With a pressure vacuum breaker, however, a drop in the pressure of the water enables the spring to snap the check valve shut. As soon as the water pressure drops, the check valve closes and backflow does not occur.n a pressure vacuum breaker, the water travels through a check valve and causes a poppet to raise up a guide into an air inlet. The air inlet also has a valve which ordinarily remains closed.
Peter Marshall was born Ralph Pierre LaCock on March 30, 1926, to Ralph and Jean LaCock, a show business family, in Huntington, West Virginia. Following his father's death when Marshall was a teenager, he moved to New York City to be with his mother, a costume designer.
1 John Marshall was born 13 Jan 1798 at Richmond, VA; he married Elizabeth Maria Alexander, daughter of Dr. Ashton Alexander and Catherine Hanson Thomas, 3 Feb 1820; he died 18 Nov 1833 at 'Mt Blanc', Fauquier Co., VA, at age 35. 2  He was graduated at Harvard College, Cambridge, MA.