Backflow preventer for underground hydrant, has screw bolts for screwing housing with casing pipe, where each screwing bolt has head with bars for engaging at respective female key, and bars inclinedly run corresponding to threads of bolts

摘要

The preventer has a housing screwed at a casing pipe of an underground hydrant, and a sleeve wall at an upper end of the housing, where the sleeve wall has bayonet claws for connecting the wall with a hose coupling or a standpipe. Screw bolts screw the housing with the casing pipe, and each screwing bolt has a head with a number of bars for engaging at a respective female key (50), where the bars inclinedly run corresponding to threads of the screw bolts.