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3535 Diaphragm Operated Back Pressure Valve, Low Pressure, Single Seat

Wellmark’s Back Pressure Valve can be used in any installation where upstream pressure is required to be kept at a preset range. It may also be used as: a pressure relief valve, a custody transfer dump valve to hold a certain back pressure, or as a separator back pressure valve on the gas or liquid side. Upstream pressure is applied to the bottom of the diaphragm through connecting tubing. Spring tension above the diaphragm opposes this pressure, and when the pressure exceeds the pressure setting on the spring, the plug is raised off the seat. By varying the spring tension, the pressure setting can be varied.

The typical application for these valves is to hold back pressure on separators, treaters, Lact units, etc.

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  • Simple Design
  • Self-Contained:There are no pilots or small orifices to plug or freeze.
  • Easy Access: All internal parts can be removed without taking valve out of line.
  • Optional Seat: Integral or Removable
  • Available in 1″ and 2″ Size
  • Pressed Steel Topworks
  • Threaded body, Ductile Iron
  • Flanged Body, Steel



  • Size: 1″ & 2″ Threaded, 2″ Grooved, 2″ Flanged
  • Working Presure: Dictated by Spring Range
  • Spring Range: From 0 to 150 psi
  • Temperature: -50°F to +250°F Standard (other materials available)
  • Size Topworks: #10 or #20
  • (CV) Flow Coefficient: 1″ = 11 2″ = 25


  • Body: 1″ & 2″ Threaded Ductile Iron 2″ Flanged WCB
  • Topworks: #20 Press Steel, #10 Steel WCB
  • Diaphragm: Nylon Reinforced Nitrile
  • Stem: 316 SS
  • Packing: Cotton Reinforced Nitrile
  • Trim: 303 SS Molded Buna-N

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