BETEC CAD’s Heavy Duty Models VAVHB–10/20/30 For High Pressure Applications. BETEC CAD manufactures heavy duty VAVH B-10/20/30 series are designed to withstand, where VAVs are subjected to face extra high pressures and noise or to deliver high volume of constant air volume or variable air volume to the conditioned zone. Variable Air volume or Constant Air Volume delivery of conditioned air to a room through a single duct or multi duct with single outlet or multiple outlets is possible with this model. Constant Air Volume is achieved through differential pressure sensing systems by regulating the primary air flow, independent of static developed in a single duct. Variable Air Volume is achieved within the limits of Vmin to Vmax by directing required volume of air in direct response to temperature control signals from the modulating room thermostat.