The following hydropnematic tank attributes influence the transient simulation:

• Hydropneumatic Tank Type - Specify the type of Hydropneumatic Tank that this model element represents. Sealed means the tank is a fully sealed pressure vessel. Vented means the tank has an air valve attached. Dipping Tube means the tank has an internal dipping or ventilation tube.
• Diameter (Tank Inlet Orifice) - This is the size of the opening between the gas vessel and the main pipe line. It is typically smaller than the main pipe size. It is used to compute the correct velocity through the tank inlet, so the correct headloss is computed based on the minor loss coefficient (the standard head loss equation is used: Hl = K*V2/2g.)
• Diameter (Dipping Tube) - The diameter of the dipping or ventilation tube within the hydropneumatic tank (only applicable for the Dipping Tube tank type).
• Volume (Compression Chamber) - The volume of the air around the dipping tube that is compressed once the water level elevation exceeds the bottom of the dipping tube.
• Air Flow Calculation Method - Specify whether the air valve air flow rate is determined by user-entered curves of pressure vs. air flow rate, or whether it is calculated based on a user-entered orifice diameter (not applicable for a sealed hydropneumatic tank). The calculated Air Flow result attribute shown in the detailed report shows the volumetric flow rate of air at the conditions present inside the pipeline.
• Diameter (Air Inflow Orifice) - This is the equivalent orifice size of the opening that allows air to enter the tank.
• Diameter (Air Outflow Orifice) - This is the equivalent orifice 1size of the opening that allows air to leave the tank.
• Air Flow Curve (Air Inflow Orifice) - The curve that defines the rate of air inflow (a 'free air' rate, measured at atmospheric pressure) into the tank versus the differential pressure across the air valve.
• Air Flow Curve (Air Outflow Orifice) - The curve that defines the rate of air outflow (a 'free air' rate, measured at atmospheric pressure) out of the tank versus the differential pressure across the air valve.
• Elevation (Top of Dipping Tube) - The elevation of the top of the dipping tube and the dipping tube-type hydropneumatic tank.
• Elevation (Bottom of Dipping Tube) - The elevation of the bottom of the dipping tube.
• Dipping Tube Hydropneumatic Tank Parameters
  
  
• Minor Loss Coefficient (Outflow) - This is the 'k' coefficient for computing headlosses using the standard headloss equation, H = kV2/2g. It represents the headlosses for tank outflow. If you lump other minor losses through the tank assembly (bends, fittings, contractions, etc) into this coefficient, keep in mind that the velocity is calculated using the area of the "diameter (tank inlet orifice)" that you entered.

In some cases, you may want to analyze a range of different initial conditions, which could potentially change the starting hydraulic grade of your hydropneumatic tank. The gas law can be employed in this case. For example, if you know the initial gas volume is 300 L at a steady state pressure head of 50 m, you can compute the 'K' constant using the gas law, PVk=K: (50 m + 10.33 m)(0.3m3) = 18.099. (gas law exponent assumed to be 1.0) So, if your new steady state pressure head is 30 m, the new initial gas volume (which you must enter) is computed as V = (18.099)/(30 m+10.33 m) = 0.449 m3 = 449 L. The transient calculation engine always uses an atmospheric pressure head of 1 atm or 10.33 m when solving the gas law equation.

• Has Bladder? - Denotes whether the gas is contained within a bladder. If it is set to "True", HAMMER automatically assumes that the bladder occupied the full-tank volume at the preset pressure at some time and that the air volume was compressed to a smaller size by the steady-state pressure in the system. The "Volume of gas (initial)" is not used in this case, since it is calculated based on the full tank size, preset pressure and steady state pressure.
• Pressure (Gas-Preset) - This is the pressure (not a hydraulic grade) in the gas bladder before it is exposed to pipeline pressure; the pressure when it fills the entire tank volume. Often called the "precharge" pressure; it is only exposed when selecting "true" for "Has bladder?"
• Report Period - used to report extended results in the Transient Analysis Detailed Report. Represents a timestep increment. For example, entering '10' would cause extended results to be reported every 10 timesteps.
• Elevation Type - This allows you to specify the type of approach used in tracking the gas-liquid interface (a new feature as of version 08.11.01.32). By default, the liquid surface elevation is not tracked and is essentially assumed to be fixed, at the tank physical bottom elevation. For more information on how this option is used for tracking the liquid elevation, see Tracking the Air-Liquid Interface.