WO2010030227A1

WO2010030227A1 - Method and apparatus for adding a liquid additive to a pressurized liquid flowing in a conduit

Info

Publication number: WO2010030227A1
Application number: PCT/SE2009/051013
Authority: WO
Inventors: Alireza Sepehr
Original assignee: 3R Innovations Teknik Handelsbolag
Priority date: 2008-09-12
Filing date: 2009-09-11
Publication date: 2010-03-18

Abstract

The method and apparatus of the present invention make it possible to inject a predetermined exact dose of additive liquid (such as chlorine solution) into pressurized water supply lines at various pressures without any changes in power consumption or mechanical strengthby using the pressure in the water supply line. Further, the design of the apparatus is such that deposits and external factors like sand will have no effect on its continuous operation, and the apparatus will be able to work for long periods without maintenance. In a preferred embodiment, no electricity is necessary for the injection of the additive.

Description

Method and apparatus for adding a liquid additive to a pressurized liquid flowing in a conduit.

DESCRIPTION

TECHNICAL FIELD

The present invention relates to a method of and an apparatus for adding a liquid additive to a pressurized first liquid flowing in a conduit.

BACKGROUND ART

It is frequently desired to mix water with a liquid additive in metered quantities. Australian Pat. Appln. No. AU 79239/75 discloses an apparatus for feeding additives and/or admixtures such as fertilizers, insecticides etc, in water soluble or suspension form, or substances in liquid form as additives and/or admixtures but not necessarily having a water content, to irrigation or other spray distribution lines. To feed such liquid substances, additives, admixtures or treating substances at a controlled rate into an irrigation line or other spray line, the apparatus has a chamber for holding the additive. The chamber is connected to a conduit, in which water flows, by an inlet and an outlet that has a valve. The conduit is of a design intended to provide a lower pressure at the chamber outlet than at the chamber inlet. The chamber for holding the additive contains a removable piston with edge sealing gaskets. Alternatively, the additive is provided in a cartridge that has its own independent piston or a flexible seal and is placed in the chamber. As a further alternative, the chamber may be filled with solid or granular additives. The liquid additives are pressed out through the outlet into the conduit by the pressure from the water in the conduit acting on the piston or the flexible seal, while solid or granular additives require a flow of water from the conduit through the chamber to be solved and fed through the outlet into the conduit. However, this apparatus cannot give an exact dose of the additive, and the piston with edge sealing gaskets is sensitive to presence of sand or other abrasive material in the water.

An exact dose can be provided by the chemical infeed system for a sprinkler or irrigation system disclosed in U.S. Pat. Appln. Pub. No. US 2001/0048037 Al. There, the infeed system comprises at least one receptacle or container for receiving and holding a quantity of a desired chemical, a pump having an inlet or suction side for pumping or drawing the chemical from the receptacle and a discharge or outlet side connected in liquid communication with the water carrying element or supply line for pumping the chemical into the water flow therethrough. The pump is stated to be an important element of the invention, but no type of pump is specified. In case the pump is of piston type, for example, it is sensitive to the presence of sand or other abrasive material in the water. The pump can be powered by conventional line current, such as ordinary household current, and is actuated by a relay or other device which connects the pump to a power source when a power signal is received from a controller of the sprinkler or irrigation system. However, in view of the threatening "greenhouse effect", it is desirable to reduce the power consumption of electric appliances as much as possible.

Another method and apparatus is disclosed in British Patent No. GB 1,368,523 and is primarily intended for injecting a bloat control chemical into the drinking water fed to cow troughs to control bloat in cows, but may also be used in fertilizer and weed control systems, and for mixing oil and petrol. The apparatus comprises a transparent cylindrical housing having a piston with a coaxial passage therethrough closed by a bottom closure member carried on a stem passing through the passage. A cage is bolted to the bottom of the piston and carries a plunger, which in an end position of the piston is entered into a cylinder formed in a plug. Primary liquid enters from below and carries the piston, the closure member and the cage together up the cylindrical housing, forcing liquid ahead of them out of an outlet in a top cap; additive is drawn through a valve into the cylinder as the plunger rises. At the top of the cylindrical housing, a spring strikes the cap causing the closure member to separate from the bottom of the piston and open the passage; the piston, closure member and cage then sink to the bottom where the plunger re-enters the cylinder forcing the contents thereof past the valve into the cylindrical housing. The closure member has legs that strike the bottom cap causing the closure member to rise and again close the passage, and the cycle recommences. The quantity of additive pumped on each cycle may be altered by adjusting the plug along a screw. With increase in the rate of flow of the main liquid, the proportion of additive will tend to diminish, since while the movable parts are descending in the cylindrical housing, there is unobstructed flow between the inlet and outlet through the passage. This apparatus requires the entire flow to pass through the apparatus, is technically complicated and therefore expensive, and the piston with its seals is sensitive to presence of sand or other abrasive material in the water.

None of the prior art methods and devices above can inject an exact dosage of an additive liquid into a water supply pipe at various pressures in the pipe and with no change in the demand for power to accomplish the injection.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a method of and an apparatus for adding a liquid additive to a pressurized first liquid flowing in a conduit, which provides an exact dose of the additive irrespective of the pressure in the pipe, reduces power consumption, and is technically simple.

In a method of the kind referred to in the first paragraph above, this object is achieved in accordance with the invention by

- providing a measuring vessel having a first chamber for receiving and discharging the liquid additive, and a second chamber for receiving and discharging the first liquid, the two chambers being separated by a movable wall member, so that movement of the wall member causes reception of liquid in one chamber and discharge from the other chamber;

- further providing a device for moving the wall member, a source for the liquid additive, a discharge receptor for discharged first liquid, and flow circuit components for alternately connecting the first chamber to the source and to the conduit and for alternately connecting the second chamber to the conduit and to the receptor; - moving the wall member so as to increase the volume of the first chamber while reducing that of the second chamber in order to transfer a predetermined volume of the liquid additive from the source for the additive into the first chamber by moving the movable wall member in one direction, and simultaneously discharging an equal volume of the first liquid from the second chamber to the discharge receptor; thereafter - moving the movable wall member so as to increase the volume of the second chamber while reducing that of the first chamber in order to transfer an equal volume of the pressurized first liquid from the conduit to the second chamber by moving the movable wall member in a reverse direction, and simultaneously discharging the predetermined volume of the liquid additive from the first chamber into the conduit, where the pressurized first liquid flows; and

- repeating the transferring and discharging steps.

Similarly, in an apparatus of the kind referred to in the first paragraph above, this object is achieved in accordance with the invention by - a measuring vessel having a first chamber for receiving and discharging the liquid additive, and a second chamber for receiving and discharging the pressurized first liquid, the two chambers being separated by a movable wall member, so that movement of the wall member causes reception of liquid in one chamber and discharge from the other chamber; - a source for the liquid additive;

- a discharge receptor for discharged first liquid;

- a device for moving the wall; and - flow circuit components for alternately connecting the first chamber to the source and to the conduit and for alternately connecting the second chamber to the conduit and to the receptor.

In such a method and such an apparatus, the pressure of the first liquid flowing in the conduit is used for at least assisting in injecting an exact dosage of liquid additive into the conduit, irrespective of the pressure in the conduit. The present invention is technically simple, and the use thereof at various conduit pressures does not require any replacement of parts or change in power consumption.

To reduce the consumption of pressurized first liquid it is recommendable to use the discharged volume of the first liquid from the second chamber to the discharge receptor to prepare the liquid additive.

Further characterizing features in various embodiments of the invention and what is achieved thereby will be obvious from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in more detail with reference to preferred embodiments and the appended drawings.

Fig. 1 is a schematic block scheme of an apparatus in accordance with a first preferred embodiment of the present invention for adding a liquid additive to a pressurized first liquid flowing in a conduit, the apparatus including a hydraulically controlled hydraulic actuator.

Fig. 2a is a side view of a flip-flop device included in the apparatus of Fig. 1.

Fig. 2b is a bottom view of the flip-flop device of Fig. 2a.

Fig. 3 is a schematic block scheme of an apparatus in accordance with a second preferred embodiment of the present invention for adding a liquid additive to a pressurized first liquid flowing in a conduit, the apparatus including an electrically controlled hydraulic actuator.

Fig. 4 is a schematic block scheme of an apparatus in accordance with a third preferred embodiment of the present invention for adding a liquid additive to a pressurized first liquid flowing in a conduit, the apparatus including an electrically controlled linear solenoid actuator.

Fig. 5 is a schematic block scheme of an apparatus in accordance with a fourth preferred embodiment of the present invention for adding a liquid additive to a pressurized first liquid flowing in a conduit, the apparatus including an electrically controlled linear motor actuator.

MODE(S) FOR CARRYING OUT THE INVENTION A first preferred embodiment of an apparatus according to the invention for adding a liquid additive to a pressurized first liquid flowing in a conduit 1 is shown in Fig. 1. The apparatus includes a measuring vessel 2 having a first chamber 3 for receiving and discharging the liquid additive, and a second chamber 4 for receiving and discharging the pressurized first liquid, the two chambers being separated by a movable wall 5 member, so that movement of the wall member 5 causes reception of liquid in one chamber and discharge from the other chamber. The measuring vessel 2 preferably is made of a synthetic resin, such as polyethylene. The apparatus further includes a source 6 for the liquid additive, a discharge receptor 7 for discharged first liquid, a device 8 for moving the wall member 5; and flow circuit components 10-18 for alternately connecting the first chamber 3 to the source 6 and to the conduit 1 and for alternately connecting the second chamber 4 to the conduit 1 and to the receptor 7. In an exemplary embodiment, the first liquid may be water to be disinfected, for example, and the liquid additive may then be chlorinated water. Chlorinated water can be prepared in many ways well known to the skilled art worker, but suitably a hypochlorite, preferably calcium hypochlorite, Ca(ClO)₂ (also known as 'bleaching powder'), is added to the discharged water, that is to be returned to the pressurized water conduit 1 by injection thereinto.

The flow circuit components 10-18 include a two-position, three-way valve 10, a control unit 11 for controlling the valve 10, and piping 12, 13, 14 necessary for alternately connecting the conduit 1 to the second chamber 4 and the second chamber 4 to the receptor 7. The two-position, three-way valve 10 has a slide, not shown, that is movable between its two positions for connecting one of the valve ports alternately with the two other ports. In the embodiment shown in Fig. 1, pipe 12 conducts water from the conduit 1 to the two- position, three-way valve 10, pipe 13 interconnects valve 10 and the second chamber 4, and pipe 14 conducts water from valve 10 to the discharge receptor 7. Dependent on the operational position of the valve 10, water flows either from conduit 1 through pipe 12, valve 10 and pipe 13 into the second chamber 4 in the measuring vessel 2, or from the second chamber 4 through valve 10 and pipe 14 to the discharge receptor 7. The flow circuit components further include an inlet pipe 15 with a check valve 16 for connecting the source 6 of additive to the first chamber 3 and an outlet pipe 17 with a check valve 18 for connecting the first chamber 3 to the conduit 1.

In the embodiment shown in Fig. 1 , the movable wall 5 is the top portion of an inverted cup-shaped bellows, preferably of rubber, silicone or a fluoroelastomer, and the device 8 for moving the wall 5 includes a first hydraulic actuator 20, which is operatively connected to the movable wall 5 and uses the pressurized first liquid as hydraulic fluid. The use of the bellows as movable wall makes the apparatus of the invention essentially insensitive to presence of sand or other abrasive material in the water. As the fluid pressures in the first chamber 3 and the second chamber 4 are essentially equal and balance each other, the hydraulic actuator 20 as such does not have to surmount the pressure in the conduit 1 by itself, it only has to supply the extra force required on top of the pressure in the conduit to inject the liquid additive into the pressurized liquid flowing in the conduit 1. The first hydraulic actuator 20 includes a cylinder barrel 21, in which a piston 22 that is connected to a piston rod 23 can reciprocate. The barrel 21 is closed by the cylinder top and by the cylinder head, where the piston rod 23 comes out of the actuator. The piston 22 divides the inside of the cylinder into two chambers, the top chamber and the piston rod side chamber, and the piston rod 23 has one end fixed to the movable wall 5. A pipe 24 connects the second chamber 4 to the top chamber of the first actuator 20, and the piston rod chamber houses a compression spring 25.

Further, in the embodiment shown in Fig. 1, the control unit 11 includes a second hydraulic actuator 30 that uses the pressurized first liquid as hydraulic fluid, and a mechanical flip- flop device 40 that is operatively connected between the actuator 30 and the two-position, three-way valve 10. The second hydraulic actuator 30 includes a cylinder barrel 31, in which a piston 32 connected to a piston rod 33 is reciprocable. The barrel 31 is closed by the cylinder top and by the cylinder head, where the piston rod 33 comes out of the actuator 30. The piston 32 divides the inside of the cylinder into two chambers, the top chamber and the piston rod side chamber, and the piston rod 33 has one end attached to the flip-flop device 40. A pipe 34 provided with a control valve 35 connects the top chamber of the first hydraulic actuator 20 to the top chamber of the second hydraulic actuator 30, and the piston rod chamber houses a compression spring 36.

A preferred embodiment of the flip-flop device 40 is shown in Figs. 2a and 2b and comprises a cuboid housing 41 having two pairs of opposed sides, a top and a bottom. Here, the sides of the first pair are termed long sides 42, the sides of the other pair are termed short sides 43 and 44, and the top and the bottom are open. A shaft 45 is carried by the two long sides 42 substantially in the center thereof but displaced toward one of the short sides. A shorter first pivotal member 46 is pivotally attached to the shaft 45 and extends out through an opening provided in the short side 43 located closest to the shaft 45, and a longer second pivotal member 47 is also pivotally attached to the shaft 45 and extends out through an opening provided in the short side 44 located farthest away from the shaft 45. The openings extend essentially the same distance above and below a horizontal plane through the shaft 45 in Fig. 2a. At its free end, each of the pivotal members 46 and 47 is provided with a sideward extending projection 48 and 49, respectively, and two helical tension springs 50, 51 connect the sideward extending projections of one pivotal member with those of the other pivotal member. At their ends, the tension springs 50, 51 may be provided with rings 52, 53 that are hooked over the sideward extending projections 48, 49. On the short side 44 that is associated with the longer pivotal member 47, the housing 41 has an integral upper attachment lug 54 and an integral lower attachment lug 55. The housing 41 can be easily manufactured by cutting a rectangular aluminum tube, for example, and bending the attachment lugs 54 and 55 into the desired position.

The pivotal members 46 and 47 preferably are plate-shaped, and the force from the springs 50, 51 makes the pivotal members 46 and 47 abut against substantially either the upper or the lower edge of the openings in the short sides 43 and 44. Thanks to the different lengths of the two pivotal members 46, 47, a movement of the shorter pivotal member 46 from one end position towards the other will implement a positive "snap-action" to the longer pivotal member 47. The piston rod 33 of the second hydraulic actuator 30 is connected to the rod 48 of the shorter pivotal member 46, and the rod 49 of the longer pivotal member 47 is connected to the two-position, three-way valve 10.

The apparatus works as follows. Fig. 1 shows the apparatus at a moment just before the discharge of water from the second chamber 4 in the measuring vessel 2 through pipe 13, valve 10 and pipe 14 to discharge receptacle 7 and the simultaneous sucking of liquid additive from source 6 through inlet pipe 15 past check valve 16 into the first chamber 3 by the upward movement of the movable wall member 5 is completed. When the pressure in the second chamber 4, the top chamber of the first hydraulic actuator 20 and the top chamber of the second hydraulic actuator 30 has fallen sufficiently to permit the compression spring 36 in the second actuator 30 to lift the piston 32 and its piston rod 33 and thereby the rod 48 of the short first pivotal member past an equilibrium position, the rod 49 of the long second pivotal member 47 in the flip-flop device 40 will snap over from a bottom position in Fig. 1 to a top position, thereby pulling the slide in the two-position, three-way valve 10 from a lower to an upper end position. This snap action causes the valve 10 to close the passage to outlet pipe 14 and further to the discharge receptor 7 and instead open a passage from pipe 12 to pipe 13 between the valve 10 and the second chamber 4, so as to permit pressurized water from conduit 1 to fill the second chamber 4 while simultaneously discharging the liquid additive from the first chamber 3 via check valve 18 and pipe 17 into the pressurized water conduit 1.

As pressurized water flows into the second chamber 4, it passes through pipe 24 to the top chamber of the first hydraulic actuator 20 and further through pipe 34 with control valve 35 into the top chamber of second hydraulic actuator 30 in the control unit 11. The pistons 22 and 32 of the actuators 20 and 30, respectively, are pressed down against the force of the associated compression spring 25 and 36, respectively. The piston rod 23 of the first actuator 20 moves the movable wall member 5 downwards to discharge the liquid additive from the first chamber 3 into the pressurized water conduit 1. Simultaneously, the piston rod 33 of the second actuator 30 in the control unit 11 starts pressing rod 48 of the short pivotal member 46 downward, and upon passing an equilibrium position, the flip-flop device 40 is triggered and the rod 49 of the long pivotal member 47 is snapped from an upper end position to a lower end position, thereby pulling a slide in the two-position, three-way valve 10 from an upper to a lower end position. This snap action causes the valve 10 to close the passage from pipe 12 via pipe 13 to the second chamber 4 and instead open a passage from the second chamber 4 via pipes 13 and 14 to the discharge receptor 7, so as to permit pressurized water from second chamber 4 to be discharged into receptor 7, while simultaneously sucking liquid additive from the source 6 through pipe 15 with check valve 16 into the first chamber 3. Then the operating cycle is completed, and a new cycle can be started.

Figs. 3-5 show a second, a third and a fourth preferred embodiment of the apparatus of the present invention. In view of the great similarities between the embodiment of Fig. 1 and those of Figs. 3-5, most of the reference numbers are identical, but where differences exist, corresponding reference numbers will be used in the description and the drawings but selected from the 300 series in Fig. 3, the 400 series in Fig. 4 and the 500 series in Fig. 5.

The embodiment shown in Fig. 3 differs from that of Fig. 1 in respect of the control unit 311. Thus, an electric control of the movement of the slide in the two-position, three-way valve 10 is substituted for the second hydraulic actuator 30 and the flip-flop device 40. The control unit 311 comprises a push or pull linear solenoid 330 and a flip-flop controller 340 for controlling the solenoid, and the solenoid 330 is connected to the slide of the valve 10 by a plunger 333. The frequency of the stroke of the linear solenoid 330 can be adjusted by the flip-flop controller 340. Suitable solenoids are available from CRD Devices Ltd, England, for example. The embodiment shown in Fig. 4 differs from that of Fig. 3 in respect of the actuator 420 for moving the movable wall 5. An electric control of the movement of the movable wall member 5 is substituted for the first hydraulic actuator 20. The control unit 411 comprises a controller, which as shown preferably is integrated in the flip-flop controller 440, for controlling a push or pull linear solenoid 420 that is connected to the movable wall member 5 by a plunger 423. The length and the frequency of the stroke of the linear solenoid 420 can be adjusted by the combined controller 440. Also here, suitable solenoids are available from CRD Devices Ltd, England, for example.

The embodiment shown in Fig. 5 differs from that of Fig. 4 in respect of the actuator 520 for moving the movable wall 5. A linear motor actuator 520 for control of the movement of the movable wall member 5 is substituted for the linear solenoid 420. A linear motor actuator is a packaged unit that converts rotary motion into linear movement and basically consists of an electric motor, gearbox and lead screw or ball screw. As in the embodiment shown in Fig. 4, the control unit 511 for the linear motor actuator 520 comprises a controller, which as shown preferably is integrated in the flip-flop controller 540, for controlling a linear motor actuator 520 that is connected to the movable wall member 5 by a rod 523. The length and the frequency of the stroke of the linear motor actuator 520 can be adjusted by the combined controller 540. Also suitable linear motor actuators are available from CRD Devices Ltd, England, for example.

The method and apparatus of the present invention make it possible to inject a predetermined exact dose of additive liquid (such as chlorine solution) into pressurized water supply lines at various pressures without any changes in power consumption or mechanical strength. Further, the design of the apparatus is such that deposits and external factors like sand will have no effect on its continuous operation, and the apparatus will be able to work for long periods without maintenance.

In comparison with prior art, the method and apparatus of the present invention offer the following advantages:

1. By using the pressure in the pressurized water conduit, it is possible to inject the additive liquid into the wide range of pressures in the conduits without any changes in electrical power consumption, parts or their size. 2. By using the pressure in the pressurized water conduit, less electrical energy is consumed than with prior art technology. 3. In a preferred embodiment, the apparatus uses hydraulic actuators and is completely self-supported and does not need electricity for operating electrical devices such as linear motors or linear solenoids.

4. The use of a bellows instead of a diaphragm or a piston in the measuring vessel ensures that there will be no problems with deposits there.

5. In comparison with prior art equipment of a kind working by water transferring energy, the apparatus of the present invention has less drain. The volumes of injected additive and discharged water are exactly equal. The discharged water can be stored and used as solvent in the next cycle (for example in chlorine solution). 6. In the method and apparatus of the present invention, no lubricant is used and recyclable materials are preferably used in the structure of apparatus, which makes it environment-friendly.

7. Thanks to the low power consumption, if any, of the apparatus of the present invention, it produces less heat and therefore could decrease the "greenhouse effect" in comparison with prior art equipment.

INDUSTRIAL APPLICABILITY

The main application of the method and the apparatus of the present invention is for injection of a disinfectant additive into a pressurized pipe conducting drinking water or swimming pool water.

Claims

CLAIMS:

1. A method of adding a liquid additive to a pressurized first liquid flowing in a conduit (1), c h a r a c t e r i z e d b y the steps of - providing a measuring vessel (2) having a first chamber (3) for receiving and discharging the liquid additive, and a second chamber (4) for receiving and discharging the first liquid, the two chambers being separated by a movable wall member (5), so that movement of the wall member (5) causes reception of liquid in one chamber and discharge from the other chamber; - further providing a device (8, 308, 408, 508) for moving the wall member, a source

(6) for the liquid additive, a discharge receptor (7) for discharged first liquid, and flow circuit components (10-18) for alternately connecting the first chamber (3) to the source (6) and to the conduit (1) and for alternately connecting the second chamber (4) to the conduit (1) and to the receptor (7); - moving the wall member (5) so as to increase the volume of the first chamber (3) while reducing that of the second chamber (4) in order to transfer a predetermined volume of the liquid additive from the source (6) for the additive into the first chamber (3) by moving the movable wall member (5) in one direction, and simultaneously discharging an equal volume of the first liquid from the second chamber (4) to the discharge receptor (7); thereafter

- moving the movable wall member (5) so as to increase the volume of the second chamber (4) while reducing that of the first chamber (3) in order to transfer an equal volume of the pressurized first liquid from the conduit (1) to the second chamber (4) by moving the movable wall member (5) in a reverse direction, and simultaneously discharging the predetermined volume of the liquid additive from the first chamber

(3) into the conduit (1), where the pressurized first liquid flows; and

- repeating the transferring and discharging steps.

2. A method as claimed in claim 1, c h a r a c t e r i z e d b y using the discharged volume of the first liquid from the second chamber (4) to the discharge receptor to prepare the liquid additive.

3. An apparatus for adding a liquid additive to a pressurized first liquid flowing in a conduit (1), c h a r a c t e r i z e d b y - a measuring vessel (2) having a first chamber (3) for receiving and discharging the liquid additive, and a second chamber (4) for receiving and discharging the pressurized first liquid, the two chambers being separated by a movable wall member (5), so that movement of the wall member (5) causes reception of liquid in one chamber and discharge from the other chamber;

- a source (6) for the liquid additive;

- a discharge receptor (7) for discharged first liquid; - a device (8, 308, 408, 508) for moving the wall member (5); and

- flow circuit components (10-18, 311, 411, 511) for alternately connecting the first chamber to the source and to the conduit and for alternately connecting the second chamber to the conduit and to the receptor.

4. An apparatus as claimed in claim 3, characterized i n that the flow circuit components (10-18, 311, 411, 511) include a two-position, three-way valve (10), a control unit (11, 311, 411, 511) for controlling the valve (10), and necessary piping (12-14) for alternately connecting the conduit (1) to the second chamber (4) and the second chamber (4) to the receptor (7).

5. An apparatus as claimed in claim 4, characterized in that the flow circuit components (10-18, 311, 411, 511) further include an inlet pipe (15) with a check valve

(16) for connecting the source (6) of additive to the first chamber (3) and an outlet pipe

(17) with a check valve (18) for connecting the first chamber (3) to the conduit (1).

6. An apparatus as claimed in claim 5, characterized in that the device (8) for moving the wall member (5) includes a first hydraulic actuator (20), which is operatively connected to the movable wall member (5) and uses the pressurized first liquid as hydraulic fluid.

7. An apparatus as claimed in claim 6, characterized in that the control unit (11) includes a second hydraulic actuator (30) that uses the pressurized first liquid as hydraulic fluid, and a mechanical flip-flop device (40) that is operatively connected between the second hydraulic actuator (30) and the two-position, three-way valve (10).

8. An apparatus as claimed in claim 5, characterized in that the device (408, 508) for moving the wall member (5) includes an electric actuator (420, 520) operatively connected to the movable wall member (5).

9. An apparatus as claimed in claim 8, characterized in that the electric actuator includes a first linear solenoid (420).

10. An apparatus as claimed in claim 8, characterized in that the electric actuator includes a linear electric motor (520).

11. An apparatus as claimed in any one of claims 6 and 8-10, characterized in that the two-position, three-way valve (10) is a actuated by a second linear solenoid

(330, 430, 530), and the control unit (311, 411, 511) includes an electric flip-flop device (340, 440, 540) for controlling the second solenoid (330, 430, 530).

12. An apparatus as claimed in any one of claims 3-11, characterized in that the movable wall member (5) is a bellows.