Dual Piston Brake Dialog Box¶

The brake factor for a dual piston drum brake (Dual Piston, 2 Leading Shoes) is calculated by assuming the primary and secondary shoes are each a pinned leading shoe. Like a single piston brake, some dual piston drum brakes use a different piston area for the primary and secondary shoes. Therefore, the actuation force is calculated separately for the primary and secondary shoes. The dialog includes a schematic preview drawing of the brake, updated to reflect the current dimensions.

This dialog box contains the following attributes:

Wheel Cylinder¶

Area, Primary Piston (in^2) Cross-sectional area of the wheel cylinder piston acting on the primary shoe.

Area, Secondary Piston (in^2) Cross-sectional area of the wheel cylinder piston acting on the secondary shoe.

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 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 lining material.

Shoe Pin Radius (in) Radial distance from the center of the brake to the anchor pin for pinned brake shoes. (The secondary shoe value follows the primary and is not directly editable.)

Shoe Block Length (in) Length of the shoe abutment block. (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: DualPistBrkDlg.htm — updated from source code (HVEINV-64, Physics) 2026-07-05.

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