When lever 1, linked to the brake pedal, is turned about fixed axis A, shaft f is turned together with fork 2, keyed to shaft f. By means of sleeve 3 and spring 4, fork 2 pushes piston 5 upward in the housing guides. The upper guide has lug a which prevents discharge valve member 6 from dropping below a certain definite point. The hollow rod of piston 5 has a conical bore into which valve member 6 seats, disconnecting the upper and lower chambers, d and b, of the housing. When valve member 6 is raised, chambers d and b are connected together owing to a flat milled on the left side of the stem of valve member 6. Delivery valve 7, at the top of the housing, is held in its seat 9 by spring 8. Compressed air is delivered from the tank to the brake application valve through ports 10 and 11 to delivery valve 7. In the absence of braking action, piston 5 is in its lower position owing to the action of spring 12. Delivery valve 7 is closed and discharge valve 6 rests on lug a. Chamber d, connected with the brake chambers through port 13, is also connected, in this case,ke with chamber b and with the atmosphere through port 14. When the brake pedal is depressed, piston 5 moves upward and valve member 6 is seated in the piston rod, disconnecting chambers b and d. Upon further movement, valve member 6 pushes up valve 7, opening it and admitting compressed air into the brake chambers. At the same time, due to the provision of passage e, the pressure above piston 5 increases, shifting it downward together with valve member 6. Valve 7 is also moved downward by spring 8. The pressure of the air in the brake chambers stops increasing. If the force applied to the brake pedal is increased, valve 7 opens again and admits additional compressed air to the brake chambers. If the force applied to the pedal is reduced, piston 5 moves downward and valve member 6 is held by lug a so that a part of the air from the brake chambers is discharged to the atmosphere, releasing the braking effect to some extent. After this, the equilibrium positions of the piston and valves are re-established. When the pedal is released, air from the brake chambers is discharged to the atmosphere and braking action ceases. The pressure of the air delivered to the brake cylinders is regulated by limiting the stroke of lever 1.
$3977$LHP,FD$