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D

DAMPER

An adjustable gate installed in a duct for the purpose of regulating airflow or introducing outside air to the ducting system.

DAMPER, BUTTERFLY

This is a flat plate inserted in a gas stream. It is rotated by means of a motor and linkage (often called an actuator) in order to control the gas stream flow. When the damper is in the closed position it almost completely blocks gas flow. When it is in the fully open position, the flat plate is aligned with the direction of gas flow, and therefore, provides very little flow restriction.

DAMPER, LOUVERED

These dampers consist of a set of blades that are controlled by a single mechanical linkage. When the dampers close, the flat blades seal against each other. Louvered dampers are somewhat similar to venetian blinds. However, the shape of the individual blades provides good surface-to-surface sealing in the closed position.

DAMPER, POPPET

These consist of a flat circular plate that is raised or lowered by an electrical or compressed air actuator. When the flat plate is in the closed position, it provides a gas seal by pressing against a seat shaped like a short cylinder. Gas attempting to pass through the cylinder is blocked. When the damper is open, there is a one to two foot gap between the flat plate and the cylinder opening. Poppet dampers are used for on-off control. They are not used to moderate gas flow.

DEGRADATION

The loss of desirable physical properties of a textile material due to some process or physical, chemical or thermal phenomenon.

DELTA P

See DIFFERENTIAL PRESSURE.

DENIER

The weight-per-unit-length measure of any linear material. The sizing of yarns used in woven fabrics including scrims are designated by denier. The weight, in grams, of 9000 meters of a single fiber strand.

DEPTH FILTRATION

A process that entraps contaminants both within the matrix and on the surface of the filter media.

DEW POINT

The temperature at which condensation begins to form as a gas is cooled.

DIAPHRAGM VALVE

A compressed air valve operated by a pilot solenoid valve used to clean the filters in pulse-jet collectors.

DIFFERENTIAL PRESSURE (Delta P)

The change in pressure or the pressure drop across a component or device located within the airstream; the difference between static pressure measured at the inlet and outlet of a component device.

DIMENSIONAL STABILITY

The ability of the fabric to retain finished dimensions under stress at operating conditions. This stability is imparted to a fabric by chemical treatment, mechanical means, construction or blends.

DOOR SEAL

Various types of gaskets used on door or door frames to prevent in-leakage of outside air by creating airtight connections between door and frame.

DRY SCRUBBER

A chemical reaction chamber that neutralizes acids in a gas stream. Two system types are common: the spray dryer system injects a slurry, whereas dry sorbent injection systems use a dry powder.

DUST (OR MIST) CONCENTRATION

The weight of dust or mist contained in a unit of gas; e.g., pounds per thousand pounds of gas, grains per actual cubic foot of gas or grains per standard dry cubic foot (the temperature and pressure of the gas must be specified if given as volume).

DUSTCAKE

Desired dust buildup on fabric to filter incoming gases and keep particulate on fabric surface.

DUST LOADING

The weight of solid particulate suspended in an air (gas) stream, usually expressed in terms of grains per cubic foot, grams per cubic meter or pounds per thousand pounds of gas.