Duplex Brake Dialog Box¶

This Brake Designer dialog is used to edit the physical parameters of a duplex drum brake, in which each shoe is actuated by its own wheel cylinder and both shoes act as leading shoes. The dialog includes a schematic preview drawing of the brake, updated to reflect the current dimensions.

Wheel Cylinder¶

Piston Diameter (in) Diameter of the wheel cylinder pistons.

Wheel Cyl. Dist (in) Distance from the brake center to the wheel cylinder actuation points.

Push-out Pressure (psi) Pressure required to overcome force associated with return springs and begin developing brake torque.

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 (deg) Arc length of the lining material in contact with the drum.

Lining Beta (deg) Angle locating the lining relative to the shoe abutment.

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 not directly editable.)

Abutment Width (in) Width of the shoe abutment. (The secondary shoe value follows the primary and is not directly editable.)

Abutment Angle (deg) Angle of the abutment contact surface. (The secondary shoe value follows the primary and is not directly editable.)

Abutment Friction Coefficient of friction at the abutment contact. (The secondary shoe value follows the primary and is not directly editable.)

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: DuplexBrkDlg.htm — updated from source code (HVEINV-64, Physics) 2026-07-05.

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