The Apollo™ Models HBV2 LF, HBVAF2 LF, HBDUC, and HBDUC LF Hose Connection Vacuum Breakers are designed to prevent cross-connection caused by back-siphonage. The Apollo™ Model HBDUC Hose Bibb Dual Check Backflow Preventer also prevents backflow due to low head back-pressure.