Section III. TECHNICAL PRINCIPLES OF OPERATION
a. The PDU is used in three configurations: LV liquid spray, ULV liquid spray, and SD solid particle. During
operation, the PDU is suspended from a helicopter by a lifting strap. All configurations consist of a bucket
containing the pesticide, a gasoline-powered engine, and a hydraulic pump. In the LV configuration, liquid
pesticide is pumped by a hydraulic motor-driven centrifugal pump from the bucket to boom spray nozzles. In
the ULV configuration, liquid pesticide is pumped by the centrifugal pump from the bucket to boom rotary
atomizers. The rotary atomizers are hydraulically driven. In the SD configuration, solid-particle pesticide drops
from the bucket to the slinger, where it is dispersed by hydraulic motor-driven vanes.
b. The hand control (figure 1-2) operates the PDU from inside the helicopter. When the POWER switch is in the
ON position, battery power is applied to the engine. When the ENGINE START switch is positioned to START
and held, the starter is engaged to start the engine. After the engine is running, the ENGINE START switch
should be released and the switch will spring to the run position. Pressing the DISPERSAL pushbutton will
release the pesticide.