Abstract: A low-differential pressure delay valve for vacuum controlled devices is disclosed. The valve has input, output and third chambers with the following: a controlled flow orifice in a separating plate between the input and output chambers; a port in the separating plate; a diaphragm operator sealingly positioned between the input and third chambers; a hollow stem with a seal on one end which stem communicates the output and third chambers by extending through the separating port, input chamber and the diaphragm, the stem is connected to and operative by the diaphragm operator; and, a bias spring of any predetermined force to maintain the port in a closed position is located in either the input or third chambers. The diaphragm operator opens the port to balance the pressures in the input and output chambers when the change in input pressure or vacuum is both greater than the bias force of the spring and too sudden for rapid dissipation through the fixed orifice.