US3840158A

US3840158A - Modular applicator system

Info

Publication number: US3840158A
Application number: US00298263A
Authority: US
Inventors: R Baker; S Tamny
Original assignee: Nordson Corp
Current assignee: Nordson Corp
Priority date: 1972-10-17
Filing date: 1972-10-17
Publication date: 1974-10-08
Anticipated expiration: 1991-10-08
Also published as: IT995894B; DE2349268A1; DE2349268C2; JPS5915035B2; FR2203293A5; JPS49101475A; CH571364A5; JPS57136968A; JPS5810150B2; CA984134A; GB1452613A

Abstract

A fluid operated system of modular guns for dispensing liquids such as molten adhesives. The system includes multiple guns in the form of readily removable cylindrical modules that mount in apertures of a fixed service block or manifold. The service block and guns have passages which register when the system is assembled whereby the guns may be easily removed from the fixed service block and replaced without disconnecting any fluid lines or other service equipment. Each gun module is secured to the service module by a connector located at one end of the gun module so that it is free for relatively unlimited thermal expansion and contraction without damage to either module.

Description

United States Patent Baker et a1. Oct. 8, 1974 1 MODULAR APPLICATOR SYSTEM 619,143 4/1961 Canada 113/315 Inventors: Robert G. Baker, Avon; Simon Z. 701,73, 12/1953 Great Brltaln 239/551 Tamny, Lorain, both of Ohio P E R b B R rima xaminer 0 ert eeves [73] Ass1gnee: Nordson Corporatlon, Amh Assista nt ExaminerDavid A. Scherbel Ohm Attorney, Agent, or Firm-Wood, Herron & Evans [22] Filed: Oct. 17, 1972 [21] Appl. No.: 298,263 [57] ABSTRACT A fluid operated system of modular guns for dispens- [52] US. Cl. 222/487, 222/504 ingliquids Such asgmolten adhesives The system [51] Int. Cl. G011 11/06 eludes multiple guns in the f f readily removable [58] Field Of Search 118/306, 315, 317; cylindrical modules that mount i apertures f a fi d 239/41 1, 551; 222/504, 518, 559, 487, 309 service block or manifold. The service block and guns have passages which register when the system is as- [56] References cued sembled whereby the guns may be easily removed UNITED STATES PATENTS from the fixed service block and replacedwithout dis- 2,764,385 9/1956 Sieling 222/559 x connecting y fl ines o other service equipment. 2,964,246 12/1960 A11101m et a1. 222/504 ux Each gun module is secured to the service module by 3,132,775 5/1964 Trumbull et a1 222/309 X a connector located at one end of the gun module so 3,194.448 7/1 65 Theall 22 X that it is free for relatively. unlimited thermal expan- 3,198,4()4 8/1965 Welches 222/504 X i and contraction without damage to i h d 3,690.518 9/1972 Baker et a1. 222/504 v FOREIGN PATENTS OR APPLICATIONS I 1,156,342 5/1958 France 222/504 1 C s 3 D'awmg F'gures MODULAR APPLICATOR SYSTEM This application is an improvement upon a Modular Adhesive Applicator disclosed in Us Pat. No. 3,690,518, which patent is assigned to the assignee of this application.

This invention relates to the application of liquids to surfaces and especially to equipment used to apply beads, ribbons or small unitary deposits of extruded or sprayed material in a desired pattern under high speed production conditions. More particularly, the invention relates to equipment which is particularly suitable for applying heated liquids such as hot melt molten adhesives to various materials such as flat sheets or webs of paper or cardboard of the type commonly used in packaging and adhering a variety of products. The invention, though, is equally applicable to the application of other liquid materials such as coating materials and paints which may be applied cold or at room temperature.

Hot melt liquids are typically of the asphaltic or synthetic resin type and are generally in their solid state at room temperature. When heated to molten form, however, they change in physical state to a relatively viscous liquid which may be pumped through the nozzle of an applicator tool or gun and applied to a surface in the form of a continuous bead or ribbon or as intermittent deposits. Normally, such hot melt materials are converted to a molten state in a heater and then transmitted to applicator guns under pressure through heated lengths of flexible hose. The applicator guns are preferably heated also to assure that the adhesive remains in molten form until it leaves the nozzles of the guns.

In many high speed packaging applications, the molten or liquid hot melt" is applied to moving sheet material such as a web of paper or flattened cardboard cartons. In other applications the hot melt is applied to filled containers prior to the sealing of the flaps or an end closure. In still other applications, the molten material is used in the coating or assembly of parts.

Certain types of applicator guns used for application of hot melt adhesives as well as the application of other liquids are operated by means of fluid cylinders which open and close a valve in the molten liquid feed line and thus interrupt the extrusion or expulsion of the liquid from the nozzle of the gun. Where air operated guns are used, it is necessary, of course, to use an air pressure line from a pressure source. Also, since the body of the gun is normally heated to maintain the liquid in a molten or low viscosity state, it is essential that electrical service lines also be connected to the gun.

A problem encountered with this type of equipment, particularly in the application of hot melt adhesives but also in the application of other liquid materials, has been the time consuming cleaning operation which must be accomplished at periodic intervals. The cleaning requires the removal of all of the fluid lines and other service lines from the gun and afterward the reconnection of the lines as well as the careful repositioning of the gun so as to extrude the beads of liquid at a proper predetermined location. All this is quite time consuming and requires the interruption of a continuous production facility at frequent intervals.

In the above-identified United Stated patent, there is disclosed a dispenser system which includes a fixed service module or manifold having a passage for viscous liquid and a passage for operating fluid. The passage for the viscous liquid communicates with the pumping system and the passage for operating fluid communicates with a fluid pressure line. One or more removable gun modules are mounted in the fixed service block module. Each gun has a passage communicating between the viscous liquid passage in the service block module and an extrusion nozzle, and a passage for operating fluid communicating between the operating fluid passage in the service block anda fluid cylinder. The guns are cylindrical and have threads for mounting in the service module so that the guns may be readily removed from the service module for service or replacement without disturbing the connections to the service module (air line, electrical lines and hydraulic lines). Each gun consists of a cylindrical body which contains a ball valve, located in a chamber which is filled with the viscous liquid when the gun is in operation. The valve is opened by a rod which is attached to the ball and passes through a seal which separates the liquid material from an atmospheric vent chamber. The rod continues through a second seal located between the vent chamber and an air cylinder where the rod is attached to a piston. By applying pressurized fluid, as for example, air, to the piston, the ball is pulled from the valve seat allowing material to flow out of the gun onto the product or substrate. When the pressure is removed from the piston, a spring returns the ball to its closed position on the valve seat. An adjustment is provided on the return spring so that the amount of fluid pressure required to actuate the gun is adjustable. Since the force required to actuate each individual gun varies because of differing internal gun friction forces, the adjustable preload of the spring allows several guns to be adjusted to equalize the pressure required to open each gun. Thus each gun may be adjusted to open at the same time. t

The above-described dispensing systemhas numerous advantages over the prior art and has proven a commercial success. However, under severe or abusive operating conditions, that system has failed. Accordingly, it has been one objective of this invention to improve upon that system soas to render it foolproof, even under very severe operating conditions or when subjected to abusive assembly or adjustment.

One problem encountered with the structure disclosed in the above-identified patent occurs periodically when the unit is subjected. to high operating temperatures. Periodically, under such conditions, the body of the gun module cracks or fails. I have determined, and one aspect of this invention is partially predicated upon the determination, that these failures occur because of thermal expansion of the gun module. The threaded mounting of the gun module into the service module in the dispenser disclosed in that patent is such that the body is not free to expand with temperature changes with the result that when tightened very tightly into the service module and then heated to a high temperature, it cracks or fails.

To eliminate this cause of failure, I have connected the gun module to the service module at one end of the gun so that it is free to expand and contract without restraint. Specifically, l have used a threaded connection over one end of this gun to secure a'tapered end portion to the service block and leave the remainder of the gun free to expand or contract in the bore of the service module.

This connection between the two modules has the advantage of eliminating one cause of breakage or failure of the gun but is also has the advantage of eliminating the need to thread the bore of the service module and the mating section of the gun module. Eliminating these threads reduces the cost of manufacture of the system. It also enables the gun module to be positioned more closely than is possible with threaded guns.

Another problem encountered with the applicator disclosed in the above-identified patent is attributable to mechanics applying an excessive preload to the gun. Preload is the force required to actuate the guns and, in the case of air operated guns, determines the air pressure required to open the valves of the guns. In the case of multiple guns located in a single service module, the preload may be accurately adjusted so that irrespective of frictional or small tolerance differences between the guns, they all open together. I have found that a mechanic may apply an excessive preload to one gun by adjusting one adjustment too tight and then find that he does not have enough air pressure to open the gun or that he cannot balance that preload force in other guns. Consequently, the preload adjustment of this gun has a built-in stop associated with it which absolutely precludes such excessive preload.

These and other objects and advantages of this invention will be more readily apparent from the followin description of the drawings in which:

FIG. 1 is a front elevation view of a modular system incorporating the invention of this application.

FIG. 2 is a cross sectional view through the service module taken generally on line 22 of FIG. 1.

FIG. 3 is an enlarged cross sectional view through a gun module taken on line 3-3 of FIG. 2.

Referring first to FIG. 1, there is illustrated a fourgun applicator system for applying a heated liquid material to a substrate. In the illustrated embodiment the four gun modules or guns ll, 12, 13 and 14 are mounted in alignment in a service module or service block 15. The guns could, though, be mounted out of alignment or in any pattern in the service module 15 but for ease of illustration they are shown in linear alignment.

The service module 15 comprises a generally rectangular block through which there extends a pressurized fluid or air passage 16 and a parallel liquid flow passage 17. In the preferred embodiment there is also an atmospheric 'vent passage 18 extending parallel to and located between the two other passages 16 and 17. These three transverse passages are intersected by four

gun mounting apertures

20, 21, 22 and 23 which are perpendicular to the passages 16-18. As best seen in FIGS. 2 and 3, the apertures -23 are step bored for reception of the guns 11-14, respectively, and each includes a small diameter end section 24, a larger diameter section 25, a still larger diameter middle section 26 and a large diameter end section 27.

In applications in which the system is intended to be used to apply hot melt or heatedmaterials, the service module or block 15 includes a transverse bore 30 within which there is mounted an electrical resistance heater 31. The flow of electrical current through this heater 31 is controlled by a thermostat 32 mounted in a recess 33 in the face of the block 15. The recess is covered by a plate 34 bolted or otherwise secured to the service module so as to enclose the thermostatcontaining recess 33.

The service module may be mounted at an applicator station in any convenient manner. In the illustrated embodiment the service block 15 is secured by a mounting clamp 38 and bolts 39 to a bar (not shown).

The four gun modules 11-14 are identical and therefore only one is illustrated and described in detail. As may be seen most clearly in FIGS. 1 and 3, the gun modulesare generally circular and tubular in configuration for mounting inthe circular cross section apertures 20-23 of the service module. Each gun includes a tubular body 45 through which there extends an axial bore 46. This bore defines a high pressure fluid or air cylinder 47 at one end and a nose piece receiving chamber 48 at the opposite end. A small diameter sec-v tion 49 of the bore 46 interconnects the cylinder 47 and chamber 48.

The bore 46 of the body. is closed at one end by an end closure cap 50. This cap 50 is secured within the bore 46 of the body by swaging or crimping of an end portion 51 of the body into an annular groove 51a on the exterior of the cap 50. The opposite end of the bore 46 in the body 45 is similarly closed but by a nose piece 53 which is secured within the end of the bore 46 by a section 54 of the body which is swaged or crimped over a radial flange 54a on the inner end of the nose piece 53. a

' A stepped axial bore 55 extends through the nose piece 53. The intermediate diameter section of this how 55 defines a liquid chamber 56 into which liquid or molten material may be supplied through radial ports 66. The chamber 56 communicates with a small diameter discharge port 57 which is open to the end of the gun. In the illustrated embodiment, a nozzle 59 of the gun is threaded onto the end of the nose piece 53.

An internal shoulder of the end piece 53 at the intersection of the small diameter bore 57 and the larger diameter chamber 56 forms a valve seat 63 for a ball valve 64. This ball valve 64 and valve seat 63 together form a check valve 65 for controlling flow of pressurizd liquid from the liquid chamber 56 of the gun. Liquid is supplied to this chamber through the ports 66 in the nose piece 53 of the gun. When the gun is assembled in the service module or service block 15, this port or passage 66 registers with the transverse liquid supply passage 17 through which liquid, as for example, hot melted adhesive, is supplied to the system 10 at high pressure, as for example, 400 pounds per square inch.

The ball valve 64 is mounted upon one end of a piston rod 68. This rod-extends upwardly through the small diameter section 49 of the bore 46 and at the opposite end terminates in a large diameter headed end section 69. A piston 70 is mounted upon the end section 69 of the rod. This piston comprises two

rings

71 and 72 sandwiched between a shoulder 73 of the end section 69 of the piston rod and a swaged end 74 of the rod.

An air seal, preferably a Teflon seal, 75 is sandwiched between the two

rings

71 and 72 of the piston. This seal 75 prevents the escape of air pressure from the high pressure cylinder 47 located beneath the piston to a low pressure chamber 76 in the closure cap 50. This latter chamber 76 is maintained at atmospheric pressure through a transverse passage 77 in the cap 50 which opens to atmosphere.

An adjustable preload spring 80 is located in the chamber 76 of the closure cap and bears against one side of the piston 70 so as to force the piston and the ball valve 64 to a closed position. The opposite end of this spring 80 bears against an adjustable seat 81 which is slideable in the chamber 76 of the closure cap. This seat 81 rests against an end 82 of a preload adjustment screw 83. The screw is threaded through a threaded nut 84 welded into the open upper end of the closure cap 50. By adjusting the screw 83 and thus the axialposition of the seat 81, the force holding the valve closed and thus the force required to open the valve may be adjusted. This adjustment enables air pressure required to open several guns to be equalized even though the internal friction of the individual guns may be different.

In order to limit the total preload force applied by the spring 80 to the piston 70, a shoulder 85 is provided in the chamber 76 of the cap 50. This shoulder limits the axial extent of movement of the seat 81 into the cap and thus the extent of compression of the spring 80. A small vent 86 extends through the seat 81 so as to connect the chamber 76 of the cap to atmosphere when the seat 81 rests against the shoulder 85.

In practice, it has been found that in the absence of a stop or limit to the extent of movement of the seat 81, an operator will often preload one gun excessively so that he is then unable to adjust the other to balance the preload force of the excessively adjusted gun. Furthermore, he may even adjust it to such an extent that the force required to further compress the spring 80 exceecls the available air pressure. The stop surface 85 on the cap 50 prevents this type of excessive preload adjustment.

Air pressure in cylinder 47 controls opening and closing of the check valve 65. This pressure, generally in the form of air pressure, is supplied to the cylinder 47 through a transverse passage 87 which registers with the passage 16 in the service module. High pressure air supplied to the passage 16 effects opening of the check valves by causing the pistons 70 of the guns to move upwardly until the tops of the pistons engage the bottom edge 88 of the caps 50. When the pressure in the passage 16 is released or opened to atmosphere, the springs 80 effect closing of the valves.

In order to prevent leakageof air pressure from the chamber 47 through the vent 98 and to prevent leakage of liquid from the chamber 48, an air seal 90is provided around the rod 68 in the air cylinder 47 and a liquid seal 91 is provided around the rod 68 in the liquid chamber 48. The seal 90 includes a pair of resilient lip seals 92 secured within the chamber 47 by a retainer ring 93. The liquid or hydraulic seal 91 also includes a resilient lip seal 94 but this seal is held in place by a washer 95 and a backing spring 96. At one end the spring bears against the washer 95 and at the opposite end it bears against a shoulder 97 of the nose piece 53. To further insure that liquid does not leak into the air cylinder, a transverse vent aperture 98 is provided in the body 45 intermediate to the

seals

90 and 91. This vent 98 is connected to the through passage 18 in the service module so that it is always open to atmosphere.

OPERATION The four guns 11-14 are individually inserted'into the service module until tapered flanges 100 on the nose pieces of the guns contact shoulders 101 formed in the

apertures

20, 21, 22 and 23. Nuts 102 are then threaded over the externally threaded end portion 103 of the nose pieces of each gun until the nuts abut against the bottom surface 105 of the service module. This has the effect of clamping the nose pieces 53 of each gun between the shoulder 101 and the outer bottom surface of the service module.

It is to be noted that the distance X between the shoulder 101 and the surface 105 of the service module is approximately l/l6 the overall length of the gun module. Because this dimension is so small, differential rate of thermal expansion between the gun and the service module does not damage the gun, even when both modules are subjected to very severe temperatures, as for example, 400F. When so assembled, the air passages 87 of the guns register the air passage 16 of the service module. Similarly, the liquid passages'66 register with the liquid passage 17 of the service module and the atmospheric vents 98 register with the atmospheric vent 18 of the service module. Air is prevented from leaking around the exterior of the gun from the passage from leaking around the exterior of the-body from the liquid passage 17 of the service module.

The individual guns are so adjusted by the preload adjustment screw 83 that all four open simultaneously when air pressure is supplied to the gun through the passage 16 of the service module. This air pressure causes the pistons of the guns to move upwardly until the top surfaces of the pistons contact the bottom surfaces 88 of the closure caps 50. This upward movement of the pistons effects the upward movement of the check ball valves 65 and permits liquid supplied to the guns athigh pressure (as for example, 400 psi) in passage 17 to pass through and out'of the liquid chambers 56 via the nozzle ports 57. After the liquid material has been deposited upon a substrate, the air pressure is passage 16 is opened to atmosphere andv the guns are caused to close as a result of the springs forcing the pistons and the attached check valves to a closed position.

When it is necessary to clean one of the guns or if foreign matter should cause a gun to break, the service lines to the service module 15 need not be disconnected from the service module. Specifically, the air line to the passage 16, the fluid line to the passage 17, and the electric lines to the heater 31 and thermostat 32 need not be disconnected. All that is required is for the lines to be closed or shut off and the clogged or broken gun to be removed by unthreading it from the mounting aperture of the service module. A new gun may then be inserted by threading it into the aperture and the system restarted. The clogged or broken gun may then be cleaned or repaired without closing down any production facilities while this cleaning or repair takes place.

While I have described only a single preferred embodiment of the invention, persons skilled in the art to which this invention pertains will readily appreciate changes and modifications which may be made without relative to each other so as to locate the deposits from the gun in even closer spacing than the spacing of the gun nozzle orifices. Additionally, the system has been specifically described as applied to a hot melt application and including a heated service module. The invention is equally applicable, though, to unheated liquid applications. Therefore, l do not intend to be limited except by the scope of the appended claims.

Having described my invention, 1 claim:

I. A modular apparatus for emitting a liquid from a pressurized source onto a substrate comprising a service block module having essentially only static parts and defining a first passage for a liquid, and a second passage for a gun actuating pressurized fluid, said module having at least one aperture intersecting said passages,

a readily removable gun module including a body mounted in said aperture of said service block module,

means for securing said gun module in said aperture,

said gun module including a nozzle,

said gun module including essentially all the movable parts of said apparatus, said gun module defining a first passage for liquid communicating between said liquid passage in said service block module and said nozzle, said first passage in said gunmodule being in sealing registration with said liquid passage in said service block module when said modules are in assembled relation, said gun module also defining a second passage for pressurized fluid communicating between said pressurized fluid passage in said service block module, said pressurized fluid passages of said gun module and service module also being in sealing registration when said modules are in assembled relation,

a movable valve element in said gun modules for opening and closing liquid flow through said nozzle, and

movable means in said gun module responsive to connection with said pressurized fluid for operating said valve,

the improvement wherein the means for securing said gun module in said aperture includes a fastener located externally of said service block and an abutment surface on said gun module located closely adjacent one end of said gun module, said abutment surface being engageable with a stop surface in said aperture when said body is mounted within said aperture, and said fastener being secured to said gun module at said one end of said gun module so that the remainder of said gun module remote from said fastener is free to thermally expand and contract within said aperture of said service block module.

2. The apparatus of claim I in which said fastener is engageable with an external wall of said service module.

3. The apparatus of claim 2 in which the distance be.-

tween said external wall of said service module and said 5. The modular apparatus of claim 4 which further includes means for biasing each of said valve elements of each of said gun modules to a closed position and adjustable preload means for adjusting the force operable to maintain said valve elements in a closed position, stop means for limiting the amount of said preload tension, and said adjustable preload means being operable to enable the several gun modules to be adjusted to equalize the pressure required to open each gun module.

6. The modular apparatus of claim 1 in which said gun module body is generally cylindrical in configuration and in which said aperture is circular in cross section, said aperture having smooth unthreaded walls throughout the length of said aperture.

7. The modular apparatus of claim 1 in which the said gun module body is a generally cylindrical body and has a through bore extending axially therethrough.

8. The modular apparatus of claim 7 in which a portion of said axial bore defines a fluid cylinder in said gun module at one end of said cylindrical body, said second passage of said gun module being in fluid com munication with said fluid cylinder.

9. The modular apparatus of claim 8 in which said movable means includes a piston slideable in said cylinder and which further includes spring means operable between said piston and a closure cap to bias said piston and said movable valve element to a closed position.

10. A module apparatusfor emitting a liquid from a pressurized source onto'a substrate comprising a service block module having essentially only static parts and defining a first passage for a liquid, and a second passage for a gun actuating pressurized fluid, said module having at least one aperture intersecting said passages,

means for securing said gun module in said aperture,

said gun module including a nozzle,

said gun module including essentially all the movable parts of said apparatus, said gun module defining a first passage for liquid communicating between said liquid passage in said service block module and said nozzle, said first passage in said gun module being in sealing registration with said liquid passage in said service block module when said modules are in assembled relation, said gun module also defining a second passage for pressurized fluid communicating between said pressurized fluid passage in said service block module, said pressurized fluid passages of said gun module and service module also being in sealing registration when said modules are in assembled relation,

a movable valve element in said gun module for opening and closing liquid flow through said nozzle,

the improvement wherein the means for securing said gun module in said aperture includes a nut threaded over an end section of said gun module externally of said service block and an abutment surface on said gun module located closely adjacent said end section of said gun module, said abutment surface being engageable with a stop surface .in said aperture when said body is mounted within said aperture so that the remainder of said gun module remote from said gun module securing means is free to thermally expand and contract within said aperture of said service block module.

11. The apparatus of claim 10 in which said nut is engageable with an external wall of said service module.

said stop surface of said aperture is less than one fou the length of said gun module rth

Claims

1. A modular apparatus for emitting a liquid from a pressurized source onto a substrate comprising a service block module having essentially only static parts and defining a first passage for a liquid, and a second passage for a gun actuating pressurized fluid, said module having at least one aperture intersecting said passages, a readily removable gun module including a body mounted in said aperture of said service block module, means for securing said gun module in said aperture, said gun module including a nozzle, said gun module including essentially all the movable parts of said apparatus, said gun module defining a first passage for liquid communicating between said liquid passage in said service block module and said nozzle, said first passage in said gun module being in sealing registration with said liquid passage in said service block module when said modules are in assembled relation, said gun module also defining a second passage for pressurized fluid communicating between said pressurized fluid passage in said service block module, said pressurized fluid passages of said gun module and service module also being in sealing registration when said modules are in assembled relation, a movable valve element in said gun modules for opening and closing liquid flow through said nozzle, and movable means in said gun modUle responsive to connection with said pressurized fluid for operating said valve, the improvement wherein the means for securing said gun module in said aperture includes a fastener located externally of said service block and an abutment surface on said gun module located closely adjacent one end of said gun module, said abutment surface being engageable with a stop surface in said aperture when said body is mounted within said aperture, and said fastener being secured to said gun module at said one end of said gun module so that the remainder of said gun module remote from said fastener is free to thermally expand and contract within said aperture of said service block module.

2. The apparatus of claim 1 in which said fastener is engageable with an external wall of said service module.

3. The apparatus of claim 2 in which the distance between said external wall of said service module and said stop surface of said aperture is less than one fourth the length of said gun module.

4. The modular apparatus of claim 1 which further includes multiple apertures intersecting said service block module passages and a readily removable modular gun mounted in each of said apertures.

5. The modular apparatus of claim 4 which further includes means for biasing each of said valve elements of each of said gun modules to a closed position and adjustable preload means for adjusting the force operable to maintain said valve elements in a closed position, stop means for limiting the amount of said preload tension, and said adjustable preload means being operable to enable the several gun modules to be adjusted to equalize the pressure required to open each gun module.

8. The modular apparatus of claim 7 in which a portion of said axial bore defines a fluid cylinder in said gun module at one end of said cylindrical body, said second passage of said gun module being in fluid communication with said fluid cylinder.

10. A module apparatus for emitting a liquid from a pressurized source onto a substrate comprising a service block module having essentially only static parts and defining a first passage for a liquid, and a second passage for a gun actuating pressurized fluid, said module having at least one aperture intersecting said passages, a readily removable gun module including a body mounted in said aperture of said service block module, means for securing said gun module in said aperture, said gun module including a nozzle, said gun module including essentially all the movable parts of said apparatus, said gun module defining a first passage for liquid communicating between said liquid passage in said service block module and said nozzle, said first passage in said gun module being in sealing registration with said liquid passage in said service block module when said modules are in assembled relation, said gun module also defining a second passage for pressurized fluid communicating between said pressurized fluid passage in said service block module, said pressurized fluid passages of said gun module and service module also being in sealing registration when said modules are in assembled relation, a movable valve element in said gun module for opening and closing liquid flow through said nozzle, movable means in said gun module responsive to connection witH said pressurized fluid for operating said valve, the improvement wherein the means for securing said gun module in said aperture includes a nut threaded over an end section of said gun module externally of said service block and an abutment surface on said gun module located closely adjacent said end section of said gun module, said abutment surface being engageable with a stop surface in said aperture when said body is mounted within said aperture so that the remainder of said gun module remote from said gun module securing means is free to thermally expand and contract within said aperture of said service block module.

12. The apparatus of claim 11 in which the distance between said external wall of said service module and said stop surface of said aperture is less than one fourth the length of said gun module.