GB2159243A

GB2159243A - Paint change valve

Info

Publication number: GB2159243A
Application number: GB08506939A
Authority: GB
Inventors: Jozsef Frikker
Original assignee: DeVilbiss GmbH
Current assignee: DeVilbiss GmbH
Priority date: 1984-03-19
Filing date: 1985-03-18
Publication date: 1985-11-27
Also published as: JPS612979A; BR8501216A; DE3410017A1; IT1185541B; FR2561138A1; BE901960A; AU3965885A; IT8519947A0; GB8506939D0

Abstract

A paint change valve comprises a valve stem (2) formed with a closure member (5) at one end and attached at the opposite end (3) to a flexible diaphragm (13) of paint solvent resistant material which seals the paint chamber (16) from a control air chamber (17). The paint pressure acts on one side of the diaphragm to close the valve while control air pressure acts on the other side of the diaphragm to open the valve. <IMAGE>

Description

SPECIFICATION Paint change valve The invention relates to a paint change valve and more particularly to a fluid actuated needle valve for use in changing paint colors in a paint spray system.

In many automated industrial paint spray systems, a series of workpieces which are to be painted different colors are conveyed past a paint station. A system control actuates control valves in supply lines for the different color paints and solvent to supply the correct color paint to spray guns for coating each workpiece and to flush the spray gun with solvent during color change. The paint and solvent control valves may be mounted in a common color change manifold. Typically, the paint and solvent control valves are pneumatically operated. When a valve is to be opened, compressed air is supplied to a chamber in the valve. The compressed air moves a piston in the chamber to open the valve. Paint under pressure then flows through the open valve, the color change manifold and a common supply line to the paint applicators.When the application of the selected color paint is completed, the system control interrupts the compressed air and a spring moves the piston to close the valve. The solvent valve then may be opened to flush the old paint from the manifold, the supply lines and the applicators prior to selecting a new color paint.

The prior art paint change valves include a valve needle located within a pressurized paint chamber. One end of the valve needle must extend out from the paint chamber to enable operation of the valve needle to open and close the paint valve. The extension of the valve needle out of the paint chamber requires a seal to prevent loss of paint. The seal, which is in the form of packings through which the valve needle slides in an axial direction, represents a weak part of the valves. The seal packings may be attacked by solvents present in the paint. Also, many paints contain abrasive pigments which can damage the packings as the valve needle is repeatedly opened and closed. This can result in a leaky seal in the paint change valve. When paint which has leaked past the seal hardens, the valve may cease to function.

The invention is directed to a needle type paint change valve in which the valve needle is confined within the paint chamber to prevent leaks by eliminating relative movement between the valve needle and the sealing element. The valve needle is mounted in a housing to extend between a valve seat on the housing and a paint chamber. A valve cone at an exterior and a paint chamber. A valve cone at an exterior end of the valve needle seals against the seat when the valve is closed. An operating end of the valve needle is attached to a flexible diaphragm which is sealed to the housing to form one side of the paint chamber. A closed control air chamber is located on the other side of the diaphragm. When compressed air is applied to the control air chamber, the diaphragm flexes and moves the valve needle in an axial direction to open the valve.The diaphragm is formed to have a larger surface area exposed to the pressurized paint than the valve cone and seat. As a consequence, the pressurized paint in the paint chamber forces the valve closed when the compressed air is removed from the control chamber. When the compressed air is removed from the control air chamber, a spring in the control air chamber also urges the valve closed. The spring will close the valve when both control air pressure and paint pressure are removed from the valve. This prevents the paint from draining from the valve in the event that paint pressure is interrupted. The diaphragm eliminates the need to have the operating end of the valve needle extend from the paint chamber and thereby eliminates wear between the valve needle and a sealing element in which the prior art valve needle slides.

Accordingly, it is an object of the invention to provide a needle typw paint change valve which eliminates potential leakage problems present in prior art paint change valves.

The single figure is a cross sectional view through a paint change valve according to the invention.

The invention is for a paint change valve through which the passage of pressurized paint is selectively opened or blocked. The valve, as illustrated in section in the drawing, has a housing 1 having a bore 1 8 in which a valve needle 2 is arranged to move in an axial direction. At its exterior or free end, the valve needle 2 has a valve cone 5 which, when the valve is closed, seals against a valve seat 4 on the housing 1. When the valve needle 2 is moved in an axial direction and the valve cone 5 separates from the seat 4, the valve is open and paint flows from a standard pressurized supply line (not shown) attached to a threaded connecting bore 1 5 in the housing 1, through a chamber 1 6 within the housings 1 and finally through the open valve.The housing 1 includes a bore 1 4 opposite the bore 1 5 which may be plugged, or may be connected through a return line and a pressure regulator (not shown) for a paint recirculating system.

The valve needle 2 has a threaded operating end 3 located within the housing 1. A washer 7, a flexible diaphragm 1 3 and a tension nut 11 are attached to the valve needle operating end 3. The diaphragm 1 3 is of a material which is resistant to attack by solvents in the paint, such as a polytetrafluoroethylene which is sold under the trademark Teflon. The diaphragm 1 3 is circular in shape and is firmly clamped around its periphery to the housing 1 to seal one side of the paint chamber 1 6. The diaphragm 1 3 is clamped to the housing 1 3 by a support washer 12 and a cap 9 which is threaded onto the housing 1.

The diaphragm 13 has a central opening through which the needle valve end 3 passes.

The washer 7 is positioned on the paint chamber side of the diaphragm 1 3 and bears on a shoulder on the valve needle 2. The tensioning nut 11 is located on the opposite side of the diaphragm 1 3 and is threaded on the valve needle end 3 to clamp the diaphragm 13 tightly against the washer 7 to form a seal which prevents pressurized paint from leaking between the diaphragm 1 3 and the valve needle 2. It should be noted that the valve needle 2 is attached only to the diaphragm 1 3. The valve cone 5 is pulled against the valve seat 4 to close the valve without the need for any positive guidance.

As a consequence, guides which may becomes worn through abrasion or plugged with hardened paint and the need for accurate tolerances are eliminated.

A compression spring 8 is positioned between the washer 1 2 and the tensioning nut 11. The spring 8 urges the valve needle 2 to a closed position wherein it forms a seal with the valve seat 4. The spring 8 and nut 11 are located in a control air chamber 1 7 located within the cap 9 and are separated from the paint chamber 1 6 by the diaphragm 13. The control air chamber 1 7 is connected through a control air feed line 10 to a compressed air supply (not shown).

In operation, paint is supplied under pressure from a conventional source through the bore 1 5 to the chamber 1 6. The paint pressure acts on the valve cone 5 and on the diaphragm 13, since the effective area of the diaphragm 1 3 is larger than the effective area of the valve cone 5, the valve needle 2 is urged in the closing direction by the differential force thus created and the paint valve is closed.For opening the valve, pressurized fluid, preferably compressed air, is introduced through the line 10 into the control air chamber 1 7. The compressed air is supplied at a sufficiently high pressure to act on the diaphragm 1 3 against the paint pressure in the chamber 1 6 and the pressure of the spring 8 to shift the valve needle 2 in an axial direction, thereby opening the paint valve. When the pressure in the control air chamber 1 7 is released, the higher pressure in the paint chamber 1 6 acting on the diaphragm 1 3 and the pressure of the spring 8 will close the paint valve. When the paint chamber 1 6 and the air chamber 1 7 are not pressurized, the spring 8 will close the valve and hold it closed. This will prevent paint from draining from the valve chamber 1 6 when both paint pressure and control air pressure are removed from the valve.

Claims

1. A paint change valve comprising a housing defining a paint chamber connected to a paint outlet and a valve seat at said outlet, characterized by a control fluid chamber separated from said paint chamber by a flexible diaphragm of a paint solvent resistant material, and a valve needle extending from said diaphragm through said paint chamber to said valve seat, said needle having a first end attached to said diaphragm and a free second end defining a valve cone located for sealing engagement with said valve seat when said paint change valve is closed.

2. A paint change valve according to claim 1, wherein the effective area of said diaphragm is larger than the effective area of said valve cone whereby pressurized paint in said paint chamber urges said valve needle to a closed position with said valve cone engaging said valve seat.

3. A paint change valve according to claim 1, wherein when said valve is open, said valve needle is supported and attached to said housing only through said diaphragm.

4. A paint change valve according to claim 1, and further including a spring mounted in said control fluid chamber for urging said valve needle to a closed position.

5. A paint change valve substantially as described with reference to, and as illustrated in, the accompanying drawing.