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Guillotine Dampers:

The guillotine damper, or slide gate damper as it is sometimes called, has the main function of isolation of equipment to permit inspection, maintenance, or repair in addition to process isolation.  Occasionally, guillotine dampers are specified for bypass ducts, if operation requirements allow enough time for the slow-moving blade to travel across the opening.

The basic mechanical elements of the guillotine damper are a blade, a peripheral-seal system to prevent gas leakage at all stages of blade movement, support members for the blade , and a drive to move the blade steadily and continuously from open to closed and back again. 

The guillotine damper has these advantages: 

  • Good isolation.

  • Low pressure drop across the wide open damper.

  • Short space needed along the duct.

  • Resistance to damage from furnace puffs and mild over pressure incidents.

  • Lower pressure drop than multi-blade louvers
  • Less required space along duct (flange-to-flange)
  • Ability to cut through particulate deposits
  • Less seal air required for 100% isolation
  • More dependable seal design
  • Fewer moving parts thus less maintenance

But this damper also has drawbacks:

  • Flow modulation is not recommended, not intended for control service.
  • Movement is slow – not suitable for emergency bypass.
  • The damper is heavy.
  • A large structure outside the duct is necessary to support the drive and the retracted blade.
  • The drive usually more susceptible to wear and corrosion than is the louver damper.
  • May require external support structure.

In addition, the guillotine damper generally requires more care in design and construction of the seals.  Perhaps this is because gas-tightness requirements are higher for guillotines than for louvers, but the fact remains that, in many guillotine dampers, the blade drags past most of the seal perimeter for the full stroke, making heavier demands on the seal material. 

Where flow control is not required but positive shut off is mandatory, guillotine dampers are the most logical choice. The amount of allowable leakage determines the seal design.  Rigid seats provide adequate closure, with leakage in the range of 0.4 to 1% of flow.  When zero leakage of flue gas is required, a seal air system must be added.  Flexible seals reduce air requirements.

The simplest form of guillotine damper is the single-thickness flat plate blade.  The one-piece blade provides verifiable closure of the duct with minimal leakage at the blade edges.  Seals are provided to control leakage where the blade enters the duct section.  These seals can be air sealed to contain gases in a positive pressure duct.  Leak paths are typically less than 0.1% of duct area with resulting flow leakage of 0.4 to 1.1%.  The blade guides insure smooth operation and are self cleaning in deposit producing environments.

As a general rule, flat-plate open-bonnet guillotine dampers are not suggested for systems with elevated temperatures (above 500 deg. F).

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