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Combination Air/Hydraulic Doctor

As one of the standard Vacuum Washer essentials, doctor or take-off assemblies accomplish the task of removing the pulp mat from the cylinder face wire without damaging the face wire or adding too much dilution. Throughout the evolution of the Pulp and Paper Industry the doctoring of the pulp mat has been accomplished in a variety of methods with varying success. Such methods include water/hydro take-off’s, air take-offs, steam take-offs, and roll take-offs.

GL&V offers a practical approach to the doctoring of the pulp mat by supplying a Combination Doctor Assembly that utilizes the both air and water. Combining the usage of air and water allows doctors to be more efficient due to only using water on start-ups or upset conditions.

The GL&V Combination Doctor merges the two most common means to lift the pulp mat off a vacuum washer cylinder into one device – low pressure air and high pressure water. The unit includes the end manifolds and seal arrangements needed to create an air chamber for a standard air-lift doctor, as well as a series of spray nozzles and piping connection(s) to allow operation as a typical water doctor.

This style equipment is typically used in applications where the line will run severe turn-down rates for extended times, producing a thin mat that is difficult for an air doctor to remove, or when thin mats at start-up demand a more aggressive doctoring means. In these situations, the hydraulic doctor is enabled for more positive mat removal and wire cleaning. The operators then switch back to the air doctor as soon as production rates increase, or when the mat formation and operation stabilizes and a thicker, uniform mat is produced.

The requirements for air or water are the same as if they were installed individually. For the air doctor, the nominal air supply is 100 cfm per foot of length, delivered at 10” WC to the air manifold. For the hydro doctor, filtered water is supplied at 5 gpm per foot of length and 120 psig at the inlet.

For many mills, the high volume of water required for the hydraulic mode has prevented the combo doctor from gaining widespread use in brown stock applications. The added evaporation load is seldom economically viable. However, when used judiciously, the operating benefits can easily outweigh the temporary increase in liquor volume to the recovery system.

GL&V can offer its Combination Doctor in a variety of lengths, end connections, and metallurgies to suit your specific piping arrangement and allow it to be installed onto any vacuum washer. We offer our Doctors in any of the 300 series stainless steels.

  • Flow Rating Information
    • Air Requirements:
      • 100 CFM per foot of length at 10" of water pressure.
    • Water Requirements:
      • 5.1 USGPM per foot of length at 120 psig (fresh water required)
  • Improved pulp mat removal
    • Underjet feature provides positive take-off at start-up and upset conditions
  • Cost savings
    • Low pressure air is lowest cost during normal operation
    • Can reuse some or all of existing hydro or air doctor/take-off components

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