein the step of forming the electrically conductive circuit on the substrate comprises screen-printing the electrically conductive circuit on the substrate.

17. A method according to claim 15 or claim 16 wherein the substrate comprises knitted nylon material.

18. A method according to any of claims 15 -17 wherein the flexible moulded body is made of an electrically insulating rubber. S. S

-12 - 19. A method according to claim 18 wherein the step of forming the flexible moulded body involves bonding the rubber to each side of the substrate using a bonding agent.

20. A method according to claim 18 wherein the step of forming the flexible moulded body involves the rubber permeating though the substrate.

21. A method according to any of claims 15 -20 further including the step of coating the flexible moulded body of the diaphragm with PTFE.

22. A diaphragm substantially as hereinbefore described with reference to the accompanying drawings.

23. A method substantiaUy as hereinbefore described with reference to the accompanying drawings.