# Modelling Tanks using a Reservoir

Tanks can be modelled using a Reservoir node or indeed a Known Pressure node. Figure 1 below provides details a simple system featuring a single tank connected to an open pipe outlet node via a 2 inch schedule 40 steel pipe with a length of 10.0M. The tank details are as follows: Liquid Level: 1.2 M. Elevation to tank base: 0 M. Surface Pressure: 1 ATM. Diameter: 1.0 M. Height: 2.0M. Type: Cylindrical Flat Bottom. Figure 1
Alternatively, this scenario can be modelled using a Known Pressure node. Pressure can be defined using either gauge or absolute units. When defining pressure as gauge, we need to calculate the pressure using the equation P = ρgh (999.1056847*9.80665*1.2 = 11757.46 Pa g). When defining the pressure in absolute units, we need to include atmospheric pressure. The new value of P therefore becomes 11757.46 + 101325 = 113082.5 Pa a. Figures 2 & 3 provide details of the data entry and results for these two options. Figure 2: Pressure Defined in gauge (g) units.
Figure 3: Pressure Defined in absolute (a) units.
We can see that the calculated results are identical for each model.