Patent Publication Number: US-9851274-B2

Title: Portable pressure switch calibration and diagnostic tool

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. application Ser. No. 14/175,188 filed Feb. 7, 2014, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to testing and calibration of pressure switches, and more particularly, to an improved portable, hand-held tool for calibrating and diagnosing problems with pressure switches associated with HVAC systems. 
     BACKGROUND OF THE INVENTION 
     A pressure switch is a mechanical device which converts a pressure change of a liquid or gas into an electrical function. The pressure change might be measured as pressure, vacuum, or differential between two pressure inputs. In every case, the pressure switch will employ a diaphragm, a piston, a signal transducer, or other pressure-responsive sensor which is coupled to the mechanical means of actuating a switch. Pressure switches fulfill a variety of monitoring and control applications, and they are employed in virtually every industry, from appliances to automobiles to computers. They are often used in pneumatic systems, such as air compressor pressure switches for furnaces or HVAC systems, as well as water pressure switches or oil pressure switches. Pressure switches are common components of high-efficiency heating systems as well as high-efficiency water heaters. Different manufactures make differing types of pressure switches, and each type is set according to the manufacturer&#39;s specifications. 
     Pressure switches activate electromechanical or solid-state switches upon reaching a specific pressure level. For example, “normally open” pressure switches are used to keep the system from operating should the pressure not be high enough or exceed the safety limit. For example, should a flue become partially plugged, the pressure in the exhaust will build up presenting a dangerous condition. Flue gases containing carbon monoxide will spill into the living space. The flames will become unstable and “float” or “spill” out of the heat exchanger creating a fire hazard. Under these conditions, the normally-open switch will not close and the furnace will not be able to run. As this example illustrates, if the pressure in a system becomes either too high or too low, depending on whether the switch is a positive pressure switch that measures positive pressures, or a negative pressure switch that measures negative (vacuum) pressures, the pressure-responsive sensor (e.g., a diaphragm within the switch) will be affected to the point where the pressure switch will not complete the circuit, such that the power to the system controls is lost and the system does not run. In contrast, “normally closed” switches can also be used to verify that it is safe for the furnace to come on. If the switch had failed and it was stuck open, then the furnace would not come on. 
     Dual, or differential, pressure switches have a normally closed and a normally open circuit. The normally closed circuit allows the furnace to safely initiate the sequence of operation resulting in a flame. Typically negative pressure is created by the expelling of the flue gases, and the normally open circuit will close. This allows the furnace to continue operating safely because the flue gases are being expelled. Most differential pressure switches have two hoses connected. The first hose is located at the vacuum side of the switch and is connected to the flue circuit (the flue circuit expels the burned gases). The second hose is located at the positive pressure side of the switch and is connected to the gas valve (the gas circuit mixes air with the gas creating the flame). Generally, there should be little or no positive pressure. Should a positive pressure exist, it is typically an indication that the primary or secondary heat exchanger is becoming plugged. As a result, pressure build up creates a positive pressure which will negate from the negative or vacuum pressure, thus causing the negative (vacuum) pressure to drop below the setting and shut the furnace down. Dual pressure switches are also used to set the gas pressure of the gas valve in high efficiency units. When the gas ignites there is a slight variance in the pressures measured by a manometer. The gas pressure is then adjusted to the manufacturer&#39;s specifications. 
     Faulty pressure switches may be one of the most misdiagnosed problems in today&#39;s modern furnaces. Many pressure switches have been replaced needlessly, simply because there was no proper way to test them. It is typically the technician&#39;s best guess as to whether a problem exists which necessitates replacement of the pressure switch. Thus, many service calls could have been resolved easily if the pressure switch was first able to be tested properly before being replaced. A service technician using a pressure-measuring device such as a manometer can test “static pressure” in the line to see if there is enough pressure to close the switch, but this will not reveal whether or not the pressure switch itself is working properly. 
     In light of this, a significant need exists in the HVAC field for the diagnosis and calibration of pressure switches. Pressure switches are “safety devices” in today&#39;s modern heating systems. These safety devices shut the heating system down should there be a problem with expelling the flue gas which contains carbon monoxide. They also insure that the system is getting enough fresh air for the correct and safe combustion of the fuel gas mixture. Since pressure switches are safety devices used on all high-efficiency heating systems used for heating residential, commercial and industrial buildings, it is extremely important that any malfunction of a pressure switch is properly diagnosed, and, if it is an adjustable pressure switch, that it is set correctly. 
     Prior art calibration devices also do not allow one to accurately diagnose pressure switch failure, or impending failure. Often the service technician must simply guess if a pressure switch has failed, or else guess the remaining life expectancy of a pressure switch by exchanging the pressure switch to see if the replacement switch corrected the problem. U.S. Pat. No. 7,441,439 to the present inventor McFarland, which is incorporated herein by reference in its entirety, teaches a portable pressure switch tool that can be used to create pressure or vacuum in order to test, set or adjust a pressure switch to the manufacturer&#39;s specifications while in the field. Prior to the &#39;439 patent to McFarland, it was not possible to accurately diagnose early failure or possible failure of a pressure switch that was starting to go bad. Even worse, technicians have wasted valuable time being called back to a worksite after replacing a pressure switch, only to find out that the problem was the flue, or a blocked intake or condensate system. 
     While the &#39;439 patent to McFarland teaches a device that is useful for creating pressure or vacuum in order to test, set, or adjust a pressure switch to the manufacturer&#39;s specifications while in the field, the device includes manual control valves for adjusting the vacuum. This typically requires the use of both hands in order to operate the device. Therefore, there exists a need for an HVAC service technician to be able to quickly, easily and accurately set and/or calibrate adjustable pressure switches in an HVAC system without having to operate manual control valves. It would also be advantageous to provide a hand-held calibration and diagnostic tool that can be used on pressure switches without having to use both hands to operate manual control valves. These and other features and advantages of the present invention will become more apparent with reference to the accompanying specification and claims. 
     SUMMARY OF THE INVENTION 
     In general, the present invention is an apparatus for calibration and testing of residential and commercial HVAC system pressure switches. The apparatus creates a controlled vacuum for testing the pressure switches, so technicians can tell exactly when a pressure switch closes and opens. This either proves that the switch is within specification, or identifies if the switch is starting to fail. 
     A first aspect of the invention provides an apparatus for calibrating and testing a pressure switch, the apparatus comprising: (a) an air compressor having a vacuum-side inlet and a pressure-side outlet; (b) at least one vacuum inlet nozzle in fluid communication with the vacuum-side inlet of the air compressor, the at least one vacuum inlet nozzle being located on the external surface of the housing; (c) a positive pressure outlet nozzle in fluid communication with the pressure-side outlet of the air compressor; (d) a circuit board located on the inside of the housing (e) a battery located on the inside of the housing for supplying power to the circuit board; (f) an increase voltage button located on the external surface of the housing and in electrical communication with the circuit board, wherein activating the increase voltage button will cause the circuit board to increase the voltage supplied to the compressor pump; (g) a decrease voltage button located on the external surface of the housing and in electrical communication with the circuit board, wherein activating the decrease voltage button will cause the circuit board to decrease the voltage supplied to the compressor pump; (h) a pair of conductivity indicator lead inputs located on the external surface of the housing and in electrical communication with the circuit board; (i) a conductivity indicator light located on the external surface of the housing and in electrical communication with the circuit board, wherein the conductivity indicator light is operable to visually indicate whether the pressure switch is open or closed; and (j) an on/off button located on the external surface of the housing for completing an electrical circuit between the battery and the circuit board, wherein when the on/off button is placed in the “on” position, the circuit is completed and the battery, the air compressor, the increase and decrease voltage buttons, and the conductivity indicator light are operational. 
     Another aspect of the invention provides an apparatus for calibrating and testing a pressure switch, the apparatus comprising: (a) a housing including an inside and an external surface; (h) an air compressor located on the inside of the housing, the air compressor including a vacuum-side inlet and a pressure-side outlet; (c) a first vacuum inlet nozzle located in the external surface of the housing, the first vacuum inlet nozzle being in fluid communication with the vacuum-side inlet of the air compressor; (d) a second vacuum inlet nozzle located in the external surface of the housing, the second vacuum inlet nozzle being in fluid communication with the vacuum-side inlet of the air compressor; (e) a positive pressure outlet nozzle in fluid communication with the pressure-side outlet of the air compressor, wherein the positive pressure outlet nozzle is located inside the housing of the apparatus; (f) a circuit board located on the inside of the housing; (g) a battery located on the inside of the housing for supplying power to the circuit board; (h) an increase voltage button located on the external surface of the housing and in electrical communication with the circuit board, wherein activating the increase voltage button will cause the circuit board to increase the voltage supplied to the compressor pump; (i) a decrease voltage button located on the external surface of the housing and in electrical communication with the circuit board, wherein activating the decrease voltage button will cause the circuit board to decrease the voltage supplied to the compressor pump; (i) a pair of conductivity indicator lead inputs located on the external surface of the housing and in electrical communication with the circuit board; (k) a conductivity indicator light located on the external surface of the housing and in electrical communication with the circuit board, wherein the conductivity indicator light is operable to visually indicate whether the pressure switch is open or closed; and (l) an on/off button located on the external surface of the housing for completing an electrical circuit between the battery and the circuit board, wherein when the on/off button is placed in the “on” position, the circuit is completed and the battery, the air compressor, the increase and decrease voltage buttons, and the conductivity indicator light are operational. 
     Another aspect of the invention provides an apparatus for calibrating and testing a pressure switch, the apparatus comprising: (a) a housing including an inside and an external surface; (b) an air compressor located on the inside of the housing, the air compressor including a vacuum-side inlet and a pressure-side outlet; (c) a vacuum inlet nozzle located in the external surface of the housing, the vacuum inlet nozzle being in fluid communication with the vacuum-side inlet of the air compressor; (d) a positive pressure outlet nozzle in fluid communication with the pressure-side outlet of the air compressor; (e) a circuit board located on the inside of the housing; (t) a battery located on the inside of the housing for supplying power to the circuit board; (g) an increase voltage button located on the external surface of the housing and in electrical communication with the circuit board, wherein activating the increase voltage button will cause the circuit board to increase the voltage supplied to the compressor pump; (h) a decrease voltage button located on the external surface of the housing and in electrical communication with the circuit board, wherein activating the decrease voltage button will cause the circuit board to decrease the voltage supplied to the compressor pump; (i) a pair of conductivity indicator lead inputs located on the external surface of the housing and in electrical communication with the circuit board; (j) a conductivity indicator light located on the external surface of the housing and in electrical communication with the circuit board, wherein the conductivity indicator light is operable to visually indicate whether the pressure switch is open or closed; (k) a pressure measuring nozzle located on the external surface of the housing; (l) a pressure measuring device located on the inside of the housing and being in fluid communication with the pressure measuring nozzle for measuring the amount of pressure communicated through the pressure measuring nozzle; (m) a pressure readout screen located on the external surface of the housing and in electrical communication with the circuit board and the pressure measuring device, wherein the pressure readout screen is operable to visually indicate the amount of pressure being measured by the pressure measuring device; and (n) an on/off button located on the external surface of the housing for completing an electrical circuit between the battery and the circuit board, wherein when the on/off button is placed in the “on” position, the circuit is completed and the battery, the air compressor, the increase and decrease voltage buttons, the pressure measuring device, and the conductivity indicator light are operational. 
     The calibration/diagnostic apparatus of the present invention provides vacuum and air pressure by means of a small battery-powered air compressor located inside its housing, which is controlled by a microchip circuit board, as is known in the art. In one embodiment, a conductivity indicator is incorporated within the housing of the apparatus and the apparatus is typically associated with a free-standing pressure test means that is removably attachable to the apparatus. In another embodiment, both the pressure test means and conductivity indicator are incorporated within the housing of the apparatus. 
     The nature and advantages of the present invention will be more fully appreciated from the following drawings and detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention. 
         FIG. 1  is a schematic view of a prior art embodiment of a portable calibration apparatus, connected to a pressure switch. 
         FIG. 2  is a schematic view of the interior air pressure circuitry of the prior art portable calibration apparatus of  FIG. 1 . 
         FIG. 3  is a plan view of the interior air pressure circuitry of the prior art portable calibration apparatus of  FIG. 1 . 
         FIG. 4  is a plan view of the interior electrical circuitry of the prior art portable calibration apparatus of  FIG. 1 . 
         FIG. 5  is a schematic view of one embodiment of a portable calibration apparatus according to the present invention, connected to a pressure switch and an external manometer. 
         FIG. 6  is a schematic view of the interior air pressure circuitry of the portable calibration apparatus of  FIG. 5 . 
         FIG. 7  is a plan view of the interior air pressure circuitry of the portable calibration apparatus of  FIG. 5 . 
         FIG. 8  is a plan view of the interior electrical circuitry of the portable calibration apparatus of  FIG. 5 . 
         FIG. 9  is a schematic view of another embodiment of a portable calibration and test tool of the invention connected to a pressure switch, in which both a pressure test means and conductivity indicator are incorporated within the housing of the apparatus. 
         FIG. 10  is a plan view of the interior air pressure circuitry of the apparatus of  FIG. 9 . 
         FIG. 11  is a plan view of the interior electrical circuitry of the apparatus of  FIG. 9 . 
         FIG. 12  is a plan view of the connection between the apparatus of  FIG. 9  and the pressure switch, showing an external bleed port that can be added for achieving low pressures. 
         FIG. 13  is a plan view of the interior air pressure circuitry of one embodiment of a portable calibration apparatus according to the present invention. 
         FIG. 14  is a plan view of the interior electrical circuitry of the portable calibration apparatus of  FIG. 13 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Definitions: 
     As defined herein, an “air pressure measuring device” is a tool for accurate measurement of air pressure. With the present invention, this tool is used to measure the pressure being transmitted from the inventive apparatus to a pressure switch. Typically, an air pressure measuring device can measure absolute pressure, typically in pressure units of “inches of water,” For example, a Ailagnehelic gage (such as one manufactured by Dwyer), a differential pressure manometer, a digital manometer, or equivalent pressure gage have all been found particularly suitable as an air pressure measuring device for the invention. 
     A “circuit board” is an insulated board on which interconnected circuits and components such as microchips are mounted or etched. The circuit board controls the sequence of events needed for proper operation of the apparatus of the invention, including the control and distribution of power to the various electronic components. 
     “Electrical components” are any elements of the apparatus that run or are powered by electricity. Typically the electrical components of the present invention include, but are not limited to, a circuit board, an air compressor, a battery, an increase voltage button, a decrease voltage button, conductivity indicator lead inputs, a conductivity indicator light, and an on/off button. 
     A “conductivity indicator” is generally an electrical measuring device used to test whether an adjustable pressure switch is open or closed. Typically the conductivity indicator of the present invention includes a pair of test leads lead inputs) and a light. 
     A “pressure test means” is the combination of an air pressure measuring device and a connecting means such as a flexible hose or tubing. 
     The present invention is a calibration and diagnostic apparatus for use with pressure switches that are typically used in HVAC systems and residential and commercial furnaces. The apparatus is able to calibrate adjustable pressure switches to manufacturers&#39; specifications. While saving contractors from carrying a large inventory of pressure switches on their trucks and from having to leave the job site to buy pre-calibrated switches. 
     While U.S. Pat. No. 7,441,439 to McFarland (the present inventor), which is incorporated herein by reference in its entirety, discloses the use of a recirculation circuit  203  and a manual control valve  18  to regulate the vacuum strength (see prior art  FIGS. 1-4 ), the present invention improves upon this and regulates the vacuum strength by controlling the amount of voltage supplied to the air compressor pump (see  FIGS. 5-14 ), thereby allowing a user to regulate the strength of the pump vacuum without the need of a recirculation circuit  203  or a manual control valve  18 . Specifically, the amount of voltage supplied to the air compressor pump is controlled by pressing an “up arrow” button  60  or a “down arrow” button  62  on the external surface of the apparatus housing (see, e.g.  FIG. 5 ). By directly controlling the speed of the motor on the air compressor pump with the down and up buttons rather than a control valve, the user can change the vacuum strength and perform tests, as needed, without the need for any other instrument, and without having to use both hands in order to hold the apparatus and operate an adjustable control valve. The technician thus has more precise control of the vacuum created in order to close and open the pressure switch being tested, and is typically able to perform the tests with one hand, with all of the important information (e.g. from a circuit board and manometer) in front of him. The present invention thus provides a fully electronic tool that eliminates the need for a manual control valve. 
     In the following Figures, positive and negative symbols are used for both pressure and electricity. Thus, for clarity sake, positive and negative pressure outlets will be indicated with [+] and [−], respectively, while positive and negative electrical poles will be indicated with (+) and (−), respectively, in the Figures. 
     With reference to  FIG. 1 , a prior art embodiment of a pressure switch calibration and diagnostic apparatus is illustrated, which incorporates a conductivity indicator  174  within the housing of the unit. The apparatus  100  includes an on/off button  12  on the top of the housing, a first vacuum inlet nozzle  14 , and a bypass control valve  18 . The bypass control valve  18  is typically a needle valve with an external control knob, and is capable of providing fine regulation of airflow. The external surface of the housing  20  further includes a second vacuum inlet nozzle  114 , a conductivity indicator light  174 , and conductivity indicator lead inputs  176  and  178 . As illustrated, the first vacuum inlet nozzle  14  can be removably connected to the pressure switch  22  by way of flexible hose  26 . The pressure switch  22  is also connected to conductivity indicator leads  176  and  178  by electrical test leads  132  and  133 . When this circuit is completed, the conductivity indicator light  174  illuminates. As illustrated, either vacuum inlet nozzle  14  or  114  of the apparatus  100  is removably connectable to an external pressure measuring device  24  (such as a manometer) by way of flexible hose  27 . 
       FIGS. 2 and 3  illustrate a schematic and plan view, respectively, of the internal air pressure circuitry of the prior art apparatus of  FIG. 1 . Specifically,  FIG. 2  shows the air compressor  34  with a vacuum inlet  36  and a pressure outlet  38  connected in fluid communication by flexible tubing  260 ,  261 ,  263 ,  124  and  126 , and T-pieces  280 A and  128  to the first vacuum inlet nozzle  14  and the second vacuum inlet nozzle  114 . A recirculation circuit  203  is created by flexible tubing  201 ,  202  running from T-pieces  280 A and  280 B to the bypass control valve  18 . Positive pressure flows freely from the unused internal positive pressure opening of T-piece  280 A into the inside of the apparatus. Also, T-piece  128  serves to divide the vacuum pressure generated by the compressor  34  into two parts, leading via flexible tubing  124  and  126  to the first vacuum inlet nozzle  14  and the second vacuum inlet nozzle  114 , respectively. 
       FIG. 3  illustrates the air circuitry of the prior art apparatus of  FIG. 2  when assembled within the housing  20 . Viewing either  FIG. 2  or  FIG. 3 , when the air compressor  34  is in the “on” position, gas or air is drawn into the vacuum-side inlet  36 , which reduces the air pressure on the vacuum-side connecting means  261 . In a closed system, a vacuum is created. The reduced pressure at the vacuum inlet  36  is communicated via the connecting means  261  and  263  and T-piece  280 B to the first and second vacuum inlet nozzles  14 ,  114 , to pull or draw air into the nozzles. Likewise, positive pressure is created by the compressor  34  as gas or air is pumped out of the pressure outlet  38 , and is communicated to the unused opening of the T-piece  280 A, i.e. an internal positive pressure opening, to expel compressed air harmlessly within the inside of the housing  20 . 
     The negative pressures at the nozzles  14 ,  114  are regulated by increasing or decreasing the amount of air being circulated through the recirculation circuit  203 . The bypass control valve  18  performs this function. When the bypass control valve  18  is closed, the recirculation circuit  203  is closed and there is no connection between the pressure circuitry and the vacuum circuitry. This enables the compressor  34  to achieve maximum vacuum and pressure exerted at the nozzles  14 ,  114 . When the bypass control valve  18  is opened, then a portion of the flow of gas from the pressure-side outlet  38  of the air compressor  34  can be re-circulated back to the vacuum-side inlet  36  through the recirculation circuit  203  via the flexible tubing  201  and  202  and T-pieces  280 A and  280 B, leading to and away from the valve  18 . Increased air recirculation decreases the vacuum pressures at nozzles  14  and  114 . Thus, the mass air flow entering the first and second vacuum inlet nozzles  14 ,  114 , and the mass air flow of air exiting the T-piece  280 A, is regulated by means of the bypass control valve  18 . Adjusting this valve  18  permits the user to control the vacuum pressure at the first and second vacuum inlet nozzles  14 ,  114 , and to both test and calibrate pressure switches. The bypass control valve  18  thus prevents undue stress on the air compressor by controlling the amount of air re-circulating through the recirculation circuit, and controls the amount of air to be pulled in from the vacuum port  42 . 
       FIG. 4  is a schematic view of the interior electrical circuitry of the prior art apparatus  100  of  FIG. 1 , and includes a battery  40  which provides electrical power to the air compressor  34 . The positive pole (+) of the battery  40  is connected to one pole of the on/off button  12 , and the negative pole (−) of the battery  40  is connected to both the negative pole (−) of the air compressor  34  and the negative pole (−) of the conductivity indicator  174 . The positive pole (+) of the air compressor  34  is connected to another pole of the on/off button  12 , such that when the on/off button is placed in the “on” position, the circuit is completed and the air compressor is operated. Turning the on/off button to the “off” position will break the circuit and the air compressor  34  will turn off. For simplicity sake, the air pressure circuitry of  FIGS. 2 and 3  is shown separately from the electrical circuitry of  FIG. 4 ; however, both of these circuitries are housed together within housing  20  of this prior art apparatus  100 . 
     In  FIGS. 5-8 , like numbers are used to indicate like parts as shown in the prior art embodiment illustrated in  FIGS. 1-4 . With reference now to  FIG. 5 , an alternative embodiment  200  of the pressure switch calibration and diagnostic apparatus of the present invention is illustrated. Similar to the apparatus  100  in  FIGS. 1-4 , this embodiment incorporates a conductivity indicator  174  within the inside of the housing of the unit, and thus provides the service technician the ability to test pressure switches without having to use an external conductivity indicator. The apparatus  200  also includes an on/off button  13  which has been moved to the center face of the housing  30  (compared to the button  12  at the top of the housing in  FIGS. 1-4 ), as well as a first vacuum inlet nozzle  14 , a second vacuum inlet nozzle  114 , an “up” arrow or increase voltage button  60 , a “down” arrow or decrease voltage button  62  conductivity indicator light  174 , and conductivity indicator lead inputs  176  and  178  in the external surface of the housing  30 . Unlike the prior art embodiment of  FIGS. 1-4 , there is no need for a bypass control valve  18  or any interior recirculation circuit  203  (see  FIG. 2 ). Pressing the increase voltage button  60  will increase the voltage supplied to, and thus the speed and the induced vacuum created by the compressor pump, while pressing the decrease voltage button  62  will do the opposite, ultimately decreasing the induced vacuum. 
     As illustrated in  FIG. 5 , the first vacuum inlet nozzle  14  can be removably connected to the vacuum port  42  of pressure switch  22  by way of flexible hose  26 . The pressure switch  22  is also connected to conductivity indicator leads  176  and  178  by electrical test leads  132  and  133 . When this circuit is completed, the conductivity indicator light  174  illuminates. As illustrated, either vacuum inlet nozzle  14  or  114  of the apparatus  100  is removably connectable to an external pressure measuring device  24 , such as a manometer or magnehelic gage, by way of flexible hose  27 . 
       FIGS. 6 and 7  illustrate a schematic and plan view respectively, of the internal air pressure circuitry of device of  FIG. 5 . Specifically,  FIG. 6  shows an air compressor  234  with a vacuum inlet  36  and a pressure outlet  38 . T-piece  128  serves to divide the vacuum pressure generated at the vacuum inlet  36  of the compressor  34  into two parts. Specifically, vacuum pressure is passed through flexible tubing  261  and splits at T-piece  128  to flexible tubing  124  and the first vacuum inlet nozzle  14 , as well as from T-piece  128  to flexible tubing  126  and the second vacuum inlet nozzle  114 . Significantly, it can be appreciated that the recirculation circuit  203  and the manual control valve  18  of the apparatus of  FIG. 2  is not present in the improved apparatus of  FIG. 6 . Also, positive pressure flows freely inside the housing, typically from flexible tubing  260  attached to the unused internal positive pressure outlet  38 . 
       FIG. 7  illustrates the air circuitry shown in  FIG. 6  when assembled within the housing  30  of the apparatus  200 . Viewing either  FIG. 6  or  FIG. 7 , when the air compressor  234  is in the “on” position, gas or air is drawn into the vacuum-side inlet  36  which reduces the air pressure on the vacuum-side connecting means  261 . In a closed system, the vacuum created at the vacuum inlet  36  is communicated via tubing  261 , T-piece  128  and tubing  124  and  126  to the first and second vacuum inlet nozzles  14 ,  114  to pull or draw air into the nozzles. The strength of the negative pressure generated at the nozzles  14 ,  114  is regulated by increasing or decreasing the motor speed of the compressor  234  by using the up and down arrows  60 ,  62  located on the external surface of the housing  30  (see also  FIG. 5 ). Increasing the motor speed of the compressor  234  in this manner enables the compressor to achieve maximum or minimum vacuum exerted at the nozzles  14 ,  114 . Thus, the degree of mass air flow entering the first and second vacuum inlet nozzles  14 ,  114 , as well as the degree of mass air flow exiting open tubing  260  is regulated by adjusting the up and down buttons  60 ,  62 . Adjusting the compressor motor speed can thus be done with one hand by the user, and permits the user to control the vacuum pressure at the first and second vacuum inlet nozzles  14 ,  114  without the need for using a manual control valve  18  or recirculation circuit  203  (as seen in  FIG. 2 ). Rather, buttons  60  and  62  perform this task, which are located on the face of the external surface of the housing  30  of the apparatus  200 . Positive pressure is also created by the compressor  234  as gas or air is pumped out of the pressure outlet  38 , and is communicated out open tubing  260  as an internal positive pressure outlet nozzle, to expel compressed air harmlessly within the inside of the housing  30 . This allows excess pressure to be released, acts as a “bleed off” to control the vacuum created by the pump  234 , and helps to regulate the amount of air expelled into the housing. This in turn helps to regulate the amount of vacuum that is produced. 
       FIG. 8  is a plan view of the interior electrical circuitry of the apparatus  200 . Similarly to  FIG. 4 , the apparatus  200  of  FIG. 12  includes a battery  40  which provides electrical power to the air compressor  234  via a circuit board  64 . The circuit board  64  receives energy when turned “on” from the battery  40 , receives input from the on/off button  13  and the up and down arrows  60 ,  62  of the apparatus, and also connects to the conductivity indicator  174 . Thus, when the on/off button  13  is placed in the “on” position, the circuit is completed and the battery  40 , the air compressor  234 , the up and down buttons  60 ,  62  and the conductivity indicator  174  are operational. Turning the on/off button  13  to the “off” position will break the circuit and these portions of the apparatus  100  will turn off. For simplicity sake, the air pressure circuitry of  FIGS. 6 and 7  is shown separately from the electrical circuitry of  FIG. 8 ; however, both of these circuitries are to be housed together within housing  30  of the apparatus  200 . 
     As seen best in  FIG. 5 , the apparatus  200  is typically used in conjunction with an air pressure measuring device  24  such as a manometer. The conductivity indicator  174  is used to measure electrical resistance in ohms across the actuation switch of the pressure switch  22 . A lack of electrical current across this switch indicates that there is not enough vacuum or air flow to complete the electrical circuit within the pressure switch, or that the pressure switch has failed. 
     The air compressor  234  within the apparatus  200  of  FIGS. 5 and 8  provides the vacuum production for the apparatus via nozzles  14  and  114 , and the up and down buttons  60 ,  62  are used to regulate the amount of voltage transmitted via the control panel to the air compressor  234 . Rather than the bypass control valve  18  and recirculation circuit  203  (including  280 A,  280 B,  201 ,  202 ,  263 ) of prior art  FIGS. 1 and 2 , the up and down buttons  60  and  62  regulate the amount of air that can be drawn through the nozzles  14  and  114 , and thus the pressure value of the vacuum. Being able to increase or decrease the vacuum strength by simply pressing the up and down buttons  60 ,  62  allows the user of the present invention to use a single hand to adjust airflow, as compared to the previous embodiment of this invention in which two hands are typically required to hold the apparatus while adjusting the bypass control valve  18 . In the configuration shown in  FIG. 5 , the vacuum inlet nozzles  14 ,  114  are connected into fluid communication with a vacuum port  42  of the pressure switch  22  (via tubing  26 ) and the manometer  24  (via tubing  27 ), respectively. The arrow buttons  60 ,  62  allow the user to easily prevent undue stress on the air compressor by controlling the amount of air to be pulled in from the vacuum port  42 . 
     In use, the various embodiments of the apparatus of the invention can be used for calibrating an adjustable pressure switch. For example, looking at  FIG. 5 , the apparatus  200  can be used to calibrate an adjustable pressure switch  22  which operates in a “normally open” manner. This means that until a sufficient vacuum is measured across the pressure switch  22 , the electrical circuit is open and no electrical signal is generated. The adjustable pressure switch  22  has a set screw  44  which is used to activate or deactivate an electrical circuit when the target pressure differential across the pressure-side port  45  and the vacuum-side port  42  is achieved. After assembling the circuitry, as illustrated in  FIG. 5 , the user adjusts the set screw  44  on the adjustable pressure switch  22  to be calibrated to “full open” so that there is little or no differential between the vacuum port  42  and the pressure port  45 , and to completely open the switch  22  to the calibration apparatus  200 . The calibration apparatus  200  is then turned “on” by pushing button  13  to operate the air compressor  34 , and the air compressor  234  strength is slowly adjusted, via pushing either the increase voltage button  60  or decrease voltage button, until the pressure reading on the manometer  24  matches the manufacturer&#39;s specified pressure (or vacuum) for the pressure switch  22 . The user then slowly adjusts the set screw  44  on the adjustable pressure switch  22  until the conductivity indicator confirms that electricity is flowing across the switch  22  and it has closed. At this point, the user slowly adjusts the set screw  44  on the adjustable pressure switch  22  until the indicator confirms that the switch is open. At this point the pressure switch is calibrated. In summary, then, if the indicator confirms that the switch is open, the user slowly adjusts the set screw on the adjustable pressure switch until the indicator confirms that the switch is closed, then slowly adjusts the set screw on the pressure switch until the indicator confirms that the switch is open. At this point the pressure switch is calibrated. 
     The apparatus of the present invention can also be used as a diagnostic tool for early detection of pressure switch failure. That is, the apparatus can also be used to hold a specific pressure differential on any pressure switch, adjustable or not, thereby enabling diagnostic testing of the pressure switch. For example, to diagnose a pressure switch failure for a “vacuum, normally open” pressure switch similar to the previous example above, the apparatus  200  is first attached to the pressure switch  22  as explained above. Once the proper air pressure (or vacuum) is attained and the test leads  176 ,  178  of the conductivity indicator  174  are attached, the user slowly adjusts the increase voltage button  60  to increase the amount of vacuum pressure transmission to the pressure switch from the nozzle  14  until the pressure switch closes (as confirmed by the conductivity indicator  174 ). If this closing pressure is not within the manufacturer&#39;s recommended specifications, then the switch should be adjusted, and, if it is not adjustable, should be considered unsafe and should be replaced, regardless of whether the furnace is presently operating properly or not. 
     Pressure switches that have had water in them are notorious for being a “sticking switch.” Water develops within pressure switches for a number of reasons. High efficiency furnaces operate at lower temperatures thus resulting in condensation. Older furnaces were often operated at much higher temperatures, thus not allowing any condensation to form. If there is a trap in the tubing (i.e. the line goes down then up) that connects the pressure switch to the furnace, the tubing may fill with water. This in turn will shut the furnace down, but water in the tubing may enter the pressure switch. Also, simply because the furnace is causing condensation, water may enter the pressure switch. Condensation contains contaminants which build up over time. If the pressure switch is made of metal it is further complicated because the water will cause rust to form on the pressure switch, which will cause the pressure switch to fail. If the pressure switch is sticking or is full of water, it should be replaced regardless of whether the furnace is presently operating properly or not. To test for a sticking pressure switch, adjust the pressure a little beyond the specified settings, using the diagnostic method explained above. The switch will be inconsistent with closing and opening if it is sticking. It also may be intermittent in operating meaning it may close then open properly one time out of about three to five trials. 
     By using the apparatus of the present invention one can also test for a ruptured diaphragm in the pressure switch, as the switch will close and then open shortly thereafter. This indicates that the diaphragm has moved and the switch closed because of the pressure, but if the pressure bleeds through the diaphragm, and the pressure remains constant, the diaphragm will move back and open the switch. To test this, once the correct pressure has been reached and the switch closes, wait 10 to 30 seconds. If the switch remains closed then the diaphragm located inside the switch is holding and is good. If the conductivity meter light goes out the switch has opened (on a normally closed switch), then there is leakage in the diaphragm. This switch should be replaced regardless of whether the furnace is presently operating properly or not. 
       FIGS. 9-12  illustrate another embodiment of the present invention which incorporates both a manometer and a conductivity indicator within the inside of the housing of the calibration and diagnostic apparatus. Similar to the apparatus  200  in  FIGS. 5-8 , the apparatus  300  in  FIG. 9  includes an on/off button  13 , a vacuum inlet nozzle  14 , an “up” arrow or increase voltage button  60 , a “down” arrow or decrease voltage button  62 , conductivity indicator light  174 , and conductivity indicator lead inputs  176  and  178  on the external surface of the housing  50 . The external surface of the housing  50  also includes a pressure measuring nozzle  214  (rather than the second vacuum inlet nozzle of  FIGS. 4-8 ), and the front face of the housing  50  includes a pressure measuring device readout screen  70  (or a manometer readout screen  70 ). Pressure measuring nozzle  214  is connected to an internal pressure measuring device (or manometer  80 , see  FIG. 10 ). As illustrated in  FIG. 9 , the pressure measuring nozzle  214  and the vacuum inlet nozzle  14  can be removably connected to a pressure switch  22  by way of flexible hose  126 , T-Piece  226 , and hoses  215  and  115 . The pressure switch  22  can also be connected to conductivity indicator leads  176  and  178  via electrical test leads  132  and  133 . When this circuit is completed, the conductivity indicator light  174  illuminates. 
       FIG. 10  illustrates a plan view of the internal air pressure circuitry of the apparatus  300  of  FIG. 9 . Specifically,  FIG. 10  shows the circuitry including the air compressor  234  having a vacuum inlet  36  and a pressure outlet  38 . The vacuum inlet  36  is connected by flexible tubing  261  to the vacuum inlet nozzle  14 . There is no positive pressure outlet nozzle connecting the pressure outlet  38  to the outside, such that positive pressure [+] flows freely inside the housing, typically from flexible tubing  260  attached to the unused internal positive pressure outlet  38 . The internal pressure measuring device or manometer  80  connects via tubing  150  to the pressure measuring nozzle  214 . 
     Viewing  FIG. 10 , when the air compressor  234  is in the “on” position, gas or air is drawn into the vacuum-side inlet  36 , which reduces the air pressure on the vacuum-side connecting means  261 , and the negative pressure created at the vacuum inlet  36  is communicated via tubing  261  to the vacuum inlet nozzle  14  to pull or draw air into the nozzle. Likewise, positive pressure is created by the compressor  234  as gas or air is pumped out of the pressure outlet  38 , and is communicated out the unused open tubing  260  as an internal positive pressure outlet nozzle, to expel compressed air harmlessly within the inside of the housing  50 . This allows excess positive pressure to be released, and acts as a “bleed off” to control the vacuum created by the pump  234 . The manometer  80  measures the pressure of the gas that is communicated through the pressure measuring nozzle  214 , which is typically connected externally to nozzle  14  via a T-piece to measure the pressure transmitted from a pressure switch (see  FIG. 9 ). The pressure at the vacuum inlet nozzle  14  is regulated by increasing or decreasing the amount of voltage being sent to the compressor  234 , via up and down buttons  60  and  62 . Increasing the motor speed of the compressor in this manner enables the compressor  234  to achieve maximum or minimum vacuum exerted at the vacuum inlet nozzle. 
     Thus, the degree of mass air flow entering the vacuum inlet nozzles  14 , as well as the degree of mass air flow exiting open tubing  260  is regulated by adjusting the up and down buttons  60 ,  62 . Adjusting the compressor motor speed can typically be done with one hand by the user. A battery  40  provides electrical power to the air compressor  234  via a circuit board  64 . The circuit board  364  receives input from the on/off button  13  and receives energy when turned “on” from the battery  40 , and also receives input from the up and down arrows  60 ,  62  in the housing  30  of the apparatus, and also connects to the conductivity indicator  174 . Thus, when the on/off button  13  is placed in the “on” position, the circuit is completed and the battery  40 , the air compressor  234 , the up and down buttons  60 ,  62 , the manometer screen  70 , the conductivity indicator  174 , and internal manometer  80  are operational. Although the manometer  80  is shown in front of the manometer screen  70  in  FIGS. 10 and 11 , it can be appreciated that the manometer  80  is typically placed behind the screen  70 , and is illustrated in this way for understanding purposes. 
     The circuit board of the apparatus of  FIGS. 9-11 and 13-14  can also be programmed to allow a user to test a pressure switch in the following manner: the user presses the “on/off” button (which, when the apparatus is already in the “on” position, is programmed to act as a “hold” or “capture” button), then presses and holds the “up” arrow. The pump output increases rapidly, and the moment the switch closes, the pressure value is captured by the manometer (this is programmed into the circuit board). The user notes the reading, then presses the “hold” (i.e. “on/off”) button again to release the captured reading. The user then presses the “hold” button once again, and then presses and holds the “down” arrow. The pump output decreases rapidly, and the moment the switch opens, that pressure value is also captured by the manometer. The user then notes the readings. 
     The circuit board can also be programmed so that the user can simply connect the apparatus to the pressure switch to be tested, press the “on/off” button (after the apparatus has already been turned “on”) and the apparatus does the above automatically. Further, it can be appreciated that while the “on/off” button can be programmed to perform these functions, it would be an easy task to add separate “hold” or “capture” buttons to the apparatus in order to separately control the pressure measuring functions of the apparatus, rather than using the “on/off” button to do so. 
       FIG. 11  is a plan view of the interior electrical circuitry of the apparatus  300 . In use, when the on/off button  13  is placed in the “on” position, the circuit within the circuit board  364  is completed and the battery  40 , the air compressor  234 , the up and down buttons  60 ,  62 , the manometer  80 , manometer screen  70 , and the conductivity indicator  174  (conductivity can also be displayed on the manometer screen) are operational. Turning the on/off button  13  to the “off” position will break the circuit and these portions of the apparatus  300  will turn off. Conductivity indicator lead inputs  176  and  178  are connected to the circuit board  364 , which is connected to the conductivity indicator light  174  (or indicated on the manometer screen). Thus, the conductivity indicator light  174  will be activated upon completion of the circuit between lead input  176  and lead input  178 . Therefore, this apparatus can be used solely as a conductivity indicator, exclusive of its ability to test pressure switches. This is true as well for the pressure measuring device. For example, if the pressure switch is a normally open switch, the conductivity indicator light  174  will illuminate if the switch is working properly. Most pressure switches with two ports on them have a “common” terminal (in the power source) a “normally open” terminal (which closes once the pressure reaches the operating setting), and a “normally closed” terminal (which opens once the pressure reaches the setting or prevents the furnace from starting if it is open). For simplicity sake the air pressure circuitry of  FIG. 10  is shown separately from the electrical circuitry of  FIG. 11 ; however, both of these circuitries are to be housed together within the apparatus  300 . 
     The apparatus  300  of  FIGS. 9-11  is used in a similar manner as explained above for the apparatus  200  of  FIGS. 5-8 ; however, manometer screen  70  is also incorporated within the housing  50 , and manometer  80  is included inside of the apparatus  300 . This allows the user to conveniently calibrate and test the function of a pressure switch with a single apparatus, without having to carry or provide a separate pressure measuring device. 
     The device of the present invention is generally able to detect pressures between negative (−) 20.00 to positive (+) 20.00 inches of water, and more typically between negative (−) 10.00 and negative (−) 0.20 inches of water. However, if an external bleed port is used, pressures at negative (−) 0.01 inches of water can be measured. Also, while the upper limit of pressures measured is typically 20 inches of water for regular purposes, depending on the strength of the air compressor used in the apparatus, larger positive pressures up to 200 inches of water can also be measured using the apparatus of the invention.  FIG. 12  shows a variation of the connection between the apparatus  300  of  FIG. 9  and the pressure switch  22 , showing an external bleed port  231  that can be added for achieving lower pressures. Tubing  116  and T-piece  230  is added between the vacuum inlet nozzle  14  and tubing  115 . Opening  231  of the T-piece  230  is left open to air, which provides a bleed port for vacuum pressure to escape, and allows the user to measure pressures as low as 0.1 inches of water. The external bleed port is used to help regulate and maintain pressures from negative (−) 0.01 inches of water to positive (+) 0.20 inches of water column. It is incorporated into the device to also test pressure switches that do not have an internal bleed port. 
     With reference to  FIGS. 13 and 14 , another embodiment of the pressure switch calibration and diagnostic device  400  of the present invention is illustrated, which includes a pressure measuring nozzle  214  and a positive pressure outlet nozzle  216  in addition to the vacuum inlet nozzle  14  on the external surface of the housing  55 , and also incorporates a manometer  80  inside the housing  55  of the calibration and diagnostic apparatus  400 . Similar to the apparatus  300  in  FIGS. 9-11 , the apparatus  400  includes an on/off button  13  in the front face of the housing, a manometer readout screen  70 , an “up” arrow or increase voltage button  60 , a “down” arrow or decrease voltage button  62 , a conductivity indicator light  174 , and conductivity indicator lead inputs  176  and  178  on the external surface of the housing  55 . While  FIGS. 9-11 and 13-14  show the indicator light  174 , it can be appreciated that, because of the use of a circuit board, the indicator light can be eliminated and incorporated on the readout of the manometer screen  70 . The internal air pressure circuitry of the apparatus  400  includes an air compressor  234  having vacuum inlet  36  and pressure outlet  38 . The vacuum inlet  36  is connected by flexible tubing  261  to the vacuum inlet nozzle  14 . The pressure outlet  38  is connected by flexible tubing  262  to the positive pressure outlet nozzle  216 . An internal pressure measuring device or manometer  80  connects via tubing  150  to the pressure measuring nozzle  214 . 
     When the air compressor  234  is in the “on” position, gas or air is drawn into the vacuum-side inlet  36 , which reduces the air pressure on the vacuum-side connecting means  261 , and a vacuum is created and communicated via tubing  261  to the vacuum inlet nozzle  14  to pull or draw air into the nozzle. Likewise, positive pressure is created by the compressor  234  as gas or air is pumped out of the pressure outlet  38 , which is communicated via tubing  262  to positive pressure outlet nozzle  216 . The manometer  80  measures the pressure of the gas that is communicated through the pressure measuring nozzle  214 , which is typically used to measure the pressure transmitted from a pressure switch (e.g. see  FIG. 9 ). The pressure at the vacuum inlet nozzle  14  is regulated by increasing or decreasing the amount of voltage being sent to the compressor  234 , via up and down buttons  60  and  62 . Increasing the motor speed of the compressor in this manner enables the compressor  234  to achieve maximum or minimum vacuum exerted at the vacuum inlet nozzle  14 . Thus, the degree of mass air flow entering the vacuum inlet nozzle  14 , as well as the degree of mass air flow exiting positive pressure outlet nozzle  216  is regulated by adjusting the up and down buttons  60 ,  62 . Adjusting the compressor motor speed in this manner can typically be done with one hand by the user. 
     As shown in  FIG. 14 , a circuit board  364  receives input from the on/off button  13  and the up and down arrows  60 ,  62 , and also connects to (and thus provides power to, via the battery  40 ) the manometer screen  70 , the conductivity indicator  174 , and internal manometer  80 . Although the manometer  80  is shown in front of the manometer screen  70  in  FIGS. 13 and 14 , it can be appreciated that the manometer  80  is typically placed behind the screen  70 , and is illustrated in this way for understanding purposes. 
     In use, when the on/off button  13  is placed in the “on” position, the circuit within the circuit board  364  is completed and the battery  40 , the air compressor  234 , the up and down buttons  60 ,  62 , the manometer  80 , manometer screen  70 , and the conductivity indicator  174  are operational. Turning the on/off button  13  to the “off” position will break the circuit and these portions of the apparatus  300  will turn off. Conductivity indicator lead inputs  176  and  178  are connected to the circuit board  364 , which is connected to the conductivity indicator light  174 . Thus, the conductivity indicator light  174  will be activated upon completion of the circuit between lead input  176  and lead input  178 . Therefore, this apparatus can be used solely as a conductivity indicator, exclusive of its ability to test pressure switches. This is true as well for the pressure measuring device. 
     The embodiments shown in  FIGS. 9-12  and  FIGS. 13-14  can also include a second internal pressure measuring device or manometer (not shown), similar to manometer  80 . The second manometer can connect via tubing to a second pressure measuring nozzle (similar to nozzle  214 ) on the external surface of the housing of the apparatus, exiting next to pressure measuring nozzle  214 . This port could also be used to measure positive or negative gas pressure. The second pressure measuring device is in fluid communication with the second pressure measuring nozzle, and in electrical communication with the circuit board  364  and the pressure readout screen  70 . Dual pressure switches are also used to set the gas pressure of the gas valve in high efficiency units. When the gas ignites there is a slight variance in the pressures measured by a manometer. The gas pressure is then adjusted to the manufacturer&#39;s specifications. 
     In the embodiments shown in  FIGS. 5-14 , the battery  40  is typically either a single 9 Volt battery or two size AA batteries, but can be any type of device that can store and provide electrical power to the apparatus. Also, it is to be noted that the apparatus is not limited to using a single battery; the manometer  80  and the air compressor  234  can be wired to run off of separate batteries as well. 
     The portable calibration apparatus of the present invention is typically able to diagnose problems with any manufacturer&#39;s HVAC pressure switch, and will also be able to calibrate any adjustable pressure switch. Adjustable pressure switches typically include both a pressure port and a vacuum port and can be used in place of the manufacturer&#39;s pressure switch, should a service technician not have an exact replacement switch at the worksite. Further, the apparatus can be used to diagnose problems with pressure signal transducers. A signal transducer is like an electronic version of the pressure switch. In the newer furnaces signal transducers are used with or used in conjunction with a pressure switch. Similar to the pressure switch, it completes or opens a circuit if the pressure is incorrect. Pressure is measured electronically, eliminating the need for a mechanical device. A more precise measurement is thus able to be measured by signal transducers. 
     The various embodiments of the portable calibration apparatus disclosed herein are typically intended to be light in weight and small enough to fit in one hand of the technician, to be carried from one work site to the next in a pocket or small carrying bag. Early detection of pressure switch failure while the pressure switch is incorporated into an HVAC system has previously not been this easy to perform. The various embodiments of the apparatus of the present invention can potentially decrease the number of return visits currently made by HVAC service technicians, reduce overtime costs, and will likely prevent property damage caused by incorrect pressure switch settings and/or previously unrecognized pressure switch failure. The pocket sized apparatus is conveniently held and operated by one hand, making it extremely suitable for HVAC service technicians. A technician will no longer have to carry large calibrating devices to the worksite, or alternatively be resigned to replacing a properly functioning pressure switch because proper testing equipment is not available. 
     While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will be readily apparent to those skilled in the art. Accordingly, departures may be made from such details without departing from the scope of the invention.