Tanks and vessels

A vessel holds a level of one material. Give it a name, set its Material and its Capacity, and it is ready to fill and draw.

The three sizes

Three boxes describe how much a vessel holds, all read in the material’s unit.

• Capacity is the working volume.
• Starting Level is how full it is when the run begins, which is often zero.
• Heel is what you cannot pump out: the material below the outlet that stays in the bottom.

Figure 1. A vessel's settings. Name, material and capacity are the three that matter here.

A vessel sitting at its heel is empty for every practical purpose.

The report calls a vessel at its heel % Time At Heel rather than empty, because the two are not the same thing, and the difference is real money in a plant. See The Bulk report.

Level marks

A vessel can carry up to four level marks, named LL, L, H and HH, at whatever level you choose. Crossing a mark does what the mark’s action says: Nothing (the mark still measures time in band for the report), Stop the inflow, Stop the outflow, Call for a refill or Alarm. A mark can also run a line of logic. That is how a high switch that shuts a fill valve is modeled: an H mark at the fill level, with its action set to Stop the inflow. A low mark can Call for a refill and a lower one can Stop the outflow, so a vessel fills and empties all day on its own.

Figure 2. Level marks on a vessel: LL, L, H and HH, each with an action.

Literal numbers only

The capacity, the starting level, the heel and every level mark take a literal number only. They will not accept a variable, an attribute or a distribution. Change the number between runs, or vary it with a scenario.