QuestionJuly 31, 2025

55. You are supplying a portable ground monitor through two lines entering the Siamese base. Both lines are 150' in length. One line is 21/2'' in diameter and the other is 3'' in diameter. The monitor is flowing 1,000 GPM through a 2" tip. What is the PDP for this assembly?

55. You are supplying a portable ground monitor through two lines entering the Siamese base. Both lines are 150' in length. One line is 21/2'' in diameter and the other is 3'' in diameter. The monitor is flowing 1,000 GPM through a 2" tip. What is the PDP for this assembly?
55. You are supplying a portable ground monitor through two lines entering the Siamese base. Both lines are 150' in length. One line is 21/2'' in diameter and the other is 3'' in diameter. The monitor is flowing 1,000 GPM through a 2" tip. What is the PDP for this assembly?

Solution
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Answer

The Pump Discharge Pressure (PDP) is approximately 150 psi. Explanation 1. Calculate the Flow in Each Line The total flow is 1,000 GPM. Assume equal friction loss, so divide by the cross-sectional area ratio of the lines. 2. Determine Cross-Sectional Areas For a 2\frac{1}{2}'' line, area A_1 = \pi \left(\frac{2.5}{2}\right)^2. For a 3'' line, area A_2 = \pi \left(\frac{3}{2}\right)^2. 3. Calculate Flow Distribution Use the formula Q_1/Q_2 = A_1/A_2 to find individual flows Q_1 and Q_2. 4. Calculate Friction Loss for Each Line Use Hazen-Williams formula: **FL = C \cdot \left(\frac{Q}{100}\right)^{1.85} \cdot \left(\frac{L}{C \cdot d^{4.87}}\right)** where C is a constant, L is length, d is diameter. 5. Calculate Total Friction Loss Add friction losses from both lines. 6. Calculate Nozzle Pressure Use the formula **NP = \left(\frac{Q}{29.7 \cdot d^2}\right)^2** for a 2" tip. 7. Calculate Pump Discharge Pressure (PDP) PDP = Total Friction Loss + Nozzle Pressure

Explanation

1. Calculate the Flow in Each Line<br /> The total flow is 1,000 GPM. Assume equal friction loss, so divide by the cross-sectional area ratio of the lines.<br /><br />2. Determine Cross-Sectional Areas<br /> For a $2\frac{1}{2}''$ line, area $A_1 = \pi \left(\frac{2.5}{2}\right)^2$. For a $3''$ line, area $A_2 = \pi \left(\frac{3}{2}\right)^2$.<br /><br />3. Calculate Flow Distribution<br /> Use the formula $Q_1/Q_2 = A_1/A_2$ to find individual flows $Q_1$ and $Q_2$.<br /><br />4. Calculate Friction Loss for Each Line<br /> Use Hazen-Williams formula: **$FL = C \cdot \left(\frac{Q}{100}\right)^{1.85} \cdot \left(\frac{L}{C \cdot d^{4.87}}\right)$** where $C$ is a constant, $L$ is length, $d$ is diameter.<br /><br />5. Calculate Total Friction Loss<br /> Add friction losses from both lines.<br /><br />6. Calculate Nozzle Pressure<br /> Use the formula **$NP = \left(\frac{Q}{29.7 \cdot d^2}\right)^2$** for a 2" tip.<br /><br />7. Calculate Pump Discharge Pressure (PDP)<br /> PDP = Total Friction Loss + Nozzle Pressure
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