ACTUATOR AND PRESSURE ADJUSTING UNIT THEREFORE

Abstract: Switch unit energizable by a medium under pressure, comprising a switch provided with a piston chamber (7) hav­ ing therein at least one reciprocally movable piston (8, 9) which separates a second chamber (11) from a first cham­ ber (10), a medium conduit (12) emerges into said first chamber, and with a drive mechanism which couples said piston with a switch element, characterized by a pressure adjust unit (68, 40) coupled with said switch, which unit is provided with a medium inlet (24) which on the one hand communicates via a high pressure medium bore (25) with the medium conduit (12) and which on the other had com­ municates via a pressure reduction unit (41) and a low pressure medium bore (27) with the second chamber, and to the pressure adjust unit per se.

Description: Switch unit and a pressure adjust unit therefore The invention relates to a switch unit engergized by a medium under pressure, comprising a switch provided with a piston chamber having therein at least one reciprocally movable piston which separates a second chamber from a first chamber, and with a drive gear which couples said piston with a switch element. Such a switch unit is known and also comprises spring means arranged in the second chamber for returing the piston to its original position should the pressure generated by the medium discontinue, so that the switch is movable between two positions. Because of the use of these spring means, this known switch unit has the drawback that, as a result of material fatigue symptoms, said spring means partially lose their force after a period of time, so that the switch no longer fulfils its function optimally and reliable. The spring means and the interior surface of the second chamber are moreover exposed to corrosion as a result of the suction of outside air into said second chamber. This drawback can however be obviated by arranging new spring means in the switch unit, which however be obviated by considerable fitting costs and the switch unit being temporarily out of use. The invention has for its object to provide a switch unit improved in this respect and which does not have the above-mentioned drawbacks because the spring means are omitted. In the switch unit according to the invention the spring means are replaced by means for generating a pressure in the second chamber, that is reduced relative to the pressure prevailing in the first chamber. This is achieved according to the invention because the switch unit also features a pressure adjust unit coupled with the switch, which unit is provided with a medium inlet which on the one hand communicates via a high pressure medium duct with the medium conduit and which on the other hand communicates via a pressure reduction unit and a low pressure medium duct with the second chamber. It is mentioned here that a switch unit is known wherein media are added to the first and second chamber from a central point via two separate pressure conduits, whereby a pressure difference between said media is present. As a result, this other known switch unit has the drawback that two pressure lines must be fed to each switch unit, which entails relatively high installation costs. It is moreover not possible here to apply varying pressure differences between both media for different switch units, which makes virtually impossible the application of different types of switch unit with different volumes for the first and second chamber. If an underpressure limiting valve is arranged in the high pressure medium duct, a minimal primary medium pressure has to be present to actuate the switch unit. If the underpressure limiting valve switches between a first position, whereby the medium inlet is blocked and the high pressure medium bore communicates with an outlet discharging into the outside air, and a second position, whereby said medium inlet communicates with said high pressure medium bore and said outlet discharging into the atmosphere is blocked, the advantage is achieved that, with the fall of the primary pressure to below a minimal value, the supply of medium with the primary pressure is blocked, and the pressue present in the first chamber is simultaneously released into the atmosphere, so that the switch unit moves to a position which is also a safety position. If an pverpressure limiting valve is arranged in the low pressure medium bore, the secondary pressure is limited to a maximum value, so that it is possible in all circumstances to switch the switch unit between both positions. If an underpressure limiting valve is arranged in the low pressure medium duct, this has the result that secondary medium pressure sufficient to move the switch unit to the failsafe position is maintained at all times. If a switch element is arranged in the high pressure medium duct, which switches between a first position, whereby the medium inlet communicates with the first chamber, and a second position whereby the communication between said medium inlet and said first chamber is blocked and said first chamber thereby communicates with the atmosphere, the switch unit can be operated in a simple manner because, with said switch element in the first position, medium with primary pressure is carried into the chamber, and with said element in the second position, the prevailing pressure in the first chamber is released into the atmosphere. A failsafe switch unit is obtained if the switch unit is energizable from outside, and if during energizing said switch element is in the first position. A particularly preferred switch unit is obtained if the pressure adjust unit is given the form of an integral block and the medium inlet is coupled via gas tight connecting means on the one hand with a section of the low pressure medium bore and on the other hand with a section of the low pressure medium bore arranged in the switch. In this way the pressure switch unit can be manufactured beforehand as a whole and possibly also be applied to existing switches, if the outlets of said pressure switch unit correspond within determined tolerance limits with the inlets of such a switch for the low pressure and high pressure medium bores. By making an optimal choice of the ratio between the volume of the second chamber and the stroke volume, which is preferably greater than 1 and more preferably is substantially equal to 1.4, with a reduced pressure in the second chamber substantially equal to 2.5 bar, a pressure increase is generated therein which is substantially equal to 1 bar by compressing the medium in said second chamber by displacement of the cylinder. Another aspect of the invention relates to the use of the pressure adjust unit with a switch unit. Said pressure adjust unit according to the invention is characterized by an integral block which comprises a medium inlet, the pressure reduction unit and a high and low pressure medium bore, and which is provided with gastight connecting means for coupling said bores with the medium conduit and low pressure medium bore section arranged in the switch unit, respectively. Mentioned and other characteristics will be explained on the basis of a non-limitative embodiment of the switch unit according to the invention given by way of example, with reference to the appended drawing. In the drawing: Fig. 1 shows a prespective, partly broken away and exploded view of a switch unit according to the invention for operating a shut-off valve; and Fig. 2-5 inclusive show section along the line II-II in fig. 1 of the same switch provided with another pressure adjust unit in various operating states. Fig. 1 shows a switch unit 2 energized by a medium under pressure 1, for example a gas, for operating a shut-off valve 4 arranged in a conduit piece 3. Said switch unit 2 comprises a switch 5 and a pressure adjust unit 6 according to the invention arranged thereon. The switch 5 is provided with a piston chamber 7 having therein two coupled reciprocally movable pistons 8, 9 which separate second chambers 11 situated on either side of said pistons 8, 9 form a first chamber 10 situated between both said pistons 8, 9. A medium conduit 12 emerges into said first chamber 10. Each piston 8, 9 is provided with three guide elements 13, 14 and 15, whereby guide element 15 is provided with a rack 16 which grips onto a pinion 18 arranged on a rotary shaft 17. Said rack 16 and pinion 18 form here the drive mechanism which couples both pistons 8, 9 with a switch element illustrated by said rotary shaft 17 which can be operated manually on the one hand via shaft stump 19 and is provided on the other hand in a manner not shown with a form complementary to a shut-off valve end 20. The piston chamber 7 is formed by a cylindrical piece and two covers 23 arranged thereon with the aid of attaching means 22. The pressure adjust unit 6 is provided with a medium inlet 24 which communicates on the one hand via a high pressure medium bore 25 with medium conduit 12 and which on the other hand communicates via a pressure reduction unit 26 and a low pressure medium bore 27 with both the two chambers 11. The pressure reduction unit 26 according to fig. 1 consists of a ball-bearing 28 which is under spring pretensioning of a spring 29 and which is pressed against a seat 30. With the rise of pressure in the low pressure medium bore 27, whereby the transport of the medium 1 is restricted via an adjustable throttle 31, said bearing will be freed from said seat 30 and medium flows vai a passage 32 to the atmosphere, so that in said low pressure medium bore 27 and in both the two chambers 11 a pressure is maintained that is reduced relative to the pressure prevailing in the first chamber 10 and which is supplied via the medium 1 along medium inlet 24. Figures 2-5 inclusive show another pressure adjust unit 40 coupled with the switch 5, which unit is also provided with medium inlet 24 which communicates on the one hand via high pressure medium bore 25 with medium conduit 12 that emerges into the first chamber 10, and which communicates on the other hand via pressure reduction unit 41 and low pressure medium duct 27 with both the two chambers 11. An underpressure limiting valve 42 is accomodated in the high pressure medium bore 25. Said valve 42 continues to block said high pressure medium bore 25 until the pressure input supplied via medium inlet 24 exceeds a pre-selected minimum value that is adjusted with the spring. Said valve 42 then first opens and medium flows to pressure reduction unit 41. Said pressure reduction unit 41 has the purpose of forming and keeping constant the secondary pressure (the operative pressure in the second chambers) derived from the primary pressure, irrespective of changed primary pressure and of the medium used. The primary pressure must always be higher than the secondary (operative) pressure. The pressure reduction unit 41 adjusts the secondary pressure with the aid of a membrane 43. One side 44 of said membrane 43 is exposed to the primary pressure, while a spring 46, the spring force whereof is adjustable using an adjusting screw 47, acts upon the other side 45. With the rise of secondary pressure, said membrane 43 moves against said spring 46, and with the aid of a valve body 48 attached to said membrane 43 alters the operative section of a valve seat 49. With a further rise in secondary pressure, said valve body 48 comes to lie on said valve seat 49 and closes off the passage. At that moment the maximum secondary pressure in low pressure medium duct 27 is reached. If the pressure in the second chambers 11 falls, membrane 43 then moves to the position indicated by dashed lines, and medium with the high primary pressure can pass valve body 48 until the maximum adjustable secondary pressure is again reached. An underpressure limiting valve 50 is also arrranged in low pressure medium bore 27. Should the primary pressure fall or be removed suddenly, said underpressure limiting valve 50 prevents the medium pressure prevailing in the second chambers 11 from likewise falling or being lost (see also fig. 4). Finally an overpressure limiting valve 51 is accomodated in the low pressure medium bore 27. The pressure adjust unit 40 is in addition provided with an electrically energizable switch element 52 accomodated in the high pressure medium duct 25, which element switches between a first position, whereby medium inlet 24 communicates with the first chamber 10 (fig. 3), and a second postion whereby the communication between said medium inlet 24 and said first chamber 10 is blocked and said first chamber 10 communicates with the atmosphere (fig. 2). Said switch element 52 is provided with magnet 53 which acts upon an anchor 55 operating under the spring force of spring 54. when said magnet 53 is energized, said anchor 55 is moved counter to the spring force of spring 54, and medium inlet 24 communicates vai high pressure medium bore 25 and medium conduit 12 with the first chamber 10. An outlet 56 communicating with the atmosphere is simultaneously blocked with the aid of anchor 55 (fig. 3). With the switch element 52 in the energized position (see fig. 3) pistons 8 and 9 are moved away from one another. If the energizing of said switch element 52 is interrupted, the first chamber 10 expels air via outlet 56, so that pistons 8 and 9, under the influence of the lower overpressure prevailing in both the two chambers 11, are moved towards one another. Because anchor 55 blocks high pressure medium bore 25, if switch element 52 is not energized the flow of medium supplied to medium inlet 24 into the atmosphere is prevented. In order to always ensure the movement of pistons 8 and 9 towards one another into a failsafe position, use of an underpressure limiting valve 42 is recommended such that, in the case where the primary pressure falls to below a minimum value, medium conduit 24 is closed off and high pressure medium bore 25 comes simultaneously into communication with the atmosphere, so that, also when there is a slow fall in primary pressure, the failsafe situation is reached. Underpressure limiting valve 42 is therefore also equipped with a valve disc 57, which, if the primary pressure falls below a minimum value, is pressed against a valve seat 58 with the aid of spring 59. High pressure medium bore 25 communicates simultaneously via a passage 60 around the disc shank 61 with an outlet 62 which emerges into the atmosphere (fig. 4). In this way is achieved that, when primary pressure falls below the minimum while switch element 52 is energized, the first chamber expels air and both pistons 8 and 9 move towards one another and thereby assume the failsafe position. The overpressure limiting valve 51 has the function that, if as a result of play 63 between for example a sealing ring 64 and piston 8, medium at high pressure flows out of the first chamber 10 to the second chamber 11, said higher pressure is released via outlet 65 into the atmosphere, until a miximum secondary pressure is again attained. Because in these circumstances underpressure limiting valve 50 blocks low pressure medium bore 27, there is sufficient pressure present in both second chambers 11 to enable pistons 8 and 9 to be moved towards one another so as to again reach the failsafe position, either when switch element 52 is not energized and/or when underpressure limiting valve 42 is in a position blocking medium inlet 24. In view of the fact that the pressure adjust units are in principle detachable from the switch 5, gastight connecting means 66 have to be present between said switch 5 and both said pressure adjust units. It is recommended for the optimal functioning of the switch unit that this pressure difference is as small as possible. This can be achieved by choosing a stroke volume for both pistons 8 and 9 at least greater than the volume of both the chambers 11 and the stroke volume of both said pistons 8, 9 is adjusted to a value substantially equal to 2.5 bar, the pressure difference is equal to a maximum 1 bar. It will be apparent that the pressure adjust unit can be used on different types of switch, whereby, depending on the stroke volumes of the pistons 8, 9 and the volumes of both the second chambers 11, and adjustable pressure can always be set in both said second chambers 11 using the pressure reduction unit, so that an optimal pressure difference resulting from the movement of both said pistons 8, 9 can be found, and an optimal moment can be applied on rotary shaft 17 for operating the shut-off valve to be coupled with said rotary shaft 17. It will be further apparent that pressure adjust unit 6 is constructed such that, with the loss of pressure on the medium inlet or with a fall below a preadjusted value, the pressure in the first chamber 10 increases and in this way the pistons are moved to a position which can correspond substantially with a failsafe position of the switch to be operated by the switch unit 2. Although the description refers to a switch provided with two coupled pistons, it will be apparent that the pressure adjust unit can also be used with a swich provided with only a single piston and consequently with a single second chamber. Air is preferably used as medium, but other gaseous media and possibly liquid media are in principle also usable.

Claims: Claims 1. Switch unit energizable by a medium under pressure, comprising a switch provided with a piston chamber having therein at least one reciprocally movable piston which separates a second chamber from a first chamber, a medium conduit emerges into said first chamber, and with a drive mechanism which couples said piston with a switch element, characterized by a pressure adjust unit coupled with said switch, which unit is provided with a medium inlet which on the one hand communicates via a high pressure medium bore with the medium conduit and which on the other had communicates via a pressure reduction unit and a low pressure medium bore with the second chamber. 2. Switch unit as claimed in claim 1, characterized in that an underpressure limiting valve is arranged in said high pressure medium bore. 3. Switch unit as claimed in claim 1 or 2, characterized in that said underpressure limiting valve switches between a first position, whereby said medium inlet is blocked and said high pressure medium bore communicates with an outlet emerging into the atmosphere, and a second posi tion, whereby said medium inlet communicates with said high pressure medium bore and the outlet emerging into the atmosphere is blocked. 4. Switch unit as claimed in claim 1, 2 or 3, characterized in that an overpressure limiting valve is arranged in said low pressure medium bore. 5. Switch unit as claimed in any of the preceding claims, characterized in that an underpressure limiting valve is arranged in said low pressure medium bore. 6. Switch unit as claimed in any of the preceding claims, characterized in that a switch element is arranged in said high pressure medium bore, which element switches between a first position, whereby said medium inlet communicates with the first chamber, and a second position, whereby the communication between said medium inlet and said first chamber is blocked and said first chamber thereby communicates with the atmosphere. 7. Switch unit as claimed in claim 6, characterized in that said switch element is energizable from outside, and that when energized said switch element is in said first position. 8. Switch unit as claimed in any of the preceding claims, characterized in that said pressure adjust unit is made in the form of an integral block and said medium inlet is coupled via gastight connecting means on the one hand with said medium conduit and on the other hand with a section of said low pressure medium bore arranged in said switch. 9. Swith unit as claimed in any of the preceding claims, characterized in that the ratio between the volume of said second chamber and the stroke volume of said piston is greater than 1. 10. Switch unit as claimed in claim 9, characterized in that said ratio is substantially equalto 1.4 and the reduced pressure in said second chamber is substantially equal to 2.5 bar. 11. Pressure adjust unit intended for use with the switch unit as claimed in claims 1-10, charachterized by an integral block which comprises a medium inlet, the pressure -reduction unit and a high and low pressure medium bore and which is provided with gastight connecting means for coupling said bores with the medium conduit and low pressure medium bore section arranged in said switch unit, respectively. 12. Pressure adjust unit as claimed in claim 11 or 12, characterized in that an underpressure limiting valve is arranged in said high pressure medium bore. 13. Pressure adjust unit as claimed in claim 11 or 12, characterized in that said underpressure limiting valve switches between a first position, whereby said medium inlet is blocked and said high pressure medium bore communicates with an outlet emerging into the atmosphere, and a second position, whereby said medium inlet communicates with said high pressure medium bore and the outlet emerging into the atmosphere is blocked. 14. Pressure adjust unit as claimed in claim 11, 12 or 13, characterized in that an overpressure limiting valve is arranged in said low pressure medium bore. 15. Pressure adjust unit as claimed in claims 11-14, characterized in that an underpressure limiting valve is arranged in said low pressure medium bore. 16. Pressure adjust unit as claimed in claims 11-15, characterized in that a switch element is arranged in said high pressure medium bore, which element switches between a first position, whereby said medium inlet communicates with said first chamber, and a second position, whereby the communication between said medium inlet and said first chamber is blocked, and said first chamber thereby communicates with the atmosphere. 17. Pressure adujst unit as claimed in claim 16, characterized in that said switch element is energizable from outside, and that when energized said switch element is in said first position.

Inventors: SCHWIND, HEINZ GUNTHER, Schwind, Heinz Günther
Applicants: EL-O-MATIC B.V.
Application year: 1985
Main classification: F16K31
IPC codes: F15B20, F16K31