Brake Tests

65 necessary) the addition of a simple check valve device in the reservoir pipe. The equipment is designed to give normally an emergency braking power of 150 per cent, when using 110 pounds brake pipe pres- sure; this insures a satisfactory stop on the one hand without the likelihood of injurious wheel sliding on the other, with an average con- dition of foundation brake rigging, track, etc. For the transition period, or where conditions of installation do not permit, or where the service requirements do not necessitate a braking power as high as this, a lower emergency braking power is available by the arrange- ment of reservoirs and apparatus mentioned above. Complete ELECTRO-PNEUMATIC Equipment. ElECTKIC Service Application. 132 When operating electrically, the service application of the brakes is actuated by a reduction in brake pipe pressure as when operating pneumatically. The equalizing portion of the universal valve causes the brakes to apply in the same manner as has already been described in Par. 120. But this brake pipe reduction is made locally on each car (instead of all at one place, namely, the engineer s brake valve). This local reduction of brake pipe pressure is accom- plished by means of the service magnet valves which open and vent brake pipe air to the atmosphere at the proper rate to produce a ser- vice brake application when the service magnets are energized by the engineer’s brake valve handle being placed in service position. The fact that the pneumatic and electric service position of the brake valve handle are the same insures the elimination of any delay in starting a pneumatic application of the brakes in case the electric control is, for any reason, inoperative.. 133. The movement of the brake valve handle back to ap position de-energizes the service magnets, which permits their valves to close and thus stop the brake pipe reduction. The valve parts then assume their lap positions as when operating pneumatically. ELECTRIC Release. 134. Whether the graduated release cap is in direct or graduated release position, the release of the brakes can always be graduated electrically by alternately energizing and de-energizing the release mag- nets which control the flow of air from the brake cylinder exhaust ports to the atmosphere. These release magnets are energized and prevent the release of the brakes when the brake valve handle is in either release or holding position. At this time the brake pipe and reservoirs on the car are being recharged and the universal valve parts are in their release and charging positions. The outlet from the bra e cylinder to the atmosphere is closed and the brakes cannot release so long as the release magnets are thus energized. The release magnets are de-energized and the exhaust of air from the brake cylinders per- mitted when the brake valve handle is in running position.