Pressure switch with a metal membrane

Abstract

 A diaphragm metal membrane pressure switch particularly for the opening/closure control of electric circuits. The pressure switch comprises a pressure switch body (2), in which there is a chamber (3) which is connected to an intake port (4) which can be connected to a duct for feeding a fluid. The chamber (3) is delimited by a diaphragm metal membrane (5) which can be deformed as a consequence of the pressure variations of the fluid within the chamber (3). The membrane (5) faces, with its opposite face with respect to the chamber (3), a contact element (6) which can move, as a consequence of the deformation of the membrane (5), with respect to the pressure switch body (2) in order to act on a switch (7) which is associated with the pressure switch body (2). The membrane (5) has, in a central region, a hole (8) at which a connecting element (9) is connected which blocks hermetically the hole (8) and can engage the contact element (6).

Description

[0001] The present invention relates to a diaphragm metal membrane pressure switch, particularly for the opening/closure control of electric circuits.

[0002] As is known, in diaphragm metal membrane pressure switches for the opening/closure control of electric circuits the membrane constitutes the pressure-sensitive element of the system to which the pressure switch is connected, and its deformation, due to such pressure, is used to cause the opening or closing movement of a switch arranged along the electric circuit to be controlled.

[0003] Diaphragm metal membrane pressure switches are capable of responding promptly to stresses even of a few tenths of a bar, since they are practically free from friction resistances which might raise even significantly the value of the starting pressure with respect to the steady-state pressure, as instead occurs in pressure switches which use a moving element instead of a deformable element.

[0004] This high sensitivity has facilitated the diffusion of diaphragm metal membrane pressure switches in many fields, including the field of small electrical household appliances for generating steam with boilers.

[0005] The pressure switch membranes that are currently most widely used in this field are generally of two types:

• with two diaphragm metal membranes, which, by being appropriately welded along their perimeter, delimit a chamber which, connected to the boiler, swells due to the pressure increase; in this case, the weld acts as a mechanical joint between the two membranes and as a sealing element between them;
• with a single diaphragm metal membrane, which is conveniently retained inside the body of the pressure switch; a usually annular gasket is interposed between the body of the pressure switch and the membrane and ensures the seal between these two elements.

[0006] Single diaphragm metal membranes generally have a circular plan shape and are connected to the body of the pressure switch proximate to their peripheral edge. The design of these membranes is rather complicated, since the rigidity of the metal, even with very low thicknesses, on the order of a few tenths of a millimeter, in fact would not allow such membranes to deform, swelling without producing permanent mechanical stresses or wrinkles or, if such deformations were possible in the elastic range, they would be so small that they would be unusable to achieve assuredly the control of an electric switch.

[0007] For these reasons, diaphragm metal membranes of this kind are given an undulated shape by means of concentric grooves formed on both faces of the membrane with the aim of increasing its flexibility and therefore its deformation even with low pressures and of converting the natural tendency of the membrane to expand into a translational movement of its central region along the axis of the membrane.

[0008] These membranes distinctly have a direction of preferred deformation which is determined by the undulations. In practice, when they are subjected to a positive pressure on one side (i.e., to a pressure which is higher than the pressure that is present on the other side), which corresponds to the condition of normal operation of the pressure switch for which the pressure switch has been designed, they undergo a deformation, following the thrust of said pressure, whereas when they are subjected on the same side to a negative pressure they are unable to deform with equal ease and regularity in the opposite direction with respect to the one for which the undulations have been provided, and accordingly they tend to yield, losing over time the repeatability of the value of the pressure at which they have to trip in order to act correctly on the switch to be controlled.

[0009] Usually, in pressure switches which use these membranes, the deformation of the membrane is transmitted to the electric switch by means of a contact element which makes contact at the center of the membrane, on the side thereof which expands as a consequence of an increase in pressure on the opposite side. The contact element is provided with a shaft which is arranged coaxially to the membrane and is supported, so that it can slide along its own axis, by the body of the pressure switch. To utilize as much as possible the deformation of the membrane for the purpose of the axial movement of the shaft, and therefore of the contact element which controls the electric switch, the central region of the membrane, on which the shaft rests, is provided in the shape of a cusp which is convex toward the shaft, i.e., on the opposite side with respect to the side subjected to positive pressure in normal operation.

[0010] The process of deforming the membrane to obtain this cusp, which necessarily has a small diameter in order to reduce as much as possible the area of contact between the membrane and the shaft, is not free from problems, since it entails intense mechanical stresses in the central part of the membrane and difficulties in maintaining good dimensional repeatability of the cusp, in particular of its height, in the industrial production of these membranes.

[0011] Another drawback which can be observed in known types of pressure switches arises from the fact that the membrane is generally locked to the body of the pressure switch by means of a component of the pressure switch which is known as "casing", is assembled to the pressure switch body, and carries the electrical switch to be actuated by means of the pressure switch. Because of this, the tests of the tightness of the locking of the membrane on the body of the pressure switch must be performed necessarily after the assembly of the pressure switch has been completed, with the drawback that if the seal is not satisfactory the entire pressure switch has to be rejected.

[0012] Another drawback which can be observed in some known types of pressure switches is an insufficiently rigid assembly between the casing and the body of the pressure switch; by causing a variation of the position of the casing and therefore of the switch fitted thereon with respect to the membrane, such assembly can cause variations in the tripping pressure of the pressure switch.

[0013] The aim of the present invention is to provide a diaphragm metal membrane pressure switch, particularly for the opening/closure control of electric circuits, which is capable of solving the problems and obviating the drawbacks described above.

[0014] Within this aim, an object of the invention is to provide a pressure switch which has a membrane which can be manufactured simply without causing significant mechanical stresses and with excellent repeatability in production.

[0015] Another object of the invention is to provide a pressure switch which effectively avoids yielding of the membrane in the presence of negative pressures.

[0016] Still another object of the invention is to provide a pressure switch in which the seal between the membrane and the body of the pressure switch can be tested before the electrical components are fitted.

[0017] This aim and these and other objects, which will become better apparent hereinafter, are achieved by a diaphragm metal membrane pressure switch particularly for the opening/closure control of electric circuits, which comprises a pressure switch body, in which a chamber is provided which is connected to an intake port which can be connected to a duct for feeding a fluid, said chamber being delimited by a diaphragm metal membrane which can be deformed as a consequence of the pressure variations of the fluid within said chamber; said membrane facing, with its opposite face with respect to said chamber, a contact element which can move, as a consequence of the deformation of said membrane, with respect to said pressure switch body in order to act on a switch which is associated with said pressure switch body, characterized in that said membrane has, in a central region, a hole at which a connecting element is connected which blocks hermetically said hole and can engage said contact element.

[0018] Further characteristics and advantages of the invention will become better apparent from the description of a preferred but not exclusive embodiment of the pressure switch according to the invention, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a side elevation view of the pressure switch according to the invention;

Figure 2 is a perspective view of the casing of the pressure switch according to the invention with the electrical components removed;

Figure 3 is an axial sectional view of the pressure switch according to the invention, with the membrane at the beginning of its outward deformation with respect to the chamber;

Figure 4 is an axial sectional view of the pressure switch according to the invention, with the membrane flexed inwardly with respect to the chamber.

[0019] With reference to the figures, the pressure switch according to the invention, generally designated by the reference numeral 1, comprises a pressure switch body 2, in which a chamber 3 is provided which is connected to an intake port 4, which is designed to be connected to the pressurized line which must be controlled by means of the pressure switch. The chamber 3 is delimited by a diaphragm metal membrane 5, which is deformable as a consequence of the pressure variations in the chamber 3. The membrane 5 faces, with its face arranged on the opposite side with respect to the chamber 3, a contact element 6 which can move, as a consequence of the deformation of the membrane 5, with respect to the pressure switch body 2 in order to act on a switch 7, which is associated with the pressure switch body 2.

[0020] According to the invention, the membrane 5 has, in a central region, the hole 8 at which a connecting element 9 is connected which blocks hermetically the hole 8 and can engage the contact element 6.

[0021] More particularly, the pressure switch body 2 is preferably made of metal, for example brass, and the intake port 4 is defined at a tab 10, which is threaded externally in the illustrated embodiment and is used to connect the intake port 4 to a duct for feeding a fluid into the chamber 3.

[0022] Proximate to the tab 10 it is possible to provide a nut-shaped portion 11, which is used to screw the tab 10 onto the feed duct by means of a suitable wrench.

[0023] The pressure switch according to the invention is completed by a casing 12, which is associated with the pressure switch body 2 and delimits therewith a compartment 15 in which the contact element 6 is accommodated, as will become better apparent hereinafter. The switch 7 is connected to the casing 12 by means of screws 13, and its movable element 7a, designed to be contacted by the contact element 6, protrudes into the compartment 15 through an opening 14 defined in the casing 12.

[0024] The connection of the casing 12 to the pressure switch body 2 is achieved by means of a threaded coupling 31, which can be locked, after assembly, by way of unscrewing-prevention means, such as for example adhesives or other known types of means.

[0025] The chamber 3 is preferably substantially frustum-shaped and the membrane 5 is arranged so as to close the larger end face of the chamber 3, while the port 4 is defined at the smaller end face.

[0026] The membrane 5 has a substantially disk-like shape, with a first annular undulation 16 which is centered on the axis 5a of the membrane 5, in relief on the face of the membrane 5 which is arranged outside the chamber 3 and with a second annular undulation 17 in relief on the face of the membrane 5 which is arranged inside the chamber 3. The second undulation 17 is concentric with respect to the first undulation 16 and is arranged between an axis 5a of the membrane 5 and the first undulation 16.

[0027] The central region of the membrane 5, at which the connecting element 9 is connected, is substantially flat, and the connecting element 9 comprises a plate 18 which rests against the face of the membrane 5 which is arranged outside the chamber 3 and in which a contact surface 19 for a portion of the contact element 6 is defined.

[0028] The plate 18 has a threaded stem 18a which passes through the hole 8 and mates with a locking nut 20 arranged inside the chamber 3. Between the plate 18 and the face of the membrane 5 arranged outside the chamber 3 there are interposed sealing means which are constituted preferably by an annular gasket 21 which is accommodated in an annular seat defined in the face of the plate 18 directed toward the membrane 5.

[0029] Advantageously, the pressure switch according to the invention comprises means for delimiting the inward flexing of the membrane 5 into the chamber 3.

[0030] As shown in particular in Figure 4, said means for delimiting the inward flexing of the membrane 5 into the chamber 3 are constituted by the nut 20, which engages by contact against the side walls of the chamber 3 when the membrane 5 flexes inwardly into the chamber 3.

[0031] The membrane 5 is locked onto the pressure switch body 2 by means of a perimetric portion thereof. Sealing means are interposed between said perimetric portion of the membrane 5 and the pressure switch body 2 and are constituted preferably by an annular gasket 22, which is accommodated in a seat defined in the pressure switch body 2 at the region for resting of the peripheral portion of the membrane 5.

[0032] More particularly, the locking of the membrane 5 on the pressure switch body 2 is actuated by means of a locking element which is disengaged from the casing 12 and is fixed directly to the pressure switch body 2.

[0033] Such locking element comprises an annular flange 23, which rests with an axial end on the face of the membrane 5 which is directed away with respect to the chamber 3 and is fixed directly to the pressure switch body 2 by way of the plastic deformation of a portion 24 of the pressure switch body 2 which surrounds the annular flange 23 and engages the axial end of the annular flange 23 which lies opposite with respect to the axial end which rests against the membrane 5. In practice, the plastic deformation of the portion 24 of the body of the pressure switch simultaneously actuates the axial locking of the annular flange 23, compressing the annular gasket 22 and thus locking hermetically the membrane 5 with respect to the pressure switch body 2.

[0034] Due to this fact, the tightness of the assembly of the membrane 5 to the pressure switch body 2 can be tested before completing the assembly of the other parts of the pressure switch.

[0035] The contact element 6 comprises a disk-like element 25, which faces coaxially the face of the membrane 5 which is arranged outside the chamber 3 and has, on one of its faces, a central protrusion 25a which faces the plate 18 and, on its opposite face, a guiding shaft 25b, which mates, so as to be able to slide along its own axis, which coincides with the axis 5a of the membrane 5, with the casing 12.

[0036] Preferably, the mating between the contact element 6 and the plate 18 is performed by providing a conical shape for the contact seat 19 and by providing for the central protrusion 25a a point-like shape which is inserted in the contact seat 19.

[0037] The disk-like element 25 faces, with a portion of its face which lies opposite with respect to the membrane 5, the movable element 7a of the switch 7.

[0038] Elastic means are provided between the casing 12 and the contact element 6 and act on the contact element 6 in contrast with the action applied by the membrane 5 as a consequence of its outward flexing with respect to the chamber 3. Such elastic means are constituted by a helical spring 27, which is arranged around the guiding shaft 25b and rests, with an axial end thereof, against the disk-like element 25 and, with its opposite axial end, against an adjustment element 26, which is connected to the casing 12 and can be used to vary the preloading of the spring 27 and therefore the calibration pressure of the pressure switch.

[0039] The adjustment element 26 is substantially cylindrical and mates, by means of a thread 26a defined on its lateral surface, with a threaded seat defined in the casing 12. The adjustment element 26 is arranged coaxially with respect to the guiding shaft 25b and the membrane 5. In the adjustment element 26, starting from its axial end which is directed toward the disk-like element 25, there is a sliding seat for the guiding shaft 25b. The axial end of the adjustment element 26 which is directed toward the disk-like element 25 is further cup-shaped, so as to define a receptacle and a contact element for an axial end of the spring 27. In the opposite axial end of the adjustment element 26 there is a notch 26b, which can be used to turn the adjustment element 26 with respect to the casing 12, for example by means of a screwdriver.

[0040] By way of the rotation of the adjustment element 26 about its own axis with respect to the casing 12, it is possible to increase or decrease the compression of the spring 27 so as to vary the extent of the elastic force which contrasts the outward flexing of the membrane 5 outside the chamber 3, thus varying the value of the minimum pressure required to cause the movement of the disk-like element 25 which causes the action of said disk-like element 25 on the movable element 7a of the switch 7 to be controlled.

[0041] Conveniently, an antifriction washer 28 is interposed between the disk-like element 25 and the axial end of the spring 27 which rests against it, in order to prevent the spring 27, if turned by the rotation of the adjustment element 26, from damaging the disk-like element 25.

[0042] Advantageously, means for delimiting the axial movement of the contact element 6 by way of the action of the membrane 5 and/or by way of the action of the elastic means constituted by the spring 27 are provided.

[0043] More particularly, such means for delimiting the axial movement of the contact element 6 comprise a stop shoulder 29, which is defined by the annular flange 23 and delimits the axial movement of the disk-like element 25 toward the membrane 5 by way of the action of the spring 27.

[0044] The delimitation of the axial movement of the contact element 6 in the opposite direction is determined by a wall 30 of the casing 12 which faces the disk-like element 25 on the opposite side with respect to the membrane 5.

[0045] Operation of the pressure switch according to the invention is as follows.

[0046] When the pressure inside the chamber 3, which can be connected by means of the intake port 4 for example to the inside of a boiler, begins to rise, the membrane 5 begins to undergo deformation, flexing outwardly with respect to the chamber 3 until it lies, with the plate 18, against the central protrusion 25a of the disk-like element 25.

[0047] It should be noted that the deformation of the membrane 5 as a consequence of its particular shape leads substantially to a movement of the plate 18 along the axis 5a of the membrane 5. This movement, once the plate 18 arrives against the central protrusion 25a of the disk-like element 25, is contrasted by the elastic reaction of the spring 27, which prevents the translational motion of the disk-like element 25 until the force applied by the plate 18 to the disk-like element 25, caused by the pressure inside the chamber 3, exceeds the preloading force of the spring 27, as shown in Figure 3.

[0048] Once this condition has occurred, the disk-like element 25 is pushed by the outward flexing of the membrane 5 along the axis 5a, upwardly in Figure 3, and the disk-like element 25 acts with one of its portions on the movable element 7a of the switch 7, switching the position of the switch.

[0049] It should be noted that the particular coupling between the central protrusion 25a of the disk-like element 25 and the contact seat 19 of the plate 18 is capable of compensating for any misalignments between the plate 18 and the disk-like element 25 caused by a less than perfectly symmetrical deformation of the membrane 5. In this manner, the disk-like element 25 performs a translational motion correctly along its own axis, avoiding any stress, at right angles to said axis, on the movable element 7a of the switch 7. This safeguards the integrity of the switch 7 and its lifetime.

[0050] When the pressure in the chamber 3 decreases, transmitting to the disk-like element 25, through the membrane 5, a force which is lower that the force due to the elastic reaction of the spring 27, the disk-like element 25 is subjected to a translational motion in the opposite direction with respect to the preceding one by way of the action of the spring 27, and the movable element 7a of the switch 7 is released while the membrane 5 returns progressively to the non-deformed condition.

[0051] It should be noted that the pressure switch according to the invention is capable of preserving over time the integrity of the membrane 5 even if a negative pressure occurs inside the chamber 3 and even if the chamber 3 is subjected to pressures which are considerably higher than the intended operating pressures.

[0052] In case of negative pressure in the chamber 3, the membrane 5 in fact flexes inwardly into the chamber 3; however, the contact of the nut 20 against the side walls of the chamber 3 limits the deformation of the membrane 5, avoiding its yielding, as shown in Figure 4.

[0053] If instead, conditions with pressures which are considerably higher than the operating pressures occur inside the chamber 3, the disk-like element 25, by resting against the casing 12, limits the outward flexing of the membrane 5.

[0054] Even any incorrect calibration operations, with an excessive preloading of the spring 27, do not damage the membrane 5, since the disk-like element 25 rests against the shoulder 29 of the annular flange 23, avoiding the discharge of excessive forces onto the membrane 5.

[0055] In practice it has been found that the pressure switch according to the invention fully achieves the intended aim, since it allows to avoid significant mechanical stresses and to achieve excellent repeatability in the production of diaphragm metal membranes.

[0056] Another advantage of the pressure switch according to the invention is that it is possible to test the seal between the membrane and the pressure switch body, before the assembly of the pressure switch with the electrical components is completed.

[0057] The pressure switch thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims; all the details may further be replaced with other technically equivalent elements.

[0058] In practice, the materials used, so long as they are compatible with the specific use, as well as the dimensions, may be any according to requirements and to the state of the art.

[0059] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. A diaphragm metal membrane pressure switch particularly for the opening/closure control of electric circuits, which comprises a pressure switch body, in which a chamber is provided which is connected to an intake port which can be connected to a duct for feeding a fluid, said chamber being delimited by a diaphragm metal membrane which can be deformed as a consequence of the pressure variations of the fluid within said chamber; said membrane facing, with its opposite face with respect to said chamber, a contact element which can move, as a consequence of the deformation of said membrane, with respect to said pressure switch body in order to act on a switch which is associated with said pressure switch body, characterized in that said membrane has, in a central region, a hole at which a connecting element is connected which blocks hermetically said hole and can engage said contact element.

2. The pressure switch according to claim 1, characterized in that said connecting element comprises a plate which rests against the face of the membrane which is located outside said chamber and in which a contact seat for a portion of said contact element is defined.

3. The pressure switch according to claims 1 and 2, characterized in that said plate has a threaded stem which passes through said hole and mates with a locking nut which is arranged inside said chamber; sealing means being interposed between said plate and the face of the membrane arranged outside said chamber.

4. The pressure switch according to one or more of the preceding claims, characterized in that the central region of said membrane in which said hole is defined and which is coupled to said plate is flat.

5. The pressure switch according to one or more of the preceding claims, characterized in that said sealing means comprise an annular gasket which is accommodated in an annular seat which is defined in the face of said plate which is directed towards said membrane.

6. The pressure switch according to one or more of the preceding claims, characterized in that said membrane has a substantially disk-like shape, with a first annular concentric undulation in relief on the face of the membrane which is arranged outside said chamber and with a second annular concentric undulation which is arranged between the axis of the membrane and said first undulation in relief on the face of the membrane which is arranged inside said chamber.

7. The pressure switch according to one or more of the preceding claims, characterized in that said chamber is substantially frustum-shaped, said membrane being arranged so as to close the larger end face of the chamber.

8. The pressure switch according to one or more of the preceding claims, characterized in that it comprises means for delimiting the inward flexing of said membrane into said chamber.

9. The pressure switch according to one or more of the preceding claims, characterized in that said means for delimiting the inward flexing of said membrane into said chamber are constituted by said nut, which engages by contact against the side walls of said chamber upon the inward flexing of the membrane into said chamber.

10. The pressure switch according to one or more of the preceding claims, characterized in that said membrane is locked on said pressure switch body by means of a perimetric portion thereof; sealing means being interposed between said perimetric portion of the membrane and said body of the pressure switch.

11. The pressure switch according to one or more of the preceding claims, characterized in that said sealing means, interposed between said perimetric portion of the membrane and said body of the pressure switch, comprise an annular gasket which is accommodated in a seat which is defined in the body of the pressure switch at the contact region of said peripheral portion of the membrane.

12. The pressure switch according to one or more of the preceding claims, characterized in that it comprises a casing which is associated with said pressure switch body and supports the switch to be controlled by means of said contact element.

13. The pressure switch according to one or more of the preceding claims, characterized in that said peripheral portion of the membrane is interposed between said contact region and a locking element which is disengaged from said casing and is rigidly fixed to said pressure switch body.

14. The pressure switch according to one or more of the preceding claims, characterized in that said locking element comprises an annular flange which rests coaxially against the face of said membrane which is directed away from said chamber and is fixed directly to said pressure switch body.

15. The pressure switch according to one or more of the preceding claims, characterized in that said annular flange is fixed to said pressure switch body by means of a plastically deformed portion of said pressure switch body.

16. The pressure switch according to one or more of the preceding claims, characterized in that said contact element comprises a disk-like element which faces coaxially the face of the membrane which is arranged outside said chamber and has, on one of its faces, a central protrusion which faces said plate and, on its opposite face, a guiding shaft which is coupled to said casing so that it can slide along its own axis; said disk-like element facing said switch with a portion of its face which lies opposite with respect to said membrane; elastic means being provided which are interposed between said casing and said contact element and act on said contact element in contrast with the action applied by said membrane as a consequence of its outward deformation with respect to said chamber.

17. The pressure switch according to one or more of the preceding claims, characterized in that it comprises means for adjusting the elastic preloading force of said elastic means.

18. The pressure switch according to one or more of the preceding claims, characterized in that it comprises means for delimiting the axial movement of said contact element by way of the action of said membrane and/or by way of the action of said elastic means.

19. The pressure switch according to one or more of the preceding claims, characterized in that said means for delimiting the axial movement of said contact element by way of the action of said elastic means comprise a stop shoulder which is defined by said annular flange.

20. The pressure switch according to one or more of the preceding claims, characterized in that said means for delimiting the axial movement of said contact element by way of the action of said membrane comprise a stop shoulder which is defined by said casing.

21. The pressure switch according to one or more of the preceding claims, characterized in that said plate has, on its side which faces said central protrusion of the contact element, a conical seat for the end of said central protrusion which is point-shaped.

Drawing