ENGINEER'S BRAKE VALVES 125 



position, thus stopping any further reduction in that chamber. 

 Air will continue to discharge from the brake pipe until its 

 pressure has fallen to an amount a trifle less than that retained 

 in chamber D, permitting the pressure in this chamber to 

 force the piston downwards gradually and stop the discharge 

 of brake-pipe air. It will be seen, therefore, that the amount 

 of reduction in the equalizing reservoir determines that in the 

 brake pipe, regardless of the length of the train. 



Lap Position. The lap position is used while holding the 

 brakes applied after a service application until it is desired 

 either to make a further brake-pipe reduction, or to release 

 them; and to prevent loss of main -reservoir pressure in the 

 event of a burst hose, a break-in-two, or the opening of the 

 conductor's valve. In this position all ports are closed. 



Release Position. The release position, which is used for 

 releasing the train brakes after an application, without releas- 

 ing the locomotive brakes, has already been described under 

 Charging and Release Position. The air flowing from the 

 main-reservoir-pipe connection through port a, in the rotary 

 valve, and port b, in the valve seat, to the brake pipe, raises 

 the pressure in the latter, thereby causing the triple valves and 

 equalizing portion of the distributing valve to go to release 

 position, which releases the train brakes and recharges the 

 auxiliary reservoirs and the pressure chamber in the distribut- 

 ing valve. When the brake-pipe pressure has been increased 

 sufficiently to cause this, the handle of the brake valve should 

 be moved to either running or holding position; the former 

 when it is desired to release locomotive brakes, and the latter 

 when they are to be still held applied. 



Holding Position. The holding position is so named because 

 the locomotive brakes are held applied while the train brakes 

 recharge to feed-valve pressure. All ports register as in run- 

 ning position, except port /, which is closed. Therefore, the 

 only difference between running and holding positions is that 

 in the former the locomotive brakes are released, while in the 

 latter they are held applied. 



Emergency Position. The emergency position is used when 

 the most prompt and heavy application of the brakes is required. 

 Port x in the rotary valve registers with port c in the valve 



