Control valves, such as pressure reducing valves (PRV), pressure sustaining valves (PSV), and flow control valves (FCV) modify their opening to control pressure or flow in the system. For example, PRV's adjust valve position to reduce inlet pressure to meet a target outlet pressure.

Through HAMMER V8i SELECT series 3, HAMMER maintained a constant valve position throughout a transient analysis. In many cases that opening is correct, but there are instances where the valve position will modulate significantly in response to the transient and must be accounted for. In some instances, valve modulation can contribute to transient problems.

Beginning with SELECT series 4 and expanded in CONNECT Edition Update 3, there is a new PRV property "Modulate Valve during Transient" which, when set to True, enables HAMMER to adjust the valve opening during a transient run. The default value for this property is False. This property is saved in the Transient alternative.

When "Modulate Valve during Transient" (found in the Properties grid under the "Transient (Operational)" section) is set to True, the user must set the "Opening Rate Coefficient" and Closure Rate Coefficient".

If the field is set to False, you can pick a valve operating rule pattern in the "Operating Rule" field.

For modulating PRVs and PSVs, valve opening rate coefficient and closure rate coefficient based on pressure difference are used. The 2 coefficients and the difference between the calculated pressure and setting pressure affect the valve opening and closure speed. The unit of valve opening rate coefficient and valve closure rate coefficient is %/s/(ft H2O).

For modulating FCVs, valve opening rate coefficient and closure rate coefficient based on discharge difference are used. The 2 coefficients and the difference between the calculated discharge and the setting discharge affect the valve opening and closure speed. The unit of valve opening rate coefficient and valve closure rate coefficient is %/s/(ft³/s).

You do not need to input the setting PRV outlet pressure, PSV inlet pressure or FCV discharge. Results from initial condition calculation are used as setting parameters.

For PRV, the valve initial condition calculation result "Hydraulic Grade Setting (Calculated)" is used as the PRV setting HGL in transient engine calculation.

For PSV, valve initial condition calculation result "Hydraulic Grade (From)" is used as the PSV setting HGL in transient engine calculation.

For FCV, valve initial condition calculation result "Flow" is used as the FCV setting discharge in transient engine calculation.

Calculation Method

• PRV
  • When valve outlet pressure P_r is higher than PRV Pressure Setting P_s:

    r_c = c_r * (P_r -P_s ),

    r_c is Valve closing rate (%/s)

    c_r (%/s/(ft H2O)) is closing rate coefficient

    Valve relative closure V_c = V_p + r_c * DT,

    where DT (second) is the calculation time step

    V_p (%) is the valve relative closure at last time step.

  • When valve outlet pressure P_r is lower than PRV Pressure Setting P_s:

    r_o = c_o * (P_s -P_r ),

    r_o is Opening rate (%/s)

    c_o (%/s/(ft H2O)) is the opening rate coefficient

    Valve relative Closure Vc = V_p - r_o * DT,

    where DT (second) is the calculation time step

    V_p (%) is the valve relative closure at last time step.

• PSV

  • When valve inlet pressure P_r is higher than PSV Pressure Setting P_s:

    r_o = c_o * (P_r -P_s),

    r_o is Opening rate (%/s)

    c_o (%/s/(ft H2O)) is the opening rate coefficient

    Valve relative Closure Vc = V_p - r_o * DT,

    where DT (second) is the calculation time step

    V_p (%) is the valve relative closure at last time step.

  • When valve intlet pressure P_r is lower than PRV Pressure Setting P_s:

    r_c = c_r * (P_s - P_r),

    r_c is Valve closing rate (%/s)

    c_r (%/s/(ft H2O)) is closing rate coefficient

    Valve relative closure V_c = V_p + r_c * DT,

    where DT (second) is the calculation time step

    V_p (%) is the valve relative closure at last time step.

• FCV

  • When valve discharge Q_r is higher than FCV Discharge Setting Q_s:

    r_c = c_r * (Q_r - Q_s ),

    r_c is Valve closing rate (%/s)

    c_r (%/s/( ft³/s)) is closing rate coefficient

    Valve relative closure V_c = V_p + r_c * DT,

    where DT (second) is the calculation time step

    V_p (%) is the valve relative closure at last time step.

  • When valve discharge Q_r is lower than PRV Pressure Setting Q_s:

    r_o = c_o * (Q_s -Q_r ),

    r_o is Opening rate (%/s)

    c_o (%/s/( ft³/s)) is the opening rate coefficient

    Valve relative Closure Vc = V_p - r_o * DT,

    where DT (second) is the calculation time step

    V_p (%) is the valve relative closure at last time step.