Type VZ 18 512 B (reaction: delayed, backwash filter: immediate): A continuous signal on connection X effects a changeover of the valve after the time that has been set. If there is no signal any more at connection X, the valve goes back into its initial position.
VZ 18 513 B type (reaction: immediate, backwash filter: delayed): A continuous signal at the connection X triggers an immediate switching of the valve. The valve switches back to the initial position according to the time set. If no signal is at connection X, then the valve also switches back to the initial position.