403 215 3373

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403 215 3373

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A flare knockout drum is a vessel in the flare header system responsible for accumulating and removing liquid or droplets from flare gas. 

You may also hear them referred to by the acronym FKO, flare KO, knockout drum or other similar names.

They can be designed in both horizontal or vertical design although horizontal is the more popular of the two. 

Why choose a horizontal FKO over a vertical one?

There are several factors to consider when choosing between a horizontal or vertical flare knockout design:

  • How it will be used (the amount of liquid gas capacity you require)?
  • How much room do you have available to build the FKO? 

A horizontal FKO design is useful when you require a large liquid storage capacity and the vapour flow is high. It’s also a good choice when space isn’t a concern and you can build out rather than having to build up.

A vertical FKO design is beneficial when liquid flow is low or when you have limited space to erect it so you build up rather than out to accommodate the drum.

Let’s take a closer look at flare knockout features that you can also choose when designing it to ensure it meets your needs.

Flare knockout features to be aware of


  • BC, AB, SK, MB CRN
  • Bi-directional
  • Over-sized In & Outlet
  • Multiple packaging optionsDesigned so it can sit on saddles, eliminating skid and house if desired for huge cost savings.
  • All-flanged designCan easily accommodate less expensive threaded, blind-flanged instruments to save money.
  • Controls can be in lean-to save money and civil engineering and piling costs.
  • Vessel-mounted lift lugs for easy handling of entire package
  • Purge gas connection on vessel
  • Anode connection is standard as FKOD’s frequently see stagnant fluids anode use is strongly recommended.
  • Saddles tall enough for under-vessel pump mounting

Design considerations for a flare knockout drum

Most flare knockout drums are horizontal in design as you’ll see on the pics on this page, including the image below to the right. But there are many other features to consider as we’ll see below.

Removable internals

  • Deflector can be switched
  • No obstructions if required
  • Easy to coat

Standard design is sour & low temperature:

  • Post Weld Heat Treated
  • 1/8” corrosion allowance
  • T-1
  • Impact tested
  • 50 psig @ -50F to +100F

Budget Packaging:

  • Flanges can be blind-tapped
  • Controls can be stab-in

Optional Package components:


  • Flanged instruments and controls
  • Cage connections for Pump controls
  • High Level Shut-downs
  • Gauge glass
  • Shut-downs

Top mount LIT connection available

  • Internally flanged
  • Stilling well can be Carbon  Steel, Stainless Steel, Fiberglass Reinforced Plastic, ABS, PVC.


  • Over-sized In & Outlet
  • 20” manway is stock
  • 24” option available as custom
  • Large drain
    • Includes vortex breaker
  • Vessel connections available on each unit:
    • High Level Shutdown
    • Low Level Shutdown
    • Level Transmitter
    • Pump start
    • Pump stop
    • Two Level Gauge connections
    • Gas Blanket connection
    • Anode connection
  • Cage connections duplicate any of above

Why choose OilPro for your flare knockout drum requirements?

When you absolutely want the best options, think about OilPro’s new stock 50# MOP, CRN’d, low temp, sour-ready offerings in 25, 50, 75 and 100 Bbl sizes compliant to most in-house spec.

These are inexpensive and can be packaged for sweet service to be a viable alternative to secondary contained atmospheric options while maintaining easy accessibility and design flexibility.

Visit our dedicated flare knockout drum page to learn more or contact OilPro directly at 403-215-3373 or by email at [email protected]

OilPro can also help you with your free water knockouts requirements. Want to learn more? Check out our this article called Free Water Knockouts From OilPro to learn more.



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