Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.


  1. Advanced Patent Search
Publication numberUS2721533 A
Publication typeGrant
Publication dateOct 25, 1955
Filing dateAug 27, 1953
Priority dateAug 27, 1953
Publication numberUS 2721533 A, US 2721533A, US-A-2721533, US2721533 A, US2721533A
InventorsCassel Alderfer Donovan
Original AssigneeCassel Alderfer Donovan
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Pressure operated alarm
US 2721533 A
Abstract  available in
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

Oct. 25, 1955 D. c. ALDERFER PRESSURE OPERATED ALARM Filed Aug. 27, 1953 FIGJ FIG.2


Application August 27, 1953, Serial No. 376,855

1 Claim. (Cl. 116-112) This invention relates to an alarm to be used in connection with the blower of a warm air furnace, winter air conditioner or air conditioner.

In furnaces of the forced warm air type the air is generally drawn from the rooms in return cold air ducts and passed through a filter, generally composed of spun glass fibers, coated to catch and retain the dust and foreign particles in the air, before it reaches the blower to be driven through the heated drum and into the hot air ducts. In many cases the filters are not replaced often enough and the suction caused by the fan furnishes less air because of the clogging of the filter and even that air carries foreign particles.

It is the object of the present invention to provide an alarm which will apprise the owner or operator of the furnace that the filters are filled with dust and foreign matter to their capacity and require replacement.

It is a further object of the invention to provide an alarm which will operate automatically and apprise the operator without periodic examination or attendance upon the furnace.

A still further object is to provide an audible alarm attached to the blower chamber of the furnace which will operate upon the reduction in air flow through the filters.

It is a still further object of the invention to provide an audible alarm which may be adjusted in its intensity and which can be adjusted as to its operating pressure so that the filter may be utilized to its full capacity, yet not forced beyond that capacity to fill the indrawn air with dust particles and to render the incoming volume of air less.

The invention is illustrated in the accompanying drawing in which: A

Figure 1 is a vertical cross-section of the alarm as attached to the wall of the furnace.

Figure 2 is a front view of the control knob for regulating the opening into the alarm.

Figure 3 is a cross-section of the alarm as mounted on a warm air furnace showing the blower chamber of the furnace and the filters in position.

Referring particularly to Figure 3, the blower compartment 7 of the warm air furnace houses a fan or blower 8 and is provided with an intake opening 9 and an outlet 10. Supported directly across and completely covering the inlet opening 9 is a filter 11. This filter is of the usual glass fiber type through which the air is drawn and the 2,721,533 Patented Oct. 25, 1955 dust and foreign particles removed by adhering to the sticky coated fibers. The air, after passing through the filter, is driven by the blower through the outlet opening 10 to the heating drum (not shown). Mounted in the side wall 12 of the blower compartment is a whistle or reed 14 serving as an audible alarm under certain conditions.

Referring to Figures 1 and 2, the reed (in the particular illustration) 14 is carried in a tubular or rectangular housing 15 which extends from the inside 16 of the blower compartment to the outside. The outside portion of the housing is enlarged to an offset circular head 17 having an annular groove 18 adjacent the wall of the compartment. Carried on the offset head is a cap 20 having a semicircular opening 21 in its upper portion. A second circular cap 22 carrying a pointer 23 is likewise formed with a semicircular opening 24 and is mounted for rotation on the first mentioned cap. Alignment of the two semicircular openings presents a maximum opening to the tubular housing of the reed and is indicated on the pointer.

In the operation of the alarm the cycle operates as follows: When the filter accumulates sufficient dust and foreign matter to provide obstruction to the flow of air, there is a tendency to draw air through the openings 24 and 21 of the caps 22 and 20. The flow of air through the tubular housing causes the reed 14 to vibrate giving an audible alarm which can be varied in intensity as desired. The saturation point for the filters may be adjusted by opening the semicircular openings more or less to provide sufficient air to operate the reed. As the filter becomes obstructed, the tendency for the air to enter the compartment through the semicircular openings becomes greater. The vibration of the reed is controlled through the selection of a reed in the manufacture of the instru- ,ment and the regulation of the opening will control within limits the time at which the alarm will operate.

What is claimed is:

In a furnace of the hot air type having a fan for drawing air through a filter and forcing said air across a heated drum and through ducts to a delivery point, an air operated alarm in said furnace Wall and between said fan and said filter, one end of said alarm projecting beyond said wall and formed with a hole so that through reduction of pressure in the area between said fan and filter due to the clogging of the filter and the operation of the fan air is drawn through the alarm to produce an auditory signal, and a cap adapted to fit over the exposed end of said alarm and also formed with a hole therein communicating with the hole in said alarm, said cap being adjustable to vary the size of the hole opening.

References Cited in the file of this patent UNITED STATES PATENTS 357,469 Davis Feb. 8, 1887 999,567 Kallstrom Aug. 1, 1911 2,172,399 Mueller Sept. 12, 1939 2,682,250 Ulrich June 29, 1954 FOREIGN PATENTS 345,440 Great Britain Mar. 26, 1931

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US357469 *Oct 19, 1886Feb 8, 1887 Steam fog-horn
US999567 *Mar 16, 1911Aug 1, 1911Lars A KallstromAttachment for cooking vessels.
US2172399 *Sep 9, 1935Sep 12, 1939Mueller Moritz LAir conditioning apparatus
US2682250 *Apr 25, 1950Jun 29, 1954Roy E UlrichAir filter signal
GB345440A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2782747 *Apr 11, 1955Feb 26, 1957Donovan C AlderferAlarm for air conditioning system
US4398491 *Jun 3, 1981Aug 16, 1983The Continental Group, Inc.Acoustic indicator of vacuum level in containers
US4747364 *Aug 5, 1986May 31, 1988Filter Alert CorporationFlow rate threshold sensor
US6110260 *Jul 14, 1998Aug 29, 20003M Innovative Properties CompanyFilter having a change indicator
U.S. Classification116/112, 116/137.00R
International ClassificationF24F3/16
Cooperative ClassificationF24F3/1603
European ClassificationF24F3/16B