Figure 13  Common 13 – Closed Loops

A Pressure Reference must be included within a closed loop system: when a system is completely recirculating, such as a heating or cooling system, then a pressure reference is required to define the initial pressurized condition of the closed system.

A tank is used to define the pressure at a node within a closed system, which allows a solution to be found with node pressures calculated relative to the pressure reference. The pressure reference will not affect the flow rates around the system. It only affects the calculated pressures at the nodes within the system. 

Pipe Flow Expert will check that the pressure at each node is above 0.000 psi (absolute). 

Note: Pressures below 0.000 psia are impossible to achieve.

A pressure reference can be supplied in various ways:

1.  Add a tank at a node to model a sealed pressurization unit (use fluid surface pressure to specify 

     the pressurized condition). 

2.  Add a branch spur with a tank at the end to model a fluid head pressure (use liquid level to specify

     the fluid head).

3.  Add a vertical pipe to a top up tank, setting the elevation of the tank exit point and the liquid level

     in the tank to provide the pressure at the entry point to the system.