Modeling a Tank with Multiple Penetrations

Often a single tank will have multiple penetrations.  The PIPE-FLO tank, spray demand, and pressure demand objects support a single pressure and or level value.  A tank with multiple penetrations can be easily modeled with multiple tanks and demands.  In this article we will see how to model a tank with multiple penetrations.
  
The supply tank below has multiple tank penetrations.  One penetration goes to the pump suction.  The second penetration is used to re-circulate fluid from the supply tank, through a cleanup filter, and back to the supply tank.   The third penetration provides the minimum flow through the pump during low flow conditions.  The water level in the tank varies from a low level of 5 ft to a high level of 10 ft above the tank base, and the tank is pressurized to 5 psig.  



The pump suction and recirculation penetrations are always under the tank liquid level, as a result each is modeled using the Tank object.  This allows setting both the level and pressure.  

With the tanks at the low water level of 5 ft (above the tank bottom), with the bottom of the tank at an elevation of 100 ft (above sea level), and the pump suction penetration elevation at 101 ft; the fluid level at the pump suction penetration is 4 ft.  With the recirculation penetration at an elevation of 103 ft, there is a 2 ft level at the recirculation penetration, at low tank level.  

Since the minimum flow recirculation line occurs at the 112 ft elevation, and the high level occurs at a level of 10 ft above the bottom of the tank (110 ft elevation), the minimum flow penetration is never under the tank fluid level.  This is why the minimum flow penetration is modeled as a spray demand.  Since the entire tank is at a 5-psig all tank and demand objects are set to 5 psig.  

If the tank level or pressure is changed, all the set values for the tank penetrations and spray must be adjusted.  The system below shows the changes made for the high tank level.