GB2318643A

GB2318643A - Measurement of leakage water in a sewer system

Info

Publication number: GB2318643A
Application number: GB9722121A
Authority: GB
Inventors: Lasse Ilves; Jukka Sandelin; Timo Tammenlarva
Original assignee: E Sarlin Oy AB
Current assignee: E Sarlin Oy AB
Priority date: 1996-10-21
Filing date: 1997-10-20
Publication date: 1998-04-29
Anticipated expiration: 2017-10-20
Also published as: FI105290B; FI964233A0; FI974394A; FI106224B; GB2318643B; FI964233A; FI974394A0; GB9722121D0

Abstract

A method for the measurement of leakage water in a sewer system, in which system the sewage flow rate is measured. In addition to flow rate, the composition of the sewage is measured by measuring its conductivity, and, based on the flow rate and the conductivity, the location of a leakage in the sewer system is determined.

Description

PROCEDURE AND APPARATUS FOR THE MEASUREMENT OF LEAKAGE WATER IN A SEWER SYSTEM The present invention relates to a procedure and apparatus for the measurement of leakage water in a sewer system.

According to a definition given in an article entitled "Survey of leakage water in a sewer system" ("ViemAriverkon vuotovesiselvitys"), Kunnallistekniikka 1979:1, by J. Kaloinen, leakage water in a sewer system comprises all other kinds of water except sewage from real property. Based on this definition, according to the article, leakage water can be divided into two categories regardless of the sewerage systems (combined and separate sewer systems) and their different variations: intentional leakage (rainwater from street inlets, water drained from basements) and unintentional leakage (water leaking via damaged or malfunctioning structures). An essential requirement for leakage water to be able to enter the sewer system is that the sewer structure has a hole that permits flow from outside the pipe. The hole may be either intentional (grating, drainage pipe, injection well or the like) or unintentional (damaged pipe, irregular contraction, mounting fault). The existence of a hole in the sewer structure is not, however, a sufficient condition for the appearance of leakage water at a given point in the sever system, but in addition it is assumed that in the area of the hole there is water under pressure, which is discharged into the sewer system. Thus, the amount of leakage water entering the sewer system via a hole located in a given climatic area is dependent on the hydrogeological characteristics of the area. According to the article, the most important of these are level of ground-water table, water permeability of the soil and extent of the drainage area.

The above-mentioned article presents one way to make a survey of leakage water in a sewer system. It is based on analysing the results of flow rate measurements taken at different points in the sewer system. In measuring the flow rate in the sewer system, use is made of water purification plant flow rate results, pumping plant service hour meters, measuring weirs installed in the system, water depth and current metering or merely water level measurunent. The amounts of leakage water in different areas and sections of the sewer system are com- pared with the sewer section envelope surface area and the system content to determine the quality of each sewer area or section with respect to leakage.

The condition of a sewer system can also be inspected using video cameras.

Prior-art methods are laborious and require labour resources and care. Moreover, e.g. the use of measuring weirs involves difficulties due to the deposit and solids on the bottom of the pipe. Mere water quantity measurements may be applicable for the determination of the amounts of leakage water in a local or limited area, but they cannot be used for the location of leakage points.

The object of the present invention is to eliminate the drawbacks of prior art and to produce a new type of system for exploring and locating leakage points, in which the amounts of leakage water in a sewer system can be monitored on a continuous basis. The solution of the invention is based on the observation that the conductivity of sewage is reduced as the amount of leakage water increases. Consequently, the procedure of the invention for the measurement of the amount of leakage water in a sewer system is characterized in that the flow rate and electric conductivity of sewage are measured in accor dint with what is pra3*nted in the claims.

In the following, the invention will be described in detail by the aid of an example by referring to the attached drawing, in which Fig. la - ic present a flow meter according to the invention, and Fig. 2a and 2b present a conductivity meter according to the invention.

As stated above, the present invention is based on the observation that the conductivity of sewage is reduced as the amount of leakage water increases. The measuring method is thus based on continuous measurement of the quantity and quality of water at collecting points in the sewer system, e.g. pumping plants. In this context, quality refers in particular to electric conductivity, and, when appropriate, other properties of sewage, such as temperature, pH, etc. On the basis of quality and quantity, it is possible to determine the area where the system leaks and the magnitude of leakage. Once the area has been determined, the actual leakage point can be located by examining each branch separately. This examination can be performed using a flow meter and by taking samples. The amounts of water can be determined using a flow meter, and the proportion of leakage water in the total amount of water can be concluded by analysing a sample (to determine its electric conductivity and other relevant properties). By proceeding in this manner along the sewer system, it is possible to estimate the amounts of leakage between different measuring points and to locate the leakage points.

In the leakage water analysing apparatus, flow rate data must be obtained in real time to enable the amount of leakage water to be determined. The flow rate meter of the invention presented in Fig. la - ic measures the stream velocity and level of surface water in a sewer pipe 1. Fig. la, presenting the meter in front view, shows a frame 10 made e.g. of steel wire, which has been bent together in the upper part and spread out in the middle and whose lower end has been set in the holes of a tubular axle 11. Moreover, the steel wire 10 has been pressed into grooves provided in two adjacent pontoons 12a, 12b having a round shape in side view and filled with urethane 13.

The function of the pontoons 12a, 12b is to keep the meter on the water surface so that the paddle wheel 14 mounted on the axle 11 will rotate on the water surface.

The pontoons 12a, 12b are made e.g. of expanded polystyrene. They are of a round shape as seen from a lateral direction, so that their floating depth will not change due to changes in water quantity and consequent change in the angular position. The purpose of the shape of te pontoons (tapering inwards) as shown in Fig. la is to allow the deposit on the pipe bottom to pass below the pontoons.

The paddle wheel 14 has vanes 15 made e.g. of acrylic plastic, whose shape is fitted to match the shape of the gap between the pontoons so that the vanes become wider towards their outer ends. The vane ends are provided with magnets 16, which are read by a reader 17 based on a magnetic field and placed above the vanes. The reader is further connected to a control system.

Mounted on the top end of the frame is an aluminium tube 18, whose upper end is connected to a vertical metal wire 19, which again is connected at its upper end to a variable resistor 20, which gives the floating angle of the meter as illustrated by Fig. lb, showing the meter in lateral view. The angle is obtained by measuring the resistance of the variable resistor 20, and it can be used to calculate the surface level. From the surface level, the area of the segment can be calculated. Volume flow is obtained by multiplying the segment area by the water flow rate. The variable resistor is attached to a horizontal guide arm 21, which is inserted into the upper part of the sewer pipe (Fig. lc) when a measurement is to be carried out. The guide arm 21 is further attached to a vertical arm 22. The direction of water flow is indicated by an arrow in Fig. ib.

According to the invention, the conductivity of sewage is measured by using a magnetic conductivity meter. The meter, presented in Fig. 2a and 2b in sectioned front view and side view, is based on two toroidal transformers, which have an annular core 30, 31 with a toroidal winding 32, 33 around it. These are fitted in the same casing 34 with a hole in its middle and isolated from each other e.g. with resin insulation provided in the casing.

The transformers are coupled to each- other via sewage e.g. through being immersed in the liquid. The primary transformer 30, 32 induces an electric field in the liquid, and the electric field in turn generates a current.

This current is proportional to the conductivity of the liquid and in turn induces a voltage in the secondary transformer 31, 33. By measuring this voltage, the conductivity of the sewage can be calculated. The meter has the advantage that it has no electrodes exposed to dirt.

It is obvious to the skilled person that different embodiments of the invention are not restricted to the example described above, but that they may be varied in the scope of the claims presented below.

Claims

1. Procedure for the measurement of leakage water in a sewer system, in which system the sewage flow rate is measured, characterized in that in addition to the flow rate, the composition of the sewage is measured by measuring the conductivity of the sewage, and that based on the flow rate and conductivity, the location of a leakage in the sewer system is determined.

2. Procedure as defined in claim 1, characterized in that the flow rate and the conductivity are measured substantially continuously.

3. Apparatus for the neasurement of leakage water in a sewer system, said apparatus comprising at least one flow rate meter, which measures the flow rate of sewage, and a control unit for the processing of measurement results, characterized in that the apparatus comprises at least one sewage conductivity meter, which measures the conductivity of sewage, and that based on the flow rate and conductivity, the control unit determines the location of a leakage in the sewer system.

4. Flow rate meter as defined in claim 3, characterized in that the meter measures the stream velocity of sewage surface water on a continuous basis, for which purpose it is provided with pontoons (12a,12b) to keep the meter on the water surface and a paddle wheel (14) or equivalent and a velocity meter (16,17) for the measurement of surface water stream velocity, and an arm structure and a sensor (20) for the measurement of the angular position of the meter, so that the volume flow can be determined on the basis of the surface water stream velocity and the water level.

5. Conductivity meter as defined in claim 3, which can be immersed in sewage, characterized in that the conductivity meter comprises a transformer circuit consisting of toroidal windings (32,33) wound on separate cores (30,31) and insulated from each other, of which the primary winding induces an electric field in the liquid and the electric field in turn generates a current, which is proportional to the conductivity of the liquid and in turn induces a voltage in a secondary winding in the meter, and that the control unit measures by measuring the voltage and determines the conductivity of the sewage.

6. Procedure for the measurement of leakage water in a sewer system substantially as herein described.

7. Apparatus for the measurement of leakage water in a sewer system substantially as herein described.