Device for the metered supply of a metering liquid

Abstract: Device for the metered supply of a liquid fertilizer or nutrient to irrigation water in a pipe (8) for hydroponic cultivation, said pipe having a branch (24) with a pump (52) for pressurising branched-off water a number of injection channels (82a..82h), each connected to the delivery side of said pump (52), and each having a widened part (83a..83h) at the position of which an individual metering liquid supply channel (86a..86h) connected to a metering liquid supply (32a..32h) opens out with in series in each metering liquid supply channel a flowmeter (64a..64h), a non-return valve (66a..66h) and a metering valve (68a..68h), in which each metering valve (68a..68h) and the corresponding flowmeter (64a..64h) are connected to a measuring and control unit (44) for pulsed control of the opening of the relative metering valve (68a..68h) the respective outlets (36a..36h) of the injection channels (82a..82h) opening into the irrigation water pipe downstream of the branch (24).

Description: The invention relates to a device such as described in the preamble of claim 1 and known in itself from EP-A-0 363 168. In this known device water is supplied via a watermeter to a main pipe into which metered amounts of nutrient and/or fertiliser are introduced; the mixture of water and nutrient and/or fertiliser is then fed to a mixing tank and from there to a distribution system with its main conduit and branch conduits. Such a device is used in the so-called hydroponic cultivation, where plants are not growing in soil containing fertiliser and nutrients, but in a substrate to which the substances necessarry for growth are supplied via irrigation water. The irrigation water is drawn from the mixing tank and fed via various valves, controlled by the control unit, to the various substrates. This known device operates in a discontinous process. The invention is based on the insight that a continous process-in which the irrigation water is circulated constantly and the remaining irrigation water is mixed with freshly supplied water-offers advantages particularly when one changes often the composition of the irrigation water by changing the relative amounts of nutrient and/or fertiliser. However, it must then be possible that the various substances to be added are acurately metered to the irrigation water without the risk that the supply channels, through which a metered amount of fertiliser or nutrient is fed into the pipe, become obstructed or clogged. According to the invention this is obtained by means of the measures as described in characterising clause of the main claim. Preferred embodiments are described in the claims 2-6. It is observed that using accurate flow sensors for adding metered amounts of liquid fertiliser to irrigation water, and positioned between supply vessels and a static mixer, is known in itself from "TUINDERIJ" volume 69, nr. 25, December 7, 1989 pages 48-49, title: "Toediening is nu exact te meten". The invention is explained with reference to the drawing, in which: Figure 1 is a general flow chart of a device for hydroponic cultivation in which the metering device according to the invention is used; Figure 2 shows, also schematically, but in greater detail, the layout of said device with the components involved; Figure 3 shows a partial cross-section of a metering module used in the device according to the invention; Figure 4 shows a top view of said module; Figure 5 shows a top view of the device according to Figure 2; and Fig. 6 shows a perspective view of said device. The flow chart of a plant for hydroponic cultivation in which the device according to the invention is used is shown in Figure 1. The circuit used there is as follows: From a connection 2 the irrigation water to be used for the irrigation, and yet to be provided with nutrients and fertilizers, is fed to a mixer tap 4 for mixing there with spent irrigation water supplied through the inlet 6. The irrigation water then passes through the pipe 8 into the suction side of a pump 10 which pumps it to the irrigation nozzles 12 situated above the cultivation substrate 16. The irrigation water which is left flows through the pipe 18 to the collection tank 20, from where it flows through the disinfecting device 22 (which can, of course, be omitted in certain cases) to the connection 6 of the three-way valve 4. At the branch 24 irrigation water is branched off and fed via the pipe 26 to the inlet 28 of the metering device 30 shown schematically by dashed and dotted lines, where it is mixed with the correct quantities of nutrients and fertilizers which are supplied via the individual tanks 32a..32h to the inlets 34a-34h of the metering device 30. The irrigation water mixed with nutrients and fertilizers is conveyed back through the two outlets 36a, 36b to the connection points 38, 40 of the pipe 8. The metering is carried out by means of pulsating metering valves, one for each of the inlets 34a..34h, and individually controlled by means of a schematically shown control manifold 42 from a control unit 44. This control unit obtains at its inlet 48 information concerning the quantity of irrigation water which has passed the metering device. Information concerning the electrical conductivity and the acidity is also supplied. It is also possible to analyze the irrigation water composition by means of sensors. The control unit receives information from eight individual flowmeters through the manifold 50, indicating how much of each fertilizer has been added. On the basis of these data, the control unit controls the opening times of the individual metering valves. Figure 2 shows in more detail the components present inside the square 30 shown by dashed lines, with the appropriate external components. It is pointed out here that the metering device is split into two identical metering modules, each for metering four different nutrients or fertilizers. This ensures that nutrients or fertilizers which are incompatible when undiluted or with little dilution do not come into contact with each other, something which could lead to undesirable reactions. The irrigation water branched off at 24 is brought to a certain pressure by the pump 52. It flows through the manually operated valve 54, which is adjusted by hand on the basis of the pressure indicated by the pressure recorder 56. The prepressure on the metering modules to be described below, and thus the maximum quantity of fertilizer to be sucked in, is determined in this way. It then flows via the dirt separator 60 to the inlets 28a, 28b of the two identical metering modules. The outlets 36a, 36b thereof are connected by means of the buffer tanks 37, 39 to the branches 38, 40 on the pipe 8. Liquid fertilizers and nutrients to be mixed with the irrigation water are supplied to each of said metering modules 62a, 62b through the inlets 34a..34d and 34e..34h respectively. In series with each inlet 34a..34h is a flowmeter 64a..64h, a non-return valve 66a..66h and a pulsatingly controlled metering valve 68a..68h. The liquid nutrients and fertilizers fed in through the injection channels 70a..70h are mixed in the metering modules 62a, 62b with the irrigation water fed in through the inlets 28a, 28b, and the resulting mixture is, as said before, discharged through the outlets 36a, 36b, and then mixed with the irrigation water flowing into the pipe 8. A practical embodiment of a metering module for four metering liquids is shown in Figures 3 and 4. Figure 3 shows a partial view, partial section through the metering module 62a, and Figure 4 shows a top view thereof. This metering module 62a comprises a first housing 80 containing a number of adjacent injection channels situated at right angles to the lengthwise direction of the housing, one of which is indicated by the reference numberal 82a. The inlet end opens into the common inlet channel 28a, and the outlet end opens via the channel 84a into the common outlet channel 36a. A metering liquid supply channel is situated at right angles to each of the inlet channels, for the inlet channel 82a indicated by 86a. Each of such metering liquid supply channels lies in line with a valve channel formed in a second housing 88, for the channel 86a indicated by 90a. Each valve channel 90a contains a valve seat 92a which can be shut off by the closing element 94a of an electromagnetic metering valve mechanism 96a. By means of a transition channel 98a, which contains a ball 100a acting as a non-return valve and co-operating with a shoulder the valve channel 90a is connected to the outlet channel 102a, the inlet of which is the metering medium inlet, thus one of the inlets 34a..34d in Figure 2. The irrigation water supplied under a certain excess overpressure through the inlet 28a to the individual channels 82a..82d flows at high speed from the outlet opening of said channel 82a into the widened part 83a, so that on this spot a vacuum is produced with the result that, when the valve element 94a opens the valve seat 92a, the metering liquid supplied through the corresponding inlet 34a is sucked in through the corresponding flowmeter 34a. The opening and closing of the valve seat 94a thus determine the metering of the metering liquid. Figures 5 and 6 show how the device according to the invention is extremely suitable for combining with a self-contained unit which can be accommodated in the irrigation water pipe. It is observed that the connection at the suction side of the pump 10 circulating the irrigation water and the use of its own process pump 52 give the advantage that the metering system works independently of the system pump 10. A particularly accurate metering system can be achieved economically with the measures according to the invention.

Claims: Device for the metered supply of a liquid containing a liquid fertiliser or nutrient to irrigation water flowing in a pipe (8) for hydroponic cultivation containing irrigation water at a predetermined pressure comprising - a number of supply channels (90a..90h) for introducing a metered amount of fertiliser or nutrient into said pipe (8), each supply channel having a metering valve (68a..68h) each metering valve being connected to a measuring and control unit (44) for control of the opening of the respective metering valve (68a..68h) depending on a desired nutrient or fertiliser concentration for supplying to the irrigation water the desired quantity of metered fluid by means of the injection unit, characterized by a branch (24) on the above mentioned pipe (8) with a pump (52) for bringing the branched-off irrigation water to a predetermined pressure and for re-introducing the branched-off irrigation water into the pipe (8), a number of injection channels (82a..82h), each of which being connected to the delivery side of said pump (52), and each having a widened part (83a..83h) at the position at which one of said supply channels (90a..90h) opens into it, in series in each of said supply channels (90a..90h) which each open into a corresponding injection channel (82a..82h) a flowmeter (64a..64h), a non-return valve (66a..66h) and said metering valve (68a..68h). Device according to claim 1, characterized in that a number of adjacent injection channels (82a..82h) are formed in a common first housing (80), the inlet end of each channel opening out into a common inlet channel (28a..28b), and the outlet end opening into a common outlet channel (36a..36b), while the supply channels (90a..90h) situated at right angles to the respective injection channels are also formed in said housing. Device according to claim 2, characterized in that each supply channel (90a..90h) connects to the outlet end of a valve (96a..96h) which is formed in a second housing and of which the inlet end interacts with the closing element of a metering valve (62a..62h), and which valve (96a..96h) is connected to the outlet channel (102a..102h) of a flowmeter (64a..64h) by means of a short transition part (98a..98h) in which a shoulder (99a..99h) co-operating with a shut-off ball (100a..100h) is formed. Device according to claim 3, characterized in that a number of adjacent supply channels (90a..90h) and transition channels (98a..98h) are formed in the second housing (88), and said second housing (88) joins, and is connected to, said first housing (80). Device according to claims 2-4, characterized in that each metering valve (62a..62h) and each flowmeter (64a..64h) forms an individual component. Device according to claims 1-5, characterized by at least two metering modules (62a..62h) which are each formed from a first and a second housing and which are each connected by means of a buffer space (37, 39) to the irrigation water pipe (8).

Inventors: OOSENBRUG ALBERT-JAN, ZWARTVELD DICK, OOSENBRUG, ALBERT-JAN, ZWARTVELD, DICK
Applicants: PRIVA AGRO HOLDING BV, PRIVA AGRO HOLDING B.V.
Application year: 1991
Main classification: A01G31
IPC codes: A01G31