Abstract:
A three-way valve for controlling the application of air to a pneumatically controllable device has a pressure chamber for pressurizing a work chamber to which the device is connectable and an exhaust chamber for expelling air from the work chamber. Unidirectional flow means prevents air in the work chamber from entering the space behind a valve member controlling the flow of air from the pressure chamber to the work chamber for avoiding valve lockup.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a solenoid-operated three-way valve for electrically controlling the application of pressurized air to a pneumatically operated tool, control valve, or other device. More specifically, this invention improves upon the pilot operated three-way valves described in U.S. Pat. No. 2,881,801, the disclosure of which is incorporated herein by reference. 
     Although the three-way valve of U.S. Pat. No. 2,881,801 performs its function admirably, its performance can be hampered under particular operating conditions. For example, if the input pressure should decrease rapidly while the valve is energized and open to apply pressurized air to a device, an instantaneous pressure differential can close and lock the valve in the closed state even after the valve is deenergized. 
     SUMMARY OF THE INVENTION 
     The aforementioned problems of the prior art are overcome by the instant invention which provides for a three-way valve which has a working chamber with an inlet port, an exhaust port and a work port, a pressure chamber with an inlet port adapted to be connected to a source of pressure, and an outlet port, and a main pressure valve seat circumscribing a main pressure valve opening at an interface between the work chamber inlet port and main pressure valve outlet port. A main pressure valve member is movable in response to differences in force exerted on a front side thereof by the pressures in the work chamber and pressure chamber, and on a rear side thereof by the pressure in a space behind the main pressure valve member for seating on, and unseating from, the main pressure valve seat. 
     The three-way valve also has an exhaust chamber with an inlet port, and an outlet port adapted to open into the ambient atmosphere, and a main exhaust valve seat circumscribing a main exhaust valve opening at an interface between the work chamber outlet port and main exhaust valve inlet port. A main exhaust valve member is movable in response to differences in force exerted on a front side thereof by the pressure in the work chamber and in the exhaust chamber, and on a rear side thereof by the pressure in a space behind the main exhaust valve member for seating on and unseating from the main exhaust valve seat. 
     One bleed passageway extends from the pressure chamber to the space behind the main pressure valve member. Another bleed passageway extends from the work chamber to the space behind the main exhaust valve member. 
     A pilot valve has a pilot pressure valve seat which circumscribes a pilot pressure valve opening at an interface between the space behind the main pressure valve member and the space behind the main exhaust valve member, and a pilot exhaust valve seat which circumscribes a pilot exhaust valve opening at an interface between the space behind the main exhaust valve member and the ambient atmosphere. 
     The pilot valve has an off state in which a pilot valve member seals the pilot pressure valve opening while exposing the exhaust pressure valve opening, and an on state in which a pilot valve member seals the exhaust pressure valve opening while exposing the pilot pressure valve opening. 
     A unidirectional flow device, e.g., a check valve, is mounted between the working chamber and the space behind the main exhaust valve member for preventing flow of fluid from the working chamber to the space behind the main exhaust valve member through the exhaust bleed passageway which would lock up the three-way valve, but permitting flow of fluid from the space behind the main exhaust valve member to the working chamber through the exhaust bleed passageway as is necessary for the three-way valve to function. 
     It is therefore an object of the invention to provide a three-way valve which is resistant to lock-up due upon loss of inlet pressure. 
     Another object of the invention is to provide a three-way valve with a unidirectional flow means between its work chamber and the space behind its exhaust valve member. 
     Still another object of the invention is to provide a three-way valve member with a check valve in its exhaust bleed port. 
     Other and further objects of the invention will be apparent from the following drawings and description of a preferred embodiment of the invention in which like reference numerals are used to indicate like parts in the various views. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic elevation view of a three way valve in accordance with the prior art in a first stage of operation. 
     FIG. 2 is a schematic elevation view of a three way valve in accordance with the prior art in a second stage of operation. 
     FIG. 3 is a schematic elevation view of a three way valve in accordance with the prior art in a third stage of operation. 
     FIG. 4 is a schematic elevation view of a three way valve in accordance with the prior art in a fourth stage of operation. 
     FIG. 5 is a schematic elevation view of a three way valve in accordance with the preferred embodiment of the invention in a first stage of operation. 
     FIG. 6 is a schematic elevation view of a three way valve in accordance with the preferred embodiment of the invention in a second stage of operation. 
     FIG. 7 is a schematic elevation view of a three way valve in accordance with the preferred embodiment of the invention in a third stage of operation. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1-4 of the drawings, there is shown a three-way valve  1  having a body  3  with a working chamber  5  having a circular region  5   a , a cylindrical region  5   c  with an end circumscribed by a main pressure valve seat  7 , a channel  5   b  extending from the circular region  5   a  to the cylindrical region  5   c,  and an outlet port  5   d  adapted to be connected to a pneumatically operated device leading from the cylindrical region  5   c.  The working chamber  5  is selectively pressurized to operate the device connected to the outlet port  5   d.    
     A pressure inlet port  13 , adapted to be connected to a source of air pressure (not shown), is in communication with a circular pressure chamber  9  which surrounds the cylindrical region  5   c  of working chamber  5 . Evacuation of the working chamber  5  is principally through an exhaust chamber  15  within the body  3 . The exhaust chamber  15  has a cylindrical region  15   a  which is surrounded by the circular region  5   a  of the working chamber  5 . The cylindrical region  15   a  has one end circumscribed by an exhaust valve seat  17  and an opposite end which is in communication with an exhaust port  15   b  which is open to the ambient atmosphere. 
     Application of pressurized air from the pressure chamber  9  to the working chamber  5  is controlled by a main pressure valve  25  having a pressure valve member  29  centrally mounted on a circular diaphragm  33 , the circumference which is captured between members  16  and  18  of the valve body  3 . 
     Expulsion of pressurized air from the working chamber  5  to the ambient atmosphere is controlled by an exhaust valve  39  having a main exhaust valve member  45  centrally mounted on a circular diaphragm  53 , the circumference of which is captured between members  16  and  27  of the valve body  3 . 
     Opening and closing of the pressure valve  25  and exhaust valve  39  is controlled by shuttling an armature  57  of a solenoid  69 , which armature  57  serves as a pilot valve member, between a pilot pressure valve seat  61  and a pilot exhaust valve seat  65 . A narrow bleed passageway  73  in body part  16  restricts the flow of pressurized air from the pressure chamber  9  into a passageway  77 . The passageway  77  leads to a passageway  81  which communicates with a pilot pressure valve opening  85  surrounded by the pilot pressure valve seat  61 , and with interconnected passageways  79   a  and  79   b  which lead to a space behind the main pressure valve member  29 . 
     A narrow bleed passageway  105  in body part  16  restricts the flow of pressurized air from the working chamber  5  into a series of passageways  106 ,  108 ,  110 , and  112  which communicate with a contiguous space  114  surrounding the pilot pressure valve opening  85 , pilot valve member  57  and pilot exhaust valve opening  93 . Conduit branches  116  and  118  extend between the passageway  108  and the space behind exhaust valve member  45 . 
     The pilot pressure valve opening  85  is sealed when the pilot valve member  57  is in its deenergized (lowermost) bottom position as shown in FIG.  1 . At the same time, a pilot exhaust valve opening  93 , surrounded by the pilot exhaust valve seat  65 , is uncovered. 
     In the position, shown in FIG. 1, the main pressure valve member  29  is seated on the main pressure valve seat  7  to prevent communication between the pressure chamber  9  and working chamber  5 . In the position shown in FIG. 2, the main pressure valve member  29  is displaced from the main pressure valve seat  7  thereby allowing the pressure chamber  9  and working chamber  5  to communicate so that pressurized air in the pressure chamber  9  can enter the working chamber  5 . 
     The exhaust main valve  39  controls communication between the working chamber  5  and the exhaust chamber  15 . As shown in FIG. 1, the exhaust main valve member  45  is in an open position, displaced from the main exhaust valve seat  17  thereby permitting pressurized air in the working chamber  5  to escape to the exhaust chamber  15  and into the ambient atmosphere. In its closed position, shown in FIG. 2, the exhaust main valve member  45  is seated on the main exhaust valve seat  17  for blocking air flow between the working chamber  5  and exhaust chamber  15  thereby preventing escape of air from the working chamber  5  to the exhaust chamber  15 . 
     FIG. 1 illustrates an initial state of the three-way valve  1  of the invention wherein the solenoid  69  is not energized and the pilot valve member  57  is seated on the pilot pressure valve seat  61  thereby exposing the pilot exhaust opening  93  to the ambient atmosphere. Pressurized air at the inlet port  13  has filled the pressure chamber  9  and, through the pressure bleed opening  73 , the space behind the pressure valve member  29 . Because the pilot pressure opening  85  is sealed by the pilot valve member  57 , air cannot escape from the pressure chamber  9  or the space behind the pressure valve member  29 . 
     With the exhaust valve  39  now open, the pressure in working chamber  5  is at ambient, hence the pressure in the space behind the main pressure valve member  29  is greater than the net opposing pressure on the main pressure valve member  29  and the main pressure valve  25  is closed. As long as the solenoid  69  is deenergized and a steady pressure, greater than ambient is maintained at the inlet port  13 , the main pressure valve  25  is intended to remain closed for preventing air in the pressure chamber  9  from entering the working chamber  5 . 
     At the same time, the space behind the exhaust valve member  45  is at ambient pressure due to communication with the ambient atmosphere through passageways  118 ,  116 ,  108 , and the space  114 . Therefore, any pressurized air entering in the working chamber  5  is vented to the ambient environment through the exhaust chamber  15 . Hence, while the solenoid  69  is deenergized and a steady pressure, greater than ambient, is maintained at the pressure inlet port  13 , the exhaust pressure valve  39  is intended to remain open for exhausting air in the working chamber  5  to the exhaust chamber  15  and into the ambient atmosphere. 
     When the solenoid  69  is energized, its electromagnet  113  raises the pilot valve member  57  to the position shown in FIG. 2, with the pilot exhaust valve seat  65  engaged by the pilot valve member  57  and the pilot exhaust valve opening  93  sealed. In this position, the pilot valve member  57  is raised off of the pilot pressure valve seat  61 . Air trapped behind the main pressure valve member  29  is then able to escape through conduits  79   b,    79   a,    81 ,  112 ,  110 ,  116 , and  118  to the space behind the exhaust valve member  45  thereby forcing the exhaust valve member  45  onto the exhaust valve seat  17  for closing the exhaust valve  39 , and, at a slower rate, through the exhaust bleed opening  105  into the working chamber  5 . Air in the pressure chamber  9  also escapes to the space behind the exhaust valve member  45 , but at a much slower rate than the air behind the pressure valve member  29  do to the restrictive size of the pressure bleed opening  73 . The resulting reduction in pressure behind the pressure valve member  57  below the pressure in the working chamber  5  forces the pressure valve member  29  away from the pressure valve seat  7  thereby opening the main pressure valve and allowing the pressurized air in the pressure inlet port  13  to enter working chamber  5 . Hence, while the solenoid  69  is energized and a steady pressure, greater than ambient is maintained at the pressure inlet port  13 , the main pressure valve  25  is intended to remain open to admission of pressurized air from the pressure chamber  9  to the working chamber  5  until equilibrium between the pressures in the pressure chamber  9  and working chamber  5  occurs. 
     With the pilot pressure valve opening  85  now exposed and the pilot exhaust valve opening  93  sealed, the space behind the main exhaust valve member  45  is at the inlet pressure urging the main exhaust valve member  45  toward the exhaust main valve seat  17 . Although pressure urging the main exhaust valve member  45  away from the main valve seat  7  is applied from within the circular region  5   a  of the working chamber  5 , the exhaust chamber  15  which the central portion of the main exhaust valve member  45  faces, is at ambient pressure resulting in a net force which closes the main exhaust valve  39 . Hence, while the solenoid  69  is energized and a steady pressure, greater than ambient is maintained at the pressure inlet port  13 , the main exhaust valve  39  is intended to remain closed to prevent air in the working chamber  5  from escaping into the ambient atmosphere. In order to prevent a pressure drop across the pilot valve opening  85  from restricting flow from the pressure valve bleed opening  73  to the exhaust valve bleed passageway  105 , the pilot pressure opening  63  and pilot exhaust opening  93  are of the same size. In order to cause the exhaust main valve  39  to open when the solenoid  69  is deenergized and the pilot valve opening  85  is sealed as shown in FIG. 1, the pilot exhaust bleed opening  105  is smaller than the pilot exhaust opening  93 . 
     To close the main exhaust valve  39 , that is to cause the main exhaust valve member  45  to move to the right in the views shown in the drawings, the exhaust bleed opening  105  must provide sufficient restriction so that back pressure is developed in the space behind the main exhaust valve member  45  when the solenoid  69  is energized and the pilot valve member  57  is raised to the position shown in FIG.  2 . 
     When the solenoid  69  is initially energized, the main pressure valve  25  opens as described above. Once the demand for pressurized air made by the device connected to the working port  5   d  ceases, and the pressures in the pressure chamber  9  and working chamber  5  reach equilibrium, the pressure diaphragm  33  returns to its rest position against the main pressure valve seat  7  as shown in FIG.  3 . 
     If the pressure at the inlet port  13  should thereafter decrease rapidly, an instantaneous pressure drop in the pressure chamber  9  will create a pressure differential across the pressure valve member  29  due to the back flow of air from the working chamber  5  to the space behind the pressure valve member  29 . That is, while the solenoid  69  is energized, back flow of air from the working chamber  5  to the space behind the pressure valve member  29 , i.e., through exhaust valve bleed opening  105 , and passageways  106 ,  108 ,  110 ,  81 ,  79   a,  and  79   b  can hamper valve performance. 
     This pressure differential can force the main pressure valve member  29  against the main valve seat  7 , resulting in a valve lock-up condition which is maintained while the solenoid  69  is energized because pressure enters the chamber behind the pressure diaphragm  33  more readily than it can flow through the pressure bleed opening  73 , and the pressure in the working chamber  5  can only be relieved at a very slow rate through the exhaust bleed opening  105 . 
     As shown in FIG. 4, when the solenoid  69  is deenergized, evacuation of air from the working chamber  5  through the exhaust valve bleed opening  105 , and passageways  108 ,  110 , and the space surrounding pilot member  57  can maintain a pressure differential across the main exhaust valve member  45  which prevents the main exhaust valve  39  from opening, again resulting in valve lock-up. 
     Referring now to FIGS. 5,  6  and  7 , in order to avoid premature closure of the main pressure valve  25  and inability to operate the exhaust valve  39  inherent in prior art three-way valves of the type heretofore described, a check valve  120  is disposed in the exhaust bleed opening  105  to prevent air flow from the working chamber to the space behind the exhaust main valve member  45  and to the ambient atmosphere. Hence transfer of pressure from working chamber  5  to the region behind the main pressure valve member  29  can only occur through the main pressure valve bleed opening  73 . That is, air in the working chamber  5  can not bypass the pressure valve bleed opening  73  and reach the region behind the main valve member directly through the conduit  81 . 
     In FIG. 5, the solenoid is deenergized so that inlet air is essentially confined to the space behind the main pressure valve member  29  and the pressure chamber  9 . The check valve  120  in the exhaust bleed port  105  has an inlet  122  in communication with the working chamber  5  and an outlet  124  in communication with the space behind the exhaust valve member  45  and the space  114  surrounding the pilot exhaust opening  93 . FIG. 5 corresponds to FIG. 1 except for the inclusion of the check valve  120  in the former. 
     When the solenoid  69  is energized, air trapped behind the main pressure valve member  29  enters the space behind the main exhaust valve member  45  and the main valve  25  is forced open, thereby allowing pressurized air in the pressure chamber  9  to fill the working chamber  5 . Once equilibrium between the pressures in the working chamber  5  and pressure chamber  9  is reached, the main pressure valve member  29  returns to its rest position on the main pressure valve seat  7  as shown in FIG.  6 . If there is now a sudden drop in pressure at the inlet port  13  so that pressure in the working chamber  5  exceeds pressure in the pressure chamber  9 , the check valve  120  will inhibit the flow of air in the working chamber  5  from entering the space behind main pressure valve member  29  faster than it can enter pressure chamber  9 , and valve lock-up is thereby prevented. 
     When the solenoid  69  is again deenergized, as shown in FIG. 7, air in the space behind exhaust valve member  45  enters the ambient atmosphere through passages  118 ,  116 ,  108 , the space  114  surrounding pilot member  57 , and pilot exhaust opening  93 . The check valve  120  prevents air in the working chamber  5  from entering the space behind exhaust valve member  45  and preventing the exhaust valve member  45  from opening. 
     It is to be appreciated that the foregoing is a description of a preferred embodiment of the invention to which variations and modifications may be made without departing from the spirit and scope of the invention.