Abstract: A method and apparatus for measuring the relative density of a gas. The apparatus includes a chamber to which a gas in question, for example natural gas, is supplied through an inlet and leaves through an outlet. The speed of sound SoS at ambient temperature is measured using any suitable method such as electronic control and a calculating device and an ultra-sound emitter and an ultra-sound receiver. The ambient temperature Ta is observed by a temperature sensor, and a thermal conductivity sensor measures the thermal conductivity of the gas at two different temperatures above the ambient temperature. One value ThCH of the thermal conductivity is measured at 70° C. above ambient and the other value ThCL of the thermal conductivity is measured at 50° C. above ambient. The control calculates the relative density RD of the gas according to the formula RD=g·ThCH+h·ThCL+i·SoS+j·Ta+k·.Ta2+l where (g, h, i, j, k and l) are constants.

Abstract: A method of measuring a gas mass fraction (X) in a mass of liquid and gas flowing in direction (A) along pipeline (2) which includes a venturi formed by throat (10), convergent portion (12) and divergent portion (14). Adjacent the venturi (12, 10, 14) but upstream is a flow conditioner (28) creating a uniform mixture of gas and liquid downstream so as to reduce or avoid slip between the gas and liquid phases in the venturi. Differential pressure (DP1) is measured between a position upstream of the flow conditioner and a position intermediate the flow conditioner and venturi. Differential pressure (DP2) is measured between the throat and a position intermediate the flow conditioner and venturi. Differential pressure (DP3) is measured across the venturi. Computer (50) calculates the gas mass fraction (X) using a formula that may take the form: X=a·(DP1)b·(DP2)c·(DP3)d·(DP2−DP3)e·(DP1+DP3)f, in which a, b, c, d, e and f are constants.

Abstract: A plate valve which includes two sliding plates and which carries seal portions with an elongated slot. A valve body of the plate valve includes a second elongated slot with further seal portions extending from a valve aperture. A cable of different diameters can be accommodated and sealed by the cooperating resilient seal portions.