The Lock Down Device is installed on top loading arms. It is designed to lock the arm in the operating position. This prevents upward movement during filling operations. When the drop tube is in the manhole the operator applies the lock and begins filling. The arm is then raised on completion of filling to release the locking mechanism.
These systems are particularly suitable for installation on loading arms where a pneumatic system is not available. They maintain the pressure on the manhole which in turn ensures a continuous seal and aids the vapour recovery.