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Stainless Steel
High Purity 2-Stage Regulator

Series 3550


The Series 3550 two stage regulators are designed and constructed for use with reactive and corrosive gases and gas mixtures. While compact in design these regulators provide outstanding performance, comparable to most larger diaphragm competitive models. The monel® internal parts installed in a 316L stainless steel body create an economical, high purity, corrosive gas regulator.


  • Monel® internal parts for added corrosion resistance.
  • High purity diffusion resistant, metal diaphragm construction on both stages.
  • Encapsulated seats on both stages.
  • Diffusion resistant, stainless steel diaphragm packless control valve installed on outlet as standard.
  • Designed to pass an inboard helium leak-rate test of 1x10-9 cc per sec.
  • All parts ultrasonically cleaned prior to assembly.


The 3550 Series regulators are ideal for critical pressure reduction applications involving higher pressure reactive and/or corrosive gases, where the precise control of pressure or flow is required. They are an excellent choice for use with gas mixtures of such components having a full cylinder pressure of 1000 psig or more.


  • Max. Inlet Pressure: 3000 psig
  • Operating Temp. Range: -40° to +185°F.
  • Flow Coefficient (Cv): 0.08
  • Inlet and Outlet: 1/4" NPT female
  • Outlet Valve Standard
  • Delivery Pressure Rise: 0.02 psig max per 1000 psi inlet pressure decay.
Stainless Steel High Purity 2-Stage Regulator Series 3500

Materials of Construction

  • Body: 316L stainless steel
  • Seat Assemblies: Monel®
  • Seats: First and Second Stage: Kel-F®
  • Diaphragm: Elgiloy
  • Diaphragm Seal: Teflon®
  • Inlet Filter: Monel®
  • Bonnet: nickel plated aluminum
  • Gauges: stainless steel
  • Outlet Valve: 316 stainless steel
  • Outlet Connections: 316 stainless steel
EZ Mounting Bracket
EZ Mounting Brackets (see page 101).

How To Order***

Del. Press. Range
Del. Press. Gauge
Inlet Press. Gauge
3551-25-CGA* 5-25 0-30 0-3000
3551-50-CGA* 5-50 0-100 0-3000
3551-100-CGA* 10-100 0-200 0-3000
  • *Specify CGA Connection Number when ordering.
  • ***For panel mounting bonnet add “PM” to base number (i.e., 3551-50-CGA).

WARNING: A Purge assembly (see pages 96 and 97) is strongly suggested when using the above regulators with any corrosive gas.

Outlet Options

 P/N Suffix
No Outlet Valve NV
1/4" Compression Fitting T4F
1/8" Compression Fitting T2F
1/4" NPT Male P4M
1/4" Hose Barb 4HB