Custom flowmeter manufacturer and distributor Litre Meter has supplied the first KRAL volumeter helical screw flow meter to be combined with an Exd enclosure to Wood Group Surface Pumping Systems, a division of Wood Group ESP.

The Exd KRAL screw flow meter from Litre Meter provides a combination of meter, sensor and display supplied in housing for use in oil and gas applications, which is certified as flameproof.

Exd certification means that the flow meter instrumentation is housed in an explosion-proof casing designed to prevent the resultant expansion gases from being expelled into the external atmosphere. These meters are fitted with a new sensor combining the design of Litre Meter’s traditional intrinsically safe externals and the internals from its popular VFF flow meter.

These meters can be constructed in a variety of materials from low-cost aluminium to 316L stainless steel. These serve almost all metering or flow control applications of viscous fluids. KRAL meters measure flow to an accuracy of between ±0.1% and ±0.4%.

Litre Meter chairman Charles Wemyss said: “Litre Meter was chosen because it was able to supply the correct combination of meter, sensor and display in Exd housing – the first time we have developed this combination in an instrument.

“The Exd meters are used to measure the flow of lubricant in bearing lubrication systems in pump units which are supplied for use in oil production.”

The basic meter, produced by KRAL of Austria, is derived from a range of screw pumps that has been widely used for over 45 years. The unit is supplied with the Litre Meter standard or intrinsically safe pick-up and pulse output transmitter system.

A positive displacement meter works by dividing the flow into discrete ‘pockets’. This prevents the flow by-passing the meter’s rotor and producing errors. The helical screw flowmeter has rotor scrolls which accept and release continuous flow. While the flow is being transported through the centre portion of the meter it is trapped by the ‘flights’ of the scrolls, which form positive displacement ‘pockets’. A sensor detects the motion of the rotor and produces a high resolution pulse output.

The flow rate range of KRAL’s OM series of meters is between 0.015l/min and 7,500l/min. The meters are supplied in sizes from 13mm (1/2in) to 150mm (6in) with BSP screwed entries or DIN flanges. Special connections to customers’ requirements are available.