Dual Wedge Brake Dialog Box¶
This Brake Designer dialog is used to edit the physical parameters of an air-actuated dual wedge drum brake, in which two air chambers drive wedges that spread the shoes against the drum. The dialog includes a schematic preview drawing of the brake, updated to reflect the current dimensions.
Air Chamber¶
Chamber Drop-down list selecting the air chamber size, by standard chamber type (Type 9, 12, 18, 20, 24, 30 or 36). Selecting a chamber type automatically sets the Chamber Area to the corresponding nominal effective area.
Chamber Area (in^2) Effective diaphragm area of the air chamber. Set automatically from the selected chamber type; may also be edited directly. (The previous manual listed this as "Area, Primary Chamber".)
Push-out Pressure (psi) Pressure required to overcome force associated with return springs and begin developing brake torque.
Wedge¶
Wedge Location (in) Location of the wedge actuation point relative to the brake center.
Wedge Angle, Primary (deg) Included angle of the wedge actuating the primary shoe.
Wedge Angle, Secondary (deg) Included angle of the wedge actuating the secondary shoe.
Maximum Stroke (in) Maximum available stroke of the air chamber push rod.
Stroke @ 2ndary Defl (in) Push rod stroke at which secondary (structural) deflection begins.
2ndary Defl. Factor Factor describing the additional stroke consumed by secondary deflection after the secondary deflection stroke is reached.
Expansion Coef (in/deg F) Thermal expansion coefficient of the drum; used to compute the additional stroke required as the drum heats and expands.
Shoe/Drum¶
Drum Diameter (in) Inside diameter of the brake drum.
Drum Lining Width (in) Width of the lining material.
Drum Thickness (in) Thickness of the drum wall (used for calculating the thermal mass of the drum).
Lining (Primary and Secondary columns)¶
The following parameters are entered separately for the primary (Pri) and secondary (Sec) shoes.
Lining Arc Length (in) Length of the lining material along the arc of contact with the drum.
Lining Alph 1 (deg) (labeled Lining Alph 1 in the dialog — a UI typo for Lining Alpha 1) Angle locating the leading edge of the lining relative to the shoe actuation axis.
Lining Thickness (in) Thickness of the lining material.
Abutment Dist (in) Distance from the brake center to the shoe abutment. (The secondary shoe value follows the primary and is read-only.)
Abutment Width (in) Width of the shoe abutment. (The secondary shoe value follows the primary and is read-only.)
Mechanical Efficiency Fraction of the actuation force actually delivered to the shoes after mechanical losses.
Buttons and Results¶
Friction ... Opens the Lining Friction Properties dialog, used to edit the lining friction coefficient as a function of lining temperature for the primary and secondary linings.
Material ... Opens the Brake Designer Material Properties dialog, used to edit the drum and lining material thermal properties.
Apply Recomputes the results below from the current physical parameters.
Brake Factor (read-only) Calculated ratio of total drum drag force to actuation force for the brake.
Actuation Factor (read-only) Calculated actuation force per unit of system pressure.
Brake Torque Ratio (in-lb/psi) (read-only) Calculated wheel brake torque per unit of system pressure. On pressing OK, this value replaces the Brake Torque Ratio in the Brake Assembly dialog.
Removed options¶
- Preview button — removed; the schematic preview drawing is now always displayed in the dialog.
Source topic: DualWedgeBrkDlg.htm — updated from source code (HVEINV-64, Physics) 2026-07-05.
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