Question

Part I. Indicate whether true or false (T or F).

__When two or more pumps are connected in series in a pipeline, the discharge is increased but the pressure head remains the same as with a single pump.

__According to DHEC guidelines, the minimum detention time in a pump station is 15 minutes and the maximum pump runtime is 2 minutes. Both times are evaluated at average daily flow (ADF).

__Given three pipes in parallel. The flow is the same in each pipe.

__The Hardy Cross method for pipe network analysis uses an iterative procedure to adjust the flow in all pipes around each primary loop until the head losses sum to zero, and in all pipes along each path until the energy equation is satisfied.

__The governing relationships for network analysis using the Hardy-Cross method are nodal continuity and energy conservation around primary loops. In the case of networks with fixed grade nodes, the energy equation is written between any two fixed-grade nodes. A sequence of pipes connecting any two fixed-grade nodes is known as a path. Given a system with n fixed grade nodes, there will be n paths.

__When the rotational speed of a pump is changed, the capacity (pumped flow rate) varies directly as the speed and head varies directly as the square of the speed.

__Turbo-hydraulic pumps include radial flow, axial flow, and mixed flow pumps. Strictly defined, a centrifugal pump is a radial-flow pump only. However, colloquial usage in the United States considers a centrifugal pump as any pump in which a rotating impeller energizes the fluid, whether the flow is radial, axial, or a combination of both (mixed).

___ Given three pipes in parallel. Even though these pipes truly may not be parallel, following different paths, and may not be the same length, diameter, or material, the flowrate and head loss are the same in each pipe.

__A pipe network (water distribution system) is an interconnected set of pipes linking one or more sources to one or more demand (delivery) points, and can involve any number of pipes in series, branching pipes, and parallel pipes.

__In any pipe network, the energy balance along a pipe or series of pipes must satisfy the conservation of energy principle as stated by the Bernoulli equation. Energy loss in any pipe or series of pipes is due only to pipe friction and minor losses and not to a change in elevation between the ends of the pipe or series of pipes.

__In the Hardy Cross method, clockwise flow results in negative head loss and counterclockwise flow results in positive head loss. Convergence is achieved when head loss around each primary loop sums to zero (or within specified tolerance).

__For the case of pressure pipe flow, the HGL is above the top of the pipe if the pressure is positive [>0]. If the pressure becomes negative [<0], then the HGL falls below the elevation of the centerline of the pipe. Negative pressure can develop in pipe flow at the intake to a pump.

___When solving pipe flow problems with the Darcy-Weisbach equation involving unknown flow rate, the solution begins by guessing a friction factor.

___The Darcy-Weisbach friction factor and Hazen-Williams coefficient differ by about 5-orders of magnitude but vary directly in the sense that a pipe flow with a high friction factor has a high Hazen-Williams coefficient. __In any pipe network, the algebraic sum of head losses along a path must be zero.

__All pipes in a system of parallel pipes have the same Kp value (hf=KpQn), even though they may differ in diameter, length and/or roughness.

__Given three reservoirs connected by a system of three branching pipes. Nodal continuity holds at the common junction. The head drop between the reservoir to which a pipe connects, and the common junction determines the flow in that pipe.

__Given three pipes in parallel. All pipes have the same head loss and flow rate. In any pipe network, the algebraic sum of head losses around any primary loop is zero. The Hazen-Williams coefficient varies with pipe material and age and is independent of flow rate. Therefore, the Hazen-Williams equation applies only to fully turbulent flow and not to any flows that exist in the developing turbulence region.

Answer 1

1. When two or more pumps are connected in series in a pipeline, the discharge is increased but the pressure head remains the same as with a single pump.

False. Because, when two or more pumps are connected in series in a pipeline, the flow remains same, ( discharge), to maintain the total head velocity head and pressure head adjust themselves against total head. Q= Q1=Q2

2. According to DHEC guidelines, the minimum detention time in a pump station is 15 minutes and the maximum pump runtime is 2 minutes. Both times are evaluated at average daily flow (ADF).

3. Given three pipes in parallel. The flow is the same in each pipe

False. Flow varies with respect to their cross-section area. Q= Q1+Q2

4. The Hardy Cross method for pipe network analysis uses an iterative procedure to adjust the flow in all pipes around each primary loop until the head losses sum to zero, and in all pipes along each path until the energy equation is satisfied.

True. Hardy cross method satisfies continuity equation as well as the energy equation.

5. The governing relationships for network analysis using the Hardy-Cross method are nodal continuity and energy conservation around primary loops. In the case of networks with fixed grade nodes, the energy equation is written between any two fixed-grade nodes. A sequence of pipes connecting any two fixed-grade nodes is known as a path. Given a system with n fixed grade nodes, there will be n paths.

True - Fixed grade nodes are nothing but reservoir points

6. When the rotational speed of a pump is changed, the capacity (pumped flow rate) varies directly as the speed and head varies directly as the square of the speed.

True - (Q1/Q2) = (N1/N2) ; (H1/H2) = (N1/N2)2

7. Turbo-hydraulic pumps include radial flow, axial flow, and mixed flow pumps. Strictly defined, a centrifugal pump is a radial-flow pump only. However, colloquial usage in the United States considers a centrifugal pump as any pump in which a rotating impeller energizes the fluid, whether the flow is radial, axial, or a combination of both (mixed).

True

8. Given three pipes in parallel. Even though these pipes truly may not be parallel, following different paths, and may not be the same length, diameter, or material, the flowrate and head loss are the same in each pipe.

False. Head losses are same but flow rates need not be same. Q= Q1+ Q2 . Q1 and Q2 can be same if cross section is same.

9. A pipe network (water distribution system) is an interconnected set of pipes linking one or more sources to one or more demand (delivery) points, and can involve any number of pipes in series, branching pipes, and parallel pipes.

True. Pipe network includes series and parallel connections and one or more demand points (junctions).

10. In any pipe network, the energy balance along a pipe or series of pipes must satisfy the conservation of energy principle as stated by the Bernoulli equation. Energy loss in any pipe or series of pipes is due only to pipe friction and minor losses and not to a change in elevation between the ends of the pipe or series of pipes.

False. Change in elevation causes energy loss in pipes.

11. In the Hardy Cross method, clockwise flow results in negative head loss and counterclockwise flow results in positive head loss. Convergence is achieved when head loss around each primary loop sums to zero (or within specified tolerance).

True. But it can be positive for clockwise, negative for counterclockwise and vice versa.

12. For the case of pressure pipe flow, the HGL is above the top of the pipe if the pressure is positive [>0]. If the pressure becomes negative [<0], then the HGL falls below the elevation of the centerline of the pipe. Negative pressure can develop in pipe flow at the intake to a pump.

True. Negative pressures are nothing but suction pressures which occurs in intake points.

13. When solving pipe flow problems with the Darcy-Weisbach equation involving unknown flow rate, the solution begins by guessing a friction factor.

True. Friction factor can be guessed or can be calculated when we know the type of flow, laminar or turbulent, by finding the Reynolds number.

14. The Darcy-Weisbach friction factor and Hazen-Williams coefficient differ by about 5-orders of magnitude but vary directly in the sense that a pipe flow with a high friction factor has a high Hazen-Williams coefficient.

15. In any pipe network, the algebraic sum of head losses along a path must be zero.

True. Hardy Cross Method is the example.

16. All pipes in a system of parallel pipes have the same Kp value (hf=KpQn), even though they may differ in diameter, length and/or roughness.

True. Head losses in parallel pipes are same.

17. Given three reservoirs connected by a system of three branching pipes. Nodal continuity holds at the common junction. The head drop between the reservoir to which a pipe connects, and the common junction determines the flow in that pipe

True. Continuity and Energy Equation apply..

18. Given three pipes in parallel. All pipes have the same head loss and flow rate. In any pipe network, the algebraic sum of head losses around any primary loop is zero. The Hazen-Williams coefficient varies with pipe material and age and is independent of flow rate. Therefore, the Hazen-Williams equation applies only to fully turbulent flow and not to any flows that exist in the developing turbulence region.

False. Flow rates are not same.