, ▁with ▁the ▁consequ ent ▁danger ▁to ▁not ▁be ▁able ▁to ▁stop ▁the ▁train ▁at ▁all . ▁This ▁is ▁prevent ed ▁in ▁units ▁with ▁B red a ▁and ▁other ▁types ▁of ▁val ves ▁as ▁the ▁bra kes ▁cannot ▁be ▁fully ▁released ▁if ▁there ▁is ▁not ▁enough ▁air ▁in ▁main ▁res er voir ▁t anks ▁to ▁bra ke ▁again . ▁ ▁There ▁is ▁a ▁risk ▁associated ▁to ▁the ▁" over load " ▁operation . ▁ ▁Inside ▁the ▁ ▁the ▁press ures ▁inside ▁the ▁two ▁ch amb ers ▁are ▁bal anced : ▁during ▁the ▁over load ▁both ▁command ▁res er voir ▁and ▁bra ke ▁pipe ▁press ures ▁rise ▁proportion ally . ▁ ▁As ▁said ▁they ▁are ▁gradually ▁lower ed ▁back ▁to ▁ ▁but ▁it ▁may ▁happen ▁that ▁the ▁command ▁res er voir ▁" gets ▁struck " ▁to ▁a ▁higher ▁pressure , ▁while ▁the ▁pipe ▁pressure ▁is ▁lower . ▁This ▁keeps ▁the ▁connection ▁between ▁the ▁auxili ary ▁res er voir ▁and ▁the ▁bra ke ▁cyl ind ers ▁and ▁consequ ently ▁the ▁bra kes ▁in ▁effect . ▁ ▁In ▁this ▁occurrence ▁a ▁possible ▁solution ▁is ▁to ▁over load ▁again ▁the ▁system ▁so ▁press ures ▁can ▁be ▁re bal anced , ▁or , ▁if ▁this ▁doesn ' t ▁work , ▁to ▁manually ▁" reset " ▁the ▁command ▁res er voir ▁( empty ing ▁it ) ▁by ▁pulling ▁a ▁lever ▁located ▁outside . ▁On ▁units ▁with ▁seven - position ▁le vers ▁the ▁risk ▁is ▁greater : ▁the ▁pipe ▁is ▁put ▁to ▁direct ▁connection ▁with ▁the ▁main ▁t anks ▁and