Patent Application
20060174686
The present invention relates generally to calibration of pressure switches, and more particularly, to a portable, hand-held tool for calibrating and diagnosing problems with pressure switches associated with HVAC systems.
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, 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's specifications.
Pressure switches activate electromechanical or solid-state switches upon reaching a specific pressure level. For example, normally-closed pressure switches are used to shut the system down should the pressure 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 closed switch will open, the circuit will be broken and the furnace will shut down. 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 “breaks” the circuit, such that the power to the system controls is lost and the system is shut down. 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.
Faulty pressure switches have been one of the most misdiagnosed problems in today'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'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. While one can test to see if there is enough pressure to close the switch simply by attaching a pressure measuring device such as a manometer in the line, but this will not tell you if the switch is working properly.
A significant need exists in the HVAC field for the diagnosis and calibration of pressure switches. Pressure switches are “safety devices” in today's modern heating systems. These safety devices shut the heating system down should there be a problem with getting rid of the flue gas which contains carbon monoxide. They also insure that the system is getting enough 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 the pressure switch is properly diagnosed, and, if it is an adjustable pressure switch, that it is set correctly. There is currently no known tool available to the service technician that can be used to create pressure or vacuum in order to test, set or adjust a pressure switch to the manufacturer's specifications while in the field.
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. Prior to the present invention, it was also not previously 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.
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. Likewise, there is a need to provide a portable apparatus to allow the technician to perform diagnostic tests on furnace pressure switches at the worksite. It would also be advantageous to provide a hand-held calibration and diagnostic tool that can be used on pressure switches that are either part of a working HVAC system or not yet assembled into such a system. These and other features and advantages of the present invention will become more apparent with reference to the accompanying specification and claims.
In general, the present invention discloses an apparatus for calibration and testing of a pressure switch typically used in residential and commercial HVAC systems, the apparatus comprising: a) a housing including an inside and an external surface; b) a battery-powered air compressor having a vacuum-side inlet and a pressure-side outlet; c) at least one battery in electrical communication with the air compressor; d) a recirculation circuit in fluid communication between the vacuum-side inlet and the pressure-side outlet of the air compressor; e) a vacuum nozzle in fluid communication between the atmosphere and the vacuum-side inlet of the air compressor; f) a pressure nozzle in fluid communication with the pressure outlet of the air compressor; and g) a bypass control valve disposed within the recirculation circuit for controlling the flow of gas passing therethrough and to control the gas pressure at the vacuum nozzle and the pressure nozzle.
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. In one embodiment, the apparatus is typically associated with a free-standing pressure test means and conductivity meter, with the pressure test means and the conductivity meter removably attachable to one of the nozzles. In another embodiment, the pressure test means and conductivity meter are incorporated within the housing of the apparatus. A pressure test means generally includes an air pressure measuring device and a connecting means. The air pressure measuring device (for example, a manometer or a Magnehelic gage) is typically used to measure the pressure being transmitted from the apparatus to the pressure switch. A conductivity meter is generally an electrical measuring device used to test whether an adjustable pressure switch is open or closed.
The portable calibration device of the present invention is typically able to diagnose problems with any manufacturer'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's pressure switch, should a service technician not have an exact replacement switch at the worksite.
The various embodiments of the portable calibration device 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. In one embodiment, the apparatus is designed to be used in conjunction with a free standing pressure measuring device such as a differential pressure manometer or equivalent pressure gage, and a conductivity meter such as an ohm meter, a multimeter (an instrument that combines the functions of an ammeter, a voltmeter and an ohm meter) or an electrical continuity tester. In another embodiment, the apparatus includes the pressure measuring device and the continuity meter within its housing.
The nature and advantages of the present invention will be more fully appreciated from the following drawings and detailed description.
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.
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. 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
Together, the flexible hose 26A-C and T-piece 28 constitute a connecting means. In the present invention, connecting means generally include connective tubing such as flexible hose and one or more T-pieces and/or valves, and is operable to bring an air pressure measuring device and an adjustable pressure switch into communication with either the vacuum inlet nozzle 14 or the pressure outlet nozzle 16, thereby transmitting either a vacuum or air pressure to both the pressure switch and the air pressure measuring device.
The air compressor 34 is typically a positive displacement air pump, and, for example, a 6 volt vacuum pump such as one made by Koge Electronics Co., LTD works well for this purpose. The air compressor 34 typically creates pressures in the range of between about minus 0.05 to about positive 25.0 inches of water. Connecting means or connective tubing used with the present invention is typically either 3 mm ( 5/32 inches) internal diameter tubing or b 1/4 inch internal diameter tubing, and bulkhead nozzles used herein are typically 1/4 inch internal diameter. However, these are merely typical examples used in the apparatus and are not intended to limit the present invention in any way. More powerful air compressors capable of generating larger air pressures, and larger bore tubing and nozzles will work equally well with the configuration disclosed herein.
Viewing either
The actual gas pressures at the nozzles 14, 16 are regulated by increasing or decreasing the amount of air being circulated through the recirculation circuit 200. The bypass control valve 18 performs this function. When the bypass control valve 18 is closed, the recirculation circuit 200 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, 16. When the bypass control valve 18 is opened, then the flow of gas from the pressure-side outlet 38 of the air compressor 34 can be recirculated back to the vacuum-side inlet 36 through the recirculation circuit 200 via the flexible tubing 201 and 202 and T-pieces 280A and 280B, leading to and away from the valve 18. Increased air recirculation decreases the vacuum and air pressures at nozzles 14 and 16, respectively. Thus, vacuum and air pressure at the nozzles 14, 16 are regulated simultaneously by means of the bypass control valve 18. Adjusting this valve 18 permits the user to both test and calibrate pressure switches, as will be explained in more detail below.
As seen best in
As described above, the air compressor 34 within the device 10 provides the pressure and/or vacuum output for the apparatus, and the bypass control valve 18 regulates the amount or value of the pressure and the vacuum output. In the configuration shown in
In use, the apparatus 10 can be used for calibrating an adjustable pressure switch 22. For purposes of illustration, the apparatus is 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
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 device 10 is first attached to the pressure switch 22 as explained above. Once the proper air pressure (or vacuum) is attained and the test leads of the conductivity meter 30 are attached, the user slowly adjusts the pressure bypass control valve 18 to increase the amount of pressure transmission to the pressure switch from the nozzle 14 until the pressure switch closes (as confirmed by the attached conductivity meter 30). If this closing pressure is not within the manufacturer'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.
To test a dual pressure switch, a user performs the steps performed on the vacuum-side port 42 of the switch, as explained above, to the positive-side port 45 of the dual pressure switch as well. First, the user measures the amount of pressure that is being generated at the pressure-side port 45. To do this, it is first necessary to turn the furnace off and disconnect the furnace from the vacuum-side port 42 of the pressure switch, then connect a hose to the pressure-side port 45. Thereafter, connect a T-piece to the end of this hose. Connect the vacuum-side port 42 to the T-piece, and then connect another hose to the final side of the T-piece. At the other end of this hose connect the manometer. Turn the furnace on and record the value of the pressure indicated on the manometer. Next, turn the furnace off and disconnect the manometer, hoses and T-piece. Reconnect the furnace to the vacuum-side port 42, and connect the positive pressure nozzle 16 of the apparatus and a manometer via a T-piece to the pressure-side port 45 of the pressure switch, and turn the furnace on. Once the furnace flames are on, open the bypass control valve 18 of the apparatus to “full open.” Turn the diagnostic apparatus 10 on by depressing the on/off button 12, and slowly adjust the bypass control valve 18 to increase the pressure. Note the pressure indicated on the manometer 24 when the furnace shuts down. Subtract this reading from the reading you took earlier. This sum is the actual operating pressure of the pressure switch. If this pressure is not within the manufacturer'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 ohm 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.
The pressures at the nozzles 54, 56 are regulated by increasing or decreasing the amount of air being re-circulated through the bypass control valve 58. When the bypass control valve 58 is fully closed, there is no recirculation of air, and a maximum vacuum and/or positive pressure generated by the compressor 34 will typically be exerted at nozzles 54, 56. When the bypass control valve 58 is fully opened the flow of gas is able to recirculate in the direction from the pressure outlet 38 towards the vacuum inlet 36, thereby decreasing the vacuum and air pressure at the respective nozzles 54, 56. The circuitry connecting the manometer 80 to this system does not affect the balance between the bypass control valve 58 and the nozzles 54, 56. However, if both valves 64 and 66 are opened, the flow of pressure will also circulate through the manometer circuit, but this will only further decrease the pressures at the nozzles 54, 56. Thus, vacuum and air pressure at both nozzles 54, 56 is regulated simultaneously by means of the bypass control valve 58. Adjusting the bypass control valve 58 permits the user to both test and calibrate pressure switches, and opening either the vacuum throttle valve 64 or the pressure throttle valve 66 while the other is closed permits the user to measure either vacuum pressure or positive pressure, as will be explained in more detail below.
Conductivity meter lead input 76 is connected to the positive pole of the conductivity meter light 74, and the negative pole of conductivity meter is connected to the negative pole of the compressor battery 90 via the negative pole of the compressor 34. Thus, the conductivity meter light 74 will be activated upon completion of the circuit between lead input 76 and lead input 78. Therefore, this apparatus can be used solely as a conductivity meter, 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 meter light 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). As best seen in
In
The apparatus 50 of
One embodiment of the apparatus of the present invention can include a “differential” manometer within the housing of the apparatus. This type of manometer has two ports (positive pressure and vacuum) instead of a single port. The positive port measures positive air pressure and the negative port measures vacuum air pressure. With a differential manometer having two ports connected within the circuitry, the valves 64 and 66, tubing 907, 908, 910, and T-piece 984 of the apparatus 50 as illustrated in
Early detection of pressure switch failure while the pressure switch is incorporated into an HVAC system has previously not been possible. 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 in one hand when being used, 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 or spirit of the invention.
| Number | Date | Country | |
|---|---|---|---|
| 60650721 | Feb 2005 | US |
