In modern tank trucks, fittings are pneumatically controlled. Operation is convenient, reliable, and control air is always available.
Valves are activate:
manually using "control blocks" which signal the open state visually and switch over to lock,
automatically using solenoid valves when these are triggered by the central control.
There are also many additional control valves available, such as: 3/2-way, OR, AND, locking valves, as well as special valves that are only used for operation in tank trucks. For complex applications, these valves can be combined to closed units.