US2379124A - Thermal expansion responsive control - Google Patents

Description

June 26, 1945. c. WASSON THERMAL EXPANSION RESPONSIVE CONTROL Filed July 15, 1945- UM Lawn/000 C'Wsssan 7 HI 5 I m x M m U o 9 n6 a Patentea June 26, 1945 CONTROL Wauwatosa, Wis., assig'nor eclalty Company, Milwau- Loerwood C. Wasson,

to Milwaukee Gas Sp kee, Wis, a corporation of Wisconsin Application July 15, 1943, Serial No. 494,798

3 Claims.

This invention relates to thermal expansion responsive controls of the type used toeffect closure of the safety valve of a gas. fired furnace upon extinction of the pilot light. Such controls generally comprise a bellows type expansion chamber connected with a temperature sensitive expansion bulb and arranged to actuate a controlling member in accordance with temperature changes at the bulb.

In the past, where controls of this type have been used on safety valves of gas fired furnaces, the bulb or temperature sensitive element was responsive to ambient temperature as well as the pilot flame of the gas burner so that in some instances the valve would not be released for closure even though the pilot light was extinguished. In any event the response was objectionably slow.

In other words, if the temperature in the burner chamber, i. e., the ambient temperature, is quite high, control devices of the past were slow to respond as the burner chamber temperature might be sufficently' high to hold the valve open for an appreciable time notwithstanding the extinction of the pilot flame.

It is therefore an object of this invention to provide a control device of the character described, the functioning of which is not dependent upon ambient temperature, but solely upon the temperature differential between the direct heat of the pilot flame and the ambient temperature. Hence, with the present invention, extinction of the pilot flame is quickly followed by release of the valve for closure.

In a broad general way, this invention achieves its objective through the provision of a pair of opposed bellows type expansion chamber having their movable ends connected with the latch or other member through which the controlling function is accomplished in such a way that expansion of these chambers applies opposed forces on the latch or controlling member, and through the further provision of separate temperature sensitive expansion bulbs, one connected with each of the expansion chambers, and with one of the bulbs in juxtaposition to the pilot flame and the other spaced therefrom.

Another object of this invention resides in the novel construction of the expansion chambers whereby one is substantially nested within the other to conserve space and to reduce the volume of the outer chamber.

Still another object of this invention is to provide an improved and simplified manner of constructing the temperature sensitive bulbs and connecting the same with their respective expansion chambers.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described, and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the hereindisclosed invention may be made as come within the scope of the claims.

The accompanying drawing illustrates two examples of the physical embodiment of the invention constructed in accordance with the best modes so far devised for the practical application of the principles thereof, and in which:

Figure 1 is a view in side elevation illustrating a safety valve for a gas burner equipped with a control device embodying this invention;

Figure 2 is an enlarged vertical sectional view through the valve and the control mechanism illustrating the manner in which the valve is latched open;

Figure 3 is a detail view partly in side elevation and partly in section illustrating the temperature sensitive compound bulb of the control device; and

Figure 4 is a view similar to Figure 3 illustrating a slightly modified construction for the compound bulb.

Referring now particularly tothe accompanying drawing, in which like numerals indicate like parts, the numeral 5 designates a gas burner or the like to which fuel is fed through a supply pipe 8. The supply pipe has a safety valve l incorporated therein, the valve disk 8 of which is biased to closed position by a spring 9 and adapted to be lifted to open position by a push button ill.

The body of the valve is substantially a T fitting and has the control device indicated generally by the numeral H mounted in its stem. The control device is contained with a bonnet l2 secured to the stem of the T with a fluid tight junction by a clamping nut I3.

A cup-shaped member I4, attachment of the bonnet stem of the valve body to the stem of the valve of the stem is is received in a pilot bore l5 extending up into an arm ll projecting in from the side of the bonnet. This arm 51 provides held in place by the i2, extends into the provide a guide for support for a pivotally mounted latch la, the free end of which is hook-shaped to engage in a slot N in the valve stem and hold the valve open against the force of its spring 9.

disk. The upper end Thelatch iliscontrolledbyapairoiexpansion chambers 2| and 2|, bothoi' the bellows type, the latter being nested wholly within the former. The expansion chamber 2| has its fixed or stationary end secured to the top of the bonnet as at 22 and has a cylinder 23 fixed in its movable end. The cylinder 2| provides a well in which the smaller expansion chamber 2| is received.

This smaller chamber comprises two bellows, one within the other, having a common movable end 2| fixed to the inner end of the cylinder 23. The opposite stationary ends of the two bellows oi the chamber 2| are fixed to a central duct 2| which has openings 2| leading to the interior of the small expansion chamber 2|.

A disk or other bridging member 21 fixed to the movable end of the bellows forming the chamber 2| and to the cylinder 2| is connected, as at 2|, to the pivoted latch Holes 2| in the disk 21 permit tree passage oi air, gas or other fluid into and out of the well formed by the cylinder 23 to preclude interference with expension and contraction of the chamber 2|.

The tube 2| to which the stationary or fixed end 01' the small expansion chamber is secured asvams the still eflective expansion force of takes placein the manachamber 2| quently, the contraction or the bellows 2| and 2| produce an additive eflect on quickly retract it from the slot in the valve stem.

The expansion chambers and the nected thereto may be filled with any suitable fluid medium,--air being satisfactory for the purpose to which this invention is especially directed,

stances a state of equilibrium exists between the expansion chambers 2| and 2|. The spring tension of the large outer chamber 2|, which apis flxed in relation to the stationary end of the large expansion chamber 2| and has open communication with a duct 3| which leads to and is connected with an expansion bulb 3|.

Surrounding the duct 3| is a tube or duct 32 which is likewise fixed with relation to the stationary end of the expansion chamber 2| and has open communication with the interior of this expansion chamber through ports 33. This outer duct leads to and connects with an expansion bulb 34.

It is to be observed that the annular-space between the two tubes or ducts provides a capillary passage connecting the expansion bulb 34 with the expansion chamber 2| and that the inner tube or duct provides a capillary pas sage connecting the bulb 3| with the expansion chamber 2|.

The bulbs may be arranged one within the other, as shown in Figure 3, or they may be constructed as illustrated in Figure 4.

The arrangement oi Figure 3, wherein the bulb II is insulated from ambient temperature by being enclosed within the bulb 34 upon which the pilot flame plays results in more rapid response while the construction shown in Figure 4 is preferable from the standpoint of simplified mechanical design as the telescoping juncture 35 between the bulbs 3i and 34' facilitates assembly of the unit.

With the bulb construction shown in Figure 4, the pilot flameplays on the lower bulb chamber 3| thus leaving the upper bulb chamber 3i exto the ambient temperature. However, this latter bulb 3| is sufiiciently close to the pilot flame to receive considerable heat therefrom byconduction so that it becomes heated to a substantial degree above ambient or burner chamber temperature.

While, as noted hereinbeiore, the construction shown in Figure 3 results in more rapid response than that of Figure 4, both arrangements are far superior to past practice as in each case it is the temperature differential at the two bulbs and not the ambient temperature at a single bulb that controls the release of the valve. Whether the bulb construction of Figure 3 or Figure 4 is employed, extinction of the pilot flame is iollowed by a more rapid contraction of the bellows forming the larger outer chamber is than plies an upward force on the latch in opposition to the downward force applied by the spring tension or the lighter and smaller expansion chamber 2|, eflects a resultant upward force on the latch to hold the same free from the valve stem II. In this, the spring tension of the bellows may or may not be augmented by a spring 3| depending upon the tension inherent in the bellows.

To set the mechanism in operation the pilot light is ignited so that its flame plays on the temperature sensitive bulb 34 (or it it the construction of Figure 4 is used). The fluids in the two bulbs 34 and 3| are thus expanded to eii'ect expansion of the chambers 2| and 2|.

By virtue of the higher temperature at the bulb 34 (or 34') the fluid therein is expanded to a higher pressure than in the bulb 3| (or Ii). The force of expansion of the chamber 2| thus exceeds that of the chamber 2| to impart a downward thrust on the latch This downward thrust on the latch holds its hooked end against the side of the valve stem making it potentially operative to engage in the slot i! and hold the valve open upon manual setting of the valve by depression of the push button i|.

As long as the pilot flame burns the valve is held open by the latch. Upon the extinction of the pilot flame, the bulb 3| cools more rapidly than the bulb Ii so that the force of expansion within the chamber 2| decays more rapidly than the expansion force of the chamber 2|. The rapid decadence of the expansion in the chamber 2| is additive with the relatively still prevalent expansion force 0! the chamber 2| thereby bringing about a rapid withdrawal of the latch is from the slot I9.

In this respect, as noted hereinbeiore, the tension applied on the latch by the inherent tension of the expansion chamber 2| may be augmented by the auxiliary spring 3|.

In any event, due to the opposed relationship of the expansion chambers and the diflerential in their pressure areas, release of the valve is effected within a relatively short time after extinction of the pilot light regardless 01' what the ambient (burner chamber) temperature at the bulbs may be.

From the foregoing description taken in connection with the accompanying drawing, it will be readilyapparent to those skilled in the art that this invention provides a substantial improvement in thermal expansion control devices through its elimination of dependency upon ambient temperature and the resulting rapid and positive response eflected thereby.

What I claim as my invention is:

1. In a thermal expansion responsive control of the character described, a thermal sensitive element comprising: a compound bulb having two compartments; and ducts, one within the other, for connecting the two compartments separated by a metal wall common to both so that fiuid in both compartments may be heated from the same heat source, one by direct application of heat on its compartment and the other by conduction through said common metal wall of the compound bulb with separate expansion chambers.

2. In a control device of the character described: two expansion chambers, one within the other; a compound temperature sensitive bulb having two separate compartments, one within the other so that fluid in the outer compartment may be heated by the direct application of heat on its wall, while fluid in the inner compartment is heated indirectly from the same heat source by the fluid in the outer compartment; and duct means, one within the other, for connecting each compartment with one of said expansion chambers.

3. A thermal expansion responsive control for the safety valve of a gas fired furnace for effecting closure of the safety valve upon extinction of the pilot light of the furnace comprising: a movable member operable to effect the desired controlling function; a pair of expansion chambers each having a movable end and a fixed end; means connecting the movable ends of said expansion chambers with said member so that the forces of expansion of said chambers are applied on said member, but in opposite directions; a compound temperature sensitive bulb having two fluid compartments separated from each other by a metal wall so that the temperature of the fluid in one compartment may be effected by the temperature of the fluid in the other compartment; means mounting said compound temperature sensitive element so that the direct flame of the pilot light plays on one of said compartments to directly heat the fluid therein and indirectly heat the fluid in the other compartment; and ducts, one within the other, connecting each compartment of the compound temperature sensitive bulb with one of the expansion chambers.

LOERWOOD C. WASSON.

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