Capsule pressure gauge are used to measure to measure mico pressure and 
  negative pressure gauge of gas that has no danger of explosion and does 
  not erode alloy. Based on common capsule pressure gauge, stainless steel 
  capsule pressure gauge introduce stainless material used in internals and 
  housing.Shockproof capsule pressure gauge is designed on base of stainless 
  steel capsule pressure gauge,with glycerine filled inside and pressure limiter 
  http://www.allgakind-instrument.com