Oil Industry Flowmeters
Accurate Measurement at High Pressures
VFF
Litre Meter has developed a flowmeter capable of operating at 4,000 bar (60,000 psi) and at a flow rate of 0.099cc per minute. The instrument has been produced for the American natural gas distribution network to help prevent compressor station failure.
Litre Meter has designed a pressure balance chamber for its VFF rotary piston flowmeter to enable it to operate at extreme pressure and at low-flow rates. The instrument has been developed to measure and verify the flow of mineral oil that lubricates machinery used to pressurise natural gas at compressor stations.
Natural gas is pumped at high pressure throughout the US via an interstate pipeline. To ensure that the gas remains pressurised it is compressed at compressor stations, which are located at 40 to 100 mile intervals along pipelines.
The machinery used to compress the gas is subjected to enormous strains as a result of the high pressure environment - conditions where metals can deform plastically. Reliable and continual operation of the equipment, however, is critical. If it fails, the supply of gas to many homes will stop and the cost of repair can easily run to $1 million.
To keep the machinery operating reliably a constant flow of mineral oil is pumped through the equipment at a low flow rate of between 0.099 and 4.788 cc/min (0.06 and 0.282 l/hr) and at a pressure of 4,000 bar (60,000psi). This is to ensure that it reaches every capillary.
Litre Meter's flowmeter has been designed to continually measure the flow rate of mineral oil at the inlet feed. This measurement is used to verify that the correct amount of lubricant is being passed through the machinery.
Litre Meter's flowmeter is capable of operating accurately and reliable in these conditions. The pressure balance chamber acts as a barrier, protecting the internal measurement components of the instrument from the high pressure conditions, preventing them from expanding and contracting under the immense pressure. By separating out the two meter functions - measurement and pressure containment - Litre Meter are able to optimise the materials of construction. Coupling this facility with a sensitive sensor and robust magnet makes high pressure measurement - with no loss in accuracy due to materials movement - a reality.
"Developing the technology to measure flow rates at the pressures involved in this application has been a tremendous feat," said Charles Wemyss, engineering director at Litre Meter. "Through developing our pressure balance chamber we are now able to offer our clients the capability of measuring low flow rates at extreme pressures."
VFF Series Meters - operating principle
The operating principles of the VFF and Helical Screw flowmeters are of positive displacement type where the flow is divided into discrete 'pockets' There is little slippage past the rotating elements and the fluid is therefore 'positively' metered with high accuracy.
The basic design of our VFF meters is very well established and appears in the British Standard BS7405: 1991 section 3.3 which reviews recognised meter types. The flow causes a rotor to move within a measuring chamber. This movement is sensed, giving an output representing an increment of volume flow. Typically repeatability is better than 0.25% and a system accuracy of 1% can be obtained.
The rotor is basically a disc shape with an annular groove on its underside capable of holding and transporting flow from the chamber inlet to the outlet. Some fluid is also transported in a cavity formed between the rotor outside wall and the chamber wall. A centre 'peg' under the rotor is constrained to run in a circular groove in the body. A web in the body is engaged with a slot in the rotor and this modifies the rotation to that of an oscillation as flow passes. It is this oscillation that produces the compartmentation of the fluid into positively displaced 'pockets'. The rotor top has a magnet encapsulated in 316 stainless steel directly above the 'peg' on the underside and so this also has a circular path which allows it to engage and disengage a reed-switch sensor located in the top cap above. An Intrinsically safe volt-free contact closure output signal is given for each oscillation representing a volume increment. The fluid is transported in a 'positive' manner at all times.
Our Products
VFF Rotary Piston
LMX Pelton Wheel
Sierra Mass Gas Flowmeter
Helical Screw