OMATI, Ennio (Viale Piave 46, Pessano Con Bornago, I-20060, IT)
OMATI, Marco Gerolamo (Via Negroni 7, Pessano Con Bornago, I-20060, IT)
OMATI, Ennio (Viale Piave 46, Pessano Con Bornago, I-20060, IT)
| CLAIMS 1. Electromechanical pressure switch comprising a hollow body formed by a base (1) and by a cap (9), between which an elastically deformable membrane (5) is clamped and closes a pressure sensing chamber (4) which communicates with an inlet hole (3)for a pressurized fluid, and lever means (15) for transmitting the deformation of the membrane (5) caused by the pressurized fluid to an actuating push button (22) of a switchable microswitch (23), characterized in that said lever means (15) consist of a one-piece third-kind lever (15) comprising at least a first end bend (16) clamped together with said membrane (5) between said base (1) and said cap (9) and a flat part (18) which bears at the free end a projecting rib (21) for control of said actuating push button (22) of the microswitch (23), said flat part (18) being adjustably fixed to an adjusting screw (13) having an axis coinciding with that of the pressure switch and a spherical tip (12) in contact with a central point (11) of the membrane (5). 2. Pressure switch according to claim 1, characterized in that said lever (15) comprises between said first bend (16) and said flat part (18) a second bend (17) which can be put into contact with fixed walls (19) of said cap (9) or spaced therefrom. 3. Pressure switch according to claim 2, characterized in that said second bend (17) of the lever (15) is in contact with said fixed walls (19) of the cap (9) so as to form the fulcrum of said lever and has such a length as to cause a power arm of the lever (15) shorter than the resisting arm of the same lever (15). 4. Pressure switch according to claim 2, characterized in that said second bend (17) of the lever (15) is in contact with said fixed walls (19) of the cap (9) so as to form the fulcrum of said lever and has such a length as to cause a power arm of the lever (15) longer than the resisting arm of the same lever (15). 5. Pressure switch according to claim 2, characterized in that said second bend (17) of the lever (15) is spaced from said fixed walls (19) so that the fulcrum of the lever coincides with the first bend of the same lever. 6. Pressure switch according to claim 1, characterized in that said lever (15) comprises an inclined plane (31) which connects said first bend (16) and said flat part (18). 7. Pressure switch according to claim 6, characterized in that said inclined plane (31) is provided with at least one window or recess (32). 8. Pressure switch according to claim 1, characterized in that said projecting rib (21) of the lever (15) extends perpendicularly to the push button (22) of the microswitch (23). 9. Pressure switch according to claim 1, characterized in that said flat part (18) of the lever (15) is provided with stiffening ribs (20). 10. Pressure switch according to claim 1, characterized by comprising a compression spring (25) wound around said adjusting screw (13) between an end head of said screw (13) and the flat part (18) of said lever (15). |
The present invention relates to an electromechanical pressure switch which may be used to check the pressure within an apparatus.
Electromechanical pressure switches are known, in which the sensed pressure is translated into a movement of a sensitive elastic membrane element, which actuates an electric switching system constructed and directly accommodated within the body of the pressure switch by means of a lever system which amplifies and transmits the electric signal originated by such a movement.
As compared to these known pressure switches, the pressure switch according to the present invention is characterized in that it includes an external microswitch and in that it contains a "disadvantageous", third-kind lever therein, which allows to amplify the even limited movement of a sensitive membrane element according to a specific ratio which may be changed according to the final application needs of the pressure switch.
The pressure switch according to the invention allows to use a membrane made of any material, such as stainless steel, copper, beryllium, carbon steel, etc., in addition to being designed and developed with relatively high thickness so as to withstand repeated mechanical stresses and high overpressures without being subjected to permanent deformations, because even the minimum movement of the same is amplified by the "disadvantageous" lever system. Furthermore, the construction simplicity makes the device particularly cost-effective, simple to be assembled and produced, because the materials used for its implementation are not high-tech materials and the mechanical tolerances are relatively high.
A practical embodiment of the pressure switch according to the present invention is shown by way of non-limitative example in the accompanying drawings, in which: figure 1 shows an embodiment of the pressure switch according to the invention in a vertical section taken along I- 1 line in figure 2; figure 2 shows the same pressure switch horizontally sectioned along line II- II in figure 1 ; figure 3 shows the pressure switch in figure 1, seen from the bottom and partially sectioned; figure 4 shows a variant of the pressure switch in figure 1 ; figure 5 shows another variant of the pressure switch in figure 1 ; figure 6 shows a further variant of the pressure switch according to the present invention; figure 7 shows a third-kind lever engaged in the pressure switch in figure 6.
The pressure switch shown in figures 1, 2 and 3 comprises a lower base 1 provided with a threaded fitting 2 longitudinally crossed by an axial hole 3 which puts the controlled apparatus into communication with a pressure sensing chamber 4 which is closed by an elastic membrane 5.
Two appropriately dimensioned annular seals 6 and 7 ensure the tightness between the threaded fitting 2 and the base 1 and between the elastic membrane 5 and the base 1. An elastic ring 8 is placed at the end of the fitting 2 inside chamber 4 to allow the upper part of the pressure switch to rotate and be manually positioned in the most suitable position for the application without using tools. Membrane 5 is kept in a firm position between the base 1 and an upper cap 9 by mechanically seaming a clip 10. The lower base 1 and the upper cap 9 form a hollow body forming the outer case of the pressure switch.
The elastic membrane 5 may be made of any material, such as stainless steel, copper, beryllium, carbon steel, etc. and be designed and developed with relatively high thickness to withstand repeated mechanical stresses and high overpressures without being subjected to permanent deformations.
A central point 11 of the elastic membrane 5, coinciding with the median vertical axis A of the pressure switch, is in contact with the spherical tip 12 of an adjusting screw 13, which is mechanically connected by means of a threading 14 to a corresponding central part of a third-kind lever 15
(referred to as "disadvantageous") on which a complementary thread part is directly obtained without the interposition of other welded or riveted parts, etc.
As shown in figure 1, lever 15 is made in one piece formed by a first end bend 16, a second bend 17 and a first flat part 18. The first bend 16 is clamped between the lower base 1 and the upper cap 9 at a side edge portion of membrane 5. The second bend 17 is placed under fixed walls 19 of the cap 9, either in contact therewith (figures 1-3 and 4) or spaced therefrom (figure 5) depending on the shape of the lever, as will be explained below. Finally, the flat part 18 on which the screw 13 is screwed has underlying stiffening ribs 20 and bears a vertically projecting tip 21 at its free end, which is intended to actuate a push button 22 of the switchable microswitch 23 firmly fixed outside the cap 9, and thus outside the pressure switch body, by means of screws 24. A compression spring 25 is positioned between the head of the adjusting screw 13 and the flat part 18 of the lever 15 to avoid vibrations or non-axial efforts from changing the position of the screw 13, thus compromising the adjustment of the pressure switch.
Lever 15 is made of elastic materials, such as appropriately treated carbon steel or stainless steel, so as to exploit the mechanical feature of elasticity of the material of which it is made and keep the tip of the adjusting screw 13 constantly in contact with the membrane 5.
The operating principle of the pressure switch in object is as follows. A pressurized fluid enters into the sensing chamber 4 through the inlet hole 3 of the threaded fitting 2 and causes the deformation of the membrane 5 in a direction according to the inlet direction of the fluid.
Membrane 5 transmits its movement to the spherical tip 12 of the screw 13 and thus to the central zone of the lever 15, withheld in position at one end by means of the bend 16 clamped between the base 1 and the cap 9. According to the embodiment shown in figures 1-3, lever 15 has the bend 17 resting on the cap 9 at the fixed walls 19 of the cap itself. This contact between the bend 17 the lever 15 and the walls 19 of cap 9 determines the fulcrum about which the lever 15 rotates to transmit and amplify the vertical movement generated by the movement of membrane 4. Because the power arm of the lever 15 is shorter than the resisting arm of the lever itself, a high sensing sensitivity of the fluid pressure is obtained.
Furthermore, as mentioned, the lever 15 is made of elastic materials, such as appropriately treated carbon steel or stainless steel, so as to exploit the mechanical feature of elasticity of the material to keep the tip of the adjusting screw 13 constantly in contact with membrane 5. This contrivance allows to immediately transmit every minimum pressure variation which occurs within the sensing chamber 4.
The movement of the lever 15 produced by the deformation of membrane 5 determines the actuation of the actuating push button 22 of the micro switch 23 by the projecting tip 21 placed at the free end of the lever 15 and positioned perpendicularly to the push button 22 of the microswitch 23 to limit the contact surface between the two parts to the minimum and thus reduce frictions and ensure a better repeatability of the electrical intervention. Ribs 20 longitudinally placed along the whole length of the flat part 18 of lever 15 confer a high degree of rigidity to the central part of the lever 15, so as to integrally transmit the movement of membrane 5 without the transmission being fouled by elastic deformations of the lever arm.
The entity of the movement of lever 15, with the fluid pressure in chamber 4 being equal, may be adjusted by means of the adjusting screw 13, which can be accessed from the upper part of the pressure switch by means of a hole 26 at the top of the cap 9. The positioning angle of lever 15 with respect to the surface of membrane 5 is increased by screwing the adjusting screw 13 against the membrane 5, because the lever 15 is hinged onto the bend 17 resting on the fixed walls 19. This movement determines the decrease of the adjustment value of the pressure switch, since the actuating tip 21 placed at the end of the lever 15 approaches the push button 22 of microswitch 23 thus requiring a smaller movement of the membrane 5 and therefore a lower fluid pressure for actuating the push button. By loosening the adjusting screw 13, instead, the opposite effect is obtained, i.e. the tip 21 of lever 15 moves away from the push button 22 of microswitch 23 thus requiring a greater movement of membrane 5 and a higher fluid pressure to actuate the push button.
Lever 15 is kept in position during the step of adjusting by means of guides 27 on the walls 19 of cap 9 at the bend 17 of the lever 15 (figure 3) and, close to tip 21, by means of two guides 28 directly obtained on the cap 9 (figure 1). These guides avoid the adjusting screw 13 from being offset and the lever 15 from twisting at the contact point between the bend 17 and the walls 19, thus conferring more stability and accuracy during the step of adjusting.
A slot 29 is present within hole 26 at the upper end of cap 9, adapted to receive a disc or plug 30 herein, made of elastically deformable plastic material, to be applied after the adjustment process by the manufacturer, as a guarantee from possible tampering by the end user. If removed, tampered or perforated, this plug 30 would determine the end of the manufacturer's responsibility about the adjustment of the pressure switch.
The difference between the pressures which determine the opening and closing of an electric circuit by means of a switching push button of the microswitch 23 may further be changed, thus modifying the length ratio of power arm and resisting arm of lever 15 with respect to the fulcrum of the lever itself.
This is obtained, for example, by replacing the lever 15 in figure 1 with another lever 15 having a reduced extension bend 17, as shown in figure 4. Thereby, the fulcrum of lever 15 is moved away from the central axis A of the pressure switch, and thus from the application point of the force from membrane 5 to lever 15, whereby the ratio between the two lever arms is decreased, and therefore the movement of membrane 5 is amplified to a lesser extent. The pressure difference between the state changes of the electromechanical circuit within the microswitch 23 is thus higher. The opposite effect is obtained by returning from the lever 17 in figure
4 to the lever 15 in figure 1 with a consequent approaching of the lever fulcrum to the central axis A of the pressure switch, whereby the ratio between the lever arms increases and the movement of membrane 5 is more amplified. The pressure difference between the state changes of the electromechanical circuit within the microswitch 23 is correspondingly decreased.
The minimum ratio condition may be obtained by moving the bend 17 of lever 15 away from the walls 19 of cap 9 (figure 5) so as to remove the contact point between the bend 17 and the walls 19 and thus moving the fulcrum of lever 15 at the end bend 16.
As a further alternative, the second bend 17 may be lacking and replaced by an inclined plane 31 connecting the first bend 16, acting as a fulcrum, and the flat part 18. The inclined plane 31 preferably includes at least one window or recess 32, capable of favoring the flexion of the lever 15 at the same window or recess, as shown in greater detail in figure 7.