Reduced Pressure Principle
The Apollo Series 4A-200 Reduced Pressure Principle Backflow Preventer is designed
to give maximum protection against backflow caused by either back-pressure or
back-siphonage from substances that are hazardous. The durable but economical
device is easily maintained in the line with modular check cartridge assemblies that
require no special tools. It consists of two independently acting spring-loaded check
valves with an automatic differential relief valve located between the check valves. All
testcocks are mounted at the top of the unit to assure easy access during repair and
maintenance when unit is installed in tight places.