GB2204663A

GB2204663A - Liquid operated valves

Info

Publication number: GB2204663A
Application number: GB08711523A
Authority: GB
Inventors: Eric Ronald Hill; Kenneth Elvet Leah
Original assignee: National Research Development Corp UK
Current assignee: National Research Development Corp UK
Priority date: 1987-05-15
Filing date: 1987-05-15
Publication date: 1988-11-16
Anticipated expiration: 2007-05-15
Also published as: GB2204663B; GB8711523D0

Abstract

A liquid-operated valve in which a closure member (9) is mounted for movement under gravity between an upper open position and a lower closed position. A first vessel (20) can contain liquid, is mounted for vertical movement, and is connected to the closure member so that as the vessel descends the closure member rises, and visa versa. A second vessel (21) for liquid is also provided, and a pump (24) and pipe (26) operable to pump liquid from the second vessel into the first. When the pump operates thus, the first vessel fills with liquid, and descends and opens the valve by lifting the closure member. As the pump continues to work, liquid leaves the first vessel by an overflow (28) and returns to the second vessel. When the pump stops, liquid returns to the second vessel by reverse flow through the pipe and pump, the first vessel rises and the valve is re-shut by the closure member (9). Operation of the pump may be controlled by a timer (33) and/or by a liquid sensor (40). The mechanism finds particular use as the outlet valve of a sludge discharge conduit (6) in a sewage treatment works, operable periodically to open so as to permit the discharge of thick settled sludge that has accumulated within the conduit, and then to close again once all such sludge has been discharged. By using a liquid sensor (such as 40) the timing of the closure of the valve may be related directly to the consistency of the sludge leaving the outlet. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO FLUID-OPERATED VALVES This invention relates to fluid-operated valves, that is to say valves which are caused to open by reason of the movement of fluid in one sense, and to close again by movement of the fluid in the reverse sense.

The invention relates particularly to valves suitable for use at the outlet end of the conduits through which settled sludge is periodically removed from the sludge settlement tanks in sewage treatment installations. Such a conduit, leaving the settlement tank at a low level, normally leads into a nearby empty vessel known as a de-sludging chamber, the outlet of the conduit within this chamber being at a height below the normal water level in the settlement tank.The customary method of removing the settled sludge from the tank into the chamber has been for an operator, at a predetermined time such as the-end of each working shift, to open a valve in the conduit so that the head of liquid within the tank drives the sludge from the tank through the conduit into the chamber, and then to shut the valve again as soon as he judges that the thickness of the sludge leaving the outlet has fallen below a predetermined value.

As manpower levels have fallen and operational practices have improved within sewage treatment works, new apparatus and methods of operation have been adopted to increase automation, and also to achieve a better-quality sludge with reduced water content by removing smaller quantities of sludge from the liquid at more frequent intervals. These apparatus have included electricallyactuated rotary valves with timer control; such valves, however, have to be very robust, need considerable electrical power to open and close them, and also require special features to ensure that they "fail safe" by returning to their closed position automatically in certain events, for instance If the electrical power supply should fail.Co-pending UK Patent Application Number 8525970 describes an alternative form of valve for the outlet end of a sludge-discharge conduit, the valve closure member being a simple tubular structure capable of linear movement between a lower closed position and an upper open position, and thus with the useful safety characteristic that it tends to seek the closed position by gravity unless means are in operation to prevent it from doing so. In the embodiments of the invention described in the specification of UK Application Number 8525970, those means involve mechanism connected to the scraper device which is periodically rotated around the cylindrical settlement tank to dislodge sludge from the inner surface of the tank and concentrate it towards the central and lowest point of the base of the tank where the inlet to the discharge conduit is located.

While the construction and method of operation of the valve described in UK Application Number 8525970 is both simple and positive, for safety it may require additional features to cause the closure member to adopt its closed position in certain circumstances, for instance should the electrical power fail when the position of the scraper is such that it is holding the member open. Also, the system as a whole is not practicable unless the outlet of the sludge discharge conduit is located very close to the settlement tank in which the scraper operates. The present invention provides an alternative system that is capable of operation when the tank and the conduit outlet are further apart, and that may be less at risk from electrical power failure.

According to the present invention a liquid-operated valve comprises a valve closure member mounted for movement under gravity from an upper open position to a lower closed position, a first vessel adapted to contain liquid and mounted for vertical movement, a connection between the closure member and the first vessel operable so that as one of these items rises the other falls and visa versa, a second liquid vessel, delivery means including a pump operable to pump liquid from the second vessel to the first vessel, and means operable, when the pump vessel is inoperative, to drain liquid from the first vessel.

The first vessel may contain overflow means to prevent liquid within it from rising above a predetermined level, and the overflow means may be positioned so that any liquid exhausting from the first vessel by way of them drains into the second vessel. The first vessel may be located higher than the second and the delivery means may serve as the means to drain the first vessel when the pump is inoperative, the pump being so constructed as to permit reverse flow of liquid through it when it is inoperative.

The connection between the closure member and the first vessel may be in the form of a cable, chain or the like, guided by pulleys.

The pump may be controlled by timing means by which it is activated at predetermined times.

The timing means may also operate so as to de-activate the pump at predetermined times. Alternatively, or in addition, there may be separate control means to turn off the pump after a period of operation.

The invention applies particularly to an installation in which the liquid-operated valve is the outlet valve of the sludge discharge conduit of a sewage treatment plant, especially where that valve and the closure member are as described in co-pending UK Application Number 8525970, in which case the further control means operable to turn off the pump may be a liquid sensor which operates to turn off the pump when the consistency of the sludge, discharging from the outlet, falls below a certain value.As explained in the specification of application 8525970, such a sensor may for instance be located in the vicinity of the conduit outlet so that it is actually contacted by the discharging sludge in certain circumstances, or may alternatively be located in a vertical column which is connected to the discharge conduit and in which the level of liquid rises as the consistency of the sludge at the conduit outlet falls.

The invention includes a method of controlling the outlet valve of the sludge discharge conduit of a sewage treatment plant, in dependence upon the predicted or actual consistency of the discharging sludge, using apparatus as described.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a diagrammatic vertical section through a fluid-operated valve, showing the closure member in its closed position, and Figure 2 is a similar section through some of the same parts showing the closure member in its open position.

Figure 1 shows in outline a sedimentation or settlement tank 1, typical of many to be found in sewage treatment works. The tank comprises a circular side wall 2, and an annular and sloping base 3 having a central recess or pit 4 into which sludge 5 tends to settle. The inlet end of a sludge discharge conduit 6 is connected to the centre of pit 4, and an upwardly-facing bellmouth 7 constitutes the outlet of conduit 6 and is located at low level within an open-topped de-sludging chamber 8. A tubular valve closure member 9 is movable from an extreme open position (as shown in Figure 2) to the closed position as shown in Figure 1 in which it is seated in bellmouth 7 and prevents sludge escaping from the bellmouth into chamber 8, but instead constrains it so that it can only rise up the hollow interior of member 9 itself. As diagrammatically shown, the normal level 10 of liquid within tank 1 is situated at such a height as to provide the necessary head to drive sludge through the conduit 6 when the outlet is open, but not enough to cause the sludge to overflow the upper rim 11 of closure member 9 when the outlet is closed. A variable-orifice valve 12, the setting of which can be varied by operation of a handwheel control 13, can if desired be used to regulate the rate of flow within conduit 6 and hence the trajectory of discharge from outlet 7 when that outlet is open.

A strap 15 across the top of closure member 9 is connected to one end of a cable 16 passing over pulleys 17 mounted on a framework 18 which stands on a supporting surface 19. First and second open-topped vessels 20 and 21, both capable of containing liquid, are mounted within framework 18; vessel 21 rests on surface 19 and is stationary. Vessel 20, which lies directly above vessel 21, is guided by framework 18 so that it can rise and fall. The second end 22 of cable 16 is attached to a strap 23 spanning the top of vessel 20.Delivery means comprising a submerged pump 24, driven by an electrical supply shown schematically at 25, rests on the bottom of vessel 21 and the means further comprise a flexible pipe 26 connecting the delivery of the pump to an inlet 27 in the base of vessel 20, which also contains an overflow device 28; the inlet 29 to this device is located at height h within vessel 20, and the outlet 30 lies beneath vessel 20 but directly above the open top of vessel 21.

Figure 1 shows the various items of the mechanism in the positions they will occupy when bellmouth 7 is closed by member 9. It may also be assumed that valve 12 is open to a predetermined degree. While this condition is maintained during the normal operation of the sewage treatment plant no liquid can discharge from bellmouth 7 but sludge 5 will gradually accumulate in pit 4, and the hydrostatic head created by tank 1 ensures that liquid fills conduit 6 and also fills hollow member 9 up to level 32 which equals level 10. A de-sludging operation begins when a timer 33 activates pump 24 causing it to pump liquid from full vessel 21 through pipe 26 into empty vessel 20.Once the mass of liquid within that vessel is such that the vessel and its contents are heavier than closure member 9, vessel 20 descends to the position in which it is shown in Figure 2, where it rests upon stops 34 mounted on framework 18. As vessel 20 descends the closure member 9 rises, so that bellmouth 7 is left open and the contents of conduit 6 are discharged through it into chamber 8 due to the hydrostatic head maintained within tank 1. At first the discharge will be of the liquid that has been standing within conduit 6 since bellmouth 7 was last open, but once that is finished settled sludge from pit 4 will reach bellmouth 7, and the consistency of the discharge will thicken.

Vessel 20 descends to stops 34 when the level of liquid within it rises to a predetermined level - say level 35 which lies below overflow inlet 29. As pump 24 then continues to operate, the liquid level in vessel 20 rises further until it reaches inlet 29. Thereafter, as pump 24 continues to operate, liquid is delivered from vessel 21 to vessel 20 through pipe 26 but returns by way of overflow 28, so maintaining the liquid level 36 in vessel 20 at the height h of inlet 29, and the level 37 in vessel 21 at a height which at least covers the pump 24.

Good practice requires that closure member 9 should descend again, to close bellmouth 7, when the consistency of the discharge from the bellmouth falls below a predetermined value, indicating that substantially all the settled sludge that had accumulated within pit 4 has been discharged. Descent of member 9 may be brought about in several ways. For instance timer 33 may be programmed to turn off pump 24 after a predetermined period of operation; when this happens liquid flows by gravity from vessel 20 through pipe 26 and pump 24 back into vessel 21, valve member 9 descends and vessel 20 rises back to its Figure 1 position when once the liquid within that vessel falls below level 35, and thereafter the liquid continues to drain until vessel 20 is empty and vessel 21, as shown in Figure 1, is full.

Such use of timer 33 to both start and finish each period of sludge discharge, and so to pre-determine the length of that period, has the advantage of simplicity but the disadvantage that it takes no account of the continual slight variations in the rate at which sludge accumulates within tank 1. On some occasions, the predetermined period will be short and so close the bellmouth before all the thick settled sludge has been discharged. On others the period will be longer than is ideal, so that the bellmouth remains open after all the entire volume of settled sludge previously lying in pit 4 has been discharged, so that some raw liquid from tank 1 follows the sludge.In an alternative mode of operation, more sensitive to the consistency of the fluid discharge at bellmouth 7, pump 24 is switched off by a signal from a suitable liquid sensor, for instance the Model AC1/L level controller for conducting liquids, as sold by Hawker Electronics Limited, Kings Norton, Birmingham. In Figure 1 such a sensor is shown firstly at 40, includes control means 45 and is mounted on a bracket 41 on the outer wall of closure member 9 so that the sensitive tip 42 of the instrument lies a predetermined distance from bellmouth 7. It will be appreciated that the first effect that follows when member 9 rises to open the bellmouth outlet 7 is that the column of liquid previously standing within conduit 6 discharges, the liquid gushing out through the gap now presented between 7 and 9.Because this liquid will be relatively thin and subject to a considerable pressure head due to the height of level 10, it will be projected from the gap with a substantial trajectory and so will make contact with the nearby tip 42 of sensor 40. The control mechanism 45 of the sensor is however programmed to create a time delay between the lifting of member 9 and the activation of sensor 40, this delay being long enough to cover the short initial period when thin liquid is discharging. Once that period is over, the head of liquid within the tank drives thick sludge 5 from the pit 4 through conduit 6 so that it also discharges into chamber 8 from the open bellmouth 7.However due to effects including the high viscosity and density of the sludge, and high friction between that sludge and the conduit wall, the trajectory of the sludge as it escapes through the bellmouth will be less great than that of the thinner fluid previously. Therefore, although the sensor 40 is now activated, the thick sludge will not reach the tip 42 of the sensor. However as the escaping liquid thins down progressively, as it will once most of the sludge has been expelled from pit 4 and some thinner liquid from the tank is able to enter the conduit 6 also, the combined effects of lower density/viscosity and lower friction losses cause an increase in the trajectory of the escaping liquid so that it again makes contact with the tip 42 of sensor 40, the output of which causes the pump 24 to shut down. In the alternative arrangement of a such a liquid sensor that Figure 1 also shows, the sensor (43) is mounted within a vertical tube 44 which branches from conduit 6 between tank 1 and valve 12. Such an arrangement has the advantages of providing a more sheltered situation for the sensor, a mode of operation in which there is less relative motion between sensor and liquid when the sensor operates to end a de-sludging operation, and more constant contact between the sensor and liquid thus avoiding malfunction due to repeated wetting and drying of the sensor. Liquid within tube 44 will stand at a relatively high level, substantially equal to the level 10 of liquid within tank 1, when bellmouth 7 is closed by member 9 between de-sludging operations.The level within tube 44 will then fall a little at the beginning of each de-sludging operation, as the column of liquid previously standing within conduit 6 discharges. Then, when thick sludge begins to move through conduit 6, the effect of the losses due to density/viscosity and friction effects within the conduit 6 will be to depress the liquid level in the tube to a lowest value.

The working tip 42 of sensor 40 should be located a little above that lowest level, and the control mechanism 45 of the sensor 40 programmed to activate the sensor as the liquid level falls to its lowest level, and then to shut down the pump 24 and also de-activate the sensor again as the level rises to contact the tip 42, so indicating that the consistency of the liquid flowing through the conduit 6 has become thinner once again.

Potential advantages of such a system include the following.

Firstly the electrical power source for pump 24, and for related instruments including timer 33 and/or sensor 40/43, can be either mains or battery-operated as desired. Secondly the system is electrically fail-safe; if the power supply fails, pump 24 does not work and closure member 9 either stays in or returns to its closed position. Thirdly the chamber 8 can be remote from tank 1 if desired. Fourthly the invention is not confined to an installation having only a single bellmouth 7, as shown; a single pair of vessels 20, 21 could be connected to a plurality of closure members 9, each associated with one of a plurality of bellmouths. Finally, while the examples of the invention of pending UK Application Number 8525970 described in the specification of that application all show circular settlement tanks fitted with the customary rotating bridge/scraper, the present invention is not in any way limited to such tank and is equally suitable, for example, for use in sewage treatment works where the tanks are of rectangular or other section.

Claims

1. A liquid-operated valve comprising a valve closure member mounted for movement under gravity from an upper open position to a lower closed position, a first vessel adapted to contain liquid and mounted for vertical movement, a connection between the closure member and the first vessel operable so that as one of these items rises the other falls and visa versa, a second liquid vessel, delivery means including a pump and operable to pump liquid from the second vessel to the first vessel, and means operable, when the pump is inoperative, to drain liquid from the first vessel.

2. A liquid-operated valve according to Claim 1 in which the first vessel contains overflow means to prevent liquid in that vessel rising above a predetermined level.

3. A liquid-operated valve according to Claim 2 in which the overflow means are positioned so that any liquid exhausting from the first vessel by way of them drains into the second vessel.

4.. A liquid-operated valve according to Claim 1 in which the first vessel is located higher than the second, and the delivery means serve as the means to drain the first vessel when the pump is inoperative, the pump being so constructed as to permit reverse flow of liquid through it when it is inoperative.

5. A liquid-operated valve according to Claim 1 in which the connection between the closure member and the first vessel is in the form of a cable, chain or the like, guided by pulleys.

6. A liquid-operated valve according to Claim 1 in which the pump is controlled by timing means by which it is activated at predetermined times.

7. A liquid-operated valve according to Claim 6 in which the timing means are also operative to de-activate the pump at predetermined times.

8. A liquid-operated valve according to Claim 7 in which there are control means separate from said timing means to turn the pump off after a period of operation.

9. A liquid-operated valve according to Claim 8 in which the control means comprise a liquid sensor.

10. A method of controlling the outlet valve of the sludge discharge conduit of a sewage treatment plant, using apparatus as claimed in any of the preceding claims.

CLAIMS 1. A liquid-operated valve comprising a valve closure member mounted for movement under gravity from an upper open position to a lower closed position, a first vessel adapted to contain liquid and mounted for vertical movement, a connection between the closure member and the first vessel operable so that as one of these items rises the other falls and vice versa, a second liquid vessel, delivery means including a pump and operable to pump liquid from the second vessel to the first vessel, and means operable, when the pump is inoperative, to drain liquid from the first vessel.

11. A liquid-operated valve according to Claim 1, substantially as described with reference to the accompanying drawings.

12. A method of controlling the outlet valve of the sludge discharge conduit of a sewage treatment plant, according to Claim 10 and substantially as described with reference to the accompanying drawings.