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Air Flow Controller Type PRD

The PRD remains the air valve of choice for critical heating, ventilating, and air conditioning applications. The unique operating principle and aerodynamic design make it ideally suited for difficult applications where long term performance is critical to system Performance.

PRDs can be used in almost any application where ventilation or exhaust air must be modulated. However, the following applications are examples where the superior capabilities of the PRD are evident:

  • Fume hood control
  • Laboratory supply, makeup and general exhaust control
  • Space pressurization control
  • Constant velocity exhaust discharge
  • Zone static control
  • Process control


  • Air flow is modulated by a series of expanding airfoils. The airfoil shape contributes to the low pressure both low and significantly reduced discharge noise levels and low turbulence. Placement of the airfoils provides for a uniform air flow profile across the inlet face and discharge of the air valve. Because modulation is not dependent on bearings, levers, springs, or other mechanical devices, the valveā€™s internal structure may be subjected to the build-up of coatings and particulate, yet operation will not be adversely affected.
  • At the heart of each PRD is the aerodynamically designed airfoil assembly. Each airfoil assembly consists of a flexible cell with end clips, and two airfoil covers. The flexible cells are manufactured of EPDM (Ethylene Propylene Diene Methylene) rubber. Chosen for its superior oxidation and corrosion resistance, EPDM cells have been in service in applications like chemical fume hoods for over thirty years. Flexible cell ends are vulcanized and strain is further relieved by end clips. End clips are manufactured in stainless steel, depending on the airfoil cover material.
  • Two airfoil cover halves surround the flexible cell with end clips to form the airfoil assembly. The airfoil cover material is stainless steel. Airfoil covers are tempered to provide the desired spring coefficient. Airfoils are assembled in a constructed case manufactured in stainless steel. Airfoils are placed inside the airfoil supports across the height of the valve body.
  • The manifold end panel is attached with bolts to allow removal in the field in the unlikely event of an airfoil assembly failure. Tube ends protrude through the manifold end panel and are connected together by an external manifold. Airfoils can be removed without removing the valve body and the duct. Side seals are provided at both the manifold and the far end panels to provide a seal at the end of the airfoils. This seal accounts for the low discharge leakage associated with a fully closed valve.
  • Because PRDs are typically used in conjunction with either air flow volume or pressure controls, a wide variety of options are provide to accommodate sensor mounting in the inlet of the air valve.


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