US2233047A - Automatic combustion control - Google Patents

Description

Feb. 25, 1941'. R El BRESSLER '2,233,047'

AUTOMATIC coMBUs'rIoN CONTROL Filed Deo. l0, 1958 f-f. THFRMOST? 412, 2! d* n [TR/INFORMER 23) a? A i Off/PLO?? C C 22 Bw? n n Q7 46 a5 Wi 252 j Il' u any Y .l ft2/z5,

Patented Feb. 25, 1941` i PATENT oFFlcE 2,233,047 AUTOMATIC COMBUSTION CONTROL Robert E. Bressler, Oregon, Ill., assigner to Kol- Master Corporation, Oregon, Ill., a corporation of Illinois Application December 10, 1938, Serial No. 244,986

l11 Claims.

This invention relates to improvements in automatic combustion controlsand it consists of the mattersvhereinafter described and more particularly pointed out in the appended c1aims. The improved control is herein illustrated and will be hereinl described as used in connection with a stoker for feeding solid fuel such as coal to a fuel bed and for supplying the air necessary to support combustion.

ln stoker fed furnaces, the amount of coalv that will be burned by a certain volume of air varies materially with the condition of the fuell bed. Also, the amount of coal that will be fed by the stoker, as when the screw or other mechanism is operating .at a certain rate will vary materially y with several different factors. One of these factors is the amount of coal in the hopper which causes a different quantity thereof to be fed to the screw or other feed mechanism. The reason therefor is that the depth of thecoal over the screw or other mechanism varies, and much more coal will be fed by a full hopper than by one only half full.

The size of coal that is being supplied to the 'f stoker will also make a large variation in the With a given setting 'of the damper controlling the volume of air supplied by the blower to the fuel bed, which damper may be on either the inlet or discharge side of the blower, a certain velocity and a certain pressure will be generated or established in the duct leading to the windboX of the Stoker and :in the windbox itself dependent upon the particular resistance which that bed causes. Therefore, the slightest change in fuel bed resistance, due to the change indepth ofthe fuel bed, will change both the pressure and the velocity. With the fan damper setting remaining the same and with a decrease in fuel bed depth, the velocity increases and the pressure decreases and with -an increase in fuel bed depth, the velocity decreases and the pressure increases. The relation between velocity and pressure in the duct is that the velocity Varies as a function of the square of the pressure.

With the fuel bed remaining at the same depth, l

(ci. 11o-fit1) but with a change in the setting of the damper to provide a greater volume of air, there will be' an increase in both pressure and velocity in the.

duct and windbox, but the ratio of pressure to velocity will remain constant and will still be on the ratio of the square as above. mentioned.

Thus, as long as the control means which is used to maintain the fuel bed, is on the same ratio as the ratio of pressure to velocity, the change in the volume of air as controlled by the setting of the damper will make no diierence in the operation of the stoker but Wllmaintain the fuel bed at the same depth independent of the setting of the damper and consequent volume and pressure and resistance encountered.

The general object of the present'invention is to provide an automatic combustion control which makes use vof the fact that the relation between the velocity and the pressure of the air passing through the air duct for delivery to the fuel bed to support combustion thereof, is a constant relation varying as a function of the square of the pressure caused by fuel bed resistance.

A further object of the invention is to provide an automatic combustion control which, though simple in construction for low cost of manufacture, maintains a constant fuel bed depth within narrow limitsl and supplies that amount of air to the bed for the morst eiiicient combustion thereof.

The above-mentioned objects of the invention, aswell as others, together with the several advantages thereof, will more fully appear as the specification proceeds.

In the drawing:

Fig. 1 is a diagrammatic view of the preferred form of the invention, in connection with a Stoker for controlling the operation thereof.

Fig. 2 is a longitudinal vertical sectional view on a somewhat enlarged scale through the burner or retort end of the Stoker as taken on the line 2--2 of Fig. 1. Y

Fig. 3 is a transverse vertical sectional view through a part oi the Stoker as taken on' the line .3 3 or Fis. a.

Referring now in detail to the accompanying drawing, 8 indicates as a whole a conventional Stoker, including a fuel hopper l, a burner or retort 1, and a coal feed conduit or tube 8 leading from the hopper to the burner. In the conf..

Sil

The feed screw 9 is rotated by a driving mechanism enclosed in a casing I2 `and this mechanism is driven through a suitable speed reducing mechanism I3 from a motor I4. Associated with the coal feed conduit 8 is an air delivery duct |5. Said duct is formed at,one end to provide a wind box or chamber IE in which the burner 1 is disposed in a manner whereby air in said chamber passes into the burner and up through the fuel bed therein to support combustion. The other end of the duct I is operatively connected to a blower I1 having an inlet side damper I8 by means of which the volume of air entering the blower may be controlled. If desired, a damper may be placed in the duct I5 beyond the discharge side of the blower instead of where described. Preferably a second and smaller motor I9 is employed to drive the blower. By the use of the two separate motors as mentioned, it is possible to burn fuel at a lower current cost. One side of one motor is connected to one side of the other motor as by a line 2D.

The improved control as a whole includes a plurality of control elements, namely a temperature responsive element such as a thermostat 2| employed in the area or space to be heated and a limit control 22, usually placed in the bonnet of Ia hot air furnace when the stcker is employed with such a furnace. On a holt water furnace the limit control is clamped to a pipe leading away from the boiler thereof. The control further includes a transformer 23, a relay 24 with a 110 v. coil, a second relay 25 with a 24 v. coil, a motor driven time switch 2B with a A10 minute interval contacter and a 60 minute interval contacter, a circuit breaker 21, which serves as an overload protection for the coal feed motor I4, and a switch 2B operable in response to the pressure and velocity of the air in the duct I 5.

The transformer 23 serves only to reduce lthe voltage in the 4circuit of the room thermostat 2| so that small wire may be used therefor to simplify installation. The relay 24 with the 110 v. coil controls the `coal feed motor I4, the motor being energized when said relay is closed and deenergized when said relay is open. The relay 25 with the 24 v. coil is the starting device for the blower motor I9 and also for theY coal feed motor when the relay 24 is closed.

The time switch 28 serves two purposes. A part thereof closes once every 10 minutes and remains closed for a period of about a half a minulte or less. This causes the coal feed motor to start and operate once every 10 minutes when the thermostat 2| is calling for heat independent of all other controls, except when the circuit breaker 21 is open or the limit control 22 is off. When the circuit breaker is open or when the limit control is off, said motor will not run. The other part of the interval contactor operates as a. hold fire control, closing once each hour for about a minute, causing operation of the stoker for that period except when the limit control is off.

The switch 28 is in the nature of a casing 29 mounted upon a part of the air duct I5. This casing which is open at the bottom, covers an A vane or target 33 is secured to the bottom end of said arm so as to be disposed substantially centrally in the duct I5. In said vane is an opening 33a (see Fig. 3), the purpose of which will later appear. The arm 32 is connected to the diaphragm 3| by a link 34 and that end of the linkassociated with the diaphragm is connected thereto by means of nuts 35 ,threaded on said end of the link. By means of said nuts, the position of the arm 32 and its vane 33 may be carefully adjusted. The arm 32 carries a contact 36 normally in engagement with respect to a contact 31 secured in that end 0f the casing 29 opposite the diaphragm. Conductors 38-39 lead away from said contacts out through suitable insulation in a part of the casing 29 for connection in circuit, as will later appear. It is pointed out at this time that the relation between the area of the vane or target 33 and the area of the diaphragm 3|, taken in conjunction with the amount of leverage for the vane or target andl for the diaphragm is on the same ratio as the relation of pressure and velocity of the air delivered to the fuel bed due to the fuel bed resistance. Such a relation of target and diaphragm provides a satisfactory operation of the control.

4U and 4| indicate respectively the main current conductors leading from a source of electrical energy or supply. Secondary conductors 42-43 connect one of the windings of the transformer 23 with said main conductors. The main conductor is connected to one side of the limit control 22 and the other side of said control is connected to one side of the coil of the relay 24 by a line 44 in which is provided a contact 45. One side of the other coil of the transformer 23 is connected to one side of the coil of the relay 25 by a line 46 and the other' side of the transformer coil is connected to one side of fthe thermostat 2| by a line 41. The other side of the thermostat is connected by a line 48 with the other side of the coil of the relay 25.

Associated with the relay 24 is a contact 49 connected by a line leading to the other side of the coal feed motor I4, the overload circuit breaker 21 being incorporated in said line. The relays 24-25 each includes a normally open armature 24a- 25a respectively, which when the coil of said relay are energized, are caused to engage the associated contacts 49 and 45 before mentioned, `The armature 24a is connected in circuit to the main conductor 4I while the armature 25a is `connected by a line 5| to the line 2D connecting one side of both motors I4 and I9 together. A branch line 4Ia connects the other side of the blower motor I9 with the main conductor 4I.

The time switch 26 includes a pair of fixed contacts 52--52a respectively and a second pair of contacts 53-53a respectively, periodically movable toward and away from the first mentioned ones. As shown herein, said switch includes a motor 54 that drives a shaft 55 which carries cams 56 and 51 respectively. In the rotation of the shaft 55, these cams so engage the contacts 53-53a as to cause 'them to periodically engage and disengage said contacts 52-52a. The cam 5S is of -such formation that the contacts 53-52 engage once every 10 minutes for about 1/2 a minute. If desired, the cam 56 could be made with a formation as to cause said contaots 52-53 to engage once every 5 minutes for a half a minute. The cam 51 is of such formation that the contacts 53a---52al engage once every 60 minutes for about a minute.

The mainconductor 4l leads to the contact 52 While the contact 53 is connected by a line 58 Ito the other side of the coil of the 11D v. relay 24. The contact 52a is connected by aline 43a with the line 48 and the contact 53a is connected by a line 41a with the line 41.` IIhus the contacts 52a-53a are in the low voltage circuit and in parallel with the thermostat. The conductors or lines 38-39 associated with the pressure and velocity actuated switch 28 previously mentioned, are connected to the lines 50 and 58 respectively as shown. t

In the operation of the control system, assume that the limit control is functioning within its temperature range as a closed switch. Also assume that the contacts 52--53 and 52m- 53a of the timer switch 26 are out of engagement and that the thermostat 2l is in its o condition wherein it is not calling for heat. 'At this time, both motors i4 and I9 are deenergized and the pressure in the windbox I5 approximates atmospheric pressure so that the contacts 36 and 31 of the pressure and velocity responsive switch 28 are engaged.

Now assume that the temperature in the space to be heated is such that the thermostat 2l calls for heat and therefore closes. As the thermostat is closed, current iiows through the secondary of the transformer 23, line 41, thermostat 2i, line 48 coil of relay 25 line 4E, thus completing the circuit for the transformer.

This energizes the coil of the relay 25 to attract its armature 25a, which engages the .contact 45. This establishes a circuit from line 40, limit control 22, contact 45, armature 25a to line 5E, through bridge 28 and the blower motor I9, line 4la. to line 4l, and starts the blower into operation. Also if the relay 24 has its amature 24a engaged with the contact 49, current ows as before to bridge 2li, through the motor I4, line 5G (and circuit breaker 21 therein which is closed) to contact 43, armature 24a to line 4i, thus energizing the fuel or coal feed motor It.

The relay coil 24 will be held in its energized condition with its armature 24a in engagement with the contact 49 soy long as the contacts 36-31 of the switch 28 are engaged, due to an. air velocity condition in the windbox I5 which predominates over the action of the air pressure condition in the casing 29 upon the diaphragm 3i. With the contacts 36-31 thus engaged, current flows from the line 46, through the limit control 22, line 44, relay coil 24, line 58, line 39, contacts 31-36, line 38, line 66, contact 48, armature 24a, to line 4I. This holds the circuit for the relay coil 24 closed.

With the stoker in operation, fuel is being fed at its maximum rate td the retort or burner .1 and air under pressure is being delivered to said burner or retort to support combustion. With this maximum feed of fuel, which is at a rate higher than the maximum burning rate, the fuelv bed increases in depth so as to produce a resistance to the passage of air therethrough, which in turn manifests itself in an increase in pressure in the chamber I 6 and duct I5 and a decrease in velocity of the air in the latter. Conversely due to the burning of the fuel bed between feeding periods, the depth of the bed decreases with a corresponding decrease in pressure and an increase in velocity of the air blast in the duct I5. When the pressure in the duct I5 increases, the velocity decreases and when the pressure therein decreases, the velocity increases. i

When the fuel bed is at the desired depth, the resistance presented td the air passing therethrough builds up a pressure in the duct I5 to be felt in the casing 28 so that said pressure operating upon the diaphragm from the inside of the casing with attendant velocity decrease, holds the arm 32 (through the' link 34) in a position where the contact 36 is out of engagement with the contact 31. This opens the circuit for the coil of the relay 24, so that the armature 24a disengages the contact 49 and opens the circuit for the fuel feed motor so that it stops the feeding ofV fuel to the retort. A this time, however, the blower motor I9 remains energized to drive the blower to provide the air necessary to support combustion of the fuel bed because the circuit therefor is being maintained from line 40, limit control 22, line 44 and contact 46, armature 25a (which is still engaged with the contact 45 under the iniluence oi the thermostat 2l) line 5I, bridge 20, line 4|a to line di.

When the fuel bed burns down, the pressure in the duct I5 decreases and the velocity increases. Thus the air moving through the duct to the burner or retort actuates the vane 33 to swing the arm 32 clockwise as viewed in Fig. 2 so that the contact 36 is moved into engagement with the contact 31. The engagement ci the contacts 36-31 at this time, however, will not energize the relay coil 24 because there is no circuit to the line 4I except when said coil is energized. Thus, even though the pressure in the windbox has decreased and thev velocity has increased, the coal feed motor I4 will not operate vuntil the relay coil is energized by another circuit as will soon appear.

It is pointed out at this time that by reason of the opening 33a. in the vane 33, eddy currents and vacuous conditions behind the vane are minimized to such an extent as to be practically eliminated. Thus the vane is sensitive and accurate in operation for its intended purpose.

Closing of the circuit for the relay coil 2t is l accomplished periodically by the constantly operating time switch 28. Every fewl minutes, the cam 56 of said switch will cause engagement of the contacts 52-53 so that current will flow from the line 48 through limit control 22, line 44, coil of relay 24, line 58, contacts 53--52 to line 4i so that said relay becomes energized. This causes the armature 24a to engage the contact 49, permitting the switch 28 through the contacts 38--31 to maintain current iow through the relay coil and energizing the coal feed motor as before described.

When the thermostat 2i is satisfied with temperature conditions, it opens the relay 25 and the Stoker' stops. When the thermostat still calls for heat and the fuel bed is of such depth as to produce a resistance to the passage' of air therethrough, this raises the pressure in the duct I5 and casing 29`to one which so operates upon the diaphragm 3l asto keep the contacts 31-36 separated against the action of the velocity of the air in the ductv I5 tending to close them. Thus-. it is apparent that the pressure of the air in the duct operates to disengage or separate the contacts 36--31 and that the velocity of said air operates to engage-or close said contacts. However, under the conditions above set forth, when the contacts 36-31 are separated by reason of the action ofthe pressure on the diaphragm 3l, the coal feed motor circuit is open but the blower circuit is still closed to provide that air necessary to support combustion. So long as the room thermostat calls for heat, the blower motor remains energized to provide that air necessary for combustion between coal feeding operations as demanded by the thermostat.

In the operation of the time switch 26, it functions through the cam 51, to engage the contacts 5MP-53a, which forms the hold fire control of ythe system. As these contacts are in parallel with the thermostat 2I, the engagement thereof produces the same function as the closing of the thermostat 2l when it calls for heat. Should the limit control be in its off condition, current from the line 40 cannot pass to any of the before mentioned parts so that the stoker will not operate under that condition.

It is important that the fuel feeding motor I4 should start whenever the thermostat or the hold fire control (as caused by the engagement of the contacts 52a--53a) is calling for operation and this is accomplished as follows: When the relay coil 25 is in its deenergized condition, current will flow from line 40, control 22, line 44, relay coil 24, line 58, line 39, contacts 36-31 (which because fan motor I9 is not operating will be in the engaged condition) line 38, circuit breaker 2l, line 50, motor I4, bridge 20, motor I9, line 41a to line 4I, completing the circuit to energize the relay coil 24 and hold it in its closed position until the thermostat 2I or the hold fire control calls for stoker operation. This circuit is possible because there is no resistance to the very small amount of current passed .by the relay coil 24 due to the resistance of both motors I4 and I9 when not in operation and this small amount of current is not sufficient to cause operation of said motors.

When the relay coil 24 becomes energized and operable, as before described, due to energication of the relay coil 25 and the engagement of its armature 25a with the Contact 45, and the starting of the motor I9 to build up a resistance in the last described circuit, then the control of the fuel feed motor I4 will be effected or come i through the time switch 26 and the switch 28.

It is apparent that the fuel feed motor I4 is started and stopped to control the fuel bed depth instead of varying the feeding of fuel as in most conventional stokers.

When the stoker is started into operation after a standby period, if the fuel bed is thin, the velocity of the air operating upon the vane 33 holds the contacts 36-31 in engagement so that the stoker is caused to feed coal at its maximum rate until the fuel bed has been brought up to its proper depth. At said depth, the resistance to air passage through the fuel bed builds up a pressure and causes a reduction in velocity, to operate upon the diaphragm 3I to disengage said contacts to stop the coal feed motor. Thereafter the coal feed motor is only energized to an extent which will maintain that depth of bed and to supply coal in accordance with the amount being burned with the volume of air being suppied and which volume is controlled by the damper I8.

It is, therefore, apparent that by reason of the construction described, that due tothe pressure in the duct operating to disengage the contacts 36-31 and the velocity of the air in the duct, tending to hold said contactsl in engagement, the arm 32, and its vane 33 seeks a balance which corresponds to the desired fuel bed depth within narrow limits.

By reason of the fact that the relation between area of the target 33 and the area of the diaphragm 3|, taken in conjunction with the leverage for said target and diaphragm, have the approximate ratio as the relation of the pressure of the air in the duct has to the velocity, as before mentioned, a change in the setting of the fan damper will not interfere with the satisfactory operation of the stoker, but will maintain the fuel bed at the same depth independent of the setting of the fan damper and consequent volume and pressure and resistance encountered.

It is pointed out at this time that the amount of fuel which can be consumed after the switch 28 functions to separate the contacts 36--31 and previous to the time that the time switch 26 will start another cycle of a feeding of fuel to the fuel bed, will not be sufficient to change the depth of the bed to any appreciable extent. However, it is desirable that the rate of fuel feed be higher than the rate of combustion of fuel. The reason therefor is in order to provide against coking of the fuel in the retort, to vary the depth of the fuel somewhat at each operation so that the amount of fuel being fed is sufficient to break up the fuel bed each time fuel is being fed.11 Thus, there is a material agitation of the fuel bed at periodic intervals in a manner that causes the l feeding of the coal at a rate faster than the caking or coking possibilities of the coal in the retort in order to eliminate the possibility of such cakng or coking. The comparatively short time which is permitted by the switch 28 after the closing or engagement of the contacts SI5-3l is not sufficient to disturb the correct functioning of the Stoker nor is the amount of coal fed by the operation of the switch 26, should the switch 28 not be calling for fuel be sufficient to disrupt Y the operation of the stoker.

When the thermostat is satisfied with heat, it opens the lcircuit to the relay coil 25 so that the stoker stops. In the continued operation of the switch 26, the contacts 52-53 are periodically engaged so that the coil of relay 24 becomes energized, the armature 24a engaging the contact 49, after which coil of relay 24 is maintained energized, holding armature 24a engaged with contact 49 through contactsI 36-31 as previously described, without starting the stoker into operation because the circuit for the blower motor is open as before described, at which time it is impossible to start the fuel feeding motor I4 for reasons before mentioned, even though the contacts 36-31 are engaged.

While in describing the invention I have referred in detail to the form, arrangement and construction of the various parts thereof, the same is to be considered only in the illustrative sense so that I do not Wish to be limited thereto except as may be specifically set forth in the appended claims.

I claim as my invention:

l. In combination with means providing a re.

tort adapted to support a fuel bed, means for feeding fuel to said retort to build up the bed to a desired depth, means for supplying air under pressure and velocity to the fuel `bed to support the combustion thereof, said bed offering av resistance to the passage of the air therethrough so that the pressure and the velocity thereof varies with the depth of the fuel bed, means dependent upon the demand for heat for starting said air delivering Imeans into operation,

means operating periodically at predetermined timed intervals for starting said fuel feeding means into operation when said means dependent upon the demand for heat is holding said air supplying means in operation, for controlling the operation of said fuel feeding means, said means including a member having one movement for holding said fuel feeding means in operation when started bysaid periodically operating means and having a second movement for stopping said fuel feeding means, means actuated by a relatively high velocity of the supplied air operatively con'- nected to said member for imparting one movement thereto, and means actuated by a relatively high pressure of the supplied air and operatively connected to said member for imparting the other of said movements thereto for stopping said fuel feeding means.

2. In combination with means providing a retort adapted lto support a fuel bed, means for feeding fuel to said retort to build up the bed to a desired depth, means for supplying air under pressure and velocity to Ithe fuel bed to support the combustion thereof, said bed offering a resistance to the passage of the air therethrough so that the pressure and the velocity thereof varies with the depth of the fuel bed, means dependent upon the demand for heat for starting said air delivering means into operation, means operating periodically at timed intervals for starting the fuel feeding means into operation when said means dependent upon the demand for heat is holding said air supplying means in operation, means for controlling the operation of said fuel feeding means, said means including a member having one movement for holding said fuel feeding means in operation when started by said periodically operating means and having a second movement for stopping said fuel feeding means, means actuated by a relatively high velocity of the supplied lair and operatively connected to said member for impartingrone of said movements thereto, means actuated by a relatively high pressure of the supplied air and operatively connected to said member for imparting the other movement thereto for stopping the operation of said fuel feeding means, and means operable independently of said fuel bed resistance for varying the pressure and the. velocity of the supplied air.

3. In combination with means providing a retort adapted to support a fuel bed, means for feeding fuel to said retort to build up the bed to a desired depth, a motor for driving said fuel feeding means, a circuit for said motor, means for supplying air under pressure and velocity to the fuel bed to support combustion thereof, said bed oering a resistance to the passage of the air therethrough so that the pressure and the velocity thereof varies with the depth of the fuel bed, means dependent upon the demand for heat for starting said air supplying means into operation, means operating periodically at predetermined timed intervals for closing said circuit and starting said motor into operation when said means dependent upon the demand for heat is holding said air supplying means in operation, a switch in said circuit and including a member movable to open or close said circuit, means actui ated by a relatively high velocity of the supplied air and connected to said member for holding said switch and said circuit closed so that said motor remains in operation when started by said periodically operating means, and means actuated by a relatively high pressure of the supplied air and connected to said member for opening said switch for stopping said motor.

4. In combination with means providing a retort adapted to support a fuel bed, means for l feeding fuel to said retort to build up the bed to a desired depth, a motor for driving said -fuel feeding means, a circuit for said motor, means including a duct for supplying air under pressure and velocity to the fuel bed to support combustion thereof said bed offering a resistance to the passage of the air therethrough so that the pressure and the velocity thereof varies with the depth of the fuel bed, means dependent upon the demand for heat for starting said air supplying means into operation, means operating periodically `at timed intervals for closing said circuit and starting said motor into operation when said means dependent upon the demand for heat is holding said air supplying means-in operation, a casing opening into said duct and including a diaphragm, a switch in Ysaid circuit arranged in said casing and including a pivotal lever with a part ldisposed in said duct and another part disposed in said casing. ay member arranged in said duct and connected to said part of said lever disposed in said duct and operable by a relatively high velocity of the supplied air through saidlever to hold said circuit closed and said motor in operation when started by said periodicaily operating means, and means for con.. necting said lever to said diaphragm so that said diaphragm operates at a, relatively high pressure through said lever to open said switch and said circuit for stopping said motor.

5. In combination with means providing a retort adapted to support a fuel bed.,- rneans for feeding fuel to said retort to build up the bed to a desired depth, a motor for driving said fuei feeding means, a, circuit forsaid motor, means for supplying air under pressure and velocity to the fuel bed to support combustion thereof, said bed offering a resistance to the passage of the air therethrough so that the pressure and the velocity thereof varies with the depth of the fuel bed, means dependent upon the demand for heat for starting said air supplying means into operation, means operating periodically at predetermined timed intervals through said circuit for closing the latter and starting said.' motor into operation, a switch in said Icircuit for controlling the same, means for actuating said switch to open and close said circuit and including a lever and a member operatively connected thereto and actuated by a relatively high velocity of the -supplied air for holding said switch and said circuit closed for maintaining said motor' in operation when started by said periodically operating means, said last mentioned means also including a second member operatively connected to the lever and actuated by a relatively high pressure of the supplied air for opening said switch and said circuit for stopping said motor.

6. In combination witif means providing a retort adapted to support a fuel bed, means for yfeeding fuel to said retort td build up the bed-to a desired depth, a motor or driving said fuel feeding means, a circuit or' said motor, means for supplying air under pressure and velocity to the fuel bed to support combustion thereof, said bed offering a resistance to the passage of the air therethrough so that the pressure and the velocity thereof varies with the depth of the fuel bed, means dependent upon the demand for heat for starting said air supplying means into operation, means operating periodically at predetermined timed intervals through said circuit for closing the latter and starting said motor into operation, a switch in said circuit for controlling the same, a casing in communication with said air supplying means and one wall of which is constituted by a diaphragm, said switch which is disposed in said casing including a lever, a member connected to said lever and actuated by a high velocity of the supplied air for holding said switch and said circuit closed for maintaining said motor in operation when started by said periodically operating means, and means connecting said lever to said diaphragm so that under a high pressure of the supplied air said lever opens said switch and said circuit and stops said motor.

7. In combination with means providing a retort adapted to support a fuel bed, means for feeding fuel to said retort to build up the bed to a desired depth, a motor for driving said fuel feeding means, `a circuit for said motor, means for supplying air under pressure and velocity to the fuel bed to support combustion thereof, means dependent upon the demand for heat for starting said air supplying means into operation, said bed oilering a resistance to the passage of the air therethrough so that the pressure and the velocity thereof varies with the depth of the fuel bed, means providing a casing in communication with the supplied air, a switch in said casing and embodied in said circuit and including pivotally hung lever to which is connected a member having a part disposed in the path of said supplied air so as to be responsive to a relatively high velocity of the supplied air to hold said switch closed to maintain said circuit, other means forming part of said casing associated with the switch and connected to said lever and responsive to a relatively high pressure of the supplied air for opening said switch to break said circuit and stop said motor, and means operating periodically at predetermined timed intervals for startlng said motor independently of said switch when said means dependentl upon the demand for heat is holding said air supplying means in operation.

8. In a Stoker construction, the combination of an air duct for the stolcer, a switch including a fixed contact and a movable contact, a

casing enclosing said switch and in communication with said duct, a member operatively connected to the movable contact and having a part arranged in said duct so as to be responsive to a relatively high velocity of the air in the duct for holding said contacts engaged, and means responsive to a relatively high pressure of the air in the casing and connected to said member connected to said movable contact for disengaging said contacts. i

9. In a stoker construction, the combination4 of an air duct for the Stoker, a switch including a fixed contact and a movable contact, a casing enclosing said switch and in communication with said duct, a member operatively connected to the movable contact and having a part arranged in said duct so as to be responsive to a relatively high velocity of the .air in the duct for holding said contacts engaged, and means responsive to a relatively high pressure `of the air in the casing and connected to said member connected to said movable contact for disengaglng said contacts, said member in said duct being formed with an opening therein so that a portion of the air in said duct may pass through said mem ber to substantially prevent the formation of a vacuous condition on that side of said member that is opposed to the direction of movement of the supplied air,

l0. In combination with means providing a retort adapted to support a fuel bed, means for feeding fuel to said retort to build up the b ed to the desired depth, a motor for driving said fuel feeding means, a blower and a duct connecting the same to the retort for supplying air under pressure and velocity to the fuel bed to support combustion thereof and which bed offers a re sistance to the supplied air so that the pressure and the velocity thereof varies with the depth of said fuel bed, a second motor for driving the blower, a circuit for both motors and a switch associated therewith, means dependent upon the demand for heat for closing said circuit to start said blower motor, means operating periodically at predetermined timed intervals for starting said first mentioned motor into operation, a switch for controlling said first mentioned motor and including a fixed contact and a movable contact, a pivoted member carrying said movable contact, means responsive to 'a relatively high velocity of the air supplied by the blower and connected to said lever for holding said first mentioned motor in operation after being started by said periodically operating means, and means responsive to a relatively high pressure of the air supplied by the blower and connected to said pivoted member for opening said switch stopping said first mentioned motor.

l1. In a. stoker construction, the combination of an air duct for the stoker having an opening therein, a casing supported on said duct above said opening, a switch in said camng comprising a xed contact and a movable contact, a member for carrying said movable contact and having a pivotal connection at one end in said casing and having a part extending through said opening into said duct, a velocity sensitive means carried by said part of said member in said duct, a pressure sensitive diaphragm forming one wall of said casing, and a link pivotally connecting said diaphragm and an upper` part of said member together.

ROBERT E. BRESSLER.

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