US2718904A - Pressure sensitive diaphragm assembly - Google Patents

Description

Sept. 27, 1955 w. R. POLYE PRESSURE SENSITIVE DIAPHRAGM ASSEMBLY Filed April 9, 1952 INVENTOR. l V/LL/AM P. POLYE HTTOR/VEY r l l 1 United States Patent'O PRESSURE SENSITIVE DIAPHRAGM ASSEMBLY William R. Polye, River Edge, N. .L, assignor to Bendix Aviation Corporation, Teterboro, N. J., a corporation of Delaware Application April 9, 1952, Serial No. 281,435

2 Claims. (Cl, 137-777) tween 10- to 10 mm. of mercury. It has been found t that such altimeters frequently effect erroneous indications with ambient temperature changes because of the expansion of residual gas within the diaphragm. Despite careful initial evacuation, gases are released from solder flux and from the metal parts which cause a rise of internal pressure after sealing off of the diaphragm.

The present invention contemplates a novel and improved high vacuum corrugated metal diaphragm which operates efficiently and effectively over a wide range of pressures and temperatures. The diaphragm comprises a pair of flexible metal discs joined together along their peripheries to form an expansible chamber. Connected to an opening in the diaphragm is a metal tube which communicates the interior of the diaphragm with the interior of an envelope sealed to the atmosphere. The envelope contains gas adsorbing material which adsorbs the residual gases within the diaphragm so that errors due to ambient temperature changes are substantially eliminated. Thus, means are provided whereby a high vacuum is maintained in the diaphragm.

An object of the invention, therefore, is to provide a novel and improved high vacuum diaphragm which operates efficiently and effectively over a wide range of pressures and temperatures.

Another object is to provide a novel high vacuum metal diaphragm wherein the residual gases released from the metal parts are effectively withdrawn therefrom.

The above and other objects and advantages of the present invention will appear more fully hereinafter from a consideration of the detailed description which follows taken together with the accompanying drawing wherein the single figure thereof illustrates one embodiment of the invention.

Referring now to the drawing for a more detailed description of the present invention, a pressure sensitive assembly is shown which comprises a metal diaphragm 12, consisting of a pair of corrugated flexible discs 14 and 16 joined together along their peripheries by a suitable solder, as at 18, to form an expansible and contractible chamber. Disc 14 is provided with a lug 20 to which one end of a suitable transmission mechanism (not shown) may be connected. Disc 16, on the other hand, has a lug 22 having an opening therein registering with an opening in the disc. Extending within the opening in lug 22 and secured thereto, as by soldering, is one end of a hollow metal tube 24 which has its other end secured .and sealed-off. ments employing diaphragms so constructed were sub- H 2,718,904 Patented Sept. 27, 1955 to a Kovar glass to metal seal 26. An elongated glass bulb or envelope 28 having its interior filled with a gas adsorbing material 30 is cemented and sealed by way of glass to metal seal 26 whereby the latter together with tube 24 form the means for communicating the interior of envelope 28 with the interior of diaphragm 12.

Gas adsorbing material 30 comprises activated cocoanut charcoal granules although other materials such as silica-gel or activated alumina may be used. Adsorbing material 30 has the characteristic of adsorbing gas when subjected to dropping temperatures and expelling or giving-01f the gas when heated. The granules are capable of adsorbing large volumes of gas and for this reason, they effectively adsorb the residual gases in the diaphram.

Heretofore, diaphragms of the type disclosed herein were exhausted by a suction pump to the desired vacuum In operation, it was found that instruject to error because of the residual gases present after completion of the exhaustion operation. Thus, the diaphragms became sensitive to temperature changes as well as to pressure changes because the residual gases expanded with changes, in ambient temperatures. The residual gases comprised the gases released from the solder flux and from the metal parts which gave rise to an increase in internal pressure after sealing off. It. is .well known that metal surfaces have the ability to retain a small amount of gas therein and consequently, the process of evacuating the diaphragm does not effectively remove all of the gas.

As hereinbefore set forth, the novel method for producing a high vacuum in diaphragm 12 forms the subject matter of divisional application Serial No. 357,280. For present purposes, the method of fabricating diaphragm 12 may comprise the following steps. After the discs 14 and 16 are soldered together and bulb 28 and tubes 26, 24 are assembled thereto, a suction pump (not shown) is connected to the interior of bulb 28 at the portion where the bulb is tipped-off, and the assembly is evacuated. A dome-shaped oven (not shown) is placed over the as sembly before evacuation to heat the latter during the exhaustion process whereby the gas within the diaphragm is substantially driven therefrom; the gas in this case being partially adsorbed by material 30 and partially taken out by the pump. The oven is brought to a temperature below the melting point of the solder, which runs about 350 degrees Fahrenheit, to prevent melting of the solder joints. Since the temperature to which the diaphragm is brought is limited by the melting point temperature of the solder, a very small amount of occluded gas will not be driven out and will remain in the diaphragm. Toward the end of the exhaustion operation, a Nichrome heater coil (not shown) is wrapped around bulb 28, and the latter is heated to drive out the gases already adsorbed by the adsorbing material 30. The Nichrome coil is brought to a temperature higher than that of the oven, for example, at approximately 600 degrees Fahrenheit. Since the temperature at which the solder melts is about 350 degrees Fahrenheit, the diaphragm is suitably insulated from the bulb as by sheets of asbestos placed between the diaphragm and bulb. Bulb 28 is made of glass in order to prevent undue transfer of heat to the diaphragm, glass being a relatively poor conductor of heat.

The bulb is then tipped-off as shown in the drawing, and the pump disconnected. The material 30 cools from its outgassing temperature to room temperature and, in cooling, adsorbs the very small amount of gas remaining in the diaphragm. The above action will continue to take place until equilibrium is established; however, the adsorbent is capable of adsorbing such large volumes of gas that equilibrium is usually not reached unless the diaphragm assembly leaks. The diaphragm assembly 3 now is capable of maintaining a low pressure in diaphragm 12.

It will now be readily apparent that the present invention provides a novel and improved high vacuum dia phragm which operates efiiciently over a wide range of temperatures and pressures. The occluded gas Within the metal parts and other gas released from the solder flux are substantially driven out of the diaphragm by heating of the latter, and, after sealing off, a low pressure is maintained in the diaphragm by the gas adsorbing material.

Although one embodiment of the present invention has been illustrated and described in detail, it is to be expressly understood that the invention is not limited thereto. Various changes can be made in the design and arrangement of the parts Without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art.

I claim:

1. A pressure-sensitive assembly for use in altimeters, comprising diaphragm means including an evacuated corrugated metal diaphragm chamber having walls movable in response to changes in ambient atmospheric pressure, a glass envelope having its interior sealed from the atmosphere, a quantity of gas-adsorbing material comprising activated cocoanut charcoal granules contained within said envelope, and means for communicating the inte rior of said envelope with the interior of said diaphragm chamber, said last-mentioned means including a glassto-metal seal, whereby gases within said diaphragm chamher are adsorbed by said granules to maintain a high vacuum within said diaphragm chamber.

2. A pressure-sensitive assembly for use in altitudesensitive apparatus, comprising diaphragm means including an evacuated corrugated metal diaphragm chamber having Walls movable in response to changes in ambient atmospheric pressure, an auxiliary container having its interior sealed from the atmosphere, a quantity of gas-adsorbing charcoal within said container, and means connected to approximately the center of one diaphragm wall for communicating the interior of said container with the interior of said diaphragm chamber, whereby gases within said diaphragm chamber are adsorbed by said charcoal to maintain a high vacuum within said diaphragm chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,146,019 Pfund July 13, 1915 1,930,899 Kollsman Oct. 17, 1933 2,162,308 Jenny June 13, 1939 2,177,564 Havill Oct. 24, 1939 2,426,663 Bevins Sept. 2, 1947 OTHER REFERENCES A Manual of Vacuum Practice, by Martin and Hill; published 1947 by Melbourne University Press; pp. 84,

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