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Radial Vane Control Dampers (RVC’s)

Flowseal RVC dampers are designed and fabricated to meet the requirements of power and industrial plants and to comply fully with the requirements of AMCA publication 850-84. They provide effective and reliable control in hot, noxious, corrosive and dirty gas flow conditions.
Dampers can be manufactured with either a Cylindrical or Conical housing configuration to suit overhung fan impellers or fans with impellers between bearings. The blades are of single thickness plate construction with aero foil shape stiffeners. In all cases the blades are driven by a series of lever arms arranged around the outside of the housing, connected to adjustable link rods, which are in turn connected to an external control ring. All RVC’s dampers are fitted with maintenance free DU bushes or similar, which have proven most reliable in all conditions.

Dampers are designed for minimum maintenance and that which is required is simple and can mostly be performed while the system is on line.

The following styles of RVC dampers are available:

Type CL Radial Vane Control Dampers?

The type CL RVC is a damper with cantilever blades, supported by a series of double bushed bearings arranged around the outside of the housing and is intended for use on small fans and fans with through shafts.

Type CH Radial Vane Control Dampers?

These dampers are fitted with central hubs which are equipped with bushes. The blades have stub shafts on both ends which fit into bushes located in the central hub and around the outside of the housing. This arrangement is suited to larger fans and can also be used on fans with through shafts. In some cases straightening vanes can be fitted to the central hub to enhance fan performance.

General Design

Dampers can be fabricated for any fan size, and can be designed to fit inside the body of the fan casing, built into the fan inlet cone, or external to the fan casing. Actuators can be direct mounted or pedestal mounted with a control rod linking the actuator and RVC control ring. RVC’s can be built for double inlet fans and operated by a single drive mechanism.


Materials of construction are selected for their suitability for the conditions of temperature and pressure, and the corrosive and abrasive environment of the system.


Housings are designed to be entirely self-supporting in the duct or fan casing with no external mounting or anchoring required. The flanges are pre-drilled to customer requirements.

The housings are designed for the system pressure and temperature as well as construction and transportation loadings.


Damper blades are of single thickness plate construction, stiffened if necessary. Stub shaft connections are adequately strengthened for the bolt fastenings. Damper blades are designed so that the maximum deflection under operating conditions does not exceed L/360.

Bearings and Bearing Housings?

Bearings are maintenance free DU or Vesconite Bushes, under no circumstances will ball or roller bearings be considered due to their potential to brinell and seize under normal damper operating conditions. The bearings are located sufficiently removed from any potential heat source to ensure that they are operating within their design temperature rating.

Lever Arms and Link Rods?

The geometry of the lever arms and link rods is such that forces are evenly transmitted throughout the arc of travel, and care taken to prevent toggle action becoming possible. All link rods are adjustable. Under no circumstances can any clearances or loose connections be permitted in the link rod geometry as this would adversely affect the operation of the damper. Rod ends are of the spherical low maintenance type.

Control Ring?

The control ring, to which individual link rods are attached, is designed to absorb all the forces exerted by the actuator and the individual link rod attachments without deflection. The inside of the ring is machined to ensure smooth travel over the guide wheels. Stops are fitted to the guide ring, during assembly and testing, to ensure that over travel is not possible.

Guide Wheels?

These support the control ring and are individually adjustable to ensure that the control ring cannot “float” through its arc of travel.

Stub Shafts?

Stub shafts will always be manufactured in grade 304 stainless steel or better. The stub shafts are designed to transmit the maximum torque potential of the drive mechanism.

It is imperative that the combined geometry of blade connection, thru bearing and lever connection is such that the potential for pushing the shaft out of alignment during operation is totally eliminated.


Dampers can be furnished with electric, pneumatic, hydraulic or manual actuators. The actuators are to be sized to function reliably over the full range of system temperatures and pressures. Actuators may be fitted with positioners, I/P converters, solenoid valves, manual overrides and fail safe open or fail safe closed devices if required. All actuators are to be fitted at the factory and fully tested prior to shipment.