The Principle Operation of a Barometric Loop Backflow Prevention Method

The Barometric Loop is a piping arrangement for controlling cross-connections. It is a loop in the piping system that effectively protects against backsiphonage only. It may not be used to protect against backpressure. The barometric loop consists of a continuous section of supply piping that abruptly rises to a height of no less than 35 feet and then returns back down to the originating level. Its operation, in the protection against backsiphonage, is based upon the principle that a water column at sea level pressure, will not rise above 33.9 feet. In general, barometric loops are locally fabricated and are 35 feet high. The barometric loop does not allow air into the loop to eliminate the vacuum and break the siphon but it works on the principle that it is physically impossible to pull a column water up 35 feet. The siphon principle is based on the concept that the atmospheric pressure cannot support a column of water in excess of 33.9 feet. The water in a barometric loop is vulnerable to freezing therefore its use is limited to areas where the temperature can be controlled or in areas where freezing is not an issue. The barometric loop should be considered equivalent to vacuum breaker whereas the barometric loop can be used to control cross-connection at location where an atmospheric or pressure vacuum breaker could be utilized.