Abstract: To detect escape or spillage of a cold liquid, for example liquefied natural gas, a narrow, robust, flexible, resilient, plastics tube, placed where the escaped or spilled cold liquid can contact it, is filled with carbon dioxide gas from a gas supply via a non-return valve and a pressure regulator which ensures that the maximum pressure in the tube is at a desired value which is preferably greater than the pressure of the ambient atmosphere surrounding the tube. A gas pressure drop detector is provided to observe a pressure drop in tube. Should escaped liquefied natural gas contact the tube the latter is so cooled that the carbon dioxide gas inside de-sublimates to a solid of greatly reduced volume causing a marked drop in pressure in the tube. This is observed by the pressure drop detector which initiates a warning or some safety action. A gas flow restrictor ensures the gas supply cannot rapidly re-charge the tube before the pressure drop detector has responded to the pressure drop.

Abstract: To measure speed of gas flow along a pipe a flowmeter is used comprising a gas flow sensor connected by tubing with an averaging pitot probe formed by first and second tubes of circular cross-section disposed side by side and closed at their one and the same ends and mounted in a gas tight manner in the wall of the pipe. The two tubes are identical in shape and dimensions and each has four circular holes through its tube wall. All the holes are of the same shape and size, and each has a diameter in the range 0.4 mm to 1.00 mm. The internal diameter of each tube is at least 1.59 mm, and the ratio of the cross-sectional area of each tube to the cross-sectional area of each hole is at least 9:1. The positions of the holes in one tube are identical to the positions of the holes in the other tube except that the holes in the first tube face directly upstream with respect to the gas flow whilst the holes in the second tube face directly downstream.