The data accompanying the photo suggests this was previously a military vehicle before being re-engineered and converted to a fire appliance. If so, very likely to be the answer to the tyre inflation system query.
This is a licenced Mercedes from Serbia, made by FAP. This particularly truck is specialy made just for Army before war in 1990. Few truck was held by Croats and they converted them to civil use after the war. This truck, as military version, was never made by Mercedes and this is fully made by FAP and other companies from former Yugoslavia. That is way this special wheels and tyres have also the tyre inflation system.
Added by Steve Prosser on 03 February 2014.