GB2198484A

GB2198484A - Syphons and liquid metering devices

Info

Publication number: GB2198484A
Application number: GB08726598A
Authority: GB
Inventors: Peter Tait
Original assignee: University of Queensland UQ
Current assignee: University of Queensland UQ
Priority date: 1986-11-13
Filing date: 1987-11-13
Publication date: 1988-06-15
Also published as: GB8726598D0

Abstract

A first syphon tube 22 has its inlet end immersed in liquid and its discharge end has an airlock 23, to prevent the ingress of air; and a second syphon tube 20, of smaller diameter, is connected to the first syphon tube by a connecting line so that liquid flow through the second syphon tube reduces the pressure in the first syphon tube and so initiates the syphonic flow in the first syphon tube. The device may be used to dispense metered doses of liquids. <IMAGE>

Description

Title: "SYPHONS AND LIQUID METERING DEVICES" THIS INVENTION relates to improvements in syphons and in liquid metering devices.

There are many applications in which liquids must be accurately metered. One common example is the addition of nutrients such as urea to stock water.

Examples of mechanical metering devices for granular and liquid nutrients are disclosed in Australian Patent Application Nos. 75972/81 (Schafer) and 4652S/86 (Bloomfield) respectively, Because mechanical devices are prone to failure, with possibly devastating effects, nonmechanical metering devices have been sought Syphons have been used- but these have not proved fully satisfactory and because the syphon tube must be of a small diameter, limited flow rates only are possible.

It is an object of the present invention to provide means for initiating syphon flow in large syphons.

It 'is a preferred object to provide a nonmechanical means for metering liquids using one or more syphons.

Other preferred objects of the present invention will become apparent from the following description.

In one aspect the present invention resides in a method for initiating flow in syphon tubes wherein: a first syphon tube has its inlet end immersed in liquid and its discharge end has an airlock to prevent the ingress of air; and a second syphon tube, of smaller diameter, is connected to the first syphon tube by a connecting line so arranged that liquid flow through the second syphon tube reduces the pressure in the first syphon tube and so cause the liquid to rise up the intake side of the first syphon tube flow into its discharge side to initiate the syphon flow in the first syphon tube.

In a second aspect the present invention resides in a syphon assembly including: a first syphon tube having its inlet end immersed in liquid and its discharge end has an air lock to prevent the ingress of air; a second syphon tube of smaller diameter than the first syphon tube; and a line interconnecting the first and second syphon tubes; so arranged that liquid flow through the second syphon tube reduces the pressure in the first syphon tube to cause the liquid to use up the intake side of the first syphon tube and flow into the discharge side to initiate syphon flow in the first syphon tube.

The airlock may be provided by maintaining the discharge end of the first syphon tube immersed in liquid or by a substantially U-shaped bend containing liquid.

Preferably the flow of liquid through the second syphon tube draws air from the connecting line and so reduce the pressure at the crest of the first syphon tube, which interconnects the intake and discharge sides thereof.

Preferably the connecting line is connected at or adjacent the crest of the first syphon tube.

Preferably the connecting line is connected at or adjacent to the crest of the second syphon tube, or to the intake side of the second syphon tube a small distance be w the highest level of the liquid in which the intake side is immersed.

The first syphon tube may be connected to a third syphon tube of larger diameter and so initiate a syphon flow therein. Additional syphon tubes may be interconnected so each syphon tube initiates or triggers the flow in a syphon tube of greater diameter.

In a third aspect the present invention resides in a liquid metering device including: the syphon assembly hereinbefore described; a supply tank for liquid to be dispersed; a metering container connected to the supply tank; a first line connecting the metering container and at least one of the syphon tubes to at least partially evacuate the metering container to cause the liquid to be drawn from the supply tank to the metering container when liquid flows through the one syphon tube; and a metering syphon connected to at least one of the syphon tubes by a second line to transfer a metered volume of liquid from the metering container to the one syphon tube when liquid flows through the syphon tube.

The second line may be connected directly to the one syphon tube or to a chamber having a weir which dispenses the liquid into the vessel containing the liquid in which the first syphon tube is immersed.

To enable the invention to be fully understood, preferred embodiments will now be described with reference to the accompanying drawings, in which: FIG. 1 is a schematic view of the "Soxhlet" chemical apparatus which forms part of the known prior art; FIG. 2 is a schematic view of a syphon assembly of the present invention; FIG. 3 is a schematic view.of a liquid metering device incorporating a syphon assembly of the present invention and FIG. 4 is a schematic view of an alternative liquid metering device.

Referring to FIG. 1, this is an inverted syphon 10 as used in the "Soxhlet" chemical apparatus. Starting with the vessel 11 empty and filling with water, no discharge will occur. When the level reaches point A a syphon will initiate in the syphon tube 12 and the level will be briskly drawn down to level B where the syphon will fail.

The diameter of the syphon tube 12 cannot be very large, otherwise a stable flow over the crest will be achieved without the initiation of a syphon. The diameter should be sufficiently small so that surface tension effects dictate there is either full flow or no flow. This characteristic rather limits the ability to scale up the system for use as a "no moving parts fluid metering or batching device". The embodiment of the present invention shown in FIG. 2 overcomes this problem.

Referring to FIG. 2, the drawing shows a small inverted syphon tube 20 as in FIG. 1, which is connected by a small line 21 to a larger inverted syphon tube 22.

The larger inverted syphon tube 22 is slightly different in that it has an air lock 23 at its discharge end 24 to eliminate ingress of air at zero or low flow conditions.

When the water container or vessel 25 is filled to level A, flow initiates in the small bore syphon tube 20 as described with reference to FIG. l. Upon excluding the air flow from its outflow leg 25, a small suction will be present at the crest 26 of the syphon tube, This suction draws air from the larger syphon tube 22 and exhausts it with the outflow. The withdrawal of this air reduces the pressure in the syphon tube 22 and so draws water up both sides of the larger syphon tube 22, i.e. from the water container 25 and from the 'U" tube air lock 23. As more air is excluded, water begins to flow over the crest 27 of the larger syphon tube 22 at an ever increasing rate until a full syphon flow is initiated.This syphon tube 22 is capable of discharging at a much greater rate than the small syphon tube 20 and yet can be initiated by just a "droop at a time" inflow into the water container 25 because of the small bore of the Small syphon tube 20.

This concept can be scaled up.further by using three (or more) syphons of increasing diameter. It is likely in an application where very large flows are to be initiated by very small flows that many interconnected syphons would be used where the diameters are roughly a geometric progression e.g. 6mm, 18mum, 50mm, 150mm.

FIG. 3 shows how the syphon assembly may be used to dispense metered doses of liquids into e.g. a stock water through.

The water trough 30 has a water level 31 monitored by a float 32 connected to a water supply float valve 33. The valve 33 isboperable to discharge water into an open-topped tank 34.

A triggering syphon tube 35 is provided within a cylinder 36 in the tank, the cylinder being sealed at its base and having a mesh filter 37 to prevent the ingress of rubbish. The approximate maximum and minimum water levels in the tank 34 are indicated by dashed lines A & B. The level A is set by when overflowing into the cylinder 36 occurs while the level B is dependent on the inflow of water into the tank during the discharge cycle.

A line 38 connects the triggering syphon tube 35 to a larger diameter second syphon tube 39, which, in 'turn, is connected to a larger diameter syphon tube 40 via a line 41. it will be noted that line 41 is connected to the second syphon tube 39 just below the maximum water level A.

Both the second and third syphon tubes 39, 40 have respective air locks 42, 43. (In an alternative embodiment (not shown)1 their discharge ends 44, 45 may be below the water level 31 at which the float 32 opens the valve 33.) A line 46 connects the third syphon tube 40 to a manifold unit 47 which has three outlets 48 controlled by "on-off" valves 49.

Three sealed metering containers 50-52 have respective air lines 53-55 connected to the manifold 47, and liquid supply lines 56-58 arranged to draw liquids from respective supply tanks 59-6l.

Respective metering syphons 62-64 are provided to dispense metered volumes of liquid from the metering containers 50-52 into a mixing container 65. The outlet pipe 66 from the mixing container 65 has its inlet spaced above the floor of the container and the pipe is connected via a line 67 to the discharge side 68 of the third syphon tube 40.

The operation of the device will now be described.

The device is installed in the trough as shown in FIG. 3, with the air locks 42, 43 filled with water and suitable'additives e.g. urea, phosphoric acid are provided in the supply tanks 59-61. When the water level 31 in the trough falls, the float 32 opens float valve 33 and water flows into the tank 34.

When the water level reaches level A, water flows into the cylinder 36 and rises up until a syphon flow is initiated in the trigger syphon tube 35. This syphon flow triggers the second syphon tube 39, which then triggers syphon tube 40, in the manner hereinbefore described.

The flow through the syphon tube 40 generates a low pressure in the manifold 47 and thereby, in turn, a low pressure in metering containers 50-52. Atmospheric pressure in the supply tanks 59-61 causes the additives to flow up lines 56-58 to fill the metering containers 5 -5 and part-way up the air lines 53-55 and the discharge sides of the metering syphon tubes 62-64.

The triggering syphon tube 35 acts as a timer for the system and always fails first. The failure of the triggering syphon tube allows air into the other syphon tubes 39 and 40, failing then and stopping the syphons flows therein.

When the flow ceases in the third syphon tube 40, the suction effect is lost and the excess additives in the metering containers 50-52 are returned to their respective supply tanks. Syphon flows in the metering syphon tubes 62-64 transfer metered doses of the additives from the metering containers 50-52 to the mixing tank 65.

In the next cycle of the third syphon tube 40, i.e. when the tank 34 has refilled and syphon flows initiated, the additive mixture is drawn from the mixing tank 65 via the line 67 and is mixed with the water being-discharged from the tank 34 to the trough 30 via the third syphon tube. In this way the additives are dumped into the trough one cycle after they have been delivered into the mixing tank 65.

The outlet pipe 66 and the line 67 (and preferably the mixing tank 65) are arranged to below the height at which the pipe 67 is connected to the discharge side 68 of the third syphon tube 40 to prevent uncontrolled flow additives from the mixing tank 65 into the trough when the syphon tube is not operating. (The liquid in the lowest portion of the outlet pipe 66 and line 67 provide an airlock.) As the concentration levels of the additives in the 8ystem will also be lower, and can never exceed preset levels, the device is very safe and the dumping of the additives (or other chemicals) into the trough with the incoming water flow, efficient mixing of the additives -(or chemicals) in the water will occur.

While three metering containers 50-52 and three additive supply tanks 59-61 have been shown, the number may vary and a metering container may be connects ed to two or more supply tanks. Similarly two or more mixing tanks 65 may be used where pH sensitive additives or chemicals should not be mixed in concentrated forms.

The valves 49 allow the respective additives to be isolated, or selected, as required.

FIG. 4 shows an alternative liquid dispensing device using the present method to discharge a dose of additive to the water container 70.

The suction tube 71 draws the additive 72 up from the additive tank 73 but cannot draw it up sufficiently high to initiate a syphon within itself. Water will also be drawn up the discharge tube 74 from the weir reservoir 75 in the water container 70 but this too will reach an equilibrium height or cease to flow.

On failure of the syphon the suction tube 71 returns to atmospheric pressure thus dumping excess additive 72 back in the additive tank 73. The water drawn up the discharge tube 74 falls back thus creating a syphon in the discharge tube 74 which drains the metered dose of additive into the weir reservoir 75 in the water container 70. Thus a known volume of additive 72 has been added to a known volume of water in the water container 70 with no moving parts.

The volume of additive 72 dispensed each time can be varied by varying the distance C-D in the measuring tank 76, which receives the additive from the tank 73 via tube 77, and the distance between the bottom of the discharge tube 74 and the floor of the tank 76. By e.g. making the intake leg of the discharge tube 74 adjustable in height in the measuring tank 76, the volume of the additive can be selectively varied.

It will be readily apparent to the skilled addressee that the suction and discharge tubes 71, 74 can be connected to the measuring tank(s) 46 for a number of different additives 72.

The potential applications for the present invention are almost limitless and they can be found, e.g. in the agricultural, chemical and food industries where liquids must be accurately dispensed.

The embodiments described with reference to FIGS. 2 to 4 are by way of illustrative examples only and various changes and modifications may be made thereto without departing from the scope of the present invention as defined in the appended claims.

Claims

CLAIMS:

1. A method for initialing flow in syphon tubes wherein: a first syphon tube has its inlet end immersed in liquid and its discharge end has an airlock to prevent the ingress of air and a second syphon tube, of smaller diameter, is connected to the first syphon tube by a connecting line so arranged that liquid flow through the second syphon tube reduces the pressure in the first syphon tube and so cause the liquid to rise up the intake side of the first syphon tube flow into its discharge side to initiate the syphon flow in the first syphon tube.

2. A method according to Claim 1 wherein: the airlock ia provided by maintaining the discharge end of the first syphon tube immersed in liquid or by a substantially U-shaped bend containing liquid.

3. A method according to Claim 1 or Claim 2 wherein: the first syphon tube is connected to a third syphon tube of larger diameter to initiate syphon flow in the syphon tube.

4. A syphon assembly including: a first syphon tube having its inlet end immersed in liquid and its discharge end has an air lock to prevent the ingress of air; a second syphon tube of smaller diameter than the first syphon tube; and a line interconnecting the first and second syphon tubes; so arranged that liquid flow through the second syphon tube reduces the pressure in the first syphon tube to cause the liquid to use up the intake side of the first syphon tube and flow into the discharge side to initiate syphon flow in the first syphon tube.

5, An assembly according to Claim 4 wherein: the airlock is provided by maintaining the discharge end of the first syphon tube immersed in liquid or by a substantially U-shaped bend containing liquid.

6. An assembly according to Claim 4 or Claim 5 wherein: the connecting line is connected at one end at or adjacent to the crest of the first syphon tube, and at the other end, at or adjacent the crest of the second syphon tube or to the intake side of the second syphon tube a small distance above the highest level of the liquid in which the intake side is immersed.

7. An assembly according to any one of Claims 4 to 6 wherein: the first syphon tube is connected to a third syphon tube of larger diameter to initiate syphon flow in the third syphon tube.

8. An assembly according to Claim 7 wherein: additional syphon tubes are interconnected so that each syphon tube initiates syphon flow in a syphon tube of larger diameter.

9, A liquid metering device including: a syphon assembly according to any one of Claims 4 to 8 including: the syphon assembly hereinbefore described; a supply tank for liquid to be dispersed; a metering container connected to the supply tank; a first line connecting the metering container and at least one of the syphon tubes to at least partially evacuate the metering container to cause the liquid to be drawn from the supply tank to the metering container when liquid flows through the one syphon tube; and a metering syphon connected to at least one of the syphon tubes, by a second line to transfer a metered plume of liquid from the metering container to the one syphon tube when liquid flows through the syphon tube.

10. A liquid metering device according to Claim 9 wherein: the first line is connected to a manifold connected to a plurality of metering containers through respective valves; each metering container has a respective supply tank; and the second line is connected to a mixing tank which receives liquid from the metering containers.

11. A liquid metering device according to Claim 9 or Claim 10 wherein: the second syphon tube acts to time the syphon flow in the assembly, the failure of the syphon flow in the second syphon tube enabling air to enter the first syphon tube and fail the syphon flow in the first syphon tube.

12. A method for initiating flow in syphon tubes substantially as hereinbefore described with reference to any one of FIGS. 2 to 4 of the accompanying drawings.

13. A syphon assembly substantially as hereinbefore described with reference to any one of FIGS. 2 to 4 of the accompanying drawings.

14. A liquid metering device substantially as hereinbefore described with reference to FIG. 3 or FIG. 4 of the accompanying drawings.