IMPROVEMENTS IN OR RELATING TO VALVES

Abstract: Valves for controlling pressurised fluids and assemblies of similar valves connectable so a single pressurised fluid source to provide a variable supply. The basic valve comprises a body (1) having a fluid inlet (2) which is connected to two outlets (4 and 6). The arrangement is such that fluid supplied to inlet (2) will preferentially flow out through outlet (4). A double-acting electromagnetic valve is provided which can close outlet (4) causing the fluid to exit through operational outlet (6). To provide variable control this basic arrangement is expanded so that there can be several vent outlets (53, 54, 55, 56) of differing apertures each associated with an individual electromagnetic valve.

Description: I PROVΞMEMTS IN OR RELATING TO VALVES The present invention concerns valves for controlling pressurised fluid. It is especially, though not exclusively, concerned with valves for supplying a controlled flow of air to air brushes. The intensity of colour painted by an air brush is largely dependant on the air flow it receives. Previously this air flow has been controlled by a needle valve mounted on a diaphragm and connected to a solenoid. Proportional control is achieved by varying the voltage supplied to the solenoid in accordance with the flow required* in the hope that the position taken up by the valve member in relation to its seat, and thus the through-put, will be correlated to the supply voltage. However this arrangement has a number of disadvantages. In particular the weight of the valve parts to be moved is high and this causes problems in view of the very short response times required. The lack of any control loop makes the flow control inaccurate which causes distortion of the colour values. Finally the opening of the valve on removal of the control voltage is carried out by the back pressure of the air being controlled. This makes the return of the valve longer than its closure time, further reducing the overall response time. SUBSTITUTE SHEET The present invention has for an object to meet or at least reduce the above disadvantages. Accordingly the present invention consists in a valve for controlling pressurised fluid comprising an inlet for the fluid, a pair of outlet ports in comπunication with the inlet, the inlet and outlet ports being so arranged that with both outlet ports opened the pressurised fluid will flow preferentially through only one of the outlet ports, and an electrcmagnetically controlled valve member adapted in use to close said one outlet port so as to divert the flow of pressurised fluid to the other outlet port. Preferably the electromagnetic means are double-acting so as in operation positively to open and close the valve member. In accordance with a feature of the invention a plurality of valves of the kind as set out hereinbefore may be associated with a single inlet port for pressurised fluid and with a single outlet port, the arrangement being such that for a given volume of pressurised fluid supplied to the inlet port, the flow through the outlet port can be controlled by selectively opening one or more of the valves. In order that the present invention may be more readily understood various embodiments thereof will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic section showing the operational principle of a valve according to the present invention, Figure 2 is a plan view of a valve constructed in accordance with the present invention, Figure 3 is a diagram which shows how the valve of Fig. 2 can be cembined with similar valves to provide a varialble controlled output, Figure 4 shows another way in which the valve of Fig. 2 can be combined with similar valves, Figure 5 is a section through a manifold arrangement associated with a plurality of valves of the type shown in Fig. 2 which is also capable of controllable output, and Figure 6 shows some electrical signal waveforms associated with the opening and closing of a valve of the type shown in Fig. 2. Referring now to Figure 1 of the accompanying drawings there is shown a valve for controlling the flow of a pressurised fluid and in particular ccmpressed air. The valve is intended for use with air brushes of the kind used in colour printing in which the intensity of .colour produced by the brush depends on the volume of air flowing through the brush per unit of time. A very important consideration with brushes of this type is that the turn-off and turn-on times of the ccmpressed air supply should be as short as possible as only in this way can fine detail be reproduced. The valve shown in Fig. 1 is designed to provide extremely rapid opening and closure times. OMPI Various methods of achieving variable flows by using a plurality of similar valves will be described later in this specification. Thus the valve shown in Fig. 1 comprises a metal block 1 having an inlet port 2 which is provided with a suitable means 3 whereby it ca be connected to a source of compressed air. Port 2 leads directly to a vent outlet port 4. An operational outlet port 6 is connected to a main passage 5 in block 1 by a branch passage 5', the passage 5 extending between the inlet port 2 and the vent outlet port 4. The arrangement of ports and passages is such that if no constraints are placed on the two output ports 2 and 4 the compressed air supplied to port 2 will exit via the vent port 4. Thus in this condition if the operational outlet port is connected to an air brush there will be an insufficient flow of air to operate the brush. Mαunted above the port 4 is a valve pad 7 which in its rest position, as shown in Fig. 1, is sufficiently space above the port 4 to have no affect on the free flow of air out of the port. Pad 7 is coupled to an electromagnet 8 which on actuation moves the pad 7 downwardly to close port 4 and thus divert the ccmpressed air supplied to inlet port 2 to operational outlet port 6. Fig. 2 of the drawings shows a more detailed embodiment of a valve with a double-acting electromagnetic arrangement. A ccmpressed air pipe 10 is coupled to the inlet 2 but no line is shown connecting the operational outlet 6 to a device such as an air brush. The vent outlet 4 is surrounded by a Neoprene (RIM) pad 11. A pair of electromagnets 12 and 13 are mounted one above the other to one side of block 1. Each electromagnet comprises a central core 14, the two cores 14 being arranged to act on the respective ends of a rocker arm 15. The lower end of arm 15 cooperates with pad 11 so as to be capable of sealing vent outlet 4. To ensure proper sealing the outer surface of pad 11 is inclined as shown in the drawing. Another feature to ensuring proper sealing is the provision of an opening 21 in the end of arm 15 opposite to pad 11. This opening has a diameter greater than that of pad 11 and has a covering of Neoprene (RIM) stretched over it. The purpose of this is to compensate for any misalignment between pad 11 and arm 15 when the latter is in its operative or closure position. The arm 15 is mounted so that it lies in a generally vertical plane on the central limb of a T-shaped mounting arrangement 16 for the electrαnagnets. The mounting arrangement 16 is made from two L-shaped steel plates 17 and also acts to complete the magnetic circuits of the electromagnets 14. The coils 18 of the electromagnets 14 are secured to the plates 17 and each coil has 1568 turns of 36 SWG wire. These values are, of course, purely by way of example, -founted above tha valve block 1 is an adjustable stop which provides a limit to the open position of rocker arm 15 and which comprises a Neoprene (RTM) pad 19 carried by a threaded rod 20 extending through a mounting bracket 21. The electromagnets 12 and 13 are connected to a suitable current source by a switching arrangement in such a manner that the rocker arm 15 is positively driven in both its opening and closing directions. f m C PI - - As already mentioned an important factor for the successful operation of air brushes is that both the turn-on and turn-off times of the air supply should be extremely fast. The valve just described can achieve this because the mass to be moved by the electromagnets is relatively small and the arm 15 is positively driven in both its opening and closing directions. However in order to achieve really short reaction times the manner in which the electromagnets are driven is also an important factor. Figure 6 shows graphically a preferential method of driving electromagnets 12 and 13. In Fig. 6 L indicates diagrammatically a section through a black and white image being scanned by an opto-electric scanner to derive image signals. For the purpose of the present description it will be assumed that the image being scanned is merely bi-tonal, that is has no grey shades so that an air brush reproducing the image will only require switching on and off. As shown in Fig. 6 the image has three sections, namely a wide section 101 of black, a shorter section 102 and a line 103. The upper of the two waveforms is the voltage applied to the coil of electromagnet 13 which acts positively to hold the rocker arm 15 away from the pad 11 and the vent opening 4 so that ccmpressed air : supplied to the valve escapes preferentially through the vent opening 4 and not through the operational outlet- 6. When the opto-electric scanner, diagrammatically indicated at 104, reaches the start of the black section 101 of the image the valve is actuated to close the vent opening 4 so that the ccmpressed air is supplied to the air brush. Thus voltage V13 is cut off releasing the lower end of rocker arm 15 and the coil of electromagnet 12 is energised to attract the upper end of arm 15 and swing the lower end into engagement with the pad 11 so as to seal vent outlet 4. However as can be seen from Fig.6 it is not the normal coil voltage V12 which is supplied to the coil at switch on but a very short spike approximately 10 times the normal coil voltage which then falls to V12. In this way the electromagnet is over-driven to provide very sharp actuation. Conversely when the scanner leaves the section 101 and reaches a white section of the image electrcmagenet 13 is over-driven in the same manner to ensure that the valve is opened as quickly as possible. For a very narrow image . line such as section 103 only a signal of Vpeak is applied to electromagnet 12. As mentioned a suitable value for Vpeak for both of the electromagnets is ten times the normal coil voltage though this ratio may be varied in accordance with the type of electromagnet used. By using the valve arrangement and switching method just described a switching time of approximately 750 microseconds can be achieved. It will be appreciated that a valve of the type just described is not suitable for giving variable throughputs of ccmpressed air such as are required in an air brush application to give a grey scale or different colour intensities. In order to provide such a variation a plurality of similar valves can be mounted together in an assβnbly with their output ports all connected to a single manifold. Qne example of such an assembly is shown in Fig. 3 of the drawings. In the assembly of Fig. 3 there are shown twelve individual valves with the respective output ports 6 of the valves all connected to a manifold 30 the output of which is a single line coupled to an air brush 31. By selectively switching in one or more of the valves twelve different levels of colour, or of grey scale, can be obtained. Thus for the lowest colour intensity only valve VI is opened to supply compressed air to the air brush. For the next colour level both valves VI and V2 are opened and so on for the entire 12 levels. Figure 4 shows an alternative arrangement giving binary control of the output of the valve assembly. In Fig. 4 valve VI is assumed to give, when open, an output of X, valve V2 an output of 2X, valve V3 an output of 4X and valve V4 an output of 8X. It will thus be seen that by selecting appropriate combinations of the four valves in the assonbly fifteen levels of intensity can be obtained. As in the Fig. 3 embodiment the output ports of the four valves are taken to a single manifold which in this figure has the reference numeral 40. In the binary assembly of Fig. 4 the design of the manifold is of greater importance than in the assembly of Fig. 3. this is because with the Fig. 3 assembly there will be a flow of compressed air from valve VI for every level of flow required. Because of this there will be no tendency for the air from the other valves to "flow back" in the manifold and distort the output value. However with the binary assembly of Fig. 4 there will be many occasions when valves downstream in the assembly will not be open. In order to stop air flowing back in the manifold all the outlets of the valves are arranged to open as close as possible to one another at one end of the manifold. This is the arrangement which is shown in Fig. 4 where it can be seen that the various pipes from the outlet pors of the valves all lead into one end of manifold 40. A potential problem with the Fig. 4 assembly is that it may not be possible to provide from a single valve the maximum flow of 8X required from valve V4. Thus valve V3 may be divided into two valves each with a flow capacity of 2X, that is the same capacity as valve V2. Similarly valve V4 may actualy be four individual valves each having the same capacity as valve V2. In this manner the requisite ratios of flow outputs can be obtained. However even though the arrangement described in Fig. 4 reduces the effect of back flow it is still believed that this might be a problem particularly ■ hen high resolution is required. The embodiment of Fig. 3 represents another approach to this problem and which is thought to give even better results that the arrangement of Fig. 4. In the embodiment of Fig. 5 air from a suitable source is supplied to the inlet 50 of a tubular body 51 having an outlet 52 which can be connected to an air brush. The body 51 is also formed with four vent outlets 53, 54, 55 and 56 each of which is associated with a valve 57 basically of the kind shown in Fig.2. Thus each valve will have a rocker arm which can be driven by an electromagnet to seal its associated vent. Similarly each valve will have a second electromagnet to drive the valve into its open condition. The vent outlets 53 to 56 all have differing areas with vent 54 being twice the area of vent 53, vent 55 twice the area of 54 and vent 56 twice the area of 55. The four vents accordingly make up a binary suste in a manner very similar to the valves of Fig. 4. It will also be appreciated that the air brush itself will afford an appreciable resistance to the flow of air and that the four vents should be so dimensioned that with all the vents open and the air brush connected as it were in circuit the bulk of the air supplied to the inlet 50 will escape through the open vents oly leaving a very small residual flow through the outlet 52. With the arrangement just described closure of all the four vents will mean that all the ccmpressed air supplied to the inlet 50 will be passed directly to the air brush. This, of course, will give maximum intensity. For the next graduation of the available scale vent 53 is opened and so on throughout the full range of 15 scales. When starting all the vents will be open so that the closure of vent 53 will be the start of the colour or grey scale. As already mentioned the air brush itself provides a degree of resistance to the flow of compressed air. In fact the entire arrangement is analagous to an electrical circuit in which the vents 53 to 56 act in the manner of tappings or shunts of differing resistances and the air brush is a resistive load. This load can vary from air brush to air brush as it depends on small manufacturing tolerances in the nozzle of the brush and of the needle valve which lies coaxially in the nozzle to control the nozzle area. In view of these variations it may be necessary to "tune" the diameters of the vent openings for any one arrangement of the kind shown in Fig. 5 to the air brush with which it is to be used, thus the areas of the vent openings may not have the exact relationship which has been described. It will also be appreciated that the number of vent openings can be greater or less than 4 in accordance with the degree of variation in supply required. Furthermore whilst the embodiments just described have been set in the context of supplying compressed air to air brushes it will be understood that the present invention is in no way intended to be limited to such a use and is applicable to any situation in which a controllable flow of pressurised fluid is needed. - ii

Claims: -CLAIMS- 1. A valve for controlling pressurised fluid comprising an inlet (2) for the fluid, and and a pair of outlet ports (4,6) in communication with the inlet (2), the valve being characterised in that the inlet and outlet ports (2,4,6) are so arranged that with both outlet ports open the pressurised fluid will flow preferentially through only one of the outlet ports (4), and in that the valve includes an electro-magnetically controlled valve member (7) adapted in use to close port (4) so as to divert the flow of pressurised fluid to the other port (6). 2. A valve as claimed in claim 1, and further characterised in that the electromagnetic valve means (7,12,13,15) are double-acting so as in operation positively to open and close the valve member (7). 3. A valve as -claimed in claim 2, and further characterised in that it includes an arm (15) carrying a pad (7) for sealing port (4). 4. A valve as claimed in claim 3, and further characterised in that the arm (15) is mounted to pivot about a post (16) on either side of which are mounted electromagnets (12,13). 5. A valve as claimed in Claim 4 and further characteriased in that stop means (19,20,21) are provided to limit the opening movement of valve member (7). 6. A valve as claimed in claim 5 and further characterised in that the post froms part of a generally T-shaped mounting arrangement (16) for the electromagnets (12,13), the post being the central limb of this arragement and normally lying substantially horizontally. 7. A valve as claimed in any one of the preceding claims and characterised in that the electromagnets (12,13) are over-driven at the start of a respective opening or closing operation to provide very sharp actuation. 8. A valve assembly including a plurality of valves as claimed in any one of the preceding claims and connected to a single inlet for pressurised fluid. 9. A valve assembly comprising an inlet (50) for pressurised fluid and a main outlet vent (52), and characterised in that the vlave includes a plurality of secondary outlet vents (53,54,55,56) each associated with electromagnetic valve means (57) , the arrangement being such that the electromagnetic means (57) associated with each secondary outlet vent can be individually controlled so that selected combinations of the secondary outlet valves can be opened and closed so as to provide various flow rates at vent (52). 10. An assembly as claimed in claim 9 and further characterised in that the outlet apertures of at least some of the secondary outlet vants (53,54,55,56) are of differing sizes. 11. An assanbly as claimed in claim 10 and further characterised in that the apertures of the secondary outlet vents (53,54,55,56) are such that by apprpriately controlling the electromagnetic valves (57) associated therewith digital control of the pressurised fluid can be obtained. 12. An assembly as claimed in claim 11 and characterised in that the electromagnetic valves (57) are as claimed in any one of claims 1 to 9. 13. A valve substantially as hereinbefore described with reference to any one of the figures of the accompanying drawings.

Inventors: FULLER PAUL, FULLER, PAUL
Applicants: FULLER PAUL, FULLER, PAUL
Application year: 1984
Main classification: B05B15
IPC codes: B05C11