FINDING BURIED PIPES

Press, Volume LXXXIII, Issue 25247, 28 July 1947, Page 6

FINDING BURIED PIPES

DEVICE RESEMBLING MINE-DETECTOR

USE IN CHRISTCHURCH Equipment essentially the same as the mine-detecting gear used by infantry in the last war is in everyday use in Christchurch by several local bodies to locate underground pipes and cables for maintenance work. When a reporter of “The Press” questioned an employee of the Christchurch Gas Company who was tracing 30-year-old gas mains with an apparatus resembling a portable mine-de-tector in one of Christchurch’s busiest buildings,* he was told that the company had been using a device similar in principle for the last 15 or more years. What was now in use was greatly modified from the original bulky equipment and was simpler than the gear developed by the Army. Beneath the buildings and streets of Christchurch is a network of wires and pipes which in. recent years has grown so complicated that local bodies and the gas company are trying to bring records of changes to these installations up to date. Co-operating with each other whenever a maintenance job is done on a building or in a street, they have been able to make some progress with this work. It is a task which may never be quite finished, and it keeps a small staff of men continuously occupied. In day-to-day repairs to gas and water mains the use of the equipment saves much time. Drawback Overcome One drawback of the mine-detector was that the apparatus reacted to the presence in the ground of any metalhc object, wha tever it may be. This difficulty has been simply overcome by the gas company. With an earth connexion, the gas main is energised from a low-powered source of lowfrequency alternating current. When a set of balanced coils of wire, mounted on an instrument resembling a housemaid’s floor mop, is passed oyer the magnetic field coming from the gas main it reacts with a buzzing sound in a set of earphones carried by the opertaor. Unless other sets of pipes, such as water mains, are actually in touch with the mains being traced no signal will be received In the event of the pipes being in contact, an experienced operator can still tell the difference by the sounds he receives.

Mr J. S. Jarman, who operates this equipment for the Christchurch Gas Company, explained to a reporter that he had become so interested in the work that he had made experiments to cut down the weight ana bulk of the old-fashioned gear, and had developed the lightweight set now in use.

By designing more efficient coils, using lower power from dry-cell batteries, and introducing the idea of coupling the gas main directly to the set. the work of the operator had been lightened.

One of the hardest jobs the company is working on was the location of more than 2000 iron boxes for siphoning water from mains buried under the roads in Christchurch. There are also hundreds Of valves which have to be mapped. One thing making for simplicity is that the apparatus does not include anv of the electronic amplifying gear that the Army needed to overcome the noises of war.