US3764070A

US3764070A - Dampening fluid pump and metering apparatus for offset printing press

Info

Publication number: US3764070A
Application number: US00268735A
Authority: US
Inventors: D Glaser
Original assignee: Didde Glaser Inc
Current assignee: DIDDE Corp
Priority date: 1972-07-03
Filing date: 1972-07-03
Publication date: 1973-10-09
Anticipated expiration: 1990-10-09
Also published as: AU5692073A; IT989692B; DE2332827A1; CA996407A; JPS4943705A; CH558718A; FR2190618A1

Abstract

Dampening fluid is successively pumped in metered, very small individual volumes by a series of pump units to sprayers which nebulize the fluid and discharge the same onto a roll of an offset printing press. Each pump unit has as its primary component a relatively small, resilient, tubular element which positively displaces a predetermined volume of fluid to its sprayer during each operating cycle by successively constricting and expanding its flow passage when a compressive force is applied and relaxed to the element in the direction of fluid flow therethrough. A bubble-releasing and guiding channel in each element is open along its length to the flow passage of the element and has an entry at the inlet end of the element configured to avoid the formation of a ledge or the like upon which bubbles could collect and thereby expand and contract during operation of the element to appreciably affect the volume of fluid displaced by the element. Individual lever arm control assemblies for the pumping elements of the units are provided with adjustable limit stops to permit metering of the fluid from each element independently of all others.

Description

United States Patent [191 Glaser Oct. 9, 1973 [21] Appl. No.: 268,735

Primary ExaminerAllen N. Knowles Assistant Examiner-Gene A. Church Attorney-Schmidt, Johnson, Hovey 8; Williams [57] ABSTRACT Dampening fluid is successively pumped in metered, very small individual volumes by a series of pump units to sprayers which nebulize the fluid and discharge the same onto a roll of an offset printing press. Each pump unit has as its primary component a relatively small, resilient, tubular element which positively displaces a predetermined volume of fluid to its sprayer during each operating cycle by successively constricting and expanding its flow passage when a compressive force is applied and relaxed to the element in the direction of fluid flow therethrough. A bubble-releasing and guiding channel in each element is open along its length to the flow passage of the element andhas an entry at the inlet end of the element configured to avoid the formation of a ledge or the like upon which bubbles could collect and thereby expand and contract during operation of the element to appreciably affect the volume of fluid displaced by the element. Individual lever arm control assemblies for the pumping elements of the units are provided with adjustable limit stops to permit metering of the fluid from each element independently of all others.

25 Claims, 9 Drawing Figures Patented Oct. 9, 1973 3,764,070

2 fjhuntrzqilmud,

Patented Oct. 9, 1973 3,764,070

2 Sheets-Sheet 2 DAMPENING FLUID PUMP AND METERING APPARATUS FOR OFFSET PRINTING PRESS This invention relates to fluid supply apparatus which is especially suited for the pumping and metering of dampening fluid used to wet the printing plate of offset printing presses so non-printing areas will repel ink.

In an offset printing process, print quality is highly sensitive to supply of water to the system. Effective control over the quantity of water delivered to the printing plate is difficult to maintain, however, because although only very small amounts of water must be delivered to the plate, the supply must be capable of being infinitely varied to accommodate different ink densities, types of ink, total ink coverage, press speed and similar highly variable factors.

Therefore, one of the most important objects of this invention is to provide apparatus for repeatedly supplying very small yet precise volumes of dampening fluid to the rolls of an offset printing press whereby print quality may be maintained on an exceptionally high level.

Another importnat object of the instant invention is to provide apparatus as aforesaid which, although displacing only a very small volume of fluid during each operating cycle, is capable of accurate variation of even this small fluid volume so that print quality may be accurately controlled to an even greater degree.

An additional important object of the present invention is to provide dampening apparatus having a simple, positive displacement, resilient, tubular'pumping elementor plug in which a minute yet precise pumping action is effected by successive constriction and expansion of its fluid passage in a transverse direction when a compressive force is applied to the plug in the direction of fluid flow therethrough, thereby permitting accurate metering of the volume of fluid displaced by simply controlling the extent of compression and expansion of the plug.

Another important object of the present invention is the provision of pumping apparatus as aforesaid wherein the provision of a directing channel or way for bubbles at the inlet end of the passagethrough the resilient element eliminates the formation ofa ledge at such inlet end which might otherwise collect bubbles that would be subject to expansion and compression during the pumping action. If bubbles were allowed to colledt they would appreciably affect the amount of fluid displaced by the pump because of the relatively small volume of dampening liquid delivered by the apparatus during each cycle. I

An additional important object of the instant invention is to provide dampening apparatus as aforesaid, which utilizes a pneumatically powered sprayer for discharging a fine mist onto the roll or other surface to be dampened, wherein dampening fluid is delivered to the sprayer by virtue of a positive displacement, resilient pumping element, without the assistance of air pressure, so that the amount of fluid displaced during each pumping cycle may be very accurately metered by the use of mechanical, readily adjustable mechanism which controls the extent of compression and expansion of the element.

A further important object of the invention is to provide dampening apparatus as set forth above having a series of sprayers and pumping elements therefor, each of which is provided with a non-complex, yet highly accurate control assembly which allows compression and expansion of each element to be individually controlled independently of all other elements, whereby to provide local control of dampening fluid application across the full width of the roll or surface being dampened.

Another important object of the instant invention is the provision of such a control assembly for each pumping element which not only affords precise calibration for accurate regulation of the fluid displaced by each element, but, in addition, is designed for convenient and rapid installation and removal in order to provide access to the corresonding pumping elements for service or replacement thereof.

In the drawings:

FIG. 1 is an essentially schematic view of the pumping and metering apparatus of the present invention shown in conjunction with rolls of an offset printing press;

FIG. 2 is an enlarged, fragmentary and elevational view of the appratus;

FIG. 3 is an enlarged, fragmentary plan view of apparatus;

FIG. 4 is a plan view similar to FIG. 3 with the apparatus rotated ninety degrees from its orientation of FIG. 3;

FIG. 5 is an enlarged, fragmentary cross-sectional view of the apparatus taken along line 5-5 of FIG. 4;

FIG. 6 is an enlarged, fragmentary cross-sectional view through the sprayer head of the apparatus taken along line 6-6 of FIG. 5;

FIG. 7 is an enlarged, detail view of an individual pump unit of the apparatus, showing the piston thereof fully extended;

FIG. 8 is a cross-sectional view through the unit taken along line 8-8 of FIG. 7; and

FIG. 9 is an enlarged, detail view of the pumping unit similar to FIG. 7, but with the piston thereof forced into the unit to compress the resilient pumping element thereof.

The apparatus 10 is shown in FIG. 1 in its normal inclined disposition for spraying dampening fluid onto the rolls of an offset printing press. Apparatus 10 is mounted directly on the press and may be disposed to direct a mist of the damping fluid onto a vibrator roll 12 of the press which ultimately transfers the fluid to theplate cylinder 14 via an intermediate form roll 16. Ink may be supplied to plate cylinder 14 by a distributor roll 18, a second vibrator roll 20, and a pair of form rolls 22. If desired, a small intermediate transfer roll 24 may be provided between form rolls l6 and 22 in order to supply a small quantity of ink to roll 12, such that spray from apparatus 10 is actually applied to the surface of ink film on roll 12 before the fluid is transferred to plate cylinder 14.

Apparatus 10 includes a main elongated, rectangular head 26 having a series of sprayers 28 spaced longitudinally along head 26. A longitudinally extending air line 30 (FIG. 6) formed internally of head 26 has an external fitting 32 (FIGS. 3 and 4) which is adapted for connection to a source of pressurized air (not shown). An annular inlet 34 for each sprayer 28 communicates line 30 with the nozzle 36 of each sprayer 28, and a fluid receiving bore 38 in head 26 for each sprayer 28 communicates with nozzle 36 and houses a reciprocable, spring-located cleaning pin 40.

A plurality of spaced apart dividing plates 42 are secured to head 26 along the length of the latter to define individual bays which contain the means for supplying fluid to each of the sprayers 28. Within each bay is a pump unit 44 forming a part of apparatus 10, having a pump cylinder 46 which is partially received by head 26. Each cylinder 46 has an elongated internal chamber which is closed at one end by an end wall 48 having an outlet port 50 therein which communicates with the corresponding bore 38 via a short line 52. A stationary abutment block 54 lies against the end wall 48 within the chamber of cylinder 46, and has a counterbored outlet 56 therein aligned with port 50 which has a check valve 58 biased by a coil spring 60 away from port 50. The diameter of outlet 56 in the area of the valve 58 is such that fluid may pass around the periphery of valve 58 for flow through outlet 56 toward port 50.

Also contained within the chamber of cylinder 46 is an elongated cylindrical, resilient, pumping element or plug 62 having a central bore or passage 64 extending longitudinally therethrough. Passage 64 is smaller in diameter than the counterbored area of outlet 56, and the head of valve 58 is coneshaped such that valve 58 is biased into the outlet end of passage 64 by spring 60 to normally close passage 64. The opposite inlet end of passage 64 is provided with a directing channel or way 66 which leads from the inlet end of passage 64 toward the outlet end thereof, but terminatesshort of outlet 56. Channel 66 progressively diminishes in size as outlet 56 is approached and, as seen in FIG. 8, channel 66 tangentially intersects passage 64 on opposite lateral sides thereof.

Also normally housed within cylinder 46 of each pump unit 44 is a reciprocable piston 68 forming a part of mechanism 70 for manipulating pumping element 62. A counter-bored inlet 72 in piston 68 communicates with passage 64 and has a check valve 74 normally biased into sealing engagement with an O-ring 76 by a coil spring 78. The head of valve 74 is coneshaped to form a tight seal with O-ring 76 when valve 74 is seated thereagainst, but the periphery of valve 74 is not in tight engagement with the proximal counterbored area of inlet 72 so that fluid can, therefore, escape around valve 74 when the latter is unseated from O- ring 76. The counterbored area of inlet 72 is of greater diameter than passage 64 such that the inlet end of the latter is encircled by the corresponding end of inlet 72. Note, however, that the entrance to channel 66 extends, transversely of passage 64, along the interface between piston 68 and plug 62 from within the dimensional limits of the counter-bored area of inlet 72 to outside of the same whereby to eliminate the existence of a ledge or the like or plug 62 at this location. Inlet 72 is coupled via a short, flexible line 80 to a supply line 82 common to all of the units 44 and coupled with a source of dampening fluid (not shown).

Mechanism 70 for operating each pump unit 44 includes, in addition to each piston 68, a common drive shaft 84 hournaled by bearings in the plates 42 for rotation by a motor and chain assembly 86 supported by a large plate 88 at one end of head 26. A series of eccentrics 90 are affixed to shaft 84, there being one eccentric 90 between each adjacent pair of plates 42, and a control assembly 92 is provided for each unit 44 for transmitting driving power from the corresponding eccentric 90 to the corresponding piston 68. The main component of each control assembly 92 is a swingable lever arm 94 pivoted intermediate its ends by an external fulcrum shaft 96 which projects from the adjacent plate 42. Each arm 94 has a rocker 98 thereon disposed below fulcrum 96 which bears against piston 68 during operation and has a suitable opening for clearing the short, flexible line 80. The upper end of each arm 94 is provided with a follower bolt 100 whice is threadably received by arm 94 for adjustment toward and away from eccentric 90, there being a locking nut 102 provided on bolt 100 for retaining the latter in any one of a number of selected positions.

A bar 104 extending across the plates 42 is tied to the latter and to plate 88 and threadably carries a series of lower adjusting screws 106, one for each arm 94, for controlling the limits of swinging of the corresponding arms 94 to thereby control the length of stroke of the corresponding pistons 68. The innermost end of each limit screw 106 is engageable with a flat, impact area 108 on the lowermost end of arm 94 during swinging of the latter to thereby determine its limits. As shwon best in FIG. 5, an enlarged, indicia-bearing poriion 1 10 may be provided on each limit screw 106 for cooperating with a suitable pointer 112 or equivalent structure on bar 104 for visually indicating the length of stroke which has been selected for piston 68 upon actuation of apparatus 10.

OPERATION As shown in FIG. 1, apparatus 10 is normally inclined at an attitude of 45 so that dampening fluid supplied to sprayers 28 is pumped uphill, thereby minimizing the formation of bubbles within the various flow lines and passages leading to sprayers 28. Assuming, for purposes of illustration, that apparatus 10 is initially in the condition illustrated by FIGS. 5 and 7, actuation of the motor and chain assembly 86 causes drive shaft 84 to simultaneously rotate all of the eccentrics 90. As each eccentric rotates from its FIG. 5 position with the follower bolt bearing thereagainst, its corresponding arm 94 is swung in a counterclockwise direction viewing FIG. 5 as the end of arm 94 forces piston 68 inwardly against plug 62. The rocking connection between rocker 98 and the outer face of piston 68 permits longitudinal movement of piston 68 at this time, while arm 94 swings in its arcuate path of travel.

Inward movement of piston 68 toward its position of FIG. 9 causes the inlet valve 74 to seat firmly against O-ring 76 and thereby preclude the movement of fluid in either direction through inlet 72. However, because abutment block 54 prevents movement of plug 62 in the direction of fluid flow through passage 64 and because cylinder 46 precludes outward expansion of plug 62 transversely of such direction of fluid flow, passage 64 is forced to constrict intermediate its ends and thereby force any fluid contained therewithin against outlet valve 58. Thus, as shown in FIG. 9, valve 58 is pushed out of its seating relationship with the outlet end of passage 64 to allow fluid within the latter to exit around valve 58, through outlet 56, port 50 and into bore 38 by way of line 52. The volume of fluid thus displaced travels through bore 38 .and into nozzle 36 of sprayer 28 where it is nebulized by air flowing into the latter from the annular inlet 34 for issuance as a fine mist onto the vibrator roll 12, as shown in FIG. 1.

As shaft 84 then continues its rotation, the arms 94 are allowed to return to their initial positions, each swinging in a clockwise direction as their compressed plug 62 seeks to return to its normal, uncompressed condition. As this expansion stroke of the piston 68 takes place, outlet valve 58 is returned to its sealing engagement with passage 64 by virtue of spring 60 and the vacuum created within passage 64. Simultaneously, inlet valve 74 is unseated from O-ring 76 by the vacuum created within passage 64 to thereby allow a volume of fluid to flow past O-ring 76 and around valve 74 into passage 64 in preparation for the next compresion stroke of piston 68. When piston 68 reaches its limit of extension, determined either by the throw of eccentric 90 or the selected setting for adjustable limit screw 106, the loading of passage 64 with fluid ceases. At this time, the components are again disposed as shown in FIGS. 5 and 7 in preparation for the next comprssion stroke of piston 68.

By way of example, it is contemplated that each piston 68 may have a stroke of from zero to 0.025 inches with a normal stroke (depending upon the particular ink conditions at hand) being approximately 0.005 inches. The diameter of each passage 64 is preferably from five-eighths to seven-sixteenths inches. Accordingly, it can readily be seen that the volume of fluid pumped by each plug 62 during each pulse or cycle is extremely small so that only a fine mist is discharged to the press system as opposed to a high volume, heavy spray. The unique design and mode of operation of plugs 62 permit such small quantities to be displaced without an attendant sacrifice in the degree of precision required for quality printing.

The bubble channel or way 66 of each plug 62 plays an important role in the displacement of consistently uniform amounts of fluid to the corresponding sprayer 28, such role being especially significant because of the small volume of fluid ejected by plugs 62. To this end, the presence of one or more bubles trapped between inlet and

outlet valves

74 and 58, respectively, during each operating cycle would appreciably affect the volume of fluid displaced as the bubbles expanded and contracted along with plug 62. Because of the attitude of apparatus 10, bubbles 'within the system move along the upper reaches of

lines

80, 82 and inlet 72 and would normally become trapped against the outside of plug 62 adjacent the inlet end of passage 64 because of the decreased diameter of the latter with respect to inlet 72. However, bubble channel 66 eliminates the existence of any collecting ledge on plug v62 for the bubbles such that the same are directed back into passage 64 for flow therethrough with their corresponding volume of fluid without appreciably affecting the true volume of fluid dispensed. Without channel 66, bubbles could collect over a prolonged period of operation and thereby have a significant effect on the amount of fluid displaced, and hence on the quality of printing performed by the press.

The provision of the adjustable limit screw 106, with its indicia portion 110 and the adjustable follower 100 for each pumpunit 44, permits local control of the volume of fluid sprayed on the roll 12 at all points across the width thereof. Initially, in order to properly calibrate theflcontrol assemblies 92, the limit screws 106 may be rotated to their full of position corresponding to 0" on indicia portion 110 which causes their corresponding pistons 68 to be pushed to the full extent within their corresponding pump cylinders 46. By then setting the follower bolt 100 for only extremely light engagement with their corresponding eccentrics 90 during rotation of the latter, no dampening fluid will be pumped to any of the sprayers 28. Then, by backing off selected limit screws 106 an amount desired depending upon the volume of spray required for that particular location on roll 12, fluid will be pumped to the selected sprayers 28 as the plugs 62 are successively compressed and relaxed by their corresponding pistons 68. In this manner, the control assemblies 92 may be accurately calibrated and certain of the sprayers 28 may be redneered completely inoperable, while still others are displacing their full volumes of fluid.

It should also be appreciated that the nature of each control assembly 92 contributes to its ease of installation and removal. By virtue of the fact that the fulcrum shaft 96 for each assembly 92 is disposed exteriorly of its arm 94, the latter may be easily removed by loosening bolt and screw 106, removing line 80, and pulling arm 94 free from fulcrum 96 in either a downward or upward direction. Access is thereby easily gained to the pumping plug 62 for service or replacement thereof as required.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent is: 1. In positive displacement fluid supply apparatus:

a resilient pumping element having a fluid passage extending therethrough;

retaining structure precluding movement of the element in the direction of fluid flow through said passage and precluding outward expansion of the element transversely of said direction of fluid flow; and

mechanism for successively compressing and relaxing said element in said direction of fluid flow to thereby transversely constrict and expand said passage for pumping a metered volume of fluid therethrough.

2. In appararatus as claimed in claim 1, wherein said structure includes a stationary abutment against the element at one end of said passage and having a fluid outlet, said mechanism including a pistion reciprocable against the element at the opposite end of said passage and having a fluid inlet.

3. In apparatus as claimed in claim 2, wherein said structure further includes a housing receiving said element, said piston and said abutment.

4. In apparatus as claimed in claim 2, wherein said piston is provided with a valve for said inlet operable to close the latter during compression of the element by said piston and to open the inlet during relaxation of said element by the piston.

5. In apparatus as claimed in claim 4, wherein said abutment is provided with a valve for said outlet operable to open thelatter during compression of the element by said piston and to close the outlet during relaxation of the element by said piston.

6. In apparatus as claimed in claim 1, wherein said passage has an inlet end, said element being provided with a bubble way open to said inlet end of the passage for preventing the collection of bubbles on said element externally of said passage.

7. In apparatus as claimed in claim 6, wherein said passage has an outlet end, said way extending alongside said passage in open communication therewith toward said outlet end and terminating short of the latter.

8. In apparatus as claimed in claim 7, wherein said way progressively decreases in size and as said outlet end is approached.

9. In apparatus as claimed in claim 6, wherein said way tangentially intersects said passage on opposite sides of the latter at its inlet end.

10. In appratus as claimed in claim 6, wherein said mechanism includes a reciprocable piston having a fluid inlet for said passage of greater cross-sectional size than said inlet end of the passage, said way extending, transversely of said passage, at least to the dimen-. sional limit of said inlet.

11. In apparatus as claimed in claim 1, wherein is provided a pneumatically-powered sprayer communicating with said passage for receiving and nebulizing the metered volume of fluid displaced by said element.

12. In apparatus as claimed in claim 1, wherein said mechanism includes a reciprocable piston, drive means for operating the piston, and a control assembly between said driven means and the pistion for varying the stroke of the latter to thereby regulate the volume of fluid displaced by said element during each operating cycle.

13. In apparatus as claimed in claim 12, wherein said assembly includes a lever arm receiving power adjacent one end thereof from said drive means and transmitting said power adjacent its opposite end to said piston.

14. In apparatus as claimed in claim 13, wherein said assembly further includes a variable limit stop for said arm.

15. In apparatus as claimed in claim 14, wherein said limit stop is disposed for engagement with said arm adjacent said opposite end thereof.

16. In apparatus as claimed in claim 13, wherein said drive means includes an eccentric, said assembly further including a variable follower for said eccentric on said arm adjacent said one end thereof.

'17. In apparatus as claimed in claim 13, wherein said arm is provided with a power-transmitting rocker adjacent said opposite end thereof bearing against said piston during actuation of said arm.

18. In apparatus as claiemd in claim 13, wherein said arm is provided with a fulcrum disposed externally thereof against which the arm rides during actuation, whereby the arm may be readily removed from the fulcrum.

19. In apparatus as claimed in claim 1, wherein is provided a pneumatically-powered sprayer communicating with said passage for receiving and nebulizing fluid displaced by said element, said structure including a housing about said element and a stationary abutment at one end of said passage having a fluid outlet and a valve in said outlet, said mechanism including a reciprocable piston at the opposite end of said passage having a fluid inlet and a valve in said inlet, said mechanism further including a drive for said piston, swingable lever arm between said drive and the piston for transmitting power from said drive to the piston, and an adjustable limit stop for said arm for varying the stroke of said piston to thereby control the volume of fluid displaced by said element to said sprayer, said inlet valve in the piston and said outlet valve in the abutment being operable to close and open respectively during the compression stroke of said piston and to open and close respectively during the expansion stroke of the piston, said element being provided with a bubble way extending along said passage in open communication therewith from said opposite end of the passage toward saidone end thereof for directing bubbles into and through said passage.

20. In apparatus as claimed in claim 1, wherein is provided a plurality of said elements, each provided with a said retaining structure and each having a pneumaticallypowered sprayer associated therewith for receiving displaced fluid from the corresponding element and nebulizing the same.

21. In apparatus as claimed in claim 20, wherein said mechanism includes a reciprocable piston for each element, a drive shaft common to all of said pistons for operationg the same, and a control assembly for each piston between said shaft and the corresponding piston for varying the length of its stroke independently of the other pistons to thereby permit individual regulation of the fluid displaced to said sprayers.

22. In apparatus as claimed in claim 21, wherein each of said assemblies includes a lever arm receiving power adjacent one end thereof from said shaft and transmitting said power adjacent its opposite end to its corresponding piston, each of said assemblies further including an adjustable limit stop for controlling the swinging of its corresponding arm.

23. In apparatus for repeatedly delivering small metered volumes of dampening fluid to a printing system:

'a plurality of neumatically powered sprayers;

a series of individual pump units corresponding in number to said sprayers for physically displacing fluid thereto for nebulization thereby.

each of said units including a compressible, resilient pumping element having a passage therethrough for moving fluid to the corresponding sprayer in response to the application of repeated compressive forces to the element;

drive means for supplying power for compression to the pump units; and

a control assembly for each unit respectively operable to selectively vary the extent of compression and expansion of the corresponding pumping element independently of the other elements whereby to vary the volume of fluid delivered to the corresponding sprayer.

24. In apparatus as claimed in claim 23, wherein said drive means includes a shaft common to said units, each of said assemblies including a swingable lever arm between the shaft and the corresponding element and a variable limit stop for said arm. 7

25. In apparatus as claimed in claim 23, wherein each of said units is provided with structure precluding both movement of its element in the direction of fluid flow therethrough and outward expansion of the element transversely of the direction of fluid flow when a compressive forceis applied to the element in said flow direction whereby to constrict said passage and force fluid from the same.

Claims

1. In positive displacement fluid supply apparatus: a resilient pumping element having a fluid passage extending therethrough; retaining structure precluding movement of the element in the direction of fluid flow through said passage and precluding outward expansion of the element transversely of said direction of fluid flow; and mechanism for successively compressing and relaxing said element in said direction of fluid flow to thereby transversely constrict and expand said passage for pumping a metered volume of fluid therethrough.

2. In apparatus as claimed in claim 1, wherein said structure includes a stationary abutment against the element at one end of said passage and having a fluid outlet, said mechanism including a piston reciprocable against the element at the opposite end of said passage and having a fluid inlet.

5. In apparatus as claimed in claim 4, wherein said abutment is provided with a valve for said outlet operable to open the latter during compression of the element by said piston and to close the outlet during relaxation of the element by said piston.

10. In appratus as claimed in claim 6, wherein said mechanism includes a reciprocable piston having a fluid inlet for said passage of greater cross-sectional size than said inlet end of the passage, said way extending, transversely of said passage, at least to the dimensional limit of said inlet.

12. In apparatus as claimed in claim 1, wherein said mechanism includes a reciprocable piston, drive means for operating the piston, and a control assembly between said drive means and the piston for varying the stroke of the latter to thereby regulate the volume of fluid displaced by said element during each operating cycle.

17. In apparatus as claimed in claim 13, wherein said arm is provided with a power-transmitting rocker adjacent said opposite end thereof bearing against said piston during actuation of said arm.

18. In apparatus as claimed in claim 13, wherein said arm is provided with a fulcrum disposed externally thereof against which the arm rides during actuation, whereby the arm may be readily removed from the fulcrum.

19. In apparatus as claimed in claim 1, wherein is provided a pneumatically-powered sprayer communicating with said passage for receiving and nebulizing fluid displaced by said element, said structure including a housing about said element and a stationary abutment at one end of said passage having a fluid outlet and a valve in said outlet, said mechanism including a reciprocable piston at the opposite end of said passage having a fluid inlet and a valve in said inlet, said mechanism further including a drive for said piston, swingable lever arm between said drive and the piston for transmitting power from said drive to the piston, and an adjustable limit stop for said arm for varying the stroke of said piston to thereby control the volume of fluid displaced by said element to said sprayer, said inlet valve in the piston and said outlet valve in the abutment being operable to close and open respectively during the compression stroke of said piston and to open and close respectively during the expansion stroke of the piston, said element being provided with a bubble way extending along said passage in open communication therewith from said opposite end of the passage toward said one end thereof for directing bubbles into and through said passage.

20. In apparatus as claimed in claim 1, wherein is provided a plurality of said elements, each provided with a said retaining structure and each having a pneumatically-powered sprayer associated therewith for receiving displaced fluid from the corresponding element and nebulizing the same.

21. In apparatus as claimed in claim 20, wherein said mechanism includes a reciprocable piston for each element, a drive shaft common to all of said pistons for operating the same, and a control assembly for each piston between said shaft and the corresponding piston for varying the length of its stroke independently of the other pistons to thereby permit individual regulation of the fluid displaced to said sprayers.

23. In apparatus for repeatedly delivering small metered volumes of dampening fluid to a printing system: a plurality of neumatically powered sprayers; a series of individual pump units corresponding in number to said sprayers for physically displacing fluid thereto for nebulization thereby, each of said units including a compressible, resilient pumping element having a passage therethrough for moving fluid to the corresponding sprayer in response to the application of repeated compressive forces to the element; drive means for supplying power for compression to the pump units; and a control assembly for each unit respectively operable to selectively vary the extent of compression and expansion of the corresponding pumping element independently of the other elements whereby to vary the volume of fluid delivered to the corresponding sprayer.

24. In apparatus as claimed in claim 23, wherein said drive means includes a shaft common to said units, each of said assemblies including a swingable lever arm between the shaft and the corresponding element and a variable limit stop for said arm.

25. In apparatus as claimed in claim 23, wherein each of said units is provided with structure precluding both movement of its element in the direction of fluid flow therethrough and outward expansion of the element transversely of the direction of fluid flow when a compressive force is applied to the element in said flow direction wherebY to constrict said passage and force fluid from the same.