EE - Forum Styles

What is the Difference Between a Monoflange and a Keyblok Valve?

Monoflange and Keyblok valves are both types of primary isolation valves used to isolate the process media from a given location, often for safety or maintenance purposes.  They are typically installed within an instrument hook up loop as the “take off valve” or the “first valve” off from the process flow line.  This safely isolates instrumentation devices from the process media while still meeting piping class codes and standard valve requirements.  TESCOM Anderson Greenwood Instrumentation Monoflange and Keyblok valves can be arranged for use in many applications including instrument isolation, gauge/pressure isolation, instrument drain, and chemical injection/ sampling.                           

While both types of valves serve a similar purpose, they do have some distinct differences and applications listed below:


Monoflange Type

Keyblok Type

Bore Size

  • 3/16” (5 mm)
  • 3/8” to 2” (10 – 50 mm)

Valve & Bonnet Type

  • Globe Style Pattern
    • Rising Ball End Stem
    • Screwed or Bolted Bonnet
    • Integral Seat
  • Floating Type Ball Valve
    • Metal or Soft Seat
  • Optional Globe Style Pattern
    • Venting
    • Rising Ball End Stem
    • Screwed Bonnet
    • Integral Seat

Inlet Connection Types

  • Flanged
  • Flanged
  • Screwed
  • Welded

Outlet Connection Types

  • Threaded
  • Welded
  • Threaded
  • Flanged

Body Type

  • Forged body compact wafer style
  • Forged body with one, two or three-piece designs

Valve Configurations

  • Block
  • Block & Bleed
  • Double Block
  • Double Block & Bleed


  • Compact envelope
  • Lower weight
  • Best for use on lighter hydrocarbons or non-plugging fluids
  • Roddable multiple size bore(s)
  • Compact envelope versus typical assembly of standard multiple isolation valves
  • Best for use on heavier hydrocarbons or plugging fluids
  • Available for flanged outlets


  • Meets line class piping codes and standards, fire safe and bubble tight for instrument shutoff


  • Both have a lower installation cost compared to individual valve assemblies
  • Single body design results in negligible non-destructive examination (NDE) Requirements/Cost – ex: PMI, MPE, DPE
  • Monoflanges are typically less expensive than Keybloks due to orifice size.


When choosing between the two types, the most important things to keep in mind are the application and the service conditions.  Due to the differences in size and configuration, factors that are typically considered when selecting a TESCOM primary isolation valve include:

Monoflange Type

Keyblok Type

  • With a flanged inlet
  • In non-flow (static) applications only
  • With gas/liquid clean service
  • For the following applications:
    • Measurement
    • Static pressure with bubble tight seats
  • For positive shut-off
  • In applications with space or weight limitations
  • With higher temperature operating conditions.


  • With a flanged, screwed, or welded inlet
  • In non-flow (static) and high-flow applications
  • With heavier hydrocarbons or plugging fluids
  • For the following applications:
    • Measurement
    • Static pressure
    • Isolation
    • Flow
    • Drain
    • Sample/injection
  • When the valve needs to be roddable
  • When a larger bore size is required
  • Has some higher temperature limitations


Still not sure which valve style and configuration to use?  Please comment below!