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Control Valve for Parking Brake

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TM 5-3805-260-24 The  parking  brake  will  not  let  the  output  shaft  of  the transmission   turn   when   the   air   pressure   to   the   brake chamber is below 40 + 5 psi (280 + 35 kPa).  The brake drum   with   shoes   inside   is   on   the   output   shaft   of   the transmission. The brake chamber activates the shoes.  The parking brake   is   activated   by   a   spring   and   released   by   air pressure.  Force of the spring moves the rod of the brake chamber  and  the  brake  lever  is  pulled  UP  by  the  rod  to activate the brake.  Air pressure works on the diaphragm to cause compression of the spring and extension of the rod.        The    rod    pushes    the    brake    lever    DOWN    to RELEASE the brake. Control Valve for Parking Brake The  control  valve,  which  is  on  the  dash,  has  control over  the  supply  of  air  that  goes  to  the  chamber  of  the parking brake. With valve knob (I) pulled OUT, the line to the   brake   chamber   is   open   to   the   atmosphere   and causes the application of the brake.  With valve knob (1) pushed IN, air goes from the reservoir into the chamber of the parking brake and releases the brake. FLOW OF AIR; APPLICATION OF PARKING BRAKE 1. Knob and pin assembly. 2. Valve body. 3. Spring. 4.Orifice. 5. Outlet (to chamber of the parking brake). 6. Inlet (from air reservoir). 7. Exhaust (to atmosphere). 8. Valve assembly. Parking Brake Chamber Parking   brake   chamber   (7)   releases   (disengages) and   activates   (engages)   the   emergency   and   parking brake.  Rod assembly (I) is connected to lever (6) which moves    the    shoes    in    the    brake.    When    there    is    no pressure   from   the   parking   brake   control   valve   at   air inlet(s),   there   is   no   air   pressure   in   air   chamber   (3). Springs  (2)  hold  piston  (4)  all  the  way  to  the  right  and keep the parking brake engaged. PARKING BRAKE CHAMBER IN ACTIVATED (BRAKE ON) POSITION 1. Rod assembly. 2. Springs. 3. Air chamber. 4. Piston. 5. Air Inlet. The brake stays activated until the air system is at the correct   pressure   for   operation   and   the   parking   brake control   valve   is   moved   to   the   OFF   position   (knob   is pushed   in).      At   this   time,   air   pressure   goes   to   air chamber   (3)   and   pushes   piston   (4)   to   the   left.      Rod assembly (1) moves lever (6) which releases the parking brake. When air pressure decreases to approximately 40 psi (280    kPa),    the    parking    brake    control    valve    closes automatically  (moves  to  the  ON  position)  and  stops  the flow  of  air  to  chamber  (3).  Springs  (2)  are  no  longer  in compression   and   pull   rod   assembly   (I)   into   the   brake chamber.  The parking brake is activated. This  same  operation  takes  place  when  the  parking brake control valve is manually moved to the ON position (pulled out).  This activates the brake for parking. LOCATION OF PARKING BRAKE CHAMBER 1. Rod assembly. 5. Air inlet. 6. Lever. 7. Parking brake -chamber. 2-142

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