Definition:   The backflow preventer is a tandem device consisted of two separately functional check valves  which can strictly prevent the backpressure water inside pipeline from reversing flow ,The protection class of double check backflow preventer is lower than that of the reduced-pressure type backflow preventer. Both the preventers have the same working principle and structure except that the double check backflow preventer has not pressure differential drain valve. They have two separate spring assisting closed action of resilient seated check valves, and four testing ports.

Application: The double check backflow preventer shall only be applied to piping systems with mild backflow contamination rather than in toxic and poisonous contaminated area.

A.       Low head loss: the double check backflow preventer has a capacity of low head loss. It is not meeting with demands of domestic low pressure piping system, but also it plays the role of preventing backflow from contamination.

B.       Double separate check valve structure: the double check backflow preventer adopts two separate check valves structure. From the stand view of mechanical kinematics and probability analysis, the relative motion of the two end check valves is an independent event. Only assumed both of them becoming failure to work or mishandling, backflow will occur at the time. So its reliability is much higher than the structure of backflow preventer with “two check in one shaft”.

Two separate check valves with detachable structure is available for maintenance and testing to leave a pathway beforehand while the backflow preventer is operating in future, providing an easy access to maintenance and inspection.

The most abroad advanced double check backflow preventer’s structure all adopts such double separate check valve structure.

The backflow preventer (non-bypass) has four ball valves. Such four testing ports provide composite functional test with gate valve sealing, check valve sealing ability, and each parts pressure loss. 

 C.      Customized pressure differential testing analysis gauge: we entrust American authoritative backflow preventer testing company to customized make private pressure differential testing analysis gauge. With a view to the double check backflow preventer’s relative low pressure, and its frequent switch on/off of disc, the testing frequency will be definitely more than that of reduced-pressure backflow preventer. We advised to take testing every 6-12 months. The testing shall use special pressure differential analysis gauge whose testing precision needs to reach 1KPa at lest rather than use pressure gauge. However, many factories connect pressure gauge on both end of the backflow preventer, but the precision is only 50KPa which can’t make high precision data.