AIR VALVE FOR SPRAY GUN

Abstract: An air valve, for controlling feedback air in spray guns, comprising a valve body (10) and valve member (9), a spindle (6) slidably sealed through valve body (10) and valve member (9), spindle (6) having a shoulder (7) closing a first seating (8) in valve member (9), the rear of spindle (6) slidable in a shuttle (15) which also slides in a fixed valve spool (12) having a second seating (12a) closed by the rear of shuttle (15). Two ports (22, 23) are provided one either side of second seating (12a) between spool (12) and shuttle (15) for feedback air past the valve and two ports (24, 25) provided either side of first seating (18) between valve member (9) and spindle shoulder (7) for main air through the valve, so that operation of spindle (6) opens the first valve prior to the second valve and closes the second valve prior to the first valve.

Description: AIR VALVE FOR SPRAY GUN This invention relates to an air valve more particularly for controlling the feedback air in HVLP spray guns. An aim of the present invention is to shut off the feedback line when the spraygun is in the Off position. According to the present invention there is provided an air valve for controlling the feedback air in spray guns comprising a valve body and valve member, a spindle slidable and sealingly passing through the valve body and valve member, the spindle having a shoulder engaging and closing a first seating in the valve member the rear of the spindle slidable in a shuttle which is itself slidable in a fixed valve spool, the spool having a second seating closed by the rear of the shuttle wherein two ports are provided one at either side of the second seating between the spool and shuttle for the passage of feedback air past the valve and two further ports are provided one at either side of the first seating between the valve member and spindle shoulder for the passage of main air through the valve so that operation of the spindle opens the first valve prior to the second valve and closes the second valve prior to the first valve. Preferably, the spindle is returned to its closed position by a spring engaging the valve spindle. An embodiment of an air valve according to the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a cross-sectional elevation of a spray gun fitted with an air valve; and Figs. 2 to 5 are diagrammatic cross-sections of the air valve shown in Fig. 1 in different operational positions. The spray gun shown in Fig. 1 comprises a main body 1, a handle 2 and an air cap 4. The paint is fed from a reservoir under the control of a regulator (not shown) . The air valve illustrated controls the feedback air sensed at the gun air cap 4 and is operated by the gun's trigger 5. Fig. 2 illustrates the air valve in the off position with an operating spindle 6 in a released or forward position with its shoulder 7 engaging a first seating 8 of a stationary valve member 9. The spindle 6 passes through a hole in member 9 and an air valve body 10 with the interposition of a rubber or resilient plastics seal 11. The valve member 9 is aligned with a valve spool 12 with annular ports 13 and 14. Sliding in the valve spool is a slidable shuttle 15 one end of which engages the rear of the spindle shoulder 7 and its other end is engageable with a cup 16 spring loaded by a spring 17 in the gun body 1. A second seating 12a on valve spool 12 cooperates with a shoulder 15a on the shuttle 15 to provide a closeable passage between the inlet port 22 and the outlet port 23. The shuttle 15 and valve spool 12 are sealed between one another by O-ring seals 18 and 19 respectively and the shuttle 15 is sealed in the body 1 of the spray gun by an O-ring seal 20. The feedback line is connected to ' the end of the spray gun handle 2 via pipe 21 which is connected to the air valve at port 23. The air pressure fed back from the air cap 4 is connected to the air valve at port 22. The main air enters the air valve at the main inlet 24 and leaves the air valve at the main port 25 to the atomising/spreader air circuit. Figs. 3 to 5 illustrate three operational positions of the trigger 5 from a slight pressure on the trigger to its fully depressed position. On applying pressure to the trigger 5 the shuttle 15 is engaged by the rear of spindle shoulder 7 and is moved against the tension of spring 17 to unseat it from engagement with seating 8 in the valve member 9. The progressive movement of the spindle 6 and shuttle 15 by pressing the trigger 5 unseats the valve shuttle 15 from the seating 15a and provides through passages between ports 22 and 23 for the feedback air as shown by the arrows 26 and between ports 24 and 25 for the main air as shown by the arrows 27. It will be appreciated that the smooth operation of the trigger 5 will control the flow of the main air to the air cap 4 based on the pressure of the feedback air sensed at the gun air cap to maintain a fixed air pressure e.g. 10 psi (0.7 bar) at the air cap.

Claims: CLAIMS: 1. An air valve for controlling the feedback air in spray guns comprising a valve body (10) and valve member (9), a spindle (6) slidable and sealingly passing through the valve body (10) and valve member (9), the spindle (6) having a shoulder (7) engaging and closing a first seating (8) in the valve member (9), the rear of the spindle (6) slidable in a shuttle (15) which is itself slidable in a fixed valve spool (12), the spool having a second seating (12a) closed by the rear of the shuttle (15), characterised in that two ports (22, 23) are provided one at either side of the second seating (12a) between the spool (12) and shuttle (15) for the passage of feedback air past the valve and two further ports (24, 25) are provided at either side of the first seating (8) between the valve member (9) and spindle shoulder (7) for the passage of main air through the valve so that operation of the spindle (6) opens the first valve prior to the second valve and closes the second valve prior to the first valve. 2. An air valve as claimed in Claim 1, characterised in that the spindle (6) is returned to its closed position by a spring (17) engaging the valve spindle. 3. An air valve as claimed in Claim 1 or 2, characterised in that the shuttle (15) is sealed by an 0- ring seal between the spindle (6) and shuttle (15) against the passage of air past the seal. 4. An air valve as claimed in any preceding claim, characterised in that the shuttle (15) is sealed by an 0- ring seal between the shuttle (15) and valve spool (12) against the passage of air past the seal (19). 5. An air valve as claimed in any preceding claim, characterised in that the valve spool (12) is sealed in the body (1) of a spray gun by an O-ring seal (20) against the passage of air past the seal (20). 6. An air valve as claimed in any of Claims 2 to 5, characterised in that one end of the spring (17) is held by a cup (16) and the other end of the spring engages the body (1) of a spray gun, the spring cup (16) engaging the shuttle to close the seating between the spool and ' shuttle (15). 7. An air valve as claimed in any preceding claim, wherein a resilient seal (11) is located in a recess in the valve body (10) to surround and seal the passage of air past the spindle (16).

Inventors: BATE ANTHONY JOHN, SMITH ROWLAND CHARLES, BATE, ANTHONY, JOHN, SMITH, ROWLAND, CHARLES
Applicants: ITW LTD, ITW LIMITED
Application year: 1993
Main classification: B05B7
IPC codes: B05B1, B05B7