5.8 Leak detection
Detection of leakage:
•Direct observation
•Using sounding rods
•Plotting hydraulic gradient line
•Using waste detection meters
Direct observation:
Practical observation of wet spots on unpaved ground or luxurious growth of grass in a lawn or emergence of a spring at an odd place. These kind of occurrence is found when the pipes are laid below loamy or clay soil. This observations is not suitable on sand soil.
Using Sounding rods:
Sharp pointed metal rod is thrust into the ground and taken back. Presence of moist or muddy point will indicate the leakage. Escaping water sound is also heard using Aqua phone or Sonoscope instrument for magnified sound.
Plotting hydraulic gradient line:
Pressure at different points in the pipe line is measured and hydraulic line is graphed. Kink or change in slope of a hydraulic gradient line indicates the leak.
Using waste detection meters:
These meters will measure any unusually high flow passing through pipe mains during low consumption i.e during early morning or night. The test is conducted only at night. Individual supply lines are tested to detect leakage.
5.8.1 Methods
There are few leak detection techniques are known. Performances regarding to detecting sensitivity are presented in figure. Because of their advantages we shall concentrate attention on the helium mass spectrometer technique.
The spark coil technique:
Uses a high voltage or Tesla ciol and sparkling point to create the electromagnetic radiation, which causes the generation of glow discharge in neighbouring evacuated ampoules. Normally it is possible only in non metal envelopes, that means in glass and plastic elements or tubing.
Drawing the leak antenna along the tested element we can see plasma inside and coming to the leak, a sharp arc passage between plasma and antenna appears. The defect spot is very clearly marked and a skilled person can from the colour of plasma also estimate the inner pressure. This simple method however has a number drawbacks; since besides the restricted application, it is also to be avoided because of radio disturbances.
Pressure change method:
Uses pressure gauges which are ordinarily used to monitor the system performance. Suspected leak sites can be squirted with a solvent (i.e. acetone or similar) while watching the gauge for a pressure rise that occurs when the solvent enters the leak.
This method has limited sensitivity and some shortcomings (possibility of solvent freezing causes temporary stuffing of leak, solvents may attack vacuum grease and elastomer gaskets).Sensitivity ranges of various leak detection methods are shown in below table.
image
Over pressure methods:
It can be performed by fluid or gas with which the tested element must be filled. Usually the water from house installation is used. Observing the outside surface the weted areas show us great leaks and smaller ones up to approx. I mbarl/s.
Testing with gas, the vessel is subjected to over pressure of some bars and immersed into the water. At leaks the gas bubbles begin to escape. In this manner the leaks up to 1. 10-3 mbarl/s can be detected.
If the vessel is too great for immersion, the suspected points should be painted by soap solution and again we can see the bubbles escaping if there is a leak. This method enables detecting the leakage up to 10-5 mbarl/s and is usable also for very large systems.
Halogen leak detectors:
Used in the detector-probe mode, requiring that the system be pressurized with a gas containing an organic halide, such as one of the Freons. Exterior of the system is then scanned with a sniffer probe sensitive to traces of the halogen-bearing gas.
This principle is based on the increased positive ions emission because of sudden halide composition presence. The ion current is the measure for a leak size. Halogen detectors can be used in turned mode: evacuated vessel is connected to detecting instrument and is sprayed by freon. In this manner its performance is up to 5 x 10-7 mbarl/s and is used in rough, medium and high vacuum.
Halogen leak detectors
Dye penetrant method:
An adaptation of a technique used to find cracks in metals and defects in welds. Uses a low viscosity fluid that exhibits a high rate of surface migration. This fluid is painted on one side of a suspected leak site and after a time, it is detected on the other side of the wall. The test is simple, low cost, it leaves records, the sensitivity can be as high as 10-6 mbarl/s
Acoustical leak detection:
Uses the sonic or ultrasonic energy generated by gas as it expands through an orifice. Pressurized gas proceeds from a tested system through leaks which are detected outside by a sensible microphone. Widely used in testing high pressure lines, ductworks etc. Requires modest instrumentation. Simple and fast, but is limited to about 10-3 mbarl/s.
Radioisotope method:
Useful only for testing hermetically sealed components. Are placed in a chamber which is to be evacuated and filled with radioactive tracer gas (typically krypton 85). It diffuses through present leaks in the components and after removing it from environs test gas expands through leaks and can be detected by radiation sensor. Instruments for this type leak tracing are very expensive, but they enable the measurement of flows up to 10-11 mbarl/s.
Mass spectrometers:
As leak detectors are used as most sensitive instruments for stating leak existence and presence in vacuum systems. First suitable gas for leak detection purposes would be H2 but it is dangerous.Residual atmosphere in vacuum systems always contains this gas. There are also spectrometers adjustable to other gases e.g. argon.
5.8.2 Principles of design of water supply in buildings
Water quantity:
It has been estimated that the use of at least 20 litres of drinking-water per capita per day represents the minimum quantity required for drinking, food preparation and basic personal hygiene; A quantity higher than 50 litres per capita per day should ensure basic laundry and bathing in addition to the latter uses; Quantities beyond 100 litres per capita per day would represent an optimal access and should ensure all the previous uses plus a considerable level of comfort and well-being.
Water quality and safety:
At least 1.8 million people die every year from diseases, including cholera. 90% are children under the age of five, mostly in developing countries. WHO estimates that 88% of diarrhoeal disease is attributed to unsafe drinking water supply and inadequate sanitation and hygiene.
Studies have indicated that improved drinking-water supply reduces diarrhoea morbidity by 6% to 25%, and improved sanitation reduces it by 32%. Hygiene interventions, including education and hand washing, can achieve up to 45% reduction of diarrhoea cases.
In the absence of a good-quality drinking-water supply use of household water treatment, such as chlorination with a few drops of bleach at the point of use, can reduce diarrhoea episodes by 39%.
Public drinking-water supplies:
Drinking-water supply system consists of three major elements: source, treatment and distribution to the users.
Contamination can occur in any of those segments and the prevention and mitigation of contamination are essential roles of the water supplier, as well as assuring that the water continuously delivered to the consumer’s entry point is safe and aesthetically acceptable. Each element in the system has vulnerabilities to be managed.
Best protection is the multiple barrier approach, which relies upon a series of barriers from the protection of the source water to multiple treatment processes and distribution system integrity to ensure that potentially harmful contaminants are removed with confidence before they reach the consumer’s tap.
Prevention, mitigation and elimination of contamination risks are the key responsibilities of water providers and regulators in their oversight role. Consuming public also has responsibilities to protect the safety of the water within their dwellings by ensuring the integrity of their piped systems, providing quick repairs when needed and properly storing and using drawn water so as to protect its quality and safety.
In the event of usage of non-publicly distributed water or when the public supply is unreliable or unsafe, users can also take measures to ensure that their water is safe to drink.