Abstract:
A multi-mode pressure relief valve includes a body having fluid inlet and outlet ports and a compressed gas inlet port. The fluid ports and gas port isolated from one another. A reciprocating piston is in communication with the gas port. A valve stem is movable between an open condition and a closed position to permit and stop flow communication between the fluid ports. A spring is disposed between the valve stem and the piston and urges the piston and valve stem away from one another. The valve is operable in at least three modes, an operating mode in which the valve is open, the stem is spaced from the piston, and the piston applies pressure on the stem, and in which the pressure is balanced by fluid pressure the inlet, a zero-state mode in which the valve is open, the stem is spaced from the piston, the spring is in a relaxed state, and the piston applies no pressure on the valve stem, and a relief mode in which the valve is open, the stem contacts or is in close proximity to the piston and the spring is in a compressed state due to the fluid pressure.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a multi-mode valve. More particularly, the present invention relates to a multi-mode pressure relief valve for use in pressurized hot-melt adhesive systems. 
     Pressurized hot-melt adhesive systems are in use in a multitude of production facilities, in countless industries. For example, these system are used to seal cartons and containers for commercial products ranging from soda-pop to breakfast cereals to tools and consumables. 
     In pressurized hot-melt systems a pressure relief valve is provided to protect against failure of the equipment in the event of an abnormally high pressure situation. Typically this protection is provided by a mechanical pressure relief valve that vents high pressure to the tank or reservoir that supplies the adhesive. 
     It is also desirable to have the ability to quickly reduce the pressure within the system to a zero-pressure condition (known as zero-state). This is desirable for maintenance of the system, for emergency-stop situations, or the like. A mechanical pressure relief is not suitable for this purpose. As such, a separate pneumatic actuated valve is often provided for this function. Pneumatic operation allows the valve to be quickly deenergized to reduce system pressure. This, however, requires the use of a pneumatic circuit, actuator and other components. 
     Further, in some installations it is desirable to have the ability to adjust the adhesive pressure curve to match production speed requirements. This function maybe provided by a separate mechanical adhesive bypass valve, and/or by adjusting the pump speed dynamically with the parent machine line speed. 
     While this method functions well, often the adhesive pressure cannot be reduced quickly enough during a parent machine line stop. The result is excessive glue application on the final products. 
     As will be understood, each of these functions requires the use of a separate valve. These individual components each require maintenance, testing and the like in order to assure that they function properly. In addition, there is an initial capital cost associated with each. And, if a single component requires repair (or maintenance), it can adversely affect operation, not only of the adhesive system but of the parent line operation. 
     Accordingly, there is a need to reduce the number of components (valves) needed to carry out the pressure relief, zero-state and line speed following functions in a holt-melt adhesive application system. Desirably, such a valve has minimal moving parts. More desirably, such a valve is controlled by the pneumatic circuit of the adhesive system in which it is installed. 
     BRIEF SUMMARY OF THE INVENTION 
     A multi-mode pressure relief valve carries out the pressure relief, zero-state and line speed following functions in a holt-melt adhesive application system. The valve has minimal moving parts and is preferably controlled by the pneumatic circuit of the adhesive system in which it is installed. 
     The valve has a body having a fluid inlet port and a fluid outlet port that define a fluid chamber. The body includes a seat at the fluid chamber between the inlet port and the outlet port. The body further includes a compressed gas inlet port and defines a compressed gas chamber in flow communication with the gas inlet port. The compressed gas chamber and the fluid chamber are isolated from one another. 
     A piston is disposed in the compressed gas chamber and is configured for reciprocating movement in the chamber. The piston has a spring receiving region. 
     A valve stem is movable within the fluid chamber between an open condition in which flow communication is established between the inlet port and the outlet port and a closed position to stop flow through the valve. The valve stem has a spring receiving region. 
     A spring, such as a coil spring, is disposed between the valve stem and the piston. The spring urges the piston into the compressed gas chamber toward the gas inlet and urges the valve stem into the fluid chamber to the closed position. 
     The valve is operable in at least three modes. In an operating mode, the valve is in the open condition, the valve stem is spaced from the piston, and the piston applies a pressure on the valve stem, through the spring. The piston pressure is balanced by fluid pressure exerting a force on the valve stem. 
     In a zero-state mode, the valve is in the open condition, the valve stem is spaced from the piston and the spring is in a relaxed state. The piston applies no pressure on the valve stem. 
     And, in a relief mode, the valve stem is in the open condition with the valve stem contacting or in close proximity to the piston. The spring is in a compressed state due to the fluid pressure of fluid entering the inlet exerting a force on the valve stem and gas pressure on the piston. 
     In a present valve, the piston has a piston face opposing the valve stem and the valve stem includes a shoulder portion for contacting the piston face when the valve is in the relief mode. The valve includes a piston stop surface that prevents the piston face from contacting the valve stem shoulder portion when in the operating mode and the zero state mode. 
     A stem guide is annularly disposed about the valve stem, positioned in the valve body. The piston stop surface is formed on the stem guide. 
     The valve can also operate in a maximum pressure mode, which is an operating state, in which the valve stem may be in the open condition, the valve stem is spaced from the piston, and the piston face rests on the piston stop surface. The piston applies a pressure on the valve stem through the spring and the valve stem shoulder portion is spaced from the piston face. 
     The valve body defines a space between the piston and the valve stem and the spring is disposed, at least in part in the space. The space is open to the environs to prevent influence from the compressed gas or the fluid on the valve operation or function. The piston can be cup-shaped, with the spring receiving region positioned in the cup. 
     The valve includes a valve seat in the fluid chamber between the fluid inlet port and the fluid outlet port. The stem engages the seat to close the valve. 
     These and other features and advantages of the present invention will be apparent from the following detailed description, in conjunction with the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The benefits and advantages of the present invention will become more readily apparent to those of ordinary skill in the relevant art after reviewing the following detailed description and accompanying drawings, wherein: 
         FIG. 1  is a schematic illustration of an adhesive system having a multi-mode pressure relief valve embodying the principles of the present invention; 
         FIG. 2  is a cross-sectional view of the valve in the neutral or operating condition; 
         FIG. 3  is a cross-sectional view of the valve in the maximum pressure relief condition; 
         FIG. 4  is a cross-sectional view of the valve in the zero-state condition; and 
         FIG. 5  is a cross-sectional view of the valve in the maximum pressure condition. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the present invention is susceptible of embodiment in various forms, there are shown in the drawings and will hereinafter be described several preferred embodiments with the understanding that the present disclosure is to be considered an exemplification of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
     It should be further understood that the title of this section of the specification, namely, “Detailed Description of the Invention,” relates to a requirement of the United States Patent and Trademark Office, and does not imply, nor should be inferred to limit the subject matter disclosed herein. 
     Referring now to the figures and in particular to  FIG. 1 , there is shown a schematic illustration of a hot melt adhesive system  10  having a multi-mode pressure relief valve  12  in accordance with the principles of the present invention. The adhesive system  10  includes an adhesive supply, such at the illustrated tank  14 , which contains a specified volume of adhesive maintained at a temperature that allows for transport or conveyance of the adhesive. In a typical operation, the tank temperature is maintained about 50° F. lower than the adhesive application temperature. A present system has the tank temperature maintained at about 300° F. 
     An adhesive dispenser head  16 , four shown, heats the adhesive to an operating or application temperature (for example, about 350° F.) at which the adhesive is discharged onto the desired object. It will be appreciated that the object can be, for example, a carton or container for commercial products ranging from soda-pop to breakfast cereals to tools and consumables. The adhesive is dispensed at the desired temperature and at a desired flow rate to control the application of the adhesive to the object. The flow rate is determined so that the adhesive flows onto the object without affecting or slowing the production line speed, but is applied in a sufficient volume to effect the adhesive process. 
     A pump  18  supplies the adhesive to the applicator heads  16 . In present systems, the adhesive is supplied at relatively high pressures, as high as 1000-1100 psi. A filter  20  can be provided to filter the adhesive prior to routing to the applicator heads  16 , and various pressure and temperature monitors  22  can be provided in the system  10 . 
     The overall operation of the production line (not shown) and the adhesive system  10  is carried out using a pneumatic control system, pneumatic supply being shown generally at 24. Such systems are sufficiently versatile to allow for controlling the valves needed for operation, as well the other components within the system. In certain production line systems, the pressure of the pneumatic system is used to control the overall production (packaging) operation. In these system, the speed of production is controlled by the pneumatic system  24  pressure. 
     The present multi-mode pressure relief valve  12 , which is shown in the operating condition, is illustrated in  FIG. 2 . Referring briefly again to  FIG. 1 , the valve  12  is positioned in a branch line  26  along the adhesive flow path, between the pump  18  and the filter  20 . In this manner, system  10  pressure is controlled by returning a portion or all of the fluid flow from the pump  18  back to the tank  12  through the discharge side branch line  27  from the valve  12 . 
     Referring back to  FIG. 2 , the valve  12  includes a valve body  28  having an adhesive inlet port  30  and an adhesive outlet port  32 . The inlet and outlet  30 ,  32  are shown in transverse relation to each other, but it will be appreciated by those skilled in the art that the configuration of the inlet  30  and outlet  32  can be varied. An adhesive flow path F is defined between the inlet  30  and outlet  32 . The valve  12  also includes a compressed gas (air) inlet  34  isolated from the adhesive inlet  30  and outlet  32 . The body  28  thus defines an adhesive chamber  36  between the adhesive inlet  30  and outlet  32 . A present body  28  is formed as two parts—a main body  38  and a cap  40  that are threaded together, with a seal  42  between the parts. 
     A valve stem  44  is positioned in the body  28  to move into and out of the adhesive flow path F. A valve seat  46  is an annular element on which the stem  44  seats to permit or isolate the flow of adhesive. As seen in  FIG. 2 , when the stem  44  moves off of the seat  46 , flow of adhesive is established between the inlet  30  and the outlet  32 . The stem  44  includes an annular recess  48  in which a spring  50  (described below) resides and which defines an annular shoulder  52 . 
     A stem guide  54  is positioned in the body  28  to guide the stem  44  as it moves between the open ( FIG. 1 ) and closed ( FIG. 3 ) positions. The guide  54  maintains the stem  44  positioned in the valve  12  and guides the stem  44  as it moves to open and close the valve  12 . A stem seal  56  is positioned between the stem  44  and the guide  54  to prevent the flow of adhesive around the stem  44  and into the “clean” areas of the valve body  28 . The seal  56  can be of the packed-type seal with a spring to assure good contact and isolation between the stem  44 , the body  28  and guide  54 . 
     The valve  12  includes a piston  58  in the body  28 , opposite of the seat  46 . The spring  50  positioned between the piston  58  and stem  44 . A compressed gas (or air) chamber  60  is defined between the air inlet  34  and a top  62  of the piston  58 . The piston  58  is positioned to move within the air chamber  60  toward and away from the valve stem  44 . The piston  58  is an inverted U-shaped or cup-shaped reciprocating member and includes a seal  64  to prevent the leakage of air around the periphery of the piston  58 . A region around the cup-shaped portion  66  defines a piston face  68 . 
     The spring  50  is positioned between the stem  44  and the piston  58  and resides in the cup portion  66  of the piston  58 . The spring  50  is held in place about the stem  44  by a post or finger  70  extending from the end of the stem  44 , about which the spring  50  is positioned, and resides in the stem annular recess  48 . Although the spring  50  is shown as a coil spring, those skilled in the art will appreciated that the spring can be of a number of different types, such as Belleville washers or the like and that such other constructions are within the scope and spirit of the present invention. A space  72  between the bottom of the piston  58  and the top of the valve stem  44  is open to the environs. In this manner, pressure either from the adhesive side (chamber  36 ) or air side (chamber  60 ) that may escape around their respective seals, does not adversely affect the operation of the valve, and does not influence the valve operation or function. 
     It will be appreciated from a study of the figures that the force exerted on the piston  58  from the air-side  60  pressure, in conjunction with the spring  50  force, counteracts or balances the force exerted on the valve stem  44  from the adhesive side  36  pressure. In a present valve  12 , there is an adhesive-side  36  to air-side  60  pressure ratio of 14:1 at which the pressures are balanced. That is, for each 1 psi of air pressure the system provides 14 psi of adhesive pressure. The valve  12  ratio can, of course, be configured as desired for a particular adhesive system or control system. 
     Various other features of the valve have been included to achieve desired operating characteristics. As best seen in  FIG. 2 , the valve  12  includes a piston stop surface  74  on the stem guide  54 . The stop surface  74  prevents over travel of the piston  58  (see  FIGS. 3 and 5 ) in the event that air pressure is greater than a maximum setting and to prevent shut-off when the adhesive pressure is greater than a minimum threshold. It provides a physical stop for movement of the piston  58 . Referring to  FIG. 2 , the valve  12  also includes a free clearance, indicated at  76 , for zero-state operation (described in more detail below) relative to the normal or operating condition to allow the piston  58  to move fully up into the air chamber  60  (as seen in  FIG. 4 ). 
     The valve  12  has at least three and preferably four operating conditions or states.  FIG. 2  shows the valve  12  in a normal operating condition. Adhesive pressure is exerted on the stem  44  urging the valve  12  open, while air pressure is exerted on the piston  58 , urging the piston  58  and spring  50  to close the valve  12  (stem  44 ). The air pressure and adhesive pressure are in balance and the valve  12  remains open to permit the flow of adhesive. 
     When it is desired to relieve the pressure in the adhesive system  10 , as when the pump discharge pressure is too high, or for example, in a high pressure fault condition, the upward force on the valve stem  44  will urge the stem  44  up to open the valve  12 , regardless of the air pressure in the system  10 . This pressure relief condition is shown in  FIG. 3 , in which the piston  58  is shown at maximum air pressure, but the force on the stem  44  and spring  50 ) urges the valve  12  open nevertheless. Even with the high air pressure, it can be seen that the piston stop surface  74  prevents over-travel of the piston  58  and allows the stem  44  to rise and the valve  12  to open. In this condition, the annular shoulder  52  is in contact with the piston face  68  and the valve  12  is open even though the piston  58  is at a maximum downward position. That is, even with the piston  58  subjected to maximum air-side  60  pressure, there is sufficient, physical space between the annular shoulder  52  and the piston face  68  to allow the stern  44  to rise (until the shoulder  52  contacts the face  68 ) to relieve system  10  pressure. 
     When it is desired to de-pressurize the adhesive system  10  (to dump system pressure, for example, for system  10  maintenance), the valve  12  is in the zero-state condition as seen in  FIG. 4 . Here, the air pressure is reduced to or close to zero, and the piston  58  moves fully up in the body  28  toward the air inlet  34 . In this condition, the piston  58  moves into the free clearance or zero-state condition space  76  and rests against an upper piston stop  78  in the valve body  28 . Thus, the stem  44  likewise moves up against a reduced spring  50  force to open the valve  12  and drops or dumps the pressure in the adhesive supply system  10 . 
     A last operating condition is shown in  FIG. 5  which illustrates a maximum operating condition. Here, the air supply pressure is at a maximum with the piston  58  resting on the stop surface  74 , and with the stem  44  being urged upward to open the valve  12  by fluid pressure on the stem  44 . The stem  44  is spaced from the piston  58  (that is, there is no contact between the stem annular shoulder  52  and the piston face  68 ) and thus the stem  44  can move, as by adhesive pressure, up toward the piston  58  to allow adhesive flow, and/or to prevent over-pressurization with the stem  44  moving up, against the piston face  68 , into the pressure relief condition. 
     As set forth above, the present multi-mode valve  12  replaces three presently used valves, namely a pressure relief valve, a zero-state device (valve) and a line speed following valve. The present multi-mode valve  12  performs all three functions. That is, the zero-state condition is provided by isolating air flow to the valve  12 , and thus allowing the valve  12  to go to full open; pressure relief is provided by allowing pressure against the stem  44 , to open the valve  12 , regardless of the air-side pressure  60  acting on the piston  58 ; and, line speed following is provided in the normal operating to maximum pressure conditions, by a balance of the air-side  60  pressure acting on the piston  58  and the counter-balancing adhesive-side  36  pressure acting on the valve stem  44 . Moreover, the present valve  12  advantageously provides these operating and safety modes in a single compact component with a minimum number of moving parts. 
     In the present disclosure, the words “a” or “an” are to be taken to include both the singular and the plural. Conversely, any reference to plural items shall, where appropriate, include the singular. All patents referred to herein, are hereby incorporated herein by reference, whether or not specifically done so within the text of this disclosure. 
     From the foregoing it will be observed that numerous modifications and variations can be effectuated without departing from the true spirit and scope of the novel concepts of the present invention. It is to be understood that no limitation with respect to the specific embodiments illustrated is intended or should be inferred. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.