US3761071A

US3761071A - Laundry folding machine with static electricity dissipating means

Info

Publication number: US3761071A
Application number: US00205913A
Authority: US
Inventors: S Behn
Original assignee: SUPER LAUNDRY MACHINERY CO Inc
Current assignee: SUPER LAUNDRY MACHINERY CO Inc
Priority date: 1971-12-08
Filing date: 1971-12-08
Publication date: 1973-09-25
Anticipated expiration: 1990-09-25

Abstract

There is provided in association with the vertically oriented endless conveyor belts of laundry folding machines one or more spray heads for directing a mist of air and water on the bottom surfaces of the bottom section of the endless conveyor belts which will ultimately become the upper laundry supporting surfaces of the belts. Each spray head has air and water inlets respectively connected to controllable air and water valves. The air and water valves are operated by an adjustable timer which cyclically opens and closes the air and water valves for limited adjustable intervals during each cycle of operation thereof. The air valve is open for a time interval each cycle which encompasses, and extends preferably beyond the beginning and end of, the interval during which the water valve is opened during each cycle.

Description

[4 1 Sept. 25, 1973 LAUNDRY lFUlLlDlNG MAUEHNE 'WllTll-ll STATE C lElLECTRlUl'lIY DllSSllPA'lllNG MEANS [75] inventor: Sheidon 11. hit, Highland Park, 111.

[73] Assignee: Super Laundry Machinery Qompany, lne, Chicago, Ill.

[22] Filed: 8, 11971 [21] Appl. No.: 205,913

[52] US. Cl 270/61 R, 38/143, 223/37,

270/62, 270/69, 317/2 R, 317/2 A, 317/2 C [51] int. U EfiSh 415/00 [58] Fieidl all Search 270/61-67, 69, 83-85;

1,766,512 6/1930 Hausmann 15/308 X Primary Examiner-Robert W. Michell Assistant Examiner-L. R. Oremland Att0meyWal1enstein, Spangenberg, l-lattis 5 7 ABSTRACT There is provided in association with the vertically oriented endless conveyor belts of laundry folding machines one or more spray heads for directing a mist of air and water on the bottom surfaces of the bottom section of the endless conveyor belts which will ultimately become the upper laundry supporting surfaces of the belts. Each spray head has air and water inlets respectively connected to controllable air and water valves. The air and water valves are operated by an adjustable timer which cyclically opens and closes the air and water valves for limited adjustable intervals during each cycle of operation thereof. The air valve is open for a time interval each cycle which encompasses, and extends preferably beyond the beginning and end of, the interval during which the water valve is opened during each cycle.

14 Claims, 7 Drawing Figures PATENTED $EP25 I975 SHEET 2 OF 2 IN VEIV TOR SHEL 0o- BBL-741v l LAUNDRY FOLDING MACHINE WITH STATIC ELECTRICITY DISSIPATING MEANS This invention relates to improvements in laundry folding equipment which eliminates the build up of excessive static electricity in the conveyor belts of such equipment and in the dried ironed laundry fed therethrough.

Laundry folding machines commonly include a series of endless ribbons or narrow belts forming a conveying system for conveying the dried pressed laundry pieces to various folding stations of the machine. The conveying belts. are commonly made of'a woven material of cotton or a'combination of cotton and synthetic plastic fibers. In a dry atmosphere, the friction occurring between the fibers of woven material like cotton and the like can generate appreciable static electricity which, if occurring in the conveying belts referred to and in the dried pressed laundry, frequently results in difficulties in folding the laundry and, in some cases, jamming of the folding machine.

It is known that static electricity can be substantially reduced or eliminated by controlling the humidity level of the air in the room in which a folding operation takes place. Also, air ionization bars and the like have been integrated into folding machines to reduce or eliminate static electricity. However, these prior methods of eliminating static electricity in laundry folding machines have left much to be desired from the standpoint of the cost and effectiveness thereof. For example, the proper control of the moisture level of the air circulating within a room in which a laundry folding operation takes place requires very specialized and costly humidity control equipment capable of handling large quantities of air circulating throughout the entire room or building involved. The use of conventional air ionization bars leaves much to be desired from the standpoint of the effectiveness thereof. For example, the positioning of the bars and ionization wires extending therefrom is critical because the ionization wires are effective only over a limited extent and in the immediate vicinity thereof.

It is, accordingly, one of the objects of the invention to provide laundry folding and conveyor apparatus which includes static electricity dissipating apparatus which effectively dissipates static electricity in the conveyor apparatus and in the laundry fed thereby and which static electricity dissipating apparatus is relatively inexpensive to manufacture. A related object of the invention is to provide static electricity dissipating apparatus as just described which can be readily installed in laundry folding machines of a variety of different types and constructions not initially designed to receive such apparatus and wherein the precise positioning thereof is not critical to the effectiveness thereof throughout the area of the laundry folding machine where it is located.

Another object of the invention is to provide laundry static electricity dissipating apparatus as described where moisture in just sufficient quantities to dissipate the static electricity can be applied, despite variations in atmospheric and other conditions, so that the desirably dry laundry is not unduly wetted thereby.

In the most advantageous form of the invention, there is mounted in the vicinity of the conveyor belts of a laundry folding machine one or more spraying heads which spray a mist or fog of moisture beneath the conveyor belts so that a mist or fog of moisture is sprayed on the bottom surfaces of the conveyor belts which ultimately contact and support the laundry pieces in the laundry folding machine. It is very important that the conveyor belts be merely moisturized rather than wetted, for the wetting of these conveyor belts would undesirably wet the laundry which would make the laundry folding operation more difficult and cause dust to more readily adhere thereto. To keep a very close control over the amount of moisture which is sprayed, valve means which control the flow of water and air to the water inlets of the sprayer heads are cyclically operated by a timer so that these valve means are open for only limited intervals in each cycle of operation thereof, and the duration of these intervals is variable, preferably along with the volume of the mist which is sprayed during these variable intervals.

In accordance with an important specific aspect of the invention, to prevent the spraying or dripping of excessive moisture or water, the flow of air through the air valve means is terminatd each cycle after termination of the flow of water to the sprayer heads to prevent any dripping or accumulation of water in the sprayer heads. Also, most preferably, the flow of air through the air valve means is initiated before the flow of water through the water valve means so that there is no risk that water flow through the spray heads will start before the air flow therethrough.

In the most preferred form of the invention, the sprayer heads, the valve means and the timer for intermittently cyclically operating the valve means form a single integral mountable unit which can be conveniently attached to a portion of the frame of a laundry folding machine at a position beneath the conveyor belt thereof.

The above and other objects and features of the invention will be understood upon making reference to the specification to follow the claims and the drawings wherein:

FIG. I is a perspective viewof a laundry folding machine incorporating the static electricity dissipating unit of the invention;

FIG. 2 is an enlarged front elevational view of the static electricity dissipating unit shown in FIG. 1 applying a mist or fog of moisture to the bottom surfaces of the laundry conveyor belts of the laundry folding machine of FIG. 11; I

FIG. 3 is a top plan view of the static electricity dissipating unit shown in FIG. 2;

FIG. 4 is an enlarged plan view of the control box portion of the static electricity dissipating unit shown in FIGS. 1-3;

FIG. 5 is a view of the interior of the timer used in the static electricity dissipating unit of FIGS. 1-3 to control the feeding of water and air through the spray heads thereof;

FIG. 6 is an end elevational view of the cam apparatus forming a part of the timer shown in FIG. 5; and

FIG. 7 is an electrical circuit diagram for controlling the various solenoids associated with the static electricity dissipating unit of FIGS. 1-5.

Refer now more particularly to FIG. 1 which illustrates the more or less conventional laundry folding machine 2 having the conventional vertically oriented fabric conveyor ribbons or belts 3 which receive laundry pieces like sheets, towels, and the like and convey the same to folding apparatus (not shown) in the interior of the machine 2. The narrow conveyor belts 3 have upper sections 3a on the upper surfaces of which the laundry pieces to be folded are placed manually or otherwise, and bottom sections 3b (F IG. 2). As viewed in FIG. 1, the upper sections 3a of the narrow conveyor belts 3 move continuously in the direction indicated by the arrows 5 and the bottom section 3b of the narrow conveyor belts, therefore, move in the direction indicated by the arrow 5'. The narrow belts 3 extend around and are guided by various metal guide rollers (not shown) in a conventional manner.

In accordance with the present invention, a static electricity dissipating unit generally indicated by reference numeral 4 is positioned adjacent the conveyor belts 3. It is most preferred (although not necessary in accordance with the broadest aspects of the invention) that the static electricity dissipating unit 4 be positioned below the bottom sections of the narrow conveyor belts 3, and to this end the unit 4 is shown mounted by a bracket 8 in the space 6 below the front end portions of the narrow conveyor belts 3. In a manner to be described, the static electricity dissipating unit 4 directs a mist or fog of moisture against the bottom surfaces of the bottom sections 3b of the conveyor belts 3 which moistens without substantially wetting the bottom surfaces of the conveyor belt which become the laundry supporting surfaces upon reaching the upper sections of the paths of the conveyor belts. Dried, pressed laundry conveyed by the upper sections of the conveyor belts 3 will, therefore, remain in a dried, pressed state, and any static electricity generated therein or in the fibers of the material out of which the conveyor belts 3 are made are dissipated or grounded through the metal rollers which engage the conveyor belts. As will appear, the simplicity, compactness and unitary nature of the static electricity dissipating unit 4 is such that it can be manufactured at a very modest cost and can be readily mounted and adjusted to direct the necessary amount of mist or fog of moisture upon the conveyor belts for practically all types of laundry folding machines and under practically all atmospheric conditions.

Refer now more particularly to FIGS. 2 and 3 which best illustrates the construction of the preferred exemplary form of the present invention. The unit 4 as illustrated includes a pair of spray heads 12-12 located at opposite ends of the unit 4 which spray heads may be any one of a number of commercially available spray heads for providing a mist comprising particles of water or the like distributed in an air stream and directed in fan-shaped patterns 13-13. The spray heads 12-12 have nozzles 12a-12a which are directed in an upward direction toward one another in the illustrated form of the invention. The direction of the stream of air and water particles can be adjusted by rotating knurled rings 12b-12b' respectively on the bodies of the sprayer head 12-12. The volume of the spray directed through the spray heads 12-12 may be adjusted by rotating knurled knobs l2c-l2c projecting from the bodies of the spray heads. The spray heads have water inlet fittings l2e-l2e and air inlet fittings 12f-ll2f into which water and air are respectively directed. The inlet fittings l2e-12e are respectively connected to solenoid operated valves 14-14, in turn, connected by conduits 16-16 to a T-joint fitting 17 connecting with a common water inlet pipe 18 leading to a commercial water supply or an air pressurized housing filled with water. The solenoid operated valves 4 14-14 include solenoids 14a-14a' (FIG. 7) which, when energized, open passages through the valves 14-14 enabling the passage of water from the conduits 16-16 to the water inlet fittings 12e-l2e of the spray heads 12-12.

The air inlet fittings 12f-12f of the spray heads 12-12 are respectively connected by conduits 20-20 to a T-fitting 21 having a common inlet connected to the outlet 220 of a solenoid operated air valve 22. The air valve 22 includes a solenoid 22a (FIG. 7) which, when energized, effects the opening of a passageway through the air valve to connect an inlet 22b of the air valve 22 to the outlet 220 of the valve. An inlet conduit 24 extends between the inlet 22b of the air valve 22 and an air pressure control unit 25 which includes an air pressure gauge 26 and a control knob 28 for adjusting the pressure of the air in the conduit 24. An inlet conduit 27 extending from a source of air under pressure extends to the inlet of the pressure control unit 25.

The solenoids 14a-l4a of the water control 14-14 are connected by conductors contained within conduits 30-30 extending between the water control valves 14-14 and a control box 32 located at the center of the unit 4. Similarly, conductors extending from the solenoid 22a pass within a conduit 31 extending between the air control valve 22 and the control box 32.

The control box 32 has a pivotally mounted door 32a which can be opened to expose electrical control apparatus contained therein. This electrical control apparatus includes an adjustable timer unit 33 to be described which cyclically opens the valves 14-14 over adjustable limited time intervals during each cycle of opera tion thereof. The control box 32 also houses various conductors forming the control circuit 35 shown in FIG. 7 and to be described later on in the specification.

Projecting from the control box 32 is a pilot light 38 (FIG. 4) to indicate the energization of the control circuit 35, a main ON-OFF control lever 34 controlling the opening and closing of a single-pole, single-throw switch 34a (FIG. 7) and an override control lever 36 controlling the operation of a double-pole, doublethrow override switch unit having switches 36a and 36b (FIG. 7). When the control lever 34 is moved from its OFF to its ON position, a source of power, which may be a conventional volt A.C. current power line connected to the control box through a power cord 39, energizes power buses 40-41 (FIG. 7) of the control circuit 35. When the control lever 36 is in a position identified by the letters INT., the air control solenoid 22a and the water control solenoids 14a-I4a are intermittently opened and closed under control of

microswitches

37a and 39a forming part of the timer unit 33. If the control lever 36 is in its position identified by the letters CONT, these microswitches are shunted by the aforementioned override switches 36a and 36b, so that the solenoids 14a, 14a and 22a are continuously energized, thereby effecting the continuous feeding of water and air to the spray heads 12-12.

The timer unit 33 includes an electric motor 42 connected between the power busses 39-41. The timer motor has an output shaft 44 (FIG. 5) which continuously rotates. The output shaft 44 carries a water control cam assembly 46 and an air control cam assembly 48. These cam assemblies respectively include pairs 46a-46b and 48a-48b of relatively movable cam members.

Refer now to H6. 45 which illustrates the cam assembly 43, it being understood that the cam assembly is identically constructed. The cam members 4418b respectively have pairs Eda-hr! and Ebb-5% of diammetrically disposed cylindrical peripheral circular segments fibril-513a and Ebb-541th each of which encompasses a relatively small arc, for example, an arc in the neighborhood of 90. The relative angle of the corresponding pairs of segments cam members lba-48b, 5 011-3027 and 5tla-50b can be varied between positions where they occupy the same 90 arc and positions where they occupy different arcs which overlap to varying degrees by adjustment of the relative positions of the cam member d-dbb in any suitable way, such as by means of a locking screw 51 which anchors one of these cam members to the timer motor output shaft M. Riding on the respective peripheries of the cam assemblies teas are follower members 37-39 which control the opening and closing of the aforementioned microswitches 3711-390. The cam follower members 37-39 are of a width to ride upon both of the corresponding peripheral segments of the pairs of cam members tea-dub and Aha-48b. Thus when the

cam follower member

37 or 39 rides upon either of the corresponding peripheral segments of either of the associated cam members, the associated

microswitch

37a or 39a is closed until the cam follower member drops into the space between these peripheral segments.

As shown in FIG. 7, the air control solenoid 22a is connected between one of the busses dll and one of the terminals of the microswitch 39a whose opposite terminal is connected to the power bus 410. The water control solenoids I la-Ma are connected in parallel with one another and between the power bus 41 and one of the terminals of the microswitch 37a whose other terminal is connected to the power bus 4t). it is thus apparent that the water control solenoids Ida-Ma and the air control solenoid 22a are cyclically energized for intervals determined by the degree to which the corresponding peripheral segments of the associated cam members den-dob or aha-4% are out of alignment. There is thus provided a fine control over the intervals of each cycle of operation of the timer unit 33 during which the air and water control solenoids are operative to pass air and water respectively to the spray heads 1l2-ll2.

in accordance with an important aspect of the present invention, the timer unit cam assemblies are adjusted so that the intervals during which the air solenoid 22a is energized (i.e. is in its valve-opening position) encompasses and extends at least beyond one of the ends of the corresponding interval during which the water control solenoid is energized (i.e. is in its valve opening position). Most advantageously, the intervals during which the air solenoid 22a is in its valve opening condition encompasses and extends beyond both of the limits of the intervals during which the water control solenoids are in their water valve opening conditions. Thus, the air solenoid 22a is energized in advance of the time the water controlled solenoids Eda-14a are energized, and are de-energized after the water control solenoids +1 1 -Ma' are de-energized. With such a sequence of operation of the air and water control valves, the spray heads will always be initially free of water when air is applied thereto so the water will always be applied in a well aerated form, that is in the form of a mist or fog where, as in the case of steam, the surfaces of the conveyor belts will be moisturized but unwetted.

Since the flow of water to the spray heads 12-12 is terminated before the flow of air thereto is terminated, water does not accumulate within or drip from the spray heads. Such assumulation of water could result in the initial blowing of undesired quantities of unaerated water upon the conveyor belts to cause an undesired degree of wetting thereof.

Although the relative quantities and pressures of the air and water (or other gas or static electricity dissipating liquid) useful in the practice of the present invention may vary widely to provide the desired mist or fog sprayed upon the conveyor belts, in one exemplary form of the invention, the air pressure applied to the spray heads was lbs. per square inch and the water pressure applied to the spray head was 30 lbs. per square inch.

It should be apparent from a description of the invention given above that it provides a very effective means for dissipating static electricity in practically any laundry folding machines by addition thereof of a unit which can be manufactured and installed at a very modest cost. Moreover, the static electricity dissipating means of the invention is reliable and permits a very close control over the amount of moisture applied to the conveyor belts so the conveyor belts are not unduly wetted, and so just the right amount of moisture is supplied thereto, to effect a proper dissipation of static electricity in the conveyor belts and in the laundry pieces carried thereby.

it should be understood that numerous modifications may be made in the most preferred form of the invention described above without deviating from th broader aspects thereof.

I claim:

11-. in combination, laundry folding apparatus f0; folding dried pressed laundry; laundry conveying means including moving endless belt means for carrying'fthe dried prossed laundry to said laundry folding apparatus; and static electricity dissipating means including liquid spray head means adjacent to the path of travel of a portion of said endless belt means and oriented for spraying a mist of conductive liquid selectively onto the same, so the mist is not sprayed onto the dried laundry carried thereby, and means for feeding a mixture of a gas and a conductive liquid to said spray head means to form said mist of conductive liquid directed upon a portion of said endless belt means passing thereby, which mist substantially moistens said endless belt means to a point which dissipates static electricity but does not substantially wet the side of said endless belt means which engages the laundry to be folded.

2. In combination, laundry folding apparatus for folding dried pressed laundry; dried pressed laundry conveying means for carrying the laundry to said laundry folding apparatus; and static electricity dissipating means for dissipating static electricity in the dried laundry on said conveying means comprising liquid spraying apparatus for spraying a mist of a conductive liquid upon said conveying means which does not wet the side of the conveying means contacting the dried laundry so as to adversely affect the dried condition of the laundry but which moistens the conveying means to a sufficiently modest degree as to dissipate static electrictiy thereat, said spraying apparatus including spray head means oriented to spray a mist of conductive liquid selectively onto the conveying means so the mist is not sprayed onto the dried laundry carried thereby, and

control means for cyclically feeding a mixture of gas and a conductive liquid through said spray head means and including means for adjusting the intervals of time within each cycle during which the misture is sprayed, to control the average quantity of the conductive liquid mist sprayed upon said conveying means, the speed of said conveyor means and the frequency of the intervals during which said conductive liquid mist is sprayed being in asynchronous relation so that substantially all portions of the conveyor means which are to engage the dried laundry have said mist of conductive liquid applied thereto.

3. The combination of claim 2 wherein said conveyor means are vertically facing endless belt means having an upper section upon the top surface of which the dried laundry is carried and a bottom section, said spray head means applying said mist of conductive liquid to the bottom surfaces of said bottom section of said endless belt means which becomes the upper laundry contacting and supporting surface when moved along the upper section of the endless belt means.

4. The combination of claim 2 wherein said sprayer apparatus includes a source of water, a source of air, controllable valve means between said sources of water and air and said spray head means to form a mist of water when the water and air are allowed to pass through said spray head means, said control means includes timer means for intermittently opening said controllable valve means during said adjustable intervals of time.

5. The combination of claim 4 wherein said timer means includes electrical switch means which are intermittently operated, said controllable valve means including electric solenoid means which, when operated, open the valve means, the switch means of said timer means operating said electric solenoid means, and there is provided manually operable override, switch means shunting the switch means of said timer means to override the operation of the switch means of said timer means for continuously operating said solenoid means, continuously to operate said valve means in an open position where the spray continuously issues from said spray head means.

6. The combination of claim 2 wherein there is provided means for controlling the quantity of said gas and conductive liquid flowing through said spray head means during said adjustable intervals of time.

7. In combination, laundry folding apparatus for folding dried, pressed laundry; conveying means for conveying the dried pressed laundry to the folding apparatus; static electricity'dissipating means for dissipating static electricity in the dried laundry on said conveying means comprising spray head means including water inlet means, air inlet means and outlet means from which issues a mist comprising a mixture of air and fine water particles from said water and air inlet means which is applied to said conveying means, a source of water under pressure, a source of air under pressure, controllable water valve means connected between said water source and said water inlet means of said spray head means, controllable air valve means connected between said source of air under pressure and said air inlet means of said spray head means, first control means for cyclically opening said water valve means for a limited time interval during each cycle of operation thereof, second control means for cyclically opening said air valve means for a limited time interval during each cycle of operation thereof, the length of each interval during which said air valve means is open each cycle encompassing, and extending beyond at least one of the ends of, each of the intervals during which the water valve means is open each cycle.

8. The combination of claim 7 wherein each time interval during which said air valve means is open is initiated before the beginning of each interval during which the water valve means is open, to prevent the initial dripping of water from said spray head means.

9. The combination of claim 7 wherein the end of each interval during which the air valve means is open occurs after the termination of the interval during which the water valve means is open, to eliminate any accumulation of water in the spray head means.

10. The combination of claim 7 wherein the length of each of the intervals during which the air valve is open extends beyond both the beginning and the end of the corresponding interval during which the water valve means is open, to prevent the dripping of water from said spray head means and the flowing of accumulated water from spray head means.

11. The combination of claim 7 wherein said first and second control means is adjustable to vary the duration of the intervals during which the water and air valve means are opened.

12. The combination of claim 11 wherein there is provided means for adjusting the quantity of air and water which are forced through said spray head means during the time said air and water valve means are opened.

13. The combination of claim 7 wherein said conveyor means comprises inlet belt means made of a woven material in which static electricity accumulates on the same when in a dry state.

14. The combination of claim 7 wherein said conveyor means are vertically oriented endless belt means having an upper section upon the top surface of which the dried laundry is carried and a bottom section, said spray head means applying said mist of conductive liquid to the bottom surfaces of said bottom section of said endless belt means which becomes the upper laundry contacting and supporting surface when moved along the upper section of the endless belt means.

Claims

1. In combination, laundry folding apparatus for folding dried pressed laundry; laundry conveying means including moving endless belt means for carrying the dried prossed laundry to said laundry folding apparatus; and static electricity dissipating means including liquid spray head means adjacent to the path of travel of a portion of said endless belt means and oriented for spraying a mist of conductive liquid selectively onto the same, so the mist is not sprayed onto the dried laundry carried thereby, and means for feeding a mixture of a gas and a conductive liquid to said spray head means to form said mist of conductive liquid directed upon a portion of said endless belt means passing thereby, which mist substantially moistens said endless belt means to a point which dissipates static electricity but does not substantially wet the side of said endless belt means which engages the laundry to be folded.

2. In combination, laundry folding apparatus for folding dried pressed laundry; dried pressed laundry conveying means for carrying the laundry to said laundry folding apparatus; and static electricity dissipating means for dissipating static electricity in the dried laundry on said conveying means comprising liquid spraying apparatus for spraying a mist of a conductive liquid upon said conveying means which does not wet the side of the conveying means contacting the dried laundry so as to adversely affect the dried condition of the laundry but which moistens the conveying means to a sufficiently modest degree as to dissipate static electrictiy thereat, said spraying apparatus including spray head means oriented to spray a mist of conductive liquid selectively onto the conveying means so the mist is not sprayed onto the dried laundry carried thereby, and control means for cyclically feeding a mixture of gas and a conductive liquid through said spray head means and including means for adjusting the intervals of time within each cycle during which the misture is sprayed, to control the average quantity of the conductive liquid mist sprayed upon said conveying means, the speed of said conveyor means and the frequency of the intervals during which said conductive liquid mist is sprayed being in asynchronous relation so that substantially all portions of the conveyor means which are to engage the dried laundry have said mist of conductive liquid applied thereto.

7. In combination, laundry folding apparatus for folding dried, pressed laundry; conveying means for conveying the dried pressed laundry to the folding apparatus; static electricity dissipating means for dissipating static electricity in the dried laundry on said conveying means comprising spray head means including water inlet means, air inlet means and outlet means from which issues a mist comprising a mixture of air and fine water particles from said water and air inlet means which is applied to said conveying means, a source of water under pressure, a source of air under pressure, controllable water valve means connected between said water source and said water inlet means of said spray head means, controllable air valve means connected between said source of air under pressure and said air inlet means of said spray head means, first control means for cyclically opening said water valve means for a limited time interval during each cycle of operation thereof, second control means for cyclically opening said air valve means for a limited time interval during each cycle of operation thereof, the length of each interval during which said air valve means is open each cycle encompassing, and extending beyond at least one of the ends of, each of the intervals during which the water valve means is open each cycle.