US3557498A

US3557498A - Remotely controlled sandblaster

Info

Publication number: US3557498A
Application number: US799231A
Authority: US
Inventors: Philip K Lindsay
Original assignee: P K Lindsay Co Inc
Current assignee: P K Lindsay Co Inc
Priority date: 1969-02-14
Filing date: 1969-02-14
Publication date: 1971-01-26
Anticipated expiration: 1988-01-26

Abstract

SANDBLASTING APPARATUS WITH REMOTELY CONTROLLED APPATUS COMPRISING A FLUID-DISPLACEABLE MEMBER OPERATING THE SAND TO AIR RATIO CONTROL. SHOWN ARE PRESSURIZED AIR FROM THE SANDBLASTING APPARATUS AS THE SOURCE OF FLUID, A PISTON-ROTARY DRIVE VALVE ASSEMBLY FOR THE RATIO CONTROL, AND MANUALLY TRIGGERED SELECTION VALVES, WITH OPTIONAL DEAD MAN SAFETY FEATURES.

Description

Jan. 26,1971 v LINDSAY: I 3,

REMOTEEYZCONTROLLED SANDBLASTER Filed Feb. 14, 196 9 2 Sheets-Sheet 1 Jan. 26, 1971 p, K" DS I 3,557,498

I REMOTELY CONTROLLED SANDBLASTER Filed Feb. 14,- '1969 2 Sheets-Sheet 2 United States Patent 3,557,498 REMOTELY CONTROLLED SANDBLASTER Philip K. Lindsay, Deerfield, N.H., assignor to P. K.

Lindsay Company, Inc., Deerfield, N.H., a corporation of New Hampshire Filed Feb. 14, 1969, Ser. No. 799,231 Int. Cl. B24e 3/00 U.S. Cl. 51-8 Claims ABSTRACT OF THE DISCLOSURE Sandblasting apparatus with remotely controlled apparatus comprising a fluid-displaceable member operating the sand to air ratio control. Shown are pressurized air from the sandblasting apparatus as the source of fluid, a piston-rotary valve assembly for the ratio control, and manually triggered selection valves, with optional dead man safety features.

This invention relates to sandblasting and, particularly, to controlling the sand to air ratio delivered by a sandblaster.

Sandblasting operations often require adjustment of the mixture of sand and air being fed through the sandblasting nozzle onto the work surface. Also, where sand is maintained under pressure in a tank, the moisture content of the compressed air being fed to the tank to keep the sand under pressure gradually causes agglomeration of the sand. Particularly in field operations, where the pressurized air may contain a great deal of moisture, water vapor in the air will gradually condense on the walls of the tank or on the sand. To free these sand agglomerates and prevent clogging of the sand exit aperture from the tank, this aperture must be periodically opened, the freed agglomerates being largely broken up by this action. Additionally, passage of moisturized sand through the hose may eventually lead to blockage in the hose or, particularly, in the restricted opening of the nozzle. These blockages may be largely freed if one is able to close the sand aperture and feed only pressurized air through the hose to blow out agglomerated sand. Thus, the sand and air apertures must be manipulated during sandblasting operations to maintain a free flow of the desired sand through the nozzle.

It is desirable that means providing efiicient, reliable and rapid manipulative ability be located .close to the nozzle so that the workman operating the nozzle, who is aware of its flow characteristics, may himself control the sand-air ratio through the nozzle. Since the workman is often unable to carry his sand tank with him (e.g., for skyscraper cleaning) it is desired that this provision be available no matter how far away he is from the sand tank. Although long-standing, this need has not been satisfied. Previously proposed electrically-operated remote control systems, for instance, have the disadvantage that one must either be near a power source, which is not available for many sandblasting operations, or must carry ones own power, which is impractical in many instances.

It is therefore an object of the present invention to provide an efficient, reliable, simple and rapid control system having all controls located at or near the nozzle operator, for regulating remotely the sand-air ratio from the sandblasting apparatus.

Another object is to provide a rugged, durable and safe remotely actuated control device for regulating sand feed from a sand container and the sand-air ratio through the nozzle of a sandblasting apparatus, having a minimum of exposed moving parts and which allows the full range of aperture openings to be quickly, easily, and simply selected by the nozzle operator.

The invention features a proportion control device for controlling the sand to air ratio fed to the nozzle of a sandblasting apparatus, which device comprises a fluid displaceable control device regulating flow between the nozzle and at least one of a sand inlet and an air inlet, a first control line for admitting pressurized fluid from a remote actuation point to the control assembly to operate it in a first mode tending to decrease the sand to air ratio and a second control line for admitting pressurized fluid from a remote actuation point to the control assembly to operate it in an opposite second mode, tending to increase the sand to air ratio.

Advantageously, a pressurized fluid supply is provided to the control lines and valve means remote from the control assembly selectively increases fluid flow from the fluid supply to one control line. Simple triggers mounted on the nozzle end of the hose can control this assembly and the motive fluid can be obtained from the air source of the sandblasting machine. Conveniently, such a pneumatic valve means cooperatively vents one control line while opening the other to pressurized air. In the described valve means, biasing structure, which may be overcome by the triggers, vents both control lines to atmosphere.

In preferred embodiments, a dead man safety feature is provided which automatically opens the first control line to pressurized air when the sandblasting apparatus is not in use, thus preventing at least sand flow through the nozzle and, preferably, also air flow, this dead man being readily manually overcome when the sandblaster is in use.

An advanatgeous air-displaceable control assembly, in combination with a remotely actuated penumatic cylinder, comprises a rotatable valve member having at least two spaced ports for communicating, respectively, with the sand inlet and the air inlet, this valve being rotatable through a series of positions including an OFF position when neither port communicates with an inlet, and a number of ON positions in which the ratio of sand to air is gradually increased, including an all-air position. Although the described embodiment has only two ports, any number of sand and air ports may be provided, being sized and located to deliver the desired sand-air mixture.

The air-displaceable control assembly preferably includes a pressure chamber including a displaceable piston, the two air control lines communicating with the chamber, one on each side of the piston, to displace the piston in the chamber in accordance with the relative air pressure in the air control lines, and linking structure for securing the piston to the aforesaid rotatable valve member and translating displacement of the piston in a first and opposing second directions to rotate the valve member toward the OFF and ON positions, respectively. Where a disc-shaped or similarly rotary valve member is employed, the pressure chamber may be mounted a fixed distance from the valve member and linked thereto by a rod extending from the center of the valve disc, to which it is fixed, to the piston, the end secured to the piston being free to rotate and also to slide in a direction perpendicular to piston displacement, the resultant transverse movement of the rod during piston movement tending to rotate the rod, and the perpendicular sliding capability compensating for changes in the distance be tween the rod mounting on the piston and the fixed center of the valve member.

If desired, pneumatic piston displacement may be damped by employing a second piston, attached to the first and displaceable therewith, but operating in a hydraulic chamber, containing a constant filled amount of heavy fluid which must pass in one direction through a tiny aperture in the piston to permit piston movement in the opposite direction. Closing of the piston (i.e., turning the rotatable valve member OFF) may be made more rapid by locating a large opening in the piston and a smaller aperture in a flexible member mounted on the piston face and free to flex around its periphery, such that oil flow must be through the smaller aperture during movement of the piston in the open (ON) direction, but may be through the large piston aperture and around the unsecured periphery of the flexible member during movement in the close (OFF) direction, a safety feature permitting rapid shutting OFF of the apparatus while slowing the rush of air and sand to the nozzle when the apparatus is turned ON.

A preferred valve means suitable for regulating flow through the two air control lines comprises: a housing which receives the control lines and an air supply line and which includes first and second supply ports between the air supply and the first and second control lines, respectively, and first and second vent ports between atmosphere and the first and second control lines, respectively, first and second valve members movable relative to the first and second pairs of ports, respectively, for cooperatively opening and closing the respective pairs of ports such that when either supply or vent port is fully open or fully closed, the corresponding vent or supply port is fully closed or fully open; and, a pair of triggers operating these first and second valve members, respectively, to open the corresponding supply ports.

In another aspect, the invention features a hand-operated control system for controlling air flow through ON and OFF air control lines, the line under greater air pressure tending to regulate the sandblasting apparatus, respectively, in an ON direction (increasing the sand to air ratio through the nozzle) or in an OFF direction (decreasing the sand to air ratio through the nozzle). This hand-operated control system includes an OFF valve assembly including an OFF supply valve for admitting pressurized air to the OFF control line, an ON valve assembly including an ON supply valve for admitting pressurized air to the ON control line, means for venting each said control line whenever pressurized air is admitted to the other control line, and at least two hand operable triggers for controlling, respectively, the two supply valves. Preferably, the venting means comprises vent valves for each line which are also operated by the corresponding trigger, and structure for biasing these venting valves open; the triggers are located to overcome independently this biasing. Thus, each trigger operates in a first direction to open its supply valve and in an opposite direction to open its vent valve. Both supply valves will remain closed and both venting valves open until a trigger is operated to open one of the supply r valves, the other supply valve remaining biased closed, thus admitting pressurized air to only one control line and venting the other control line to atmosphere. A removable dead man may also be provided which is handreleasable, when sandblasting operations are discontinued, to bias the OFF supply valve open, thus automatically shutting off the sandblasting apparatus. The whole hand-operated system is conveniently secured at the nozzle end of the hose.

Other objects, features and advantages will appear from the following description of a preferred embodiment of the invention, taken together with the attached drawings thereof, in which:

FIG. 1 is a somewhat diagrammatic front elevational view of a portion of a sandblasting apparatus embodying the present invention, but not including the nozzle region;

FIG. 2 is an elevational view of the nozzle region of the apparatus of FIG. 1;

FIG. 3 is a view of the embodiment of FIG. 2 through plane 33 thereof;

FIG. 4 is an enlarged rear view of the piston assembly of the embodiment of FIG. 1 with the cover partially broken away, along line 4-4 of FIG. 6:

FIG. 5 is an enlarged, somewhat idealized sectional view, along line 55 of FIG. 7, of a portion of the em- 4 bodiment of FIG. 1 showing, in detail, the mixing valve assembly of the sandblasting apparatus;

FIG. 6 is a bottom elevational view, partially in section, of the embodiment of FIG. 1, along line 66 thereof, showing particularly the cooperation between the piston assembly of FIG. 4 and the mixing valve assembly of FIG. 5, with the mixirig Valve in a position to supply only air; and

FIG. 7 is a view of the mixing valve alone, rotated from its position in FIG. 6 to supply a sand-air mixture.

In the figures there is shown a sandblasting apparatus, designated generally at 10, including a sand container 12, of sand inlet funnel 14, an air control assembly 16, a mixing control assembly 18, and a remote control assembly (FIG. 2).

Air control assembly 16 includes an air inlet 22, a valve 24 for admitting air to de-moistening tank 25, a first air outlet line 26 leading, through bleeder valve 27 and inlet line 28, to the interior of sand container 12, a pressure indicator 30 being mounted above valve 27 to monitor the inlet pressure to the tank. Valves 24 and 27 are cooperatively operated to shut off air flow and bleed the said container, respectively, when it is desired to depressurize the container for filling.

A second air outlet line 33 leads from de-moistening tank 25 to mixing control assembly 18, as later described, and ultimately to sandblasting hose 34. Remote control air supply line 36 extends directly from air inlet line 22 to remote control assembly 20, so that operation of the latter is independent of air pressure in the sand container.

Referring now to FIG. 5, mixing valve assembly 40 includes a housing 42 consisting of two

plates

43, 44, formed, e.g., of cast iron, bolted together by bolts 45, and sealed by annular gasket 46. Plate 43 is secured by bolts 47 to the bottom plate 48 of container 12, and

includes a sand inlet funnel 50, tapering to a sand inlet orifice 51, and an air inlet cavity 53, leading to air inlet orifice 54. Surrounding each

orifice

51, 54, and seated in notches of plate 43 are a soft rubber valve cushion 57 and a hardened steel valve washer 5'8. Mixing valve 60 is in the form of a plate having an air inlet port 62 and a sand inlet port 64, shown in communication, respectively, with

orifices

54, 51 of plate 43. It will be noted that FIG. 5 is not a true planar section since, as Will be apparent from FIG. 7, the air and sand cavities are not both coplanar with both inlet line 33 and hose 34. Since

ports

62, 64 are 180 apart whereas

orifices

54, 51 are somewhat less than 180 apart, it is impossible to fully open both

orifices

54, 51.

Ports

62, 64 also communicate with an annular mixing chamber 65, where sand and air proportionally metered by mixing valve 60, are mixed and the mixture fed to hose 34. Valve plate 60 includes a rectangularly shaped center opening into which is fitted a similarly sized and shaped rectangular cam 67 on valve spindle 68. A bolt 69 extends through washer 70 into a threaded opening in cam 67, securing the valve plate 60 to valve spindle 68 such that rotation of spindle 68 will rotate valve plate 60. Valve spindle 68 is sealed by packing collar 72, surrounding valve packing 73, and includes an annular flange 74 upon which spring 75 is biased against valve plate 60, thus both securing valve plate 60 against washers 58 and also compressing valve packing 73 around spindle 68. Thus sand is unable to leak, under air pressure, into the area around spindle 68. Spindle 68 extends rotatably through collar 72 and lower bore 77 in plate 44. Hose 34 is threaded into an end of plate 44 at 80, to seal the hose to mixing chamber 65.

Spindle 68 includes a second rectangularly shaped cam 81 at its lower end, which extends through a similar rectangularly shaped opening 83 in valve spindle arm 85, a bolt 87 extending through washer 88 into an interior threaded opening in spindle 68 through its rectangularly shaped cam. Rectangular cams 67, 81, of course, need not be aligned but may be offset in any way desired.

Thus, transverse motion of spindle arm will rotate valve spindle 68, and hence valve plate 60.

Referring to FIGS. 4 and 6, piston assembly is mounted on flat plate 92, which is also secured, by bolts 47 (FIG. 5) to the lower plate 48 of sand container 12, and includes two

central plates

93, 94 of rectangular cross-section bolted, by bolts 95, to flat plate 92, two end plates 96, 97, also of rectangular cross-section, and four supporting rods 99' extending, respectively, through the four corners of

plates

93, 94, 96, 97, each rod including an increased diameter portion 101 between

plates

93, 94, and each rod secured, by appropriate means (not shown) to the outer ends of plates 96, 97. Piston rod 102 extends through

plates

93, 94, and also through a bore 103 in spindle arm mounting block 104 which is secured to rod 102 by set screw 105. Two guard plates 109, are secured, by bolt 107 and nuts 108, to block 104; each plate has a flange 111 through which bolt 107 extends, and a valve spindle arm track 114, bolt 107 extending through a hole in one perpendicular side 115 thereof. Bolted to valve spindle arm 85 by bolt 116 is an annular rider 117 sized to rotate and slide in track 114 upon movement of track 114 in a direction perpendicular to its upstanding sides 115.

Air cylinder 120 is secured between plates 94, 96 and positioned thereon by tightly mating cylindrical notches cut in the interior surfaces of these plates. Plate 96 includes a control port 123 communicating with the interior of air cylinder 120 and with air control line 124, through which air may be admitted or vented, as later described, control line 124 being secured to plate 96 by appropriate air-tight connectors (not shown). Plate 94 also includes a control port 126 communicating with the interior of air cylinder 120 and with air control line 127, control line 127 being secured to plate 94 also by appropriate air-tight connectors. Piston rod 102 extends sealingly through plate 94 and has secured, at its end, a cylindrical air piston 130, which is free to slide axially along the cylindrical interior wall of air cylinder 120 on appropriate piston rings (such as 0 rings) which restrict air flow around piston 130 to make its movement responsive to pressure changes in

control lines

124, 127.

Oil cylinder is sealingly secured between

plates

93, 97, again by tight cylindrical notches cut into the plates (not shown). Piston rod 102 extends sealingly (gaskets 137) through a central bore 138 in plate 93, to the interior of oil cylinder 135, and has piston 140 secured to its end, piston 140 being free to slide in oil cylinder 135 on gaskets 142, which prevent passage of oil therearound.

Piston 140 includes a through aperture 144, and cylindrical notches 1-45, 146. Secured centrally of piston 140 to the end of piston rod 102 by bolt 148 is a flexible element 150 having aperture 151 aligned with but smaller than aperture 144 of piston 140; the periphery of element 150 remains free to flex. Fexible element 150 thus will flex away from notch 145 in piston 140 during movement of the piston from left to right, permitting oil flow through large aperture 144 and around the periphery of flexible element however, during movement of the piston from right to left, flexible element 150 will cover aperture 144, forcing oil to flow through the smaller aperture 151 in element 150, thus causing slower piston movement in this direction. The arrows in FIG. 6 indicate these oil flow paths. Flexible element 150 may, of course, be removed to provide uniform piston movement in both directions, at a speed dependent only on the size of aperture 144.

Oil cylinder 135 is kept full of oil by oil reservoir 154 communicating, through threaded conduit 155, with aperture 157 in plate 93, and therethrough with oil cylinder 135. Bleeder plug 160 is threaded into a threaded aperture 162 in plate 97 to seal that aperture, and may be removed for filling, changing oil, etc.

Referring now to FIGS. 2 and 3, air control lines 124,

127, and air supply line 36 communicate, through air tight connectors 165 with three metal connecting tubes 124a, 127a, 36a, surrounded by aluminum sleeve 168. Housing 169 includes threaded openings (not shown) for receiving the other ends of tubes 124a, 127a, 36a. Tube 124a communicates, through one such opening, with air control port 170, and tubes 127a, 36a similarly communicate with air control port 171 and air supply port 172, respectively, in the interior of housing 169. Ports 170, 171 communicate, respectively, with

valve recesses

173, 174, in the interior of housing 169. Recess 173 includes a lower cylindrical portion 176, and an upper cylindrical portion 177, these portions having opposed

valve seats

178, 179, respectively. Elongated apertures 180, 181 open

cylindrical portions

176, 177, respectively, to air control port recess 174 includes similar lower and upper

cylindrical portions

183, 184, having opposed

valve seats

185, 186, connected, through elongated apertures 187, 188, respectively, to air control port 171. Valve member resides in valve recess 173 includes upper and lower

spherical lands

191, 192, and an elongated spacer tube 193, slightly longer than the distance between

valve seats

178, 179 whereas valve member resides in valve recess 174 and includes upper and lower spherical lands 196, 197 and an elongated spacer tube 198, slightly longer than the distance between

valve seats

185, 186.

Valve members

190, 195 are biased upwardly by

springs

200, 201, each of which is connected, by an appropriate airtight threaded

connector

202, 203, to threaded openings 204, 205, respectively, in housing 169, thus seating seat Spherical lands 192, 197 in

valve seats

178, 185, respectively, and thereby opening air control ports 170, 171 to atmosphere through

valve recess portions

177, 184, respectively. L-shaped

triggers

209, 210 pivot, on pin 212 and each includes an

upper portion

213, 214 having flat

interior surfaces

217, 218, respectively, for bearing against spherical lands 191, 196, respectively, when

portions

213, 214 are depressed to seat lands 191, 196 in

valve seats

179, 186, respectively, thereby closing ports 170, 171 to the atmosphere. Since

triggers

209, 210 rotate freely about pin 212, mounted between

sides

235, 236 of mounting bracket 240,

valve members

190, 195, under biasing by

springs

200, 201, can lift

trigger portions

213, 214 off housing 169, opening ports 170, 171 to atmosphere. The amount of upward lift is limited, however, by the remaining L-shaped portions 219 of

triggers

209, 210, which are trapped by the rear wall 222 of housing 169.

Remote control assembly 20 also includes a dead man assembly 225 having a handle 227 rotatably secured, through bar 228, to fixed pin 232, mounted between

sides

235, 236 of mounting bracket 240,

sides

235, 236 being bolted (not shown) to plate 169. Bar 228 is also welded to pin 241 which in turn is mounted through the U-shaped end 242 (FIG. 3) of dead man actuator 244, which extends along plate 169, and terminates in a perpendicular bar 246, located adjacent portion 214 of trigger 210. Dead man spring 250 is mounted, by central guide pin 252, between bar 246 and top plate 254 of mounting bracket 240, biasing bar 246 against trigger 210, thus tending to connect air control port 171 to air supply port 172, by depressing spherical land 197 away from valve seat 185.

Hose 34, to which is secured nozzle 260, is mounted, by standard adjustable ring clamps 262, to a swivel support 263 which is rotatably mounted, by bolt assemblies 264, between a depending portion 266 of mounting bracket 240 and another mounting bracket 270, which is secured between connectors 165 and sleeve 168.

For operation, container 12 is partially filled with sand through funnel 14 (including a sieve for rejecting large sand agglomerates) and partially demoistened compressed air is directed into container 12 through inlet 28. A pressure plug (not shown) is used to seal the container after filling, this plug being maintained against the top wall by the air pressure in the container. Compressed 7 air is also fed, through line 33, into air inlet cavity 53 in mixing valve assembly 40. Until it is desired to operate the apparatus, both air inlet orifice 54 and sand inlet orifice 51 are maintained closed, mixing valve 60 being in a position slightly counterclockwise rotated from the position shown in FIG. 6. The valve is closed automatically by the dead man assembly 225, spring 250 depressing valve member 195 to overcome the bias of valve spring 201, thus opening air control port 171 to air supply port 172, air being continuously fed to port 172 from air supply line 36, while valve member 190 will remain lifted, by biasing spring 200, to open air control port 170, through aperture 179, to atmosphere. Referring to FIG. 6, control line 127 will therefore be under pressure, whereas control line 124 will be vented to atmosphere, thus forcing

pistons

130, 140 all the way to the right, rotating mixing valve 60 in a counterclockwise direction to close both

ports

62, 64 to

orifices

54, 51, respectively.

When it is desired to use the sandblasting aparatus, the operator first grasps dead man handle 227 and squeezes it against sleeve 168 thus relieving the pressure in control line 127 by opening air control port 171 to atmosphere by action of biasing spring 201 against valve member 195. Air piston 130 will not move, however, due to the oil in oil cylinder 135 which inhibits movement of oil piston 140 and hence, by virtue of common attachment to piston rod 102, thereby damps movement of air piston 130.

Mixing valve 60 is then rotated in a clockwise direction to open only air port 62 to air inlet orifice 54, allowing air to pass through the hose and out the nozzle, clearing them of any accumulated sand. Mixing valve 60 is thus rotated by the operator by depressing trigger 209, while maintaining the dead man handle against sleeve 168, thus feeding compressed air through line 124, urging air piston 130 to the left. The damping movement of oil piston 140, caused by oil flow through the tiny aperture in flexible element 150, slows the opening of mixing valve 60, thus preventing a quick, potentially dangerous blast of air from nozzle 260. The movement of the pistons may be stopped at any time simply by allowing the trigger to return, opening both control lines to atmosphere, thus equalizing pressure on both sides of the air piston. By further depressing trigger 209, mixing valve 60 is rotated further clockwise until sand inlet orifice 51 is opened the desired amount, through port 64, to mixing chamber 65. By depressing trigger 210 (or simply releasing dead man handle 227), the piston displacement is reversed, and the sand-air ratio subsequently decreased.

When it is desired to shut down the apparatus (e.g., to change nozzles), dead man handle 227 is released, thus directing compressed air through control line 127. Since flexible element 150 will be flexed away from piston notch 145 by oil travelling from right to left, oil flow will bypass small aperture 151 and the piston may move rapidly to the right to close both ports, first sand port 64 and then air port 62, automatically clearing sand from the hose prior to shut down. Thus, in the case of emergencies, a rapid shut down may be accomplished.

As an additional safety feature, the hose 34 is mounted on a freely pivoted swivel support 263, so that sudden pressure changes in the hose line, and consequent jerking of the hose, will not jerk the control means from the operators hands.

Other embodiments will appear to one skilled in the art and are within the following claims.

What is claimed is:

1. In a sandblasting apparatus in which sand from a sand inlet is mixed with air from an air inlet and the mixture fed to a sandblasting nozzle, a proportion control for regulating the relative proportion of sand and air fed to the nozzle comprising a fluid-displaceable control assembly regulating flow through at least one said inlet, a first control line for admitting pressurized fluid from a remote actuation point to said control assembly to 8 operate said assembly in a first mode tending to decrease the sand-to-air ratio,

and a second control line for admitting pressurized fluid from a remote actuation point to said control assembly to operate said assembly in an opposite second mode, tending to increase the sand-to-air ratio.

2. In combination with the apparatus of claim 1, a pressurized fluid supply, and valve means remote from said control assembly for selectively increasing fluid pressure from said supply to one said control line.

3. The apparatus of claim 2 wherein said pressurized fluid supply comprises a conduit extending from a compressed air source at said sandblasting apparatus to said valve means adjacent the sandblasting nozzle.

4. The apparatus of claim 2 wherein said valve means selectively directs air pressure from said supply to one said control line while selectively cooperatively venting the other said control line to atmosphere.

5. The apparatus of claim 2 wherein said valve means includes biasing structure for automatically directing fluid pressure only to said first control line when said sandblasting nozzle is idle.

6. The apparatus of claim 1 wherein said fluid-displaceable control assembly comprises a rotatable valve member having at least two spaced ports for communicating with said air inlet and said sand inlet respectively, said valve member being rotatable through a series of positions including an OFF position when all ports are out of communication with said inlets, and a number of ON positions in which the ratio of sand to air is gradually increased.

7. The apparatus of claim 6 including an ON position in which only said air inlet communicates with a valve port.

8. The apparatus of claim 7 wherein said fluid-displaceable control assembly also includes a pressure chamber including a displaceable piston, one said control line communicating with said chamber on each side of said piston, and

linking structure for securing said piston to said rotatable valve member and translating displacement of said piston in a first direction by said first control line to rotation of said valve member toward the OFF position, and displacement of said piston in a second direction by said second control line to rotation of said valve toward the ON position.

9. The apparatus of claim 2 wherein said pressurized fluid supply comprises a source of pressurized air and said valve means comprises a housing connected to said first and second control lines and said pressurized air supply and including a first supply port between said first control line and said air supply, a first vent port between said first control line and atmosphere, a second supply port between said second control line and said air supply, a second vent port between said second control line and atmosphere,

a first valve member movable relative to said first supply and vent ports for cooperatively opening and closing said first ports and a second valve member movable relative to said second supply and vent ports for cooperatively opening and closing said second ports, the valve members arranged whereby when one of said supply ports is fully open the corresponding vent port is fully closed, and when one of said vent ports is fully open the corresponding supply port is fully closed,

and a pair of triggers operating, respectively, said valve members and operable to open the corresponding said supply ports.

10. The apparatus of claim 9 including biasing structure for normally biasing said valve members to close said supply ports.

/11. The apparatus of claim 9 wherein said fluid-displaceable control assembly regulates flow both through said sand inlet and through said air inlet, and is displaceable fully in said first direction to close both said air inlet and said sand inlet to said nozzle, and wherein said device includes a dead man safety assembly for normally biasing said first valve member to open fully said first supply port, thereby to displace said control assembly freely in said first direction.

12. The apparatus of claim 11 wherein said valve means includes biasing structure for normally biasing both said valve members to close both said supply ports, and said dead man safety assembly includes a spring sized and arranged to operate the trigger communicating with said first valve member to overcome said biasing structure and open said first supply port, and a handle for removing said dead man spring from operating on said trigger.

13. The apparatus of claim 1 including means for damping displacement of said control assembly at least as said assembly operates in the mode to increase the sand-toair ratio.

14. The apparatus of claim 13 wherein said displaceable control assembly comprises a pneumatic cylinder including a piston and said damping means includes a hydraulic chamber and a second piston, movable in said hydraulic chamber, and connected to said first mentioned piston for identical displacement therewith, said second piston including an aperture through which displaced hydraulic liquid flows in one direction through said piston during displacing movement of said piston in the opposite direction.

15. The apparatus of claim 14 including a flexible member, connected centrally to one face of said second piston, having its peripheral portions free to move with respect to said piston face, and including an aperture smaller than said piston aperture, said member structured to be displaced from said piston face to allow free fluid flow through the piston aperture and around the periphery of said member upon movement of the piston away from the flexible member, and displaced toward the piston to force hydraulic liquid flow through the smaller aperture in the member upon movement of the piston toward the flexible member, said flexible member secured to the piston face facing the ON direction in which the sand to air ratio is increased to slow movement of said pistons in the ON direction.

16. For use with a sandblasting apparatus in which a sand-air mixture is released under pressure, from the nozzle end of a hose controlled by a mixing valve displaceable by pressurized air in an OFF direction to decrease the sand to air ratio and in an ON direction to increase the sand to air ratio, the valve actuated by an OFF air control line for directing pressurized air to displace said mixing valve in the OFF direction, and an ON air control line for directing pressurized air to displace said mixing valve in the ON direction,

a hand-operated control system for controlling the admission of air pressure to said control lines comprising an OFF valve assembly including an OFF supply valve for admitting pressurized air to said OFF control line,

an ON valve assembly including an ON supply valve for admitting pressurized air to said ON control line,

means for venting each said control line whenever pressurized air is admitted to the other said control line, and

at least two hand-operable triggers for controlling, re

spectively, said two supply valves.

17. The control system of claim 16 wherein said means for venting comprises vent valves for each line with structure for biasing open to the atmosphere, and operating structure operable with the opening of each supply valve adapted to close the corresponding vent valve.

18. The control system of claim 17 including biasing structures for each supply valve said triggers being structured and arranged to operate against the respective biasing structure for opening the supply valve and closing the corresponding vent valve.

19. The control system of claim 18 including a dead man safety assembly comprising a third biasing structure, sized and arranged to overcome the biasing structure for the valves capable of establishing the OFF position, whereby pressurized air is directed through said OFF control line, and a hand-operable dead man handle operable to remove said third biasing structure, permitting said assemblies to be operated through said triggers.

20. The control system of claim 16 wherein said handoperated control system is mounted on the nozzle end of the hose.

References Cited UNITED STATES PATENTS 1,254,834 l/19l8 Mott 5ll2 1,443,762 1/1923 Smith 51-12 1,641,342 9/1927 Mauney et al. 51-8 1,858,475 5/1932 Wolever 5 l-l 1X 3,034,263 5/1962 McDaniel et al. 5 l12 3,056,236 10/ 1962 McMillin 5 l8 3,070,924 1/ 1963 Hastrup 5l-8 3,148,484 9/1964 Meek 51-12 LESTER M. SWINGLE, Primary Examiner