Abstract:
A multistage switching valve includes a valve stem which is adapted to open or close a fluid passage, a biasing biasing means for biasing the valve stem in a direction to close the fluid passage, a plurality of pistons which are relatively slidably fitted onto the valve stem at different axial positions to provide different flow rates, a plurality of stops which are provided on the valve stem to move the valve stem in a valve opening direction opposite to the direction of the movement of the valve stem caused by the biasing biasing means, together with the pistons when the pistons are moved in the valve opening direction, a valve opening means for exerting a pilot pressure in the valve opening direction on each piston, and a flow rate controller for individually restricting the axial displacements of the pistons in the valve opening direction. A two-stage switching valve and a toggle type two-stage switching valve are also disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a two-stage switching valve in which a large flow rate and a small flow rate can be obtained using a same passageway, and a multistage switching valve in which more than two different flow rates can be switched. 
     2. Description of the Related Art 
     In general, in a conventional fluid system in which a small flow rate (e.g., a few cc/min) and a large flow rate (e.g., a few L/min) is switched, a small flow rate valve and a large flow rate valve are provided in parallel, so that the two valves are selectively opened or closed. However, in the conventional arrangement, since the two valves, i.e., the large flow rate valve and the small flow rate valve, the parallel fluid passageways, and a branch connector (tee) provided at a connection portion to connect the parallel passageways are indispensable, the manufacturing cost of the parts is increased and the pipe laying requires a large space and increases the manufacturing cost. In theory, it is possible to switch the large flow rate and the small flow rate by varying the opening angle of a single valve, but it is next to impossible to precisely and instantaneously switch the flow rate, for example, between a few cc/min and a few L/min. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a switching valve in which a small flow rate and a large flow rate can be switched by a single valve or more than two different flow rates can be selectively obtained by a single valve. 
     To achieve the object mentioned above, according to an aspect of the present invention, there is provided a multistage switching valve comprising a valve stem which is adapted to open or close a fluid passage; a biasing means (spring) for biasing the valve stem in a direction to close the fluid passage; a plurality of pistons which are relatively slidably fitted onto the valve stem at different axial positions to provide different flow rates; a plurality of stops which are provided on the valve stem to move the valve stem in a valve opening direction opposite to the direction of the movement of the valve stem caused by the biasing means, together with the pistons when the pistons are moved in the valve opening direction; a valve opening means (pressure actuator) for exerting a pilot pressure in the valve opening direction on each piston; and a flow rate control means (a plurality of stoppers) for individually restricting the axial displacements of the pistons in the valve opening direction. 
     According to another aspect of the present invention, there is provided a two-stage switching valve comprising a valve stem which is adapted to open or close a fluid passage; a biasing means (spring) for biasing the valve stem in a direction to close the fluid passage; a small flow rate piston and a large flow rate piston, which are relatively slidably fitted onto the valve stem at different axial positions and are arranged in a same cylinder in a predetermined order, to provide different flow rates; a small flow rate stop and a large flow rate stop, which are provided on the valve stem to move the valve stem in a valve opening direction opposite to the direction of the movement of the valve stem caused by the biasing means, together with the small flow rate piston and the large flow rate piston when the small flow rate piston and the large flow rate piston are moved in the valve opening direction; a large flow rate pilot pressure chamber formed in the cylinder to exert a pressure in the valve opening direction on the large flow rate piston; a small flow rate pilot pressure chamber formed in the cylinder to exert a pressure in the valve opening direction on the small flow rate piston; a small flow rate valve opening means (small flow rate pressure actuator) for exerting a small flow rate pilot pressure on the small flow rate pilot pressure chamber; a large flow rate valve opening means (large flow rate pressure actuator) for exerting a large flow rate pilot pressure on the large flow rate pilot pressure chamber; a small flow rate piston restricting means (small flow rate piston stopper) for restricting the axial displacements of the small flow rate piston in the valve opening direction; and a large flow rate piston restricting means (large flow rate piston stopper) for restricting the axial displacements of the large flow rate piston in the valve opening direction. 
     The present invention also proposes a toggle type two-stage switching valve. In the toggle type, an increased valve opening force can be obtained for the same cylinder diameter, or a smaller diameter cylinder can be used for the same valve opening force. 
     According to yet another aspect of the present invention, a toggle type two-stage switching valve comprises a valve stem which is adapted to open or close a fluid passage; a biasing means (spring) for biasing the valve stem in a direction to close the fluid passage; a plurality of piston chambers which are defined in a cylinder and are spaced from one another in the axial direction of the valve stem; large flow rate pistons and small flow rate pistons, which are relatively slidably fitted onto the valve stem at different axial positions and are arranged in each piston chamber within the cylinder in the same order; small flow rate stops and large flow rate stops, which are provided on the valve stem, corresponding to the piston chambers within the cylinder, to move the valve stem in a valve opening direction opposite to the direction of the movement of the valve stem caused by the biasing means, together with the small flow rate pistons and the large flow rate pistons when the small flow rate pistons and the large flow rate pistons are moved in the valve opening direction; a small flow rate pilot pressure chamber formed in each piston chamber within the cylinder to exert a pressure in the valve opening direction on the corresponding small flow rate piston; a large flow rate pilot pressure chamber formed in each piston chamber within the cylinder to exert a pressure in the valve opening direction on the corresponding large flow rate piston; a small flow rate valve opening means (small flow rate pressure actuator) for simultaneously exerting a small flow rate pilot pressure on each small flow rate pilot pressure chamber; a large flow rate valve opening means (large flow rate pressure actuator) for simultaneously exerting a large flow rate pilot pressure on each large flow rate pilot pressure chamber; a small flow rate piston restricting means (small flow rate piston stopper) for restricting the axial displacements of at least one small flow rate piston in the valve opening direction; and a large flow rate piston restricting means (large flow rate piston stopper) for restricting the axial displacements of at least one large flow rate piston in the valve opening direction. 
     The small flow rate piston restricting means can be constituted, for example, by a stroke adjustment cap which is screw-engaged in the cylinder to restrict the axial displacement of the small flow rate piston in the valve opening direction. The large flow rate piston restricting means can be constituted by the large flow rate piston which is closest to the small flow rate piston. If two piston chambers are formed in the cylinder, a tandem type two-stage switching valve is obtained. 
     The present disclosure relates to subject matter contained in Japanese Patent Applications Nos. 11-131737 (filed on May 12, 1999) and 2000-5619 (filed on Jan. 14, 2000) which are expressly incorporated herein by reference in their entireties. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be discussed below in detail with reference to the accompanying drawings, in which; 
     FIG. 1 is a sectional view of a two-stage switching valve taken along the line I—I in FIG. 3, according to an embodiment of the present invention; 
     FIG. 2 is a sectional view taken along the line II—II in FIG. 3; 
     FIG. 3 is a sectional view taken along the line III—III in FIG. 3; 
     FIG. 4 is a sectional view of a two-stage switching valve in a tandem arrangement, taken along the line IV—IV in FIG. 5, according to an embodiment of the present invention; and 
     FIG. 5 is a sectional view taken along the line V—V in FIG.  4 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 through 3 show an embodiment of a multistage switching valve of the present invention, applied to a two-stage switching valve. In FIGS. 1 and 2, a passage block  11  is provided with a passageway  12  which is in turn provided with an annular valve seat  13  having a vertical axis in FIG.  1 . The passage block  11  is provided with a rod holder  14  secured thereto by a connector sleeve  15  to slidably guide a valve stem  20  coaxial to the valve seat  13 . A circular metal diaphragm  16  is provided between the rod holder  14  and the passage block  11 , with the peripheral edge being held between the lower end of the rod holder  14  and the passage block  11 , to open or close the annular valve seat  13 . A compression spring  17  is provided between the rod holder  14  and a flange  20   a  of the valve stem  20  to bias the valve stem  20  in the downward direction in FIG. 1 to thereby press the metal diaphragm  16  onto the annular valve seat  13  through the valve stem  20 . Consequently, the valve stem  20  is continuously biased in the direction to close the annular valve seat  13  through the metal diaphragm  16  by the spring. 
     The rod holder  14  is provided on its upper end in FIG. 1 with a cylinder  22  secured thereto through a slip-off prevention ring  21 . The cylinder  22  is closed at its lower end by the rod holder  14  and is open at the upper end. The valve stem  20  extends from the rod holder  14  into the cylinder  22 . 
     A large flow rate piston  23 L and a small flow rate piston  23 S are relatively slidably fitted on the valve stem  20 . The valve stem  20  is provided with stop rings  24  and  25  fitted thereon to restrict the upward movement of the large flow rate piston  23 L and the small flow rate piston  23 S, respectively. The stop rings  24  and  25  are adapted to move the valve stem  20  together with the large flow rate piston  23 L and the small flow rate piston  23 S in the valve opening direction when the large flow rate piston  23 L and the small flow rate piston  23 S are moved in the valve opening direction opposite the direction of the movement of the valve stem  20  caused by the spring force of the compression spring  17 . The stop rings  24  and  25  cannot restrict the downward movement of the corresponding large and small flow rate pistons  23 L and  23 S relative to the valve stem  20 . 
     A stroke adjustment cap  26 , coaxial to the valve stem  20  is screw-engaged in the open end (upper end) of the cylinder  22  in the drawing. The stroke adjustment cap  26  is adapted to restrict (control) the upward displacement of the small flow rate piston  23 S, so that the distance “d” between the small flow rate piston  23 S and the stroke adjustment cap  26  can be adjusted or determined in accordance with the screw engagement position of the cap  26  relative to the cylinder  22 . The distance “d” is exaggerated in the drawings. A air discharge hole  26   a  and, on the air discharge hole  26   a , a driver groove  26   b  for a screw driver to rotate the cap  26  are formed in the stroke adjustment cap  26 . The stroke adjustment cap  26  and the cylinder  22  are secured by a screw  27  after adjustment. 
     The upward displacement of the large flow rate piston  23 L is restricted by the abutment thereof (i.e., the stop ring  24 ) with the small flow rate piston  23 S. The distance “D” between the large flow rate piston  23 L and the small flow rate piston  23 S is considerably larger than the distance “d” (D&gt;d). 
     A small flow rate pilot pressure chamber  28  is defined in and by the cylinder  22 , the large flow rate piston  23 L the small flow rate piston  23 S, and the valve stem  20 . A large flow rate pilot pressure chamber  29  is defined between the large flow rate piston  23 L and the valve stem  20 . The small flow rate pilot pressure chamber  28  is connected to a small flow rate pilot pressure passage  30  and a small flow rate pilot pressure connection port  31 , formed in the housing  22 . The small flow rate pilot pressure connection port  31  is connected to a pilot pressure source  33  through a control valve  32 . Likewise, the large flow rate pilot pressure chamber  29  is connected to a large flow rate pilot pressure passage  34  and a large flow rate pilot pressure connection port  35 . The large flow rate pilot pressure connection port  35  is connected to the pilot pressure source  33  through the control valve  32 . Note that  0  in FIGS. 1 and 2 show O-rings to seal the valve. 
     The apparatus constructed as above operates as follows. 
     When no pilot pressure is introduced in the small flow rate pilot pressure connection port  31  and the large flow rate pilot pressure connection port  35 , the valve stem  20  which is biased in the valve closing direction by the compression spring  17  presses the metal diaphragm  16  onto the annular valve seat  13  to close the passageway  12 . To establish the small flow rate, the pilot pressure is introduced in the small flow rate pilot pressure connection port  31  through the control valve  32 . Consequently, the pilot pressure acts on the small flow rate pilot pressure chamber  28  through the small flow rate pilot pressure passage  30 , so that the small flow rate piston  23 S and the large flow rate piston  23 L receive the upward pressure and the downward pressure, respectively. As a result, the small flow rate piston  23 S moves the valve stem  20  in the upward direction through the stop ring  25 . The upward movement of the valve stem  20  is restricted when the small flow rate piston  23 S abuts against the stroke adjustment cap  26 . The distance d between the small flow rate piston  23 S and the stroke adjustment cap  26 , which is exaggerated in the drawings is (or can be) very small, and hence the gap formed between the metal diaphragm  16  and the annular valve seat  13  is (or can be) small enough to obtain small flow rate of a few cc/min. The large flow rate piston  23 L is moved downward relative to the valve stem  20  and abuts against the rod holder  14 , but the relative movement has no influence on the establishment of the small flow rate. 
     To obtain the large flow rate, the pilot pressure is discharged from the small flow rate pilot pressure connection port  31  through the control valve  32 , and instead, the pilot pressure is supplied to the large flow rate pilot pressure connection port  35 . Consequently, the pilot pressure is introduced in the large flow rate pilot pressure chamber  29  through the large flow rate pilot pressure passage  34 , so that the upward pressure acts on the large flow rate piston  23 L. As a result, the large flow rate piston  23 L moves upward while moving the valve stem  20  together through the stop ring  24 . The upward movement of the valve stem  20  is restricted when the large flow rate piston  23 L abuts against the small flow rate piston  23 S or when the flange  20 a of the valve stem  20  abuts against a lower stepped portion (lower shoulder) of the rod holder. Even after the small flow rate piston  23 S abuts against the stroke adjustment cap  26 , the large flow rate piston  23 L and the valve stem  20  can be moved further in the upward direction. Since the distance D between the large flow rate piston  23 L and the small flow rate piston  23 S is (or can be made) substantially larger than the distance d, the gap formed between the metal diaphragm  16  and the annular valve seat  13  is (or can be) large enough to obtain the large flow rate of a few L/min. 
     At the large flow rate mode, it is possible, as a matter of course, to introduce the pilot pressure higher than the pilot pressure to be supplied to the small flow rate pilot pressure connection port  31  into the large flow rate pilot pressure connection port  35 , in place of stoppage of the pilot pressure supply to the small flow rate pilot pressure connection port  31 . 
     In the illustrated embodiment, the small flow rate pilot pressure chamber  28  is formed between the large flow rate piston  23 L and the small flow rate piston  23 S, so that the small flow rate pilot pressure chamber  28  can be simply formed. Alternatively, it is possible to provide a stationary wall integral with the cylinder  22 , which defines the small flow rate pilot pressure chamber  28  between the stationary wall and the small flow rate piston  23 S. Also, although the illustrated embodiment is applied to a two-stage switching valve, it is possible to realize a multistage switching valve as recited in claim  1  of the present application. 
     FIGS. 4 and 5 show another embodiment of a toggle type two-stage switching valve in a tandem arrangement. In this embodiment, the cylinder  22  is divided into an upper piston chamber U and a lower piston chamber L by a separation wall  22 D. In the piston chambers U and L are relatively slidably arranged the large flow rate piston  23 LU, the small flow rate piston  23 SU, the large flow rate piston  23 LL, and the small flow rate piston  23 SL, in this order from the lower portion. The valve stem  20  which extends through the separation wall  22 D and the pistons in a fluid-tight fashion is provided with stop rings  24 U,  25 U,  24 L and  25 L fitted thereon, corresponding to the pistons  23 LU,  23 SU,  23 LL and  23 SL, to restrict the upward movement of the corresponding pistons. The stop rings  24 U and  24 L move the valve stem  20  together with the large flow rate pistons  23 LU and  23 LL in the valve opening direction (upward direction) when the large flow rate pistons  23 LU and  23 LL are moved in the valve opening direction opposite to the direction of the movement of the valve stem  20  caused by the compression spring  17 . Likewise, the stop rings  25 U and  25 L move the valve stem  20  together with the small flow rate pistons  23 SU and  23 SL in the valve opening direction (upward direction) when the small flow rate pistons  23 SU and  23 SL are moved in the valve opening direction opposite to the direction of the movement of the valve stem  20  caused by the compression spring  17 . The stop rings  24 U,  24 L and  25 U,  25 L cannot restrict the downward movement of the large flow rate pistons  23 LU and  23 LL and the small flow rate pistons  23 SU and  23 SL, relative to the valve stem  20 . 
     The stroke adjustment cap  26  screwed in the upper open end of the cylinder  22  and the securing screw  27  thereof are same as those shown in FIGS. 1 and 2. The upward movement of the small flow rate pistons  23 SU and  23 SL is restricted (or determined) by the distance d 1  between the stroke adjustment cap  26  and the piston  23 SU. 
     The upward movement of the large flow rate pistons  23 LU and  23 LL is restricted by the abutment thereof (i.e., the stop rings  24 U,  24 L thereof) against the small flow rate pistons  23 SU and  23 SL. The distances D 1  and D 2  between the large flow rate pistons  23 LU,  23 LL and the small flow rate pistons  23 SU,  23 SL are considerably larger than the distances d 1  and d 2 , respectively (D 1 , D 2 &gt;d 1 , d 2 ). 
     In the piston chamber U, the small flow rate pilot pressure chamber  28 U is defined by the large flow rate piston  23 LU, the small flow rate piston  23 SU and the valve stem  20 , and the large flow rate pilot pressure chamber  29 U is defined by the large flow rate piston  23 LU, the valve stem  20  and the separation wall  22 D. Likewise, in the piston chamber L, the small flow rate pilot pressure chamber  28 L is defined by the large flow rate piston  23 LL, the small flow rate piston  23 SL and the valve stem  20 , and the large flow rate pilot pressure chamber  29 L is defined by the large flow rate piston  23 LL and the valve stem  20 . The small flow rate pilot pressure chambers  28 U and  28 L are connected to the connection port  31  through the small flow rate pilot pressure passages  30   a ,  30   b ,  30   c  formed in the housing  22 . The small flow rate pilot pressure connection port  31  is connected to the pilot pressure source  33  through the control valve  32 . Similarly, the large flow rate pilot pressure chambers  29 U and  29 L are connected to the connection port  35  through the large flow rate pilot pressure passages  34   a ,  34   b . The large flow rate pilot pressure connection port  35  is connected to the pilot pressure source  33  through the control valve  32 . 
     In this embodiment, to establish the small flow rate mode, the pilot pressure is supplied to the small flow rate pilot pressure connection port  31  through the control valve  23 , so that the pilot pressure is introduced simultaneously in the small flow rate pilot pressure chambers  28 U and  28 L through the small flow rate pilot pressure passages  30   a ,  30   b  and  30   c . Consequently, the small flow rate pistons  23 SU and  23 SL receive the upward pressure and the large flow rate pistons  23 LU and  23 LL receive the downward pressure, respectively. As a result, the small flow rate pistons  23 SU and  23 SL are moved upward to move the valve stem  20  upward through the stop rings  25 U and  25 L. Thus, the small flow rate of, for example, a few cc/min, determined depending on the distance d 1  between the small flow rate piston  23 SL and the stroke adjustment cap  26  can be obtained. 
     When the pilot pressure is discharged from the small flow rate pilot pressure connection port  31  and instead, the pilot pressure is supplied to the large flow rate pilot pressure connection port  35  through the control valve  32  to establish the large flow rate mode, the pilot pressure is introduced simultaneously in the large flow rate pilot pressure chambers  29 U and  29 L through the large flow rate pilot pressure passages  34   a  and  34   b , so that the large flow rate pistons  23 LU and  23 LL receive the upward pressure. As a result, the large flow rate pistons  23 LU and  23 LL are moved upward to move the valve stem  20  upward through the stop rings  24 U and  24 L. Thus, the large flow rate of, for example, a few L/min, determined depending on the abutment position of the large flow rate piston  23 LU against the small flow rate piston  23 SU or the abutment position of the large flow rate piston  23 LL against the small flow rate piston  23 SL can be obtained. 
     In this embodiment, since the two pistons receive the pilot pressure either at the small flow rate mode or at the large flow rate mode, a larger opening angle of the valve can be obtained for the same pilot pressure, or a smaller diameter cylinder (piston) can be used for the same valve opening pressure. Consequently, the present invention can be advantageously applied to a normally closed valve in which the compression spring  17  has a strong spring force. 
     FIGS. 4 and 5 show the tandem arrangement. However, it is theoretically possible to realize a smaller switching valve having a larger output, by increasing the number of the piston chambers formed in the cylinder so that the small and large flow rate pistons are provided in each piston chamber. 
     Although the valve stem  20  presses the metal diaphragm  16  which opens or closes the annular valve seat  13 , in the illustrated embodiments, the present invention can be equally applied to a valve structure in which a metal bellows valve is sued or the valve stem  20  is provided on its lower end with a valve body integral therewith, or a valve structure in which the movement of the valve stem  20  is transmitted to a separate valve body. 
     Although the pistons  23 L,  23 LU,  23 LL,  23 S,  23 SU, and  23 SL are slidably fitted in the cylinder  22 , in the illustrated embodiments, the present invention can be applied to a piston using a rolling diaphragm whose peripheral edge and center portion are secured to the cylinder and the piston body, respectively. 
     Moreover, the small flow rate piston restricting means for restricting the movement of the small flow rate pistons  23 S and  23 SU in the valve opening direction can be comprised of a stop other than the stroke adjustment cap  26 . Likewise, it is possible to restrict the movement of the large flow rate pistons  23 L and  23 LL in the valve opening direction, by stops other than those located closest to the small flow rate pistons  23 S and  23 SU. 
     As can be seen from the above discussion, according to the present invention, a switching valve in which two flow rates including a small flow rate and a large flow rate or more than two flow rates can be obtained by a single valve is provided. Moreover, according to a two-stage switching valve in a tandem arrangement, a greater output can be obtained for the same cylinder diameter or a smaller diameter cylinder can be used to obtain the same output.