Can anyone identify this device hooked to water pipes
Honeywell V5012 Kombi-DP Diaphragm Unit.  Details in the URL below.  To quote a section:


  It is used in systems with variable volume flows, for example two-pipe
  heating systems or district heating exchangers, and supports a
  hydronic balance by keeping the differential pressure over consumers
  at a constant pre-set level even under changing flow conditions.


Honeywell V5012