US1624935A - Gas control for ovens - Google Patents

Description

April 19, 1927.

E. o. ENGELS GAS CONTROL FOR OVENS Filed March 16. 1926 INVENTOR Patented Apr. 19, 1927.

UNITED STATES PATENT OFFICE.

EUGENE OSCAR ENGELS, OF SAGINAW, MICHIGAN, ASSIGNOR TO BAKER-PERKINS COMPANY, INCORPORATED, OF WHITE PLAINS, NEW YORK, DOING BUSINESS AT SAGINAW, MICHIGAN.

GAS con'rnor. non ovnivs.

Application filed March 16, 1926. Serial No. 95,162.

This invention relates to gas-heated ovens and more particularly to certain improvements in the gas-and-air supply conduits to the burners.

The object of my improvement is to reduce the likelihood of accumulating combustible gases within the oven and the consequent danger of explosion, especially while the oven is being lighted.

A further object is to provide a pressure relief device in the gas-and-air conduit, which, by its construction and mode of operation, is especially well adapted for use in conjunction with the means commonly employed for automatic gas-and-air mixture control. Control apparatus of this character is well known in the art, being commonly installed as a part of the premixing gas system of baking ovens. For a typical automatic mixture control of the kind referred to reference may be had to United States patents to Keith, Numbers 1,250,319 and 1,301,272. The object of my present improvement is to make the operation of the automatic mixture control device more dependable under certain conditions of mixture pressure at the burners.

This invention is the result of extensive investigation and research into the operation of gas burners in bake ovens of various types, such as traveling tray, chain, or plate ovens, and peel and draw plate ovens.

Although extremely simple, both in in stall-ation and theory, my invention has solved satisfactorily one of the most perplexing problems that has confronted baking equipment engineers. I refer to the problem of quickly and safely lighting a great number of burners when fed by an automatic mixture control device and while the burners are surrounded by steam or extremely moist air. My improvement avoids liability of explosion.

With the foregoing and certain other objects in view, which will appear later in the specification, my invention comprises the devices described and claimed and the equivalents thereof.

In the drawings, Fig. 1 is a side elevation of a baking oven embodying my improvement.

Fig. 2 is a top plan view, on an enlarged scale, showing a back corner of the oven and part of one burner, together with the gas supply line as ordinarily connected thereto.

To clearly set forth the novelty and utility of my improvement, I will first explain the shortcomings of bake oven operation that prompted the research which resulted in this invention.

Traveling tray ovens and other bake ovens commonly have been equipped with unit premixing gas systems and automatic mixture controls of the general type shown in the Keith patents referred to. Such a control device, diagrammatically indicated by numeral 1, is usually located near the outside wall 2 of a bake oven. It is supplied through a pipe 3 with compressed air and through pipe 3 with gas. Mixing is effected while both air and gas are being passed though a suitable injector 4, into a header or supply conduit 5, from which branch pipes 6 lead to burner pipes 7 having the usual burner slots 8. Each branch pipe 6' has an individual burner shut-off cock 9.

Preferably there is one such mixture control device 1 for each header 5 which in turn supplies several burners, usually six to seventeen.

The control device is supposed to maintain the mixture at a constant gas-air ratio, regardless of variations in pressure in the header 5 as long as these variations are kept within certain limits, namely, the pressure of the gas when normally entering the burner. In practice, however, it works satisfactorily only so long as the pressure in the header 5 does not exceed the pressure needed during the time the majority of the burners connected to that header are open. hen some of the burners are turned off the pressure in header 5 gradually increases, decreasing the injector suction and finally changing from suction to pressure. The injector 4 then fails to entrain any gas, thereby unbalancing the gas-air ratio. \Vhen this occurs it is impossible to obtain a proper mixture at the burner or even to light the system, Without first opening the majority of the burners, so as to reduce the header pressure below the stated limit.

All burner shut-off cocks 9 were usually kept open. To light the oven the mixture supply was header 5 and into the oven through all the admitted from injector 4 to bitirner pipes 7. Even a little delay in lighting the burners caused trouble, for it. is practically.- impossible to light: theaburners quickly enough by handto avoid explosion All methods hereto-fore: employed for ligl it ng involved. certain amount oi risk,

The safest way to lightan oven is to ignite only one burner at a time, giving the operator'achance to see thatit is proper: ly lighted before turning onthe. next.- For reasons previously stated, lighting one burner at a time is not practicable when the unit control device 1 employed, unless the building up of pressure in the header with its consequent disarrangement of the gas-air ratio is prevented. Man-y attempts have been made to increase the worle iug range ofthe gas-air control device 1, and thereby correct that inherent defe'ct of the control system.

One method was to reduce the air pressure at the entrance to the injector by automatic regulation of the air pressu-re.- This resulted in an expensive, delicate and complicated apparatus having serious disadvantages, one of which. isthe necessity of installinga. gas blower in addition to the usual air fan. Such an attempt is describedin-Keiths British Patent 226,298, September 25, 1923.-

vly study and research which brought forth the'present invention was directed to finding a simple means forcounteracting the building up of the pressure within-header 5 when most of the burners weresh'ut off; it resulted in installing a pressure-relief device atany convenient-point of the gasair header-5, so as to let a part of the unburned mixture vent- 'to the atn-iosphere when the pressure exceeds a predetermined amount, viz, just sullicientto supply all the burners of header simultaneously It has been usedsuccessfully and affords a complete, simple and satisfactory solution of the problemiof accident hazard in lightbake. oven burners.

The essential. structural differences that demarlr an oven. embodying: my invention from the same-oven as heretofore. commonly used, are found in the pipe' lines-that lead from the automatic-mixture control device and supply the' combustiblemixture of air and gas to the numerous burner tubes Within ihc oven.

7 vidualiburner cocks 9 are closed.

A relief valve 11 located at any convenient place ands communicating; with. header 5 V constitutes my; preferred means. for. relieving thepressure within the header. The gas may escapethrough. a, ventlpipeilt), preferably leading tohthe open air. 4 i

' The operation is as follows;

Before the oven is started all the indi- The premiXer 1 is put into operation in the usual manner.- The gas.-.and air mixture, having no access to burners 8, increases its pressure within the header 5 and thereupon a small quantity of the combustible mixture escapes into theopen air through ventpipe' 10. Relief valve Ill is adapted to open-at a' pressure that has been found by trial 'to be with inthe+pressure range of proper operation ofthecontrol device l.

One burner a time is then openedand lighted before the next is turnedon. The additional escape of gas-air mixture through the burner 8 when it is turnedon causes afurther-drop of pressure in the header 5; The relief valve 11 thereupon part ycloses and proportionally reduces the escape of mixture to the atmosphere.

Whenthemajority of=the burners 011 a header have thus been turned onand lighted, the, pressure in the header pipe 5 has dropper sufficiently to close relief va-lvell. Whenall burners on header Shavebeen lighted th'e pressure within the header becomes still=lower andthereafter there will be no automatic opening of valve 11. during the normal operatio n ofthe oven.

Pressure-in header 5 under actualioperating conditions is usually between three inches and four inches" of water column. Relief. valvell is generallyset' to. open at seven to eigh t incheswatercolumn, henceis rcpt tightwhen allibur-ners are turned on. The lossof gasv is negligible, since it does not occur except di-iringthe lighting ofthe burners, only a'few seconds for. each, and because-separate burners are never turned offgduring operations The heat control of the. oven-is atta-inech forn'ierly, by regulating the air pressure to the gas-air heade-r 5.

Possible leaks through the relief valves 11, caused bygrit or dust=onthe valve seat are prevented by providing in the vent: pipe 10- a hand-operated valve. 13, which is opened only while the-oven is beingrlighted, and isclosed during normal-operation.

Obviously-other means thancheclr valves 11 may. be. employed; for pressure-relief, and I have employed various diaphragm valves and other devices for this purpose, but find in practice that: the ordinary. type swing check valve; is entirely suitable.

The unit control system, that is, the system in i which the control devices, 1' are employed on=each:header. 5, is thus relieved of the limitations heretofore imposed upon it because of building up pressure Within the header to a degree that resulted in loss of control of the gas-air ratio and consequent inoperativeness of the gas mixing devices, especially during the starting of an oven.

With my improvement the system can be lighted by the usual bake oven gas torch or projection flame Without any danger, in cases Where no electric lighter is available.

lVhile I have shown and described the invention-as applied to a bakers tray oven, it is to be understood that it is equally applicable to any kind of gas heated oven or heater in which a. gas mixture control device or automatically controlled premixing device is employed, its function being to increase the efficiency and field of usefulness of such gas-air mixture control devices, as has been set forth herein.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In combination, a heating chamber having a plurality of burners, a header adapted to supply combustible mixtures of air and gas to said burners, a valve-controlled gas conduit connecting each burner with said header, a pressure-regulated automatic mixture control device adapted to supply gas and air in predetermined ratio to said header during normal variations of pressure therein, and independentautomatic means for relieving the pressure Within said header before said pressure can rise sufficiently to interfere With said normal operation of said mixture control device.

2. In combination, a heating chamber having a plurality of burners, "a header adapted to supply combustible mixtures of air and gas to said burners, a valve-controlled gas conduit connecting each burner With said header, a pressure-regulated automatic mixture control device adapted to supply gas and air in predetermined ratio to said header during normal variations of pres sure therein, and a relief valve communicating with and adapted to vent said header when the pressure therein rises sufficiently to interfere With said normal operation of said mixture control device.

In testimony whereof, I affix my signature.

EUGENE OSCAR ENGELS.

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