While 22901 made an unscheduled stop at Harkiakhal (because the block section ahead of us was fouled by 58911 as it chugged towards Nimach), I saw a caboose-less BOXNHL rake parked next to us and facing towards Ratlam. Most of the wagons were labeled "fitted with ESC-KE graduated release twin pipe air brake" and some of them were labeled "fitted with MBS air brake". All had the black-on-yellow oval marking with the words "दोहरे पाइप वाले" (with twin pipes).
I'm aware of the differences between SPGR and twin pipe air brakes,...
more... but these subcategories of twin pipe air brake were new to me. Does anyone know what ESC-KE and MBS stand for, and how they differ?