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RADIATION COOLING
A method of reducing exhaust gas stream temperature which involves the use of long uninsulated ducts that allow the gas stream to cool as heat radiates from the duct walls.

RAVEL
When thread becomes separated into parts, to unweave; to pop back.

RE-ENTRAINMENT
The phenomenon whereby dust is collected from the air stream and is then returned to the air stream. It occurs when dust is cleaned from the bag and then caught again by an upward moving air stream, which redeposits it on a bag.

REGISTRATION
The formality in acknowledgement by a certification body accredited by the NACCB that an organization has been assessed and shown to comply with BS 5750/ISO 9000 at the time of assessment.

RESISTANCE
In airflow, caused by friction of the air against any surface or by changing the momentum of gas.

RESISTIVITY
The electrical resistance that a meter cube of a substance (usually of packed dust) has when measured between opposite faces of the cube. The units are ohmmeters (or ohm-centimeters; a resistivity of 1 cm is equivalent to a resistivity of 100).

RETENTION
Ability of a filter to retain particles (total number or those of a specific size) suspended in a gas or liquid. Expressed as a precentage of particles originally present.

REVERSE AIR BAGHOUSE
A collector where cleaning is accomplished by stopping the dirty gas flowing into a compartment and backwashing the compartment with a low- pressure airflow. Particulate is usually collected on the inside of filter bags and removed by allowing bag collapse.

RING COVER
A fabric cover used to overlap an anti-collapse ring to prevent the ring from wearing on the bag or adjacent bags.

RING MARKS
Those marks on a pattern or bag where a ring is to be sewn on.

ROTARY AIRLOCK VALVE
An air-sealed star wheel with material buckets designed to provide an airtight seal between the inlet and discharge sides of the valve.

ROTATING VANE ANEMOMETER
A windmill-like device, small enough to be held in the hand for measuring air speed.

RUNOFF
Failure to cut or sew along a given line. To wander from the seam or fabric edge.