A fast acting bottom drain valve is mounted on tank drain openings to seal them off in case of an emergency. During normal operating conditions, the valve is kept open by a pneumatic cylinder.
In Pressure/vacuum relief valve Pressure/vacuum relief valve is an umbrella term that includes pressure or vacuum relief valve as well as pressure and vacuum relief valve. case of emergency or power outage, the valve is shut via remote release. The pneumatic cylinder is vented and the valve plug drops due to its own weight, thus shutting off the valve.