Large tank evacuation

A differential pressure transmitter is a device for detection, analysis, and regulation; it possesses certain intelligent functions and protective capabilities to prevent misoperations from damaging the stability of the system.

The key is to prevent the tank from becoming under negative pressure, which can cause suction problems; this happens quite often. As for how to design it, as long as the goal is achieved is sufficient; the design must ensure intrinsic safety

This system seems to control a certain rate of air extraction in order to prevent the storage tank from having either excessive or insufficient pressure. Both for the protection of the tank itself and for safety reasons, it is very necessary to use a differential pressure transmitter. However, such a transmitter generally requires an adjustment mechanism and an actuator in order to regulate the system pressure: changes in tank pressure → transmitter → adjustment signal sent to PLC or DCS → actuator that carries out the adjustment.

I agree with what was said above; to achieve more precise control, a cascade control system can also be used, that is, two closed loops working together to carry out the control, with the commands ultimately being executed by control valves. In situations where the process requirements are not high, single-stage control (as shown in the diagram above) is sufficient.

Does that mean each tank’s exhaust outlet must be equipped with a pneumatic control valve that is interlocked with the corresponding differential pressure transmitter on the tank top? If pneumatic control valves are installed only on the exhaust manifolds, would it be sufficient to use manual ball valves on each tank top? In the event that one of the tanks develops negative pressure, can we only respond after receiving a signal and then carry out manual operations in order to achieve individual control of each tank?

I’m not entirely clear on your description, but may I understand it this way: each storage tank functions as a gas holder, and multiple such holders together form a gas raw material storage and supply area that supplies gas to downstream processes. In that case, there is no need to install transmitters and control valves on each outlet pipe at the top of the tube; this would be excessive. More importantly, it makes automated control more difficult and can even lead to control issues. From your description, the term “air extraction manifold” appears, which suggests that your system is configured with multiple tanks connected in parallel, with air supply being centralized and combined. In this case, the exhaust manifold also serves as a connecting pipe between the various storage tanks, enabling it to balance the pressure differences between them; as a result, no tank will experience negative pressure. Therefore, it is recommended to install a transmitter and an automatic control valve in the exhaust manifold.

Several tanks are connected through an exhaust manifold; is it possible that the tank located near the compressor draws in a large amount of air, resulting in negative pressure, while the other tanks continue to operate normally?

It won’t happen, unless there are problems with the design of your process pipelines – for example, if the pipes are too narrow or too long, resulting in high resistance. Or accidental closure of the manual valve on a single tank, etc.

It seems I was deceived by the manufacturer. There’s another question: if differential pressure transmitters are installed at the manifold or at the compressor inlet, will it have the same effect if no such transmitters are used for individual tanks?