The damper resistance factor depends on the damper type (opposed blade or parallel blade damper
) and can be expressed as a function of the damper blade position [theta] for a given damper:
Respectively to the curves illustrating LIMs shutting forces discussed above resisting forces are maximal and act longer for largest size and stroke 6 mm thickness blade damper
(near 260 N and 0,54 s), while the same thickness quarter size blades induce 60 N, or 4,3 times smaller resisting force (at the end of stroke) (Fig.
Recommended damper action is referred to as either parallel blade damper
(PBD) or opposed blade damper
(OBD) (Figure 7)
Sound Level Increase in Nc: Vertical Inlet Duct Height: 3 Diameters All Inlet Diameters Case 1 Case 2 Damper: (Sliding No Damper No Damper for Round Inlet, Opposed Blade for Square Inlet) Type Duct Flex Rigid Square 1 0 (Round Inlet) Round 1 0 (Round Inlet) Type Plaque 1 0 Diffuser (Round Inlet) Perforated 1 0 (Round Inlet) Modular Core 0 0 (Square Inlet) Louvered 1 0 (Square Inlet) If a round cross opposed blade damper
is used instead of a sliding damper, subtract 2 dB from the sound increase.
diameter inlet inlet inlet inlet Damper: no no damper damper (sliding damper damper in in for round inlet inlet inlet, opposed blade for square inlet) Type of flex rigid flex rigid duct Square 1.4 1.1 1.7 1.5 (round inlet) Round (round 1.3 1.1 1.6 1.2 inlet) Plaque 1.4 1.1 1.7 1.5 (round inlet) Type of diffuser Perforated 1.3 1.1 1.6 1.2 (round inlet) Modular Core 1.2 1.1 1.4 1.3 (square inlet) Louvered 1.4 1.2 1.8 1.6 (square inlet) If a round cross opposed blade damper
is used instead of a sliding damper, subtract 0.3 from the pressure loss ratio.
The damper used for the close coupling testing was the round opposed blade damper
in the full open position.
Manufacturer C used an opposed blade damper
for both brands of motors.
Further inspection revealed that one of the blade dampers
had a leak that caused the excessive blade motion.
GE Aviation's Singapore service operation has started producing new blade dampers
and seals for GE's CF6 and CF34 aircraft and LM marine engines.
Since high-velocity dampers are selected, the damper authority is relatively high for all three dampers, and parallel blade dampers
are chosen for all three dampers (ASHRAE 2010c; Lizardos and Elovitz 2000) in the simulation.
Sequencing opposed blade dampers
will probably promote better mixing with this sequence, but opposed blade dampers
should not be used if the dampers are modulated simultaneously.