A vapor recovery unit, or VRU, captures the hydrocarbon vapors that would otherwise escape or be flared from oil storage tanks and other low-pressure equipment. It is both an emissions-control device and a way to turn wasted gas into salable product. This guide explains what a VRU is, how it works, and why operators install them.
VRU in one line: A vapor recovery unit (VRU) is a compact compression system that captures low-pressure hydrocarbon vapors from storage tanks and other equipment and boosts them into a gas gathering line, instead of letting them vent or be flared.
When treated crude enters an atmospheric stock tank, the drop to near-atmospheric pressure lets light hydrocarbons flash out of solution as vapor. Tanks also breathe with temperature swings and displace vapor as they fill. These flash and working vapors are mostly methane and other light hydrocarbons - valuable product and, if released, a source of methane and VOC emissions.
Historically this vapor was vented or flared. Tightening emissions regulation and the economic value of the gas have made capturing it the norm on many facilities, and the VRU is the equipment that does it.
A VRU draws vapor from the tanks (and sometimes other low-pressure sources) through a suction line, pulling the tank vapor space down to a slight vacuum or low pressure so vapors are captured rather than pushed out the thief hatches. The vapor passes through a scrubber that knocks out liquids, then into a compressor - often a rotary vane, screw, or reciprocating unit - which boosts it to the pressure of the sales or gathering line and discharges it there.
Controls hold the tank pressure in a tight band: the VRU ramps or cycles to keep the tanks at slight positive pressure, avoiding both emissions (too high) and drawing air in through the hatches (too low, a safety concern). A pressure/vacuum relief and safety controls protect the tanks.
A VRU delivers on two fronts: it cuts methane and VOC emissions, helping operators meet regulations and emissions commitments, and it recovers gas that would otherwise be lost, adding to sales. On a facility with meaningful flash gas, recovered volumes can pay back the unit.
Because a VRU that trips can quickly turn into a tank emissions event, its status matters. Operators monitor tank pressure, VRU run status, suction and discharge pressure, and shutdowns. A cloud SCADA such as Merobix reads VRU controller and pressure signals over Modbus, so a stalled or tripped unit is alarmed immediately across a field rather than discovered on the next site visit.
A VRU captures the light hydrocarbon vapors that flash from oil storage tanks and other low-pressure equipment, scrubs out liquids, and compresses the gas into a sales or gathering line - instead of venting or flaring it. It reduces emissions and recovers salable gas.
Two reasons: to cut methane and VOC emissions from storage tanks and meet tightening regulations, and to recover gas that would otherwise be lost to flaring or venting, adding to sales. On facilities with meaningful flash gas, the recovered volume can pay back the unit.
It holds the tank vapor space in a tight pressure band - ramping or cycling the compressor to keep tanks at slight positive pressure. Too high risks emissions through the hatches; too low can draw air into the tanks, a safety hazard. Pressure and vacuum relief and shutdown controls protect the system.
This page references the protocol specifications published by the organizations below. Editions, product capabilities, and documentation change over time - confirm current requirements and specifications directly with the source.
Last reviewed: July 27, 2026. Merobix is not affiliated with, endorsed by, or sponsored by these organizations; their names are used only to identify the standards and products discussed.
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