PNEUMATIC VALVE, PARTICULARLY FOR CONTROL OF COMPRESSED-AIR-OPERATED MEMBRANE PUMPS

Abstract: A pneumatic valve, designed to control/pressurize a membrane pump, comprises a valve body (1) having gates (8-12) for compressed-air-flow/operation/pressurization of said pump. The valve body is closed by ends (2), between which a plunger (5) is to move between two end positions. The ends of the plunger and the ends of the valve body co-operate physically magnetically in order to generate just and only a retaining force, which constitutes a threshold for a certain minimum control pressure from a control-air-gate (13 or 14) and guarantees a rapid initial movement as well as a rapid transfer of the plunger to its opposite end position. Permanent magnets (15) are inserted in said plunger ends and/or in said valve body ends and designed to co-operate with projections and/or recesses (17, 18, 20) in the opposite member in order to obtain a so-called air-cushion-damping.

Description: Pneumatic value , particularly for control of compressed-air-operated membrane pumps . The present invention relates to a pneumatic valve designed to control particularly a compressed-air-operated membrane pump and is set forth in detail in the preamble of patent claim 1 . US-A 3 465 686 discloses an air—operated hydraulic pump using a shuttle valve, the shuttle of which is effected in all positions by very strong permanent magnets mounted in the valve housing adjacent the ends of the shuttle. The idea with this valve is to influence the shuttle in any position, i.e. even any intermediate position, so that the shuttle operates fully from end to end. For achieving such a great attractive force and yet render the valve operative, the magnets are spaced from the ends of the shuttle. This is obligatory and extremely critical, as a gap as narrow as 0.5 mm creates only 1/10 of the retaining power of a gap equal to 0 mm, i.e. when physical contact has been estab¬ lished between the shuttle and one of the permanent mag¬ nets. If the control air is designed to move the shuttle from one end position to the other at a pressure of ten pounds per square inch, it will certainly not when physi¬ cal contact has been established between the shuttle and a permanent magnet and a releasing force of one hundred pounds per square inch will be required. It goes without saying that this previously known valve requires very accu¬ rate tolerances and will seize to function whenever there is a slight play or, after some time of operation, a cer¬ tain natural wear and tear. Furthermore, this valve will create a high level of noise, as the strong magnets will make the shuttle bounce from one seat on to the other, in which connection 0-rings alledgedly intended to reduce noise necessarily must render the extre¬ mely important accurate size of said gap between shuttle and permanent magnets variable and thus creating a non-de¬ sired varying influence on the retaining power due to the material used for the O-rings and not to forget varying con¬ ditions of operation and wear and tear. The object of the invention is to improve and develop valves already known in this field, in order to avoid in particular the aforementioned drawbacks as well as other drawbacks and achieve high reliability, which will be ex¬ plained in more detail in the following description. These objects are attained according to the invention by de¬ signing a valve of the kind set forth above mainly in the way set forth in the characterizing clause of patent claim 1, Additional characterizing features and advantages of the present invention are set forth in the following descrip¬ tion, reference being made to the accompanying drawings, in which: Fig. 1 shows a conventional pneumatic valve, mainly in a diametrical longitudinal section, in one of two functional positions; Fig. 2 shows a corresponding view of the same valve, its plunger being placed in an ineffective or locking inter¬ mediate position; Fig. 3 is a view which corresponds to Fig. 1 and shows a valve according to the present invention; Fig. 4 is a view which corresponds to Fig. 1 and shows another embodiment of a valve according to the invention; Fig. 5 is a perspective view of a preferred embodiment of a plunger, designed to form a part of the valves according to Fig. 3 and 4; and Fig. 6 shows a partly schematic partial section of a memb¬ rane pump r provided with a valve according to the invention. The present invention relates primarily to a main valve, i.e. a 3-way/5-gate-valve, which is pneumaticly controlled and designed e.g. for compressed-air-operated membrane pumps. Said valve mainly comprises a valve body 1, body ends 2, a plunger 5 and five connection gates 8, 9, 10, 11 and 12, which are disposed in said valve body, as well as a control air gate 13 and 14 respectively in each one of said two ends 2 respectively. Said ends are attached to the valve body by means of screws 3. Fig. 1 shows a conventional valve with a presently used design, plunger 5 being disposed in a valve can 4 having requisite O-ring seals 6 and 7 respectively. Plunger 5 is actuated through gate 13 or 14 by a compressed-air-im¬ pulse, which subsequently to the work done is exhausted. Fig. 1 shows plunger 5 in its left position. Thus, it has been actuated by compressed air, which has been fed through gate 13. When the plunger reaches its end position, its movement is damped, e.g. by means of a stop element, name¬ ly a shock absorber rubber 15. In this position the main air quantity is fed into the valve through input gate 8, out through output gate 9 and then to the pump membrane in order to perform the pumping. Exhaust gate 10, which is connected to e.g. a second air chamber of a compressed-air-operated membrane pump, com¬ municates with the exterior air and the air is exhausted through a recess 21 in plunger 5 and a ventilating gate 11. When the compressed air has performed its work, the cont¬ rol air is exhausted through gate 13, in case it has not been exhausted earlier, and gate 14 is pressurized, plung¬ er 5 thereby moving in valve cap 4 to its righthand end position. Gate 10, which so far has been vented, is now pressurized by means of air entering through gate 8 and one of two recesses 21 r 22 in plunger 5, the connection between gate 8 and gate 9 being simultaneously disrupted and gate 9 being connected to a ventilating gate 12, air chamber no. 1 thereby being exhausted. In a compressed-air-operated membrane pump the pressuri- zation and the exhaustion through gates 13 and 14 respec¬ tively are done by means of a control valve, which is ac¬ tuated by the end positions of the membranes. Additional embodiments are possible, in which said control valve is actuated e.g. by the position of the pump shaft and the pump shaft is in that case the shaft which connects the two membranes. In a compressed-air-operated membrane pump its capacity and its lifting height are controlled by means of the amount of compressed air and its pressure, when it appears at gate 8. For practical reasons a branching from gate 8 is provided, which feeds compressed air to said control valve, i.e. the same pressure is used to operate the pump as to control main valve plunger 5. Normally this system works faultlessly, but not in those instances when the pump is to be operated using a most reduced air pressure, in order to on some occasions uti¬ lize a flow, which approaches 0, from a pump having a sub¬ stantial capacity, a sufficient air pressure being avail¬ able in order to operate the pump, but an insufficient air pressure to control main valve plunger 5, and consequent¬ ly the plunger may in some instances end up in an inter¬ mediate position, shown in Fig. 2. This situation occurs often, if the air flow to the pump is cut off and there is a relatively large air volume between the cut-off area and the main valve of the pump and the pump is operated until the air has been expended. This happens often in work shops operating in an intermittent way. Shortly be¬ fore the air pressure ceases completely, an impulse inten¬ ded to shift the position of the main valve plunger may issue and due to the air expense into the air chamber of the pump, while a smaller amount of air is expended to control the plunger, the amount of air available may turn out to be insufficient to push the plunger to the opposite end position and the plunger will stop in an intermediate position, which is shown in Fig. 2. It is true that at this very moment no shut-down has occurred, but when com¬ pressed air again is fed in order to start the pump, the compressed-air-flow via gate 8 has been completely shut off from the rest of the gates and the pump cannot be started. In order to avoid this drawback the following invention is used, the main valve having been modified: At the ends of plunger 5 counter stop members in the form of magnets 16 have been inserted and in thoεes instances when ends 2 have not been made of a magnetic material a stop element in the form of a soft iron core has been dis¬ posed in the place where previously shock absorber rubber 15 was disposed. Of course, said magnets may be disposed in said ends and if the plunger is not made of a magnetic material, then said counter stop members may be made of a soft iron core. This device is shown in Fig. 3. Members 15,16 lock plunger 15 in the respective end posi¬ tions and a force is needed, which can be adjusted, in or¬ der to move plunger 5, i.e. the pressure of the compressed air which is fed into gates 13 and 14 respectively must be sufficiently large to overcome the attractive force of the magnet. In case said pressure is insufficient, plunger 5 will remain in its end position and the pump will quit, but in case the pressure is sufficient, the pressure and the air volume are also sufficient to push the plunger into its opposite end position, where it is locked by means of the magnetization force. Regarding the already known embodiments there is a risk that when the pump is hauled plunger 5, due to vibrations and shocks, v.ill end up in an intermediate position, which hinders the start of the pump. This is avoided in an effi¬ cient way by means of the present invention. The embodiment described and shown in Fig. 3 does not in¬ volve any damping of plunger 5 against ends 2, since shock absorber rubbers 15 have been replaced by a permanent mag¬ net and a soft iron core. Of course, said two parts can be designed in such a way that no strength problems will arise, but on the other hand the valve will emit a har¬ der sound, which may prove to be troublesome, particularly if large valves are used. In one embodiment of the inven¬ tion permanent magnet 16 is inserted deeper into plunger 5 and in this way a circular cavity 17 is formed in the ends of the plunger. See Fig. 4. The diameter of this cavity is adapted in such a way, on comparison with previous embodi¬ ments, that soft iron core 15 is replaced with a somewhat thicker core, which fits into cavity 17. Between core 15 and plunger 5 there is formed a narrow air gap 18, through which the air trapped in cavity 17 is to pass. This gap is adapted to provide an air-.cushion-damping here and in this way the above-mentioned drawbacks with an elevated sound level disappears. According to Fig. 5 a permanent magnet or a soft iron core 16 is fitted into the two plunger ends, and the free end surface of this magnet or core preferably is positioned in the same plane as the respective plunger ends. Member 16 is surrounded by a projection 19, which protrudes from said end surfaces and comprises a cylindrical tube fast¬ ened to the plunger end and made of e.g. aluminum. In this way a cavity 20 is formed, which can cooperate with mem¬ ber 15 in the way described above in order to provide a so called air-cushion-damping. Of course, also the plunger end itself may be so closely fitted into a recess in said ends, that a damping is ob¬ tained. A preferred field of application for a valve according to the present invention is illustrated in fig. 6. The fol ¬ lowing references numerals are used: 101 a membrane, 102 a membrane shaft, 103 a nut, 104, 113 mounting plates, 114 a control valve, 105 a control valve shaft, 106 a con¬ trol valve operating shaft, 107 a pump body, 108 a con¬ trol valve outlet, 109 a control valve connection, 110 a control valve connection, 111, 112 a brancing duct. The air flow passages are shown by arrows and the mode of ope¬ ration of the pump, which is already known, probably is easy to understand. Summarizing the present invention, this emanates from the idea of making u se of a small yet sufficient holding or retaining power as a treshold for releasing the plunger, which thus will be unaffected by magnetic power as soon as it has been released from the actual magnet. An exam¬ ple will make this quite clear. When physical contact has been established between plunger and magnet, the latter develops a retaining force of e.g. 0,34 kp, which is app. 0,75 pounds. As soon as this power or treshold has been overcome and the plunger has left the magnet for as little as 0,5 mm, which is 20/1000 ", the retaining force will be reduced to app. 0,03 kp, which is app. 0,066 pounds. Therefore, one can say that once the plunger has left one of the magnets, the magnetic influence on same cannot be measured in practice any longer. A valve designed in this way will accordingly not prevent a pump from wor¬ king in very low regions of pressure and capacity , which often is desirable if not crucial. Often, a retaining force equal to 10 mbar will be suffi¬ cient for a valve according to the invention. When in such a case the plunger has been released from its retair ned end position, it can move about freely without the magnets exerting any influence on same. Beyond a very nar¬ row gap of up to 0,5 or 1,0 mm, the power of the magnets is so small, that the friction of the plunger in relation to a surrounding sleeve is bigger. Thus, the invention conceived the idea, that a comparatively low release- treshold is all what matters, and that everything consi¬ derably stronger than so will be detrimental to the desired mode of operation of a valve of this kind and even counter¬ act if not all but som objectives. Thanks to the shock ab¬ sorbing features bringing about an air-cushion-damping and slowing down the speed of the plunger, the valve 'according to the invention will be utmost silent in operation and gain a long life. Needless to say, that in manufacture and assem- blance extreme tolerances won't have to be observed. The field of application of the valve is of course not limited to compressed-air-operated membrane pumps, but the valve is always expedient to use in e.g. vibrating, shaking machines and various equipments, in which most reduced air pressures are to be used.

Claims: PATENT CLAIMS 1. A pneumatic valve designed to control particularly a compressed-air-operated membrane pump, comprising a valve body (1) having gates (8-12) for supply of compressed air, for operation and/or for pressurizing said pump or the like respectively, ends (2) which close the valve body and have control-air-gates (13, 14), which are connected to a con¬ trol valve, a pneumatic timer or the like (114), a plunger (5) moveable in said valve body between said ends and pro¬ vided with recesses (21, 22) and/or raised portions in or¬ der to guide compressed air between selected gates, the ends of said plunger (5) and the ends (2) of said valve body are adapted to cooperate magnetically, c h a r a c ¬ t e r i z e d in that • the ends of said plunger and the ends of said valve body are designed to come in physical contact with each other and develop a very low mutual re¬ taining force in such a way, that the magnetic retaining force effective in the actual end position is intended to provide a treshold for a certain minimum control pressure from the respective control-air-gate (13 or 14) and guaran¬ tee a fast initial movement as well as safe transfer of the plunger to the other end position, that the magnetic retaining force and thus the said control-pressure-treshold for releasing the plunger from the respective valve body end is in the range of 5-200, preferably 10-50 mbar, in order to permit but control-pressure related plunger movements without measurable affect of the magnetic power on the plunger movements beyond said retaining force and releasing treshold, and that in order to promote silent valve operation and counteract wear and tear of plunger and valve body ends, in the latter and/or in the ends of the plunger there are provided shock absorbing cavities (20) effective to slow down the speed of the plunger and designed to provide a so called air-cushion-damping and disappear completely or partially, when said valve body ends and said plunger engage with each other. 2. A valve according to patent claim 1, c h a r a c ¬ t e r i z e d in that permanent magnets (17 and 16, re¬ spectively) are inserted in the ends of said plunger (5) and/or in said valve body ends (2). 3. A valve according to patent claim 1 or 2, c h a ¬ r a c t e r i z e d in that said plunger (5) and/or said valve body ends (2) comprise permanent magnets and a mag- neticly treated material, respectively. 4. A valve according to any of patent claims 1-3, c h a r a c t e r i z e d in that a soft iron core (16) is inserted in said valve body ends (2) or in said plunger ends. 5. A valve according to any of claims 1-4, c h a r a c ¬ t e r i z e d in that said cavity is formed by a tube, a ring or the like, which surrounds a magnet and/or a soft iron core or the like.

Inventors: GYLLINDER LARS, GYLLINDER, LARS
Applicants: DOMINATOR AB, DOMINATOR MASKIN AB
Application year: 1989
Main classification: F04B9
IPC codes: F01L25, F04B43