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Simplified Hydraulic Model of the Piping System |
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The pump inlet losses for submersible sump pumps do not have to be
calculated. The losses are part of the pump itself. Set QTY to zero. |
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The force main is typically the major contributor to the required pump TDH
(other than the static head). |
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The field "Others" allows you to enter any combination of
fittings by just adding the individual loss coefficients. |
The model as presented here allows for fairly accurate modeling of
multiple pump systems. Assuming that the loss coefficients have been
selected correctly the pump flows and heads for operation with fewer pumps
than design condition now allows plotting of "true" pump
performance curves by deducting the station losses from the pump head and
plotting the reduced head curve against the force main curve |
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The Diffuser option can be used when the minimum recommended velocity for
vertical riser pipes results in high system losses. Add a diffuser in the
discharge line (preferably the horizontal section). Set QTY to zero if no
diffuser is used but enter both diameter (d and D). The pipe length can be
combined in case of no diffuser. |
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Use the links provided to find typical friction loss factor. The diffuser
link will also provide a diffuser length based on diameters d and D and
opening angle α.
Loss coefficients for branch connections are the most difficult to define.
They not only vary based on design configuration but also as a function of
flow in the branches and force main. Under certain flow condition and
configurations the loss coefficient may be negative for the branch (The
force main is pulling the fluid from the branch). The velocity of the
combined flow is used to calculate the head loss. |
Need a system curve? for various flow rates, static heads and pumps
operating? Just enter the conditions, calculate and record static
head, no. of pumps operating, the minimum and maximum TDH, min. and
max. station losses and main force losses for a series of flow rates.
Enter the data in a spread sheet and plot the curves. Hint: Use the KRT selection program to plot the system curve against the pump curve for parallel operation to determine the run-out condition for single pump operation. |
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| Note: Based on the simplicity of the model the calculations are approximations. This applies especially to the branch connection. Results are sufficient for rough sizing of pumps. For more accurate results a detailed model should be built or sophisticated head loss computer codes be used. | |||||
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© 2003 - Peter R. Stech |
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