GB2468531A

GB2468531A - Sediment control tank

Info

Publication number: GB2468531A
Application number: GB0904317A
Authority: GB
Inventors: Chris Denham
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-03-13
Filing date: 2009-03-13
Publication date: 2010-09-15
Anticipated expiration: 2029-03-13
Also published as: GB0904317D0; GB2468531B

Abstract

A tank 2 comprises an inlet 1, at least one outlet 8, a water permeable cage 3 and a filter bag 4. Preferably the filter bag is secured to the water permeable cage using attachment means 5. The water permeable cage and a removable baffle 7 may be placed inside the tank. In use, water is supplied to the inlet and flows into the filter bag whereupon a sediment 6 is retained. The water then flows over the baffle plate which retains further sediment and then flows out of the outlet. Advantageously the tank is used to filter pump discharge in a drainage system.

Description

Sediment Control Tank

Background

When excavations are being completed water often becomes a hazard or at the very least a nuisance. In order for operatives to safely work in the excavation it must be drained. This drainage is imperative if there is any risk that a member of the public might be able to gain access to the excavation. This water might be due to precipitation or it might be groundwater. This also applies if work is being carried out on a body of water such as a pond or lagoon.

In the past various drainage systems have been used. The most primitive was simply to place the discharge hose from a pump or gravity fed system on the ground, downhill from the work area and to commence pumping. This method has a couple of major disadvantages. Firstly the discharged water will contain sediment which could block existing waterways, the second is that localised erosion will usually result around the discharge outlet and there is no provision for directing the flow of discharged water.

To combat the sediment issue discussed above requires a method of filtration. This filtration could be implemented before the pump (i.e. in the pump intake) or after the pump (pump discharge). The pump intake method normally takes the form of a basket-type filter which is fitted over the end of the intake pipe. To ensure high enough flow rates to be obtained the filters are normally fairly coarse, if a finer grade is used it will tend to block quickly and impair the performance of the pump, this could lead to damage to the pump and time would be wasted whilst waiting for the water to be removed from the excavation.. When the coarse grade is used it is easy to see that the filter will not remove sediment of below a comparatively large size and thus an unacceptable amount of sediment will still be discharged, possibly blocking existing drains, waterways etc. Therefore the generally accepted way is to filter the outflow from the pump discharge pipe.

A rudimentary method to filter the discharge is to construct a straw fort. A straw fort is a construction made from straw bales in a walled configuration around the pump outlet. Once pumping commences and water and sediment (henceforth known as * 2 dirty water) start to flow from the discharge hose it will proceed to fill the interior of the straw fort. Water will permeate through the straw bales with a greatly reduced percentage of sediment. These forts are limited by being labour intensive to construct, they require continual maintenance due to rotting and they are labour intensive to de-construct and clean up. They also have no way of controlling the direction of discharge, water merely flows through the straw fort onto the surrounding area.

The next improvement was a settlement tank, at its most basic this could be a large man made pond wherein the dirty water is moved very slowly from the inlet to the outlet allowing the sediment time to settle to the base of the pond. Man-made settlement tanks were then designed, these often included internal baffles (known as weirs) to increase the time taken for the dirty water to flow from the inlet of the tank to the outlet. The longer the time taken the more sediment will settle out of the dirty water.

A settlement tank has two distinct drawbacks, the first is size related, in order to settle the sediment out of dirty water supplied at a high flow rate the tank must be of large dimensions. The settlement time needs to be calculated in order to not exceed flow rates. If the water is pumped through too quickly then the settlement time is not long enough, this will lead to the sediment control failing.

The second being that once the job is completed the sludge at the bottom of the settlement tank must be cleaned out, this is normally done by a person with a shovel.

Statement of Invention.

To overcome the aforementioned problems and limitations of the prior art the proposed invention is as follows.

The following is illustrative and not restrictive and is meant to convey the spirit of the invention. S 3

Please refer to figure 1 The proposed invention consists of a filtration means consisting of, a tank (2) fitted with an inlet (1), an optional removable baffle (7), a water permeable cage (3), a filtration bag (4) and one or more outlets (8). The filtration bag is of cubic construction (although other shapes can be utilised) with an inlet but no outlet.

The bag preferably has four ties or loops situated around one face (5) which enables it to be tied to the water permeable cage (3). This would allow the bag to remain in the most efficient condition, i.e. without slumping on itself. The cage (3) is constructed from water permeable material with inherent high strength, in one embodiment steel mesh is utilised. The permeable cage is placed in the tank at the inlet end, the filter bag (4) is connected to the inlet (1) and pumping can commence.

The dirty water enters the filtration bag (4) where it passes through the surfaces of the bag and sediment is retained (6). The filtered water then passes through the permeable cage (3) into the tank (2). If the removable baffle (7) is fitted then extra sedimentation is captured before the water leaves the settlement tank (2). The outlet (8) of the tank has a fitting to enable a hose to be connected to route the discharge to wherever required, such as a sewer or watercourse. This will eliminate the localised erosion inherent with straw forts or other filtration means.

To change the filtration bag (4) simply lift the water permeable cage (3) complete with the filtration bag (4) using the lifting eyes provided on the cage. Place the cage on the floor and unhook (5) the filter bag (4). Lift this from within the cage (3) and dispose of according to your local regulations. To refit, simply hook (5) a new filter bag (4) into the water permeable cage (3) and lift the complete assembly back into the settlement tank (2). Connect the pump discharge to the inlet (1) and pumping is once more ready to commence.

Claims

Claims 1. A filtration means comprising of a tank with an inlet and one or more outlets, a water permeable cage and a filter bag.
2. A tank according to claim 1 that can be fitted with a removable baffle.
3. A settlement tank according to any preceding claim that has any combination of inlets and outlets.
4. A water permeable cage according to any preceding claim that has lifting means incorporated.
5. A filtration bag according to claim 1 that has a means of securing a hose in the inlet neck.
6. A filtration bag according to claim 1 that has a means of retaining said bag inside aforementioned water permeable cage.
7. A filtration means according to any preceding claim wherein the filter bag is of open-topped construction with no inlet, pump discharge occurs directly into said filter bag.
8. A filtration means according to any preceding claim wherein the tank is fitted with a lid.