Other Literature/Studies
Barcol VRM
Barcol VRMB
Barcol VRK


The VRK volume flow controller is an independent control element which works without an external power supply. It can be regarded as a self‐actuating duct damper, as it delivers a required volume of air regardless of changes in system pressure. In consequence, the controller overcomes the need for system balancing and ensures constant air flow in service.


The volume flow controller works with a free‐moving control plate, supported by PTFE bearings and connected to an adjustment spring. Aerodynamic forces balance the force of the spring and push the blade to a defined position that finally controls the set volume flow.

Pressure, accuracy and scope of use

The controller operates reliably from a minimum pressure difference, which depends on the air velocity (see diagram), to a maximum pressure difference of 4 in. WC. The flow rate variation is usually within a tolerance of ± 10% (up to 60cfm: ± 6cfm). If the air velocity is below 780 ft/min or the controller is installed horizontally, variations may well be higher than indicated. This will apply also if the air flow profile is not uniform or is distorted by bends, sharp edges or bottlenecks. Furthermore, the recommended air velocity is around 900 ft/min and should not be below 530 ft/min.


The controller operates within a temperature range from –22°F to 212°F. A special heat‐resistant version for temperatures up to 480°F (briefly even 570°F) is available on request. For volume flow controllers with electric or pneumatic actuators, the operating temperatures of the actuators also have to be considered.


The housing of the controller is made from galvanized and laser‐welded metal sheet without any intruding fold. The smooth surface of the housing enables the inclusion of shaped and calibrated spigot ends with rolling rubber ring seals. This sealing system is patented and offers many advantages, such as tightness, ease of installation and removal, and hence reduced installation costs. Additionally and on request, the controller is available with a new flange connection without screws. This connection allows easy maintenance and modification by removing the controller side wards without dismantling the whole ductwork.
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