Dryer Syphons

Stationary SyphonIt has been well-documented that the distance between the condensate entrance of a syphon and the dryer shell, referred to as the syphon clearance, has considerable influence on the operational efficiency of a paper dryer. Suboptimal clearance adversely affects heat transfer capacity and the cross-machine temperature uniformity of the cylinder.

The most effective syphon systems incorporate regular inspections of the equipment inside the dryer. The following are best practices for syphon inspections:

  • Check the syphon clearance during each annual inspection.
  • Modern close-clearance rotary syphons should have a distance between the syphon shoe and the dryer shell of 0.06” (1.5 mm).
  • The stationary syphon clearance should be set to the manufacturer’s recommendations (typically ranging from 3 mm to 8 mm).  These syphons are generally applied with dryer bars and should be set to provide the proper condensate thickness for resonance.
  • The syphon shoe used with older rotary syphons and modern stationary syphons must face into the direction of rotation. Note that the syphon shoe in a top dryer will face in the opposite direction as the syphon in a bottom dryer in two-tier dryer sections.