The Master Brewers Association of the Americas writes:
"The beer passes through a nonreturn valve and a reducing valve to a cooler, generally placed under the bar counter, then to the dispensing head."
http://www.mbaa.com/TechQuarterly/Abstracts/1...

It becomes apparent that the head is only one part of the /Zapfanlage/, namely the part on top of the counter. Unfortunatly, I don't know what it is called in German, neither can I present relevant dictionary entries. A Google image search, however, confirms at least "beer dispenser".