It's ICASR, not easy to see.
Air suspension reservoir isolation cock, for those uninitiated with traction. If an air suspension bellows bursts or there's a leak elsewhere on the air suspension system on a vehicle, isolating the air suspension res will stop the leak from emptying the entire air system on the unit. Once isolated, any residual air trapped in the air suspension system needs to be drained off (there are drain cocks on each surge tank) to make sure that the vehicle rides level. There are other considerations once this has been done, passengers will normally be removed from the affected vehicle if possible (if not possible then the train will run at reduced speed). Special considerations for braking and also coupling need to be made too.
Not all unit vehicles have separate air suspension reservoirs, some are fed directly from the main reservoir pipe, those usually have separate ASIC (air suspension isolation cocks) for each bogie.