GB2093803A - Metering means for liquid - Google Patents

Abstract

Metering means for liquid comprises a pump (21) for conveying liquid from a reservoir (32) to a valve (30), and means (29) for displacing a valve element of the valve between a first position for discharge of the metered liquid and a second position for return of the liquid to the reservoir (32), so that the liquid can continuously circulate in the metering means. The valve (30) is preferably actuated by an electromagnet (29) controlled by a micro-computer which receives signals from a photo-electric cell and apertured disc combination. The disc is driven by the pump drive. <IMAGE>

Description

SPECIFICATION Metering means for liquid The present invention relates to metering means for liquid.

Metering devices for liquids are commonly used in dye works, where dyes must be produced which are a mixture of various base colours in a predetermined ratio. A metering device commonly adopted comprises a bellows which, in the suction phase, sucks liquid from a reservoir and closes a discharge port, and in the compression phase discharges the liquid into an appropriate receptacle and closes the suction port. A predetermined quantity of liquid is given by the stroke of the bellows. This type of metering device possesses essentially two disadvantages: firstly, the metering is not consistently accurate, as the quantity of liquid sucked in for a given equal stroke of the bellows can vary with the variation in the density of the liquid itself and secondly an excessive amount of time is required for suction and discharge.

Another type of metering device comprises a reservoir connected to a cylinder, the piston of which is actuated by an electromagnet. A second electromagnet operates a bar which, in the suction phase, brings the reservoir into communication with the piston by closing the discharge port, then, in the compression phase of the piston, opens the discharge port while simultaneously closing the suction port. The metering is given by the stroke of the piston. In this type of metering device as well, there are passive times in which the piston either sucks or discharges. Another disadvantage is represented by the difficulty of construction of the suction chamber, in that the tolerance between the diameter of the cylinder and that of the piston must be very close, otherwise the accuracy of metering of the liquid is adversely affected.

There is accordingly a need for a metering device which permits continuous circulation of the liquid to be discharged and an adequately precise form of metering which is not sensitive to the varying densities of the liquids to be metered, at the same time avoiding passive times.

According to the present invention there is provided metering means for liquid, comprising a reservoir for liquid, a liquid discharge valve, liquid conduit means leading from the reservoir to the valve and from the valve back to the reservoir, a pump operable to continuously convey liquid along the conduit means, and control means for causing displacement of a movable valve element of the valve between a first position for discharge of liquid through the valve and a second position for return of the liquid from the valve back to the reservoir.

In a preferred embodiment, the metering means comprises a pump for conveying the liquid from a container to the valve and control means for shifting the valve into two positions, one for discharging the metered liquid and the other for returning the liquid to the container so that the liquid can continuously circulate in the metering means.

An embodiment of the present invention will now be more particularly described by way of example and with reference to the accompanying drawings, in which: Fig. 1 is a schematic view part of metering apparatus according to the said embodiment; Fig. 2 is a schematic circuit diagram of the metering section of the metering apparatus; Fig. 3 is a cross-section along the line 3-3 of Fig. 1; and Fig. 4 is a cross-section, to an enlarged scale, of a valve of the metering apparatus.

Referring now to the accompanying drawings, there is shown in Fig. 1 metering apparatus 10 for liquids, comprising an electric motor 12 which drives, by means of a toothed belt 14, a shaft 1 6 on which are fixed pulleys 1 8 each connected by means of a belt 20 to a pump 21.

By way of example, the metering apparatus has been illustrated with four pumps, but the apparatus may comprise one or any number of such pumps.

At the'end of the shaft 1 6 opposite to that of the belt 14, there is fixed on the shaft 1 6 a disc 23, in which are formed a concentric ring of apertures 25 located at predetermined spacings from each other. A photoelectric cell 27, illustrated diagrammatically in Figs. 1 and 3, detects the number of apertures which pass during the rotation of the shaft 1 6 and despatches signals to a microcomputer (not shown). The microcomputer actuates an electromagnet 29, which operates a valve 30 (Figs. 2 and 4), as will be explained in more detail below.

The liquid to be metered is held in a container 32 (Fig. 2) having an inclined base 34 so as to prevent formation of deposits, and the container is connected to a pump 21 by a pipe 36. The pump 21 draws the liquid from the container 32 and delivers it through a pipe 38 to the valve 30.

As will be explained in more detail below, with the valve 30 normally closed, the liquid, passing through a pipe 40 is returned to the container 32.

When said valve 30 is opened, the liquid passes along a pipe 41 and is discharged into a receptacle 43.

The valve 30 comprises (Fig. 4) a first cylindrical central chamber 45 which is in communication with the pipe 38 by means of a first port 47 formed in the body of the valve.

Towards the bottom, the chamber 45 widens out to form a second cylindrical chamber 49, which is in communication with the pipe 41 through a second port 50. At the top, the chamber 45 widens out to form a third chamber 52, which is in communication with the pipe 40 via a third port 54. The chamber 52 in turn widens out at the top to form a fourth chamber 56, which is closed at the top by a cover 58. The cover 58 has an aperture 60 through which passes a rod 61 which is connected to the core 63 of the electromagnet 29. The rod 61 is axially slidable in the chambers 45, 49, 52 and 56 and possesses a portion 65 of smaller diameter, the function of which will be explained below.

The liquid is pumped by means of the pump 21 through the duct 38 and the first port 47 so as to arrive in the first chamber 45 of the valve 30.

From the chamber 45 the liquid passes, by means of the rod portion 65, into the third chamber 52 and then passes through the port 54 into the duct 40. In this position of the valve 30, the liquid is prevented from entering the second chamber 49 because access thereto is closed by the lower end 67 of the rod 61,which engages in a sealing ring 69, and is prevented from entering the fourth chamber 56, because the access thereto is closed by the rod 61 engaging in a sealing ring 70.

When the electromagnet 29 is energized, the core 63 and consequently the rod 61 displace downwards in the direction of the arrow A.

The liquid passes from the first chamber 45 into the second chamber 49, because the rod portion 65 is now situated between the first chamber 45 and the second chamber 49 and therefore the liquid discharges through the port 50 and the duct 41 into the receptacle 43.

In this position of the valve 30, the liquid cannot flow from the first chamber 45 to the third chamber 52, because the passage is closed by the rod 61, which engages in a sealing ring 72.

During the energizing of the electromagnet 29, the photoelectric cell 27 (Figs. 1 and 3) emits signals, at each passage of the apertures 25 of the disc 23, to the microcomputer, which counts the number of apertures passing in front of the cell 27.

When a predetermined number of passages corresponding to the quantity of liquid to be discharged into the receptacle 43 has been reached, the microcomputer de-energizes the electromagnet 29. In the case of a shaft, such as the shaft 16, which actuates several pumps, a singie disc 23 is sufficient for the photoelectric cell 27 to transmit the signals to the microcomputer, which can control the various electromagnets, commanding them individually according to a predetermined programme to discharge different quantities of liquids into the various receptacles.

The rod 61 of the valve 30, by means of the action of a restoring spring 74 (Fig. 4), returns to the position illustrated in Fig. 4 when the electromagnet 29 is de-energized, so that the liquid can pass from the duct 38 to the duct 40 and from the latter back to the container 32.

In the above-described metering apparatus, equipped with the pump 21 and the valve 30, the liquid is always in motion and therefore deposits of sediment are avoided. Moreover, with the energizing of the electromagnet 29 and consequently the opening of the valve 30, the liquid discharges into the receptacle 43 with a continuous flow, and therefore the passive discharge and charge times of the prior art metering devices are avoided.

Claims (8)

1. Metering means for liquid, comprising a reservoir for liquid, a liquid discharge valve, liquid conduit means leading from the reservoir to the valve and from the valve back to the reservoir, a pump operable to continuously convey liquid along the conduit means, and control means for causing dispiacement of a movable valve element of the valve between a first position for discharge of liquid through the valve and a second position for return of the liquid from the valve back to the reservoir.

2. Metering means as claimed in claim 1 , the control means comprising an electromagnet drivingly coupled to the valve element, signal emitting means for emitting signals as a function of the rotation of rotary means, and processing means for evaluating the emitted signals and controlling the electromagnet in dependence on the signal evaluation.

3. Metering means as claimed in claim 2, the signal emitting means comprising a photoelectric cell and the rotary means comprising an apertured disc arranged to modulate light received by the cell during rotation of the disc.

4. Metering means as claimed in either claim 2 or claim 3, the processing means comprising a microcomputer.

5. Metering means as claimed in any one of the preceding claims, wherein the valve comprises a liquid discharge chamber, a liquid return chamber, and a liquid inlet chamber, the valve element being operable by the electromagnet to place the inlet chamber selectively in communication with the discharge chamber and the return chamber.

6. Metering means as claimed in claim 5, the valve element comprising a rod having a portion of reduced diameter, the rod being displaceable to place the inlet chamber selectively in communication with the discharge chamber and the return chamber by way of a flow region surrounding said portion.

7. Metering means as claimed in either claim 5 or claim 6, wherein the valve further comprises an inlet port communicating with the inlet chamber and a first section of the conduit means between the reservoir and the valve, a return port communicating with the return chamber and with a second section of the conduit means between the valve and the reservoir, and a discharge port communicating with the discharge chamber and with a discharge outiet opening of the valve.

8. Metering means substantially as hereinbefore described with reference to the accompanying drawings.