Principles of Hydraulics practice

All 20 free principles of hydraulics questions

1. How much pressure does each foot of water height add at the bottom of a water column?

   • A 0.433 psi Correct
   • B 2.31 psi 2.31 is the number of feet of water it takes to make 1 psi, the inverse figure, not psi per foot.
   • C 0.231 psi 0.231 is the 2.31 feet-per-psi figure with the decimal point moved, not a pressure per foot.
   • D 4.33 psi 4.33 psi puts the decimal point one place off, ten times what a foot of water makes.

   A column of water 1 ft tall presses on its base with 0.433 pounds per square inch (psi), and each added foot adds the same amount. It takes 2.31 ft of water, not 1 ft, to make 1 psi, which is why 2.31 is the feet-per-psi figure.

2. Which pipe carries water from the water source to the zone valves?

   • A The lateral A lateral runs downstream of a zone valve to the heads, not from the source to the valves.
   • B The service line The service line runs from the utility's main to the water meter, ahead of the irrigation system.
   • C The riser A riser is the short upright pipe a head sits on, not the pipe that feeds the valves.
   • D The mainline Correct

   The Texas Commission on Environmental Quality (TCEQ) defines the mainline as the irrigation pipe that delivers water from the water source to each zone valve. The laterals start at the zone valves and carry water on to the heads.

   30 TAC 344.1(28)

3. What does the term hydraulics cover in landscape irrigation?

   • A Static and moving water, and system pressure losses Correct
   • B The chemistry and quality of the water supply Water chemistry is not part of the definition, which covers water at rest and in motion and the system's pressures.
   • C How quickly the soil takes in applied water Soil intake is a soil and scheduling subject, not what hydraulics covers.
   • D How much water the plants use each day Plant water use is evapotranspiration, not hydraulics.

   The Texas Commission on Environmental Quality (TCEQ) defines hydraulics as the science of static and dynamic water, which takes in working out an irrigation system's pressure losses and pressure needs. Soil intake, plant water use and water chemistry are separate subjects.

   30 TAC 344.1(17)

4. What sets off water hammer in an irrigation pipe?

   • A High static pressure with no flow With no flow there is no change in velocity, so no shock wave forms.
   • B Too many heads on one zone Too many heads lowers the pressure at the heads; it does not set off a sudden change in velocity.
   • C A sudden change in water velocity Correct
   • D A long run of level pipe A straight level run carries water at a steady velocity; the source names sudden velocity changes and fittings that turn the water.

   Water hammer is a pressure surge made by shock waves, which come from a sudden rise or fall in the water's velocity, such as a valve opening or a pump starting or stopping. Pressure alone sends no shock wave because standing water has no velocity to change.

5. How is a drip zone's total emitter flow in GPH turned into GPM?

   • A Multiply it by 60 Multiplying by 60 turns gallons per minute into gallons per hour, the opposite direction.
   • B Divide it by 100 An hour holds 60 minutes, not 100, so dividing by 100 gives too small a flow.
   • C Divide it by 60 Correct
   • D Divide it by 24 Dividing by 24 turns a daily figure into an hourly one; it never reaches minutes.

   Because an hour holds 60 minutes, a drip zone's flow in gallons per hour (GPH) becomes gallons per minute (GPM) when it is divided by 60. Multiplying by 60 goes the other way, from GPM to GPH.

6. In what unit is the flow in an irrigation system measured?

   • A fps Feet per second measures velocity, how fast the water moves, not how much of it flows.
   • B psi Pounds per square inch measures pressure, not flow.
   • C GPM Correct
   • D Feet of head Feet of head is another way to state pressure, not flow.

   Flow is a volume of water delivered in a set time, so it takes gallons per minute (GPM) as its unit. Speed of the water takes feet per second (fps), and pressure takes pounds per square inch (psi) or feet of head.

7. How is the design pressure for an irrigation zone worked out?

   • A The static pressure measured at the water meter Static pressure at the meter is what the site has available, not what the zone needs.
   • B The head's minimum pressure plus all losses to the source Correct
   • C The static pressure less every loss to the head Static pressure less the losses is the working pressure that reaches the head, not the design pressure.
   • D The pressure rating printed on the pipe A pipe's rating is the most it may hold, not the pressure the heads need.

   The Texas Commission on Environmental Quality (TCEQ) defines design pressure as the emission device's minimum operating pressure added to every pressure loss between that device and the water source. It is the pressure the source must supply for the head to work properly.

   30 TAC 344.1(9)

8. Which unit is used to measure water pressure?

   • A GPM Gallons per minute measures flow, not pressure.
   • B fps Feet per second measures velocity, not pressure.
   • C psi Correct
   • D in/hr Inches per hour is a precipitation rate, the depth of water put on the ground, not a pressure.

   Water pressure is stated in pounds per square inch (psi) because pressure is a force spread over an area. Gallons per minute (GPM) measures flow, and feet per second (fps) measures velocity.

9. What is the pressure of water that is not moving called?

   • A Dynamic pressure Dynamic pressure is measured while water is moving.
   • B Static pressure Correct
   • C Design pressure Design pressure is what a zone needs: the head's minimum pressure plus all losses to the source.
   • D Residual pressure Residual pressure is what remains while water is being drawn, so the water is moving.

   The Texas Commission on Environmental Quality (TCEQ) defines static water pressure as the pressure of water when it is not moving, and it is generally the pressure the irrigation system has available. Dynamic, or working, pressure is measured with water flowing.

   30 TAC 344.1(42)

10. Which pump is added to raise pressure when the supply tank is too low to deliver enough pressure?

    • A A submersible well pump A submersible pump lifts water out of a well; it is not the pump added to lift the pressure a low tank gives.
    • B A sump pump A sump pump empties water out of a pit, not into a supply line.
    • C A metering pump A metering pump doses small measured amounts, such as a chemical, and does not raise system pressure.
    • D A booster pump Correct

    A tank gives pressure through the weight of its water, so a tank set too low cannot give enough. A booster pump is added in that case because it raises the pressure the tank alone can give.

11. How does each foot that water climbs on its way to a head change its pressure?

    • A A loss of 0.433 psi Correct
    • B A gain of 0.433 psi Water gains 0.433 psi a foot going downhill, not uphill.
    • C A loss of 2.31 psi 2.31 is the feet of water in 1 psi, not the psi in 1 ft.
    • D No change at all Height always changes pressure, by 0.433 psi for every foot.

    Water loses 0.433 pounds per square inch (psi) for every foot it climbs because each foot of water column presses back with that much. It gains the same amount for every foot it drops, and 2.31 is the number of feet of water in 1 psi.

12. How tall a column of water makes 1 psi at its base?

    • A 0.433 ft 0.433 is the psi in 1 ft of water, not the feet in 1 psi.
    • B 1.00 ft One foot of water makes only 0.433 psi, well short of 1 psi.
    • C 8.34 ft 8.34 is the weight in pounds of a gallon of water, not a height.
    • D 2.31 ft Correct

    Each foot of water height makes 0.433 pounds per square inch (psi), so it takes 2.31 ft of water to make 1 psi. That is why psi converts to feet of head by multiplying by 2.31.

13. What is water pressure measured with the water flowing called?

    • A Static pressure Static pressure is measured with no water moving.
    • B Dynamic pressure Correct
    • C Surge pressure Surge pressure is the spike from water hammer when flow changes suddenly, not the ordinary pressure of flowing water.
    • D Design pressure Design pressure is what a zone needs: the head's minimum pressure plus all losses to the source.

    Dynamic pressure, also called working pressure, is the pressure measured while water is moving through the system. It always reads below the no-flow reading at that same point because moving water loses pressure.

14. PVC irrigation piping must be designed so the water velocity does not exceed:

    • A 5 fps Correct
    • B 7.5 fps 7.5 fps is not the limit the rule sets for PVC irrigation piping.
    • C 9 fps 9 fps is not the limit the rule sets for PVC irrigation piping.
    • D 10 fps 10 fps is twice the 5 fps the rule allows in PVC irrigation piping.

    The Texas Commission on Environmental Quality (TCEQ) requires polyvinyl chloride (PVC) piping in an irrigation system to be designed and installed so the water does not exceed 5 feet per second (fps). Higher figures seen in classes or other sources are not the limit the rule sets.

    30 TAC 344.62(d)

15. What does a lower C factor tell you about a pipe?

    • A Its inside wall is smoother A smoother wall has a higher C factor; PVC at 150 is smoother than steel at 100.
    • B Its wall is thicker The C factor rates the roughness of the inside wall, not its thickness.
    • C Its inside wall is rougher Correct
    • D Its pressure rating is higher The C factor says nothing about pressure rating; it rates wall roughness.

    The C factor rates how rough the inside of a pipe is: a smaller C value means a rougher wall and more friction loss. Polyvinyl chloride (PVC) pipe is about 150 and standard steel about 100.

16. About how much does one gallon of water weigh?

    • A 7.48 lb 7.48 is the number of gallons in a cubic foot, not the weight of a gallon.
    • B 8.34 lb Correct
    • C 62.4 lb 62.4 lb is what one cubic foot of water weighs, not one gallon.
    • D 2.31 lb 2.31 is the feet of water in 1 psi, not a weight.

    The weight of a gallon of water is about 8.34 lb. The other figures are easy to mix up because they describe a cubic foot of water, which holds 7.48 gallons and weighs 62.4 lb.

17. Design flow through a water meter should be held to no more than ____ of the meter's maximum safe flow.

    • A 10 percent 10 percent is the meter guideline for pressure loss against static pressure, not for flow.
    • B 50 percent 50 percent is not the figure the guideline sets; it allows up to 75 percent.
    • C 75 percent Correct
    • D 90 percent 90 percent is above the 75 percent the guideline allows.

    Design flow through a meter should stay at or under 75 percent of the meter's maximum safe flow, which the meter's own chart gives. That figure is a design guideline from model irrigation standards, not a rule of the Texas Commission on Environmental Quality (TCEQ).

18. Velocity, the speed of water moving through a pipe, is measured in which unit?

    • A GPM Gallons per minute measures flow, the amount of water, not its speed.
    • B fps Correct
    • C psi Pounds per square inch measures pressure, not speed.
    • D GPH Gallons per hour measures flow, usually for drip emitters, not speed.

    Velocity takes feet per second (fps) as its unit because it is how fast the water moves, a distance covered in a set time. Flow takes gallons per minute (GPM), and pressure takes pounds per square inch (psi).

19. What is the pipe that connects the water utility's main to the water meter called?

    • A Service line Correct
    • B Mainline The irrigation mainline starts after the meter and carries water to the zone valves.
    • C Lateral A lateral runs from a zone valve to the heads.
    • D Swing pipe A swing pipe is the flexible link from a lateral to a head.

    Texas public water system rules define the service line as the pipe connecting the utility's main and the water meter. The irrigation system starts on the customer's side of the meter, where the mainline carries water to the zone valves.

    30 TAC 290.38(80)

20. What other name is used for dynamic pressure?

    • A Static pressure Static pressure is the pressure with no water moving, the opposite of dynamic pressure.
    • B Design pressure Design pressure is what a head needs plus every loss back to the source, a figure worked out on paper rather than another name for flowing pressure.
    • C Test pressure Test pressure is the pressure a line is held at to check it for leaks, not the pressure of water moving through the system.
    • D Working pressure Correct

    Dynamic pressure is the pressure while water is flowing through the system, and the term working pressure means the same thing, since it is the pressure the system has while it works.