Abstract:
A combination switch includes a pressure switch moveable between open and closed positions in response to a working pressure of a fluid; an unloader valve moveable between open and closed positions; and a mechanical interconnection between the pressure switch and the unloader valve operable to move the unloader valve in unison with movement of the pressure switch.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to air compressors and related fluid handling systems, and more particularly to valves and controls for such systems. 
         [0002]    Fluid handling systems such as air compressors typically utilize a mechanically-driven pump, usually of the positive-displacement type. Usually, the pump is connected to a storage tank or manifold. The tank stores a working volume of air, which serves as a buffer so that the pump does not have to operate continuously. Instead, the pump is run only until the tank is charged to a desired pressure, and then shut off until the pressure is depleted below a usable level. The pump cycling is controlled by a pressure-sensitive switch. Such systems usually also include a “unloader” valve which is effective to vent the pressure on the pump head when the pump is not running. This feature greatly reduces the effort required to restart the pump for a subsequent cycle. Prior art systems typically utilize the unloader valve and pressure switch as separate components, which increases complexity and cost. 
       BRIEF SUMMARY OF THE INVENTION 
       [0003]    Accordingly, it is an object of the invention to provide a single device which combines the functions of a pressure switch and an unloader valve. 
         [0004]    It is another object of the invention to provide a single device which interconnects a pressure switch and an unloader valve in a simple linear configuration. 
         [0005]    These and other objects are met by the present invention, which according to one aspect provides a combination switch, including: (a) a pressure switch moveable between closed and open positions in response to a working pressure of a fluid; (b) an unloader valve moveable between open and closed positions; and (c) a mechanical interconnection between the pressure switch and the unloader valve operable to move the unloader valve in unison with movement of the pressure switch. 
         [0006]    According to another aspect of the invention, the pressure switch includes a pair of electrical contacts which contact each other in the closed position and which are separated in the open position. 
         [0007]    According to another aspect of the invention, at least one of the contacts is carried by a current carrying member. 
         [0008]    According to another aspect of the invention, the unloader valve includes a valve pin which contacts the current carrying member. 
         [0009]    According to another aspect of the invention, the unloader valve includes a valve pin which contacts the current carrying member. 
         [0010]    According to another aspect of the invention, the current carrying member is a leaf spring. 
         [0011]    According to another aspect of the invention, the unloader valve includes a valve pin which contacts the leaf spring. 
         [0012]    According to another aspect of the invention, the unloader valve includes a valve pin which contacts at least one of the contacts of the pressure switch. 
         [0013]    According to another aspect of the invention, the pressure switch includes a diaphragm operably connected to the contacts by an actuating pin. 
         [0014]    According to another aspect of the invention, the unloader valve includes: (a) a piston axially moveable between open and closed positions, and (b) a spring which urges the piston towards the closed position. 
         [0015]    According to another aspect of the invention, the unloader valve and the pressure switch are contained within a housing and aligned for rectilinear motion along an axis of the housing. 
         [0016]    According to another aspect of the invention, a combination switch, includes: (a) a housing having a longitudinal axis, a first fluid inlet at a first end, and a second fluid inlet at a second end; (b) a pressure switch disposed at the first end of the housing in fluid communication with the first fluid inlet and moveable between closed and open positions in response to a working pressure of a fluid; and (c) an unloader valve disposed at the second end of the housing and moveable between: (i) a closed position in which the second fluid inlet is blocked; and (ii) an open position in which the second fluid inlet is connected to a fluid outlet. The pressure switch and the unloader valve are mechanically interconnected for unison movement along the longitudinal axis. 
         [0017]    According to another aspect of the invention, the unloader valve and the pressure switch are contained within a housing and aligned for rectilinear motion along an axis of the housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The invention may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
           [0019]      FIG. 1  is a perspective view of a combination switch constructed according to an aspect of the present invention; 
           [0020]      FIG. 2  is a top perspective view of the combination switch of  FIG. 1 ; 
           [0021]      FIG. 3  is an exploded perspective view of the combination switch of  FIG. 1 ; 
           [0022]      FIG. 4  is another exploded perspective view of the combination switch of  FIG. 1 ; 
           [0023]      FIG. 5  is a cross-sectional view of the combination switch of  FIG. 1 ; 
           [0024]      FIG. 6  is a partially sectioned perspective view of the combination switch of  FIG. 1 ; and 
           [0025]      FIG. 7  is a schematic view of a pump system incorporating the combination switch of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIGS. 1-6  illustrates a combination switch, generally designated at reference number  10 . The combination switch  10  has a housing  12  with a longitudinal center line or axis A, a pressure inlet  14 , and a vent inlet  16 . In this example, the housing  12  comprises a hollow, elongated body  18  which is closed off by a separate end cap  20 . Leakage between the body  18  and the end cap  20  is prevented by a lower seal  22 , such as the illustrated O-ring (see  FIG. 5 ). The type of housing is not critical, and the internal components of the combination switch  10  could also be housed in a different structure such as a manifold or a combination valve. 
         [0027]    The combination switch  10  includes an unloader valve  24  having a piston  26  which moves inside a bore  28  formed in the body  18 . The piston  26  has an elongated valve pin  30  with upper and lower ends, and an enlarged-diameter central portion  32  which defines a face  34 . A return spring  36  is disposed in the bore  28  above the piston  26  and urges it downward towards a closed position. A spring support  37  serves to locate the upper end of the valve pin  30  and the return spring  36 . In the closed position, the face  34  seals against a valve seat  38 , which in this example is formed by a resilient O-ring. A vent  40  formed in the body  18  intersects the bore  28  and forms a fluid connection between the vent inlet  16  and the exterior environment when the unloader valve  24  is in a raised, open position. The upper end of the bore  28  is closed off by a hollow plug  42  which also forms the vent inlet  16 . Any leakage between the bore  28  and the plug  42  is prevented by an upper seal  44 , such as the illustrated O-ring. 
         [0028]    A pressure switch  46  is disposed in the body  18  in a chamber  48 , beneath the unloader valve  24 . A disk-like separator  50  divides the chamber  48  into upper and lower sections. The pressure switch  46  comprises a contact assembly  52  in the upper section and a operating disk  54  in the lower section. The operating disk  54  is of a known type which responds to the differential between atmospheric pressure and the prevailing pressure in the pressure inlet  14 . The operating disk  54  has an inherent preload and restoring force that causes it to move to a closed position when pressure is removed. Structurally, the operating disk  54  can be a so-called “snap disk” having a frustoconical shape with a flattened central portion that causes it to “snap” between open and closed positions. This provides some dead band or hysteresis, so as to avoid “hunting” in operation. A flexible, gas-impermeable diaphragm  55  is trapped between the separator  50  and the O-ring  22 , and seals off the pressure inlet  14  from the interior of the combination switch  10 . The diaphragm  55  has a lower face in fluid communication with the pressure inlet  14 , and an upper face in fluid communication with the vent  40 . 
         [0029]    The contact assembly  52  includes a first terminal  56 A and a second terminal  56 B which carry first and second contacts  58 A and  58 B, respectively. The first contact  58 A is fixed and the second contact  58 B is carried at the end of a moveable, electrically-conductive, current-carrying member. In the illustrated embodiment, the current-carrying member is a leaf spring  60 . The leaf spring  60  is biased to keep the contacts  58 A and  58 B together unless an external force is applied, i.e. the contact assembly  52  is “normally closed” in an electrical sense. 
         [0030]    An actuating pin  62  extends through an opening  64  in the separator  50  and is free to move up and down along the axis A. The actuating pin  62  contacts both the operating disk  54  and the leaf spring  60 , such that when the operating disk  54  is in a lower position, the contacts  58 A and  58 B touch each other, and when the operating disk  54  is in an upper position, the contacts  58 A and  58 B are separated, breaking the electrical flow path between the terminals  56 A and  56 B. 
         [0031]    The lower end of the valve pin  30  of the piston  26  is positioned generally coaxially to the actuating pin  62 , and touches the leaf spring  60 , essentially forming a continuous linear mechanical path between the operating disk  54  and the piston  26 . In this arrangement, when the operating disk  54  is in a lower position, piston  26  is in the closed position, and when the operating disk  54  is in an upper position, the piston  26  is in the open position. 
         [0032]      FIG. 7  illustrates schematically a fluid handling system  66  utilizing the combination switch  10  of the present invention. A practical example of such a system would be an air compressor used for powering pneumatic tools and the like. The system has a pump  68  driven by a motor  70 , a storage tank  72  connected to the discharge side of the pump  68  through a discharge line  74  which includes a check valve  76 , and the combination switch  10  described above. A power source  78  (e.g. mains electrical supply) is connected to the motor  70  through the contacts of the pressure switch  46 , and the discharge of the pump  68  is directly connected to the unloader valve  24  through a vent line  80 . The storage tank  72  is connected to the pressure inlet  14  via a sensing line  82  connected downstream of the check valve  76 . It is noted that  FIG. 7  is intended to illustrate only the functional connections between the various components and not necessarily their structure; for example in a practical air compressor the motor  70  is often coupled to the pump  68  with a direct shaft coupling rather than the illustrated belt. 
         [0033]    The fluid handling system  66  would typically begin operation with the pressure inside the storage tank, denoted P tank , at atmospheric pressure. P tank  is communicated to the pressure switch  46  through the sensing line  80 . When P tank  is less than a set point pressure (P set ), the pressure switch  46  is closed. This also allows the unloader valve  24  to close against the valve seat  38  under pressure from the return spring  36 . 
         [0034]    In this condition, the motor  70  will operate the pump  68  to discharge air into the storage tank  72  through the discharge line and check valve  76 , and consequently increase the pressure P tank . When P tank  reaches P set , the pressure switch  46  will snap to the open position and stop the motor  70 . The actuating pin  62  drives the unloader valve  24  open as described above. Any air pressure within the discharge line  74  upstream of the check valve  76  and the pump  68  is allowed to bleed to atmosphere along a path through the vent line  80 , the unloader valve  24 , and finally the vent  40 . This relieves all pressure on the pump  68 . The check valve  76  holds the pressure P tank . 
         [0035]    The unloader valve  24  and pressure switch  46  stay open as long as P tank  is greater than P set . Pressure is maintained in the storage tank  72  and may be discharged through an outlet  84  in a known manner, for example to power a pneumatic tool (not shown). When P tank  falls below P set , the pressure switch  46  closes, starting the pump  68 , and it allows the unloader valve  24  to close under pressure from the return spring  36 . This allows the pump  68  to charge the storage tank  72 . The pressure switch  46  typically operates with some degree of “dead band” or hysteresis in the set point, in a known manner, so as to avoid excessive on-and-off cycling of the motor  70  and pump  68 . For example, the Pset needed to cause the motor  70  to cycle “off” may be substantially higher than the Pset needed to cause the motor  70  to cycle “on”. 
         [0036]    The foregoing has described a combination switch. While specific embodiments of the present invention have been described, it will be apparent to those skilled in the art that various modifications thereto can be made without departing from the spirit and scope of the invention. Accordingly, the foregoing description of the preferred embodiment of the invention and the best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation, the invention being defined by the claims.