22 Hydraulics Practice Questions & Answers

1. 1. A technician attaches a pressure gauge to a hose bib on the irrigation service line. With every zone off, the gauge reads 62 psi. With the zone farthest from the point of connection running, the same gauge reads 48 psi. How should the two readings be described?

   • A.Both are static readings, and the 14 psi difference means the gauge has been damaged and should be replaced.
   • B.62 psi is static pressure and 48 psi is dynamic pressure; the difference appears only when water is moving.✓ Answer
   • C.48 psi is static pressure and 62 psi is dynamic pressure; a gauge always climbs once the zone begins to flow.
   • D.Both are dynamic readings, and the 14 psi difference is caused by the elevation of the hose bib above the main.

   Static pressure is read with no water moving; dynamic (working) pressure is read while the zone flows. As soon as water moves, the meter, backflow assembly, valve, fittings and pipe all consume pressure through friction, so the dynamic reading at a given point is always lower than the static reading at that same point.

   Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — static versus dynamic (working) pressureReport a problem with this question

2. 2. The static pressure at the point of connection is 70 psi. A sprinkler head on that zone sits 22 ft higher in elevation than the point of connection. Using 0.433 psi per foot of elevation, what is the static pressure at that head?

   • A.About 50.8 psi
   • B.About 60.5 psi✓ Answer
   • C.About 79.5 psi
   • D.About 19.2 psi

   Water must be lifted to reach the head, so elevation gain subtracts pressure: 22 ft x 0.433 psi/ft = 9.5 psi, and 70 - 9.5 = 60.5 psi. The 2.31 factor converts psi into feet of head and must not be multiplied by feet, which is what produces the 19.2 and 50.8 answers.

   Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — static pressure and elevation (0.433 psi per foot)Report a problem with this question

3. 3. All of a zone's heads sit 30 ft BELOW the point of connection, where the static pressure is 65 psi. Using 0.433 psi per foot of elevation, what static pressure should the technician expect at those heads?

   • A.About 65 psi
   • B.About 13 psi
   • C.About 78 psi✓ Answer
   • D.About 52 psi

   Elevation works in both directions: dropping 30 ft adds 30 x 0.433 = 13 psi, so 65 + 13 = 78 psi. Subtracting instead of adding on a downhill run is one of the most common field errors, and the extra pressure is exactly why low heads on a slope tend to mist.

   Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — static pressure and elevation (0.433 psi per foot)Report a problem with this question

4. 4. A friction-loss table for the pipe in use lists pressure loss in psi per 100 ft at 20 gpm: 1 in — 3.55 psi; 1-1/4 in — 1.20 psi; 1-1/2 in — 0.61 psi; 2 in — 0.18 psi. A lateral carries 20 gpm through 250 ft of 1-1/4 in pipe. What is the friction loss in that lateral?

   • A.About 3.0 psi✓ Answer
   • B.About 30 psi
   • C.About 1.2 psi
   • D.About 8.9 psi

   Friction-loss tables are stated per 100 ft of pipe, so the table value must be scaled by the actual length: 250 ft / 100 ft = 2.5, and 1.20 psi x 2.5 = 3.0 psi. Reporting the raw table value of 1.2 psi forgets the scaling, and 8.9 psi comes from reading the 1 in row instead of 1-1/4 in.

   Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — friction-loss tables expressed in psi per 100 ftReport a problem with this question

5. 5. A run is made of two sections. The friction-loss table for this pipe gives, in psi per 100 ft: 1 in at 15 gpm — 3.10 psi; 1-1/2 in at 30 gpm — 2.10 psi. The first section is 100 ft of 1-1/2 in pipe carrying 30 gpm; the second is 150 ft of 1 in pipe carrying 15 gpm. What is the total pipe friction loss for the run?

   • A.About 5.2 psi
   • B.About 6.8 psi✓ Answer
   • C.About 13.0 psi
   • D.About 4.7 psi

   Each section is scaled separately and then added: 2.10 x (100/100) = 2.10 psi, and 3.10 x (150/100) = 4.65 psi, for a total of about 6.8 psi. Adding the two table values without scaling gives 5.2 psi, and applying that sum to the whole 250 ft gives 13.0 psi.

   Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — friction-loss tables expressed in psi per 100 ftReport a problem with this question

6. 6. The flow through an existing lateral is doubled while the pipe size, material and length stay the same. What happens to the friction loss in that lateral?

   • A.It falls slightly, because the faster water spends less time inside the pipe.
   • B.It rises to roughly three and a half to four times its previous value.✓ Answer
   • C.It doubles as well, since friction loss changes in direct proportion to the flow rate.
   • D.It stays about the same, because pipe diameter alone determines friction loss.

   In the Hazen-Williams relationship used for irrigation pipe, friction loss varies with flow raised to about the 1.85 power, so doubling flow multiplies the loss by roughly 2 to the 1.85 power, about 3.6. That steep rise is why an added zone or a leak on the mainline hurts pressure far more than technicians expect.

   Source: Hazen-Williams friction-loss relationship (loss varies with flow to about the 1.85 power), Irrigation Association hydraulics trainingReport a problem with this question

7. 7. A technician checks a lateral with V = 0.408 x Q / ID^2, where Q is flow in gpm and ID is the pipe's inside diameter in inches. The pipe is a nominal 1-1/2 in pipe whose actual inside diameter is 1.754 in, and the zone flows 25 gpm. What is the velocity in that pipe?

   • A.About 5.8 fps
   • B.About 8.1 fps
   • C.About 3.3 fps✓ Answer
   • D.About 4.5 fps

   The formula uses inside diameter, not nominal size: 0.408 x 25 = 10.2, and 1.754 squared = 3.08, so 10.2 / 3.08 = about 3.3 fps. Substituting the nominal 1.5 in gives the incorrect 4.5 fps, and failing to square the diameter gives 5.8 fps.

   Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — velocity of flow, V = 0.408 x Q / ID^2Report a problem with this question

8. 8. The designer's specification sets a maximum velocity for this system's laterals, and the following table already reflects that limit by listing the greatest flow each pipe size may carry: 1 in — 18 gpm; 1-1/4 in — 30 gpm; 1-1/2 in — 42 gpm; 2 in — 74 gpm. A zone requires 32 gpm. Which is the smallest pipe size the technician may install on that zone?

   • A.Nominal 2 in pipe
   • B.Nominal 1-1/4 in pipe
   • C.Nominal 1 in pipe
   • D.Nominal 1-1/2 in pipe✓ Answer

   Sizing by velocity means choosing the first pipe size whose listed capacity equals or exceeds the required flow. The 1-1/4 in pipe tops out at 30 gpm, which is below the 32 gpm demand, so the 1-1/2 in pipe at 42 gpm is the smallest acceptable size; 2 in would work but is larger than needed.

   Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — velocity-of-flow charts and sizing pipe by velocityReport a problem with this question

9. 9. A repair crew replaces a section of zone lateral with pipe one size smaller than what was there before, and the same sprinklers still operate on the zone. What is the hydraulic consequence in that section?

   • A.Velocity and friction loss both stay the same, since the nozzles set those two values.
   • B.Velocity through it rises, and friction loss rises steeply as a result.✓ Answer
   • C.Velocity through it rises, but friction loss falls because the water moves through faster.
   • D.Velocity through it falls, and the heads downstream receive higher operating pressure.

   The same flow forced through a smaller inside diameter must move faster, and friction loss climbs steeply with that velocity, so the undersized section eats pressure that the heads needed. High velocity also raises the surge produced whenever the zone valve closes.

   Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — velocity of flow and its effect on friction lossReport a problem with this question

10. 10. To address chronically low pressure at the far heads of a zone, a technician replaces the lateral with the next larger pipe size. With the same sprinklers installed, what does the larger pipe accomplish?

    • A.It raises the static pressure of the system because a bigger pipe stores a greater volume.
    • B.It draws more water from the meter, so each nozzle discharges a proportionally larger flow.
    • C.It has no hydraulic effect, because the supply pressure at the point of connection is unchanged.
    • D.It lowers velocity and friction loss, so more supply pressure survives to the far heads.✓ Answer

    A larger inside diameter carries the same flow at lower velocity, and friction loss falls steeply as diameter grows, so less pressure is spent getting water to the end of the run. Pipe size does not create additional supply; the available flow is still limited by the meter and service line.

    Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — pipe diameter, velocity and friction lossReport a problem with this question

11. 11. A homeowner reports a loud bang in the pipes each time one particular zone shuts off. What causes that bang?

    • A.The zone runs below the nozzle's minimum pressure, so large droplets strike the pipe.
    • B.Static pressure slowly climbs above the pipe's rating while the system sits idle.
    • C.Water moving at high velocity is stopped abruptly, and its momentum becomes a pressure surge.✓ Answer
    • D.Two zones with matched precipitation rates end their run times in the same minute.

    Water hammer is a surge created when a moving column of water is halted quickly, usually by a fast-closing valve; the kinetic energy of the column converts into a pressure spike that travels back through the pipe. The magnitude grows with velocity and with the length of straight pipe, and falls as closing time increases.

    Source: Irrigation Association, Irrigation System Installation and Maintenance — water hammer and surgeReport a problem with this question

12. 12. Which set of measures best protects a mainline against repeated surge damage?

    • A.Size pipe so velocity stays high, use quick-closing valves, and cap the mainline at high points.
    • B.Size pipe so velocity stays low, use slow-closing valves, and relieve trapped air at high points.✓ Answer
    • C.Raise the operating pressure of every zone and shorten each station's run time at the controller.
    • D.Run two zones at once on the mainline and open each zone's flow control stem fully at start-up.

    Surge magnitude rises with water velocity and with the length of straight pipe, and falls as valve closing time lengthens, so generous pipe sizing and slow-closing valves attack the problem directly. Trapped air compresses and then slams when it is expelled, which is why air relief at high points and slow start-up filling also matter.

    Source: Irrigation Association, Irrigation System Installation and Maintenance — surge control and air reliefReport a problem with this question

13. 13. A controller sends 24 VAC to a station and the diaphragm valve opens. Hydraulically, what has the solenoid actually done?

    • A.It pulled the diaphragm off its seat mechanically, using the magnetic force of the coil.
    • B.It pressurized the chamber above the diaphragm so the added pressure lifts it.
    • C.It drove a small motor that rotates the flow control stem to the fully open position.
    • D.It opened an exhaust port that bleeds the chamber above the diaphragm faster than it refills.✓ Answer

    A normally closed diaphragm valve is held shut by line pressure fed into the bonnet chamber above the diaphragm, which acts on a larger area than the pressure below. Energizing the solenoid opens an exhaust path that drains that chamber faster than the inlet port refills it, so line pressure underneath lifts the diaphragm; the manual bleed does the same thing without power.

    Source: Irrigation Association, Irrigation Components for Residential and Small Commercial Systems Student Workbook — diaphragm remote control valve operationReport a problem with this question

14. 14. One zone keeps running after the controller has shut the station off, and the valve still weeps when the solenoid is unplugged. Which condition best explains this?

    • A.The solenoid coil has an open circuit, so no current at all can reach it from the controller.
    • B.The station wire is broken somewhere between the controller and the splice in the valve box.
    • C.The flow control stem has been screwed all the way down against the top of the diaphragm.
    • D.Debris is holding the diaphragm off its seat, so the chamber above it cannot repressurize.✓ Answer

    A valve closes hydraulically when the bonnet chamber above the diaphragm refills with line pressure and pushes the diaphragm back onto its seat, so anything that blocks that seal keeps water flowing. Electrical faults such as an open coil or a broken wire prevent a valve from opening, not from closing, which is why the zone still weeps with the solenoid unplugged.

    Source: Irrigation Association, Irrigation Components for Residential and Small Commercial Systems Student Workbook — valve troubleshootingReport a problem with this question

15. 15. A manufacturer's chart gives the maximum length of run for a dripline at a stated emitter spacing and flow. What is that maximum length there to control?

    • A.The pressure variation between the first emitter and the last, which governs uniformity.✓ Answer
    • B.The volume of water the tubing holds between successive flushings of the end-of-line cap.
    • C.The number of stations one controller can operate before its transformer is overloaded.
    • D.The depth at which polyethylene tubing may be buried beneath a planted landscape bed.

    Every foot of dripline consumes pressure to friction and every emitter takes water out, so pressure falls along the run and the last emitter discharges less than the first. The manufacturer's maximum run length is the point at which that pressure variation exceeds what the product can tolerate and still water evenly; slope changes the limit because elevation adds to or offsets the friction loss.

    Source: Irrigation Association CIT content outline, Understanding Hydraulic Principles — drip mechanics and manufacturer run-length chartsReport a problem with this question

16. 16. A drip zone runs down a steep bank. Why are pressure-compensating emitters specified for that zone instead of non-compensating ones?

    • A.They eliminate the need for filtration because their outlets flush themselves continuously.
    • B.They hold nearly the same discharge across a range of pressures, so all emitters match.✓ Answer
    • C.They raise the pressure at the uphill end of the line so the zone needs no regulator.
    • D.They discharge in direct proportion to pressure, which balances the elevation gain down the bank.

    Elevation adds pressure toward the bottom of a slope and friction removes it along the run, so emitters see very different pressures on a bank. A pressure-compensating emitter holds nearly constant discharge across its stated pressure range, while a non-compensating emitter's flow follows the square root of pressure and would over-water the low end.

    Source: Irrigation Association, Landscape Irrigation Best Management Practices — pressure-compensating emitters on slopesReport a problem with this question

17. 17. On one zone running across a hillside, the rotors near the top of the slope turn slowly and leave a dry ring around each head, while the sprays in the low corner throw a fine mist that drifts away. What best explains both symptoms?

    • A.Elevation within the zone leaves the high heads under-pressured and the low heads over-pressured.✓ Answer
    • B.Elevation difference within the zone raises pressure at the high heads and lowers it at the low heads.
    • C.The valve's flow control stem is open too far, which starves the low heads and floods the high ones.
    • D.The nozzles in the low corner are worn open, and the rotors at the top have oversized nozzles installed.

    Pressure falls about 0.433 psi for every foot of rise and gains the same amount for every foot of fall, so one zone spread over a slope delivers very different pressures to its heads. Below the nozzle's minimum, rotors stall and throw short, leaving a doughnut of dry ground; above its maximum, the stream shatters into mist that drifts instead of landing.

    Source: Irrigation Association, Landscape Irrigation Best Management Practices — operating within the sprinkler's published pressure rangeReport a problem with this question

18. 18. A technician needs to know the actual operating pressure at a sprinkler nozzle while the zone is running. Which method gives that reading?

    • A.Read the controller's station display, which reports the pressure the valve delivers downstream.
    • B.Read a gauge on the hose bib with every zone off, since that is the pressure the nozzle sees.
    • C.Divide the zone's total flow in gpm by the number of heads operating on the zone at one time.
    • D.Hold a pitot-tube gauge in the nozzle's stream, just off the orifice, while the zone operates.✓ Answer

    A pitot tube placed in the jet just outside the orifice converts the moving stream's energy into a gauge reading, which is the nozzle's true operating pressure while the zone flows. A static reading at the point of connection tells nothing about what remains after pipe friction, component losses and elevation along the path to that head.

    Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — measuring operating pressure with a pitot tube and gaugeReport a problem with this question

19. 19. To measure the flow available at a hose bib, a technician fills a 5-gallon bucket and times it with a stopwatch. The bucket fills in 40 seconds. What is the flow rate?

    • A.8.0 gpm
    • B.200 gpm
    • C.0.13 gpm
    • D.7.5 gpm✓ Answer

    The container test converts gallons per second into gallons per minute: gallons collected divided by seconds, times 60, so 5 / 40 x 60 = 7.5 gpm. Leaving out the 60 gives 0.13 gpm, and multiplying rather than dividing by the time gives the impossible 200 gpm.

    Source: Irrigation Association, Irrigation System Installation and Maintenance — container (bucket) flow testReport a problem with this question

20. 20. Why is the pressure at the last sprinkler on a zone lower than the static pressure measured at the point of connection?

    • A.Water in the mainline loses pressure steadily with time as it sits between watering cycles.
    • B.The last sprinkler on a lateral always has a smaller nozzle than those ahead of it.
    • C.Every meter, backflow assembly, valve, fitting and foot of pipe along the path consumes pressure.✓ Answer
    • D.Supply pressure divides evenly among the heads, so each one receives an equal share of it.

    Working pressure at any point equals the static pressure at the source minus every loss along the path to it: meter, backflow assembly, master and zone valves, fittings, pipe friction, plus or minus elevation. The last head on the zone sits at the end of the longest path, so it accumulates the most loss, which is why it is the head a technician checks first.

    Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — dynamic pressure and cumulative component lossesReport a problem with this question

21. 21. The water purveyor requires the existing double check assembly on a landscape system to be replaced with a reduced pressure principle assembly. What should the technician expect hydraulically?

    • A.Additional pressure loss in the assembly, with less working pressure left at the heads.✓ Answer
    • B.No change in pressure, because backflow assemblies are sized to the service line, not to flow.
    • C.A gain in pressure, because the relief valve boosts the water leaving the new assembly.
    • D.A reduction in the static pressure that the city main supplies upstream of the assembly.

    A reduced pressure principle assembly holds two loaded check valves plus a relief valve that maintains a lower pressure zone between them, so it consumes noticeably more pressure at a given flow than a double check assembly does. That loss must be subtracted along with meter, valve, fitting and pipe losses when confirming that the critical head still receives its minimum operating pressure; which assembly is required is set by the governing authority.

    Source: USC Foundation for Cross-Connection Control and Hydraulic Research, Manual of Cross-Connection Control — reduced pressure principle assemblies; Irrigation Association hydraulics workbook on component pressure lossReport a problem with this question

22. 22. A crew adds three more sprinklers to an existing zone and extends the lateral another 60 ft to reach them. What happens on that zone?

    • A.Zone flow rises while friction loss falls, because the extra heads relieve the pipe.
    • B.Only the three new heads run at reduced pressure; the original heads are unaffected.
    • C.Zone flow and friction loss both rise, so every head on the zone loses operating pressure.✓ Answer
    • D.Nothing changes hydraulically, because the zone valve regulates pressure for the zone.

    Adding heads raises the gpm the whole zone must carry, and friction loss climbs with roughly the 1.85 power of flow and in direct proportion to added length, so losses grow on every shared section of pipe. Because the upstream pipe, valve, meter and backflow assembly are all common to the zone, the original heads lose pressure too, and a standard zone valve throttles flow rather than holding pressure constant.

    Source: Irrigation Association, Basic Irrigation Hydraulics Student Workbook — effect of flow rate and pipe length on friction lossReport a problem with this question

Practice questions based on the Irrigation Association's published Certified Irrigation Technician content — basic irrigation principles, basic electrical principles and basic hydraulics — together with standard irrigation installation, hydraulics and backflow-prevention references. This site is not affiliated with or endorsed by the Irrigation Association. Irrigation work is governed by local plumbing and irrigation codes, water-purveyor rules and licensing that vary by jurisdiction; backflow assemblies in particular must be selected, installed and tested to the rules in force where you work. Confirm current exam requirements with the Irrigation Association before testing. About IA certification →