Module 1 · 40 minutes

Water & Hydraulics Basics

Every sprinkler system is just a way of moving water from the city main to the plants with the right push and the right amount. If you understand pressure and flow, almost every problem you meet in the field — misting heads, dry spots, valves that hammer, zones that won’t pop up — starts to make sense.

By the end of this module you will be able to

Explain the difference between pressure (psi / kPa) and flow (GPM / L/min).
Measure static and working pressure with a gauge, and estimate available flow with a bucket test.
Describe friction loss and why we keep water velocity at or below 5 ft/s (about 1.5 m/s).
Calculate pressure gained or lost from elevation using 0.433 psi per foot.
Read a simple friction-loss table and build a basic pressure budget for a zone.

Pressure vs. flow — the two numbers that matter

Pressure is the push behind the water. In North America irrigation equipment is rated in pounds per square inch (psi); Canadian municipal and engineering documents often use kilopascals (kPa). 1 psi = 6.895 kPa, so 60 psi ≈ 414 kPa.

Flow is how much water moves past a point in a set time. Nozzle and valve charts use US gallons per minute (GPM) or, for drip, gallons per hour (GPH). 1 US GPM = 3.785 L/min. Watch out: an imperial gallon is about 1.2 US gallons — manufacturer charts are in US gallons.

	Pressure	Flow
Think of it as…	How hard the water pushes	How much water arrives
Units	psi, kPa, bar	US GPM, L/min, GPH (drip)
Measured with	Pressure gauge	Bucket + stopwatch, or water meter
Too much causes	Misting, fogging, blown fittings, wasted water	Low pressure at the heads, high velocity, water hammer
Too little causes	Short throw, heads not popping up, dry rings	Not enough water to run all heads on the zone

The key idea: pressure and flow trade off. The more water you try to push through a pipe at once, the more pressure is lost along the way. That is why a zone with too many heads performs poorly even when the house has “good pressure.”

Units quick reference. 1 psi = 6.895 kPa. 1 US GPM = 3.785 L/min. Elevation: 0.433 psi per foot (9.8 kPa per metre). Velocity limit: 5 ft/s ≈ 1.5 m/s. Hover or tap a dotted term later in the module to see its definition.

Module 1 · Lesson 2

Measuring pressure and flow

Static vs. working pressure

Static pressure is the pressure when no water is flowing. Working (dynamic) pressure is the pressure while water is flowing — it is always lower, because moving water loses energy to friction. Sprinklers are designed around working pressure.

A pressure gauge threaded onto a hose bib on a house wall, with a dashed stream filling a 5-gallon bucket below the bib. — Figure 1.1 — Measuring static and working pressure at a hose bib, and the bucket test for flow.

How to take a pressure reading

Thread a liquid-filled pressure gauge (0–160 psi is a good range) onto the outside hose bib closest to the water meter or irrigation connection.
Make sure nothing else is using water in the house. Open the bib fully. The reading is static pressure.
Run a zone (or open another tap) and read again. That is the working pressure at that point. For a reading at the heads, use a pitot gauge on a spray nozzle stream or a gauge on a riser/test fitting.
Record both numbers on the work order. Readings change through the day, so note the time.

The bucket test (estimating available flow)

Time how long it takes to fill a bucket of known size from a fully open hose bib (no hose attached):

Flow (GPM) = bucket size (US gal) × 60 ÷ seconds to fill

Example: a 5-gallon bucket fills in 20 seconds → 5 × 60 ÷ 20 = 15 GPM (≈ 57 L/min). A hose bib is usually only ½ or ¾ inch, so the bucket test gives a conservative (low) estimate; designers also consider the meter size and service line size.

The Rain Bird Landscape Irrigation Design Manual gives three checks for how much flow a water service can safely supply: (1) pressure loss through the water meter should not exceed 10% of the minimum static pressure; (2) flow through the meter should not exceed 75% of the meter’s maximum safe flow; and (3) velocity in the service line should be kept to about 5–7.5 ft/s. The smallest of these limits is your design flow. As a new tech you won’t design services, but you should know why a designer says “this house can only run 12 GPM per zone.”

You’ll use the field calculator in Lesson 4 to run the bucket-test math yourself. The formula above is all it uses.

Module 1 · Lesson 3

Friction loss and the 5 ft/s rule

Friction loss

As water rubs along the inside of a pipe and turns through fittings and valves, it loses pressure. This is friction loss. It goes up when:

flow goes up (doubling the flow roughly triples-to-quadruples the loss),
the pipe is smaller or longer,
there are more fittings, elbows and valves,
the pipe is rougher inside (older or poly vs. PVC).

Friction-loss tables list loss in psi per 100 feet of pipe. The table below was calculated with the Hazen-Williams formula (the same method used for manufacturer charts). Shaded cells are over 5 ft/s — avoid those sizes for that flow. Always confirm with the pipe manufacturer’s chart for the exact pipe on the job.

Table 1.1 — Class 200 PVC (SDR 21): friction loss per 100 ft and velocity (Hazen-Williams, C = 150). Calculated values — confirm with the manufacturer’s chart.
Flow (US GPM)	¾ in (ID 0.930 in)	1 in (ID 1.189 in)	1¼ in (ID 1.502 in)
6	1.67 psi · 2.8 ft/s	0.51 psi · 1.7 ft/s	0.16 psi · 1.1 ft/s
8	2.85 psi · 3.8 ft/s	0.86 psi · 2.3 ft/s	0.28 psi · 1.4 ft/s
10	4.31 psi · 4.7 ft/s	1.30 psi · 2.9 ft/s	0.42 psi · 1.8 ft/s
12	6.04 psi · 5.7 ft/s	1.83 psi · 3.5 ft/s	0.59 psi · 2.2 ft/s
15	9.13 psi · 7.1 ft/s	2.76 psi · 4.3 ft/s	0.89 psi · 2.7 ft/s
20	15.56 psi · 9.4 ft/s	4.71 psi · 5.8 ft/s	1.51 psi · 3.6 ft/s

Table 1.2 — Polyethylene (PE) pipe, inside-diameter controlled (SIDR 15): loss per 100 ft and velocity (C = 140). Calculated values — confirm with the manufacturer’s chart. Poly carries less than PVC of the same nominal size because its inside diameter is smaller.
Flow (US GPM)	¾ in (ID 0.824 in)	1 in (ID 1.049 in)	1¼ in (ID 1.380 in)
6	3.43 psi · 3.6 ft/s	1.06 psi · 2.2 ft/s	0.28 psi · 1.3 ft/s
8	5.84 psi · 4.8 ft/s	1.80 psi · 3.0 ft/s	0.47 psi · 1.7 ft/s
10	8.82 psi · 6.0 ft/s	2.73 psi · 3.7 ft/s	0.72 psi · 2.1 ft/s
12	12.37 psi · 7.2 ft/s	3.82 psi · 4.5 ft/s	1.01 psi · 2.6 ft/s
15	18.69 psi · 9.0 ft/s	5.78 psi · 5.6 ft/s	1.52 psi · 3.2 ft/s
20	31.85 psi · 12.0 ft/s	9.84 psi · 7.4 ft/s	2.59 psi · 4.3 ft/s

Velocity and the 5 ft/s rule

Velocity is how fast water travels in the pipe. Industry design guides (for example Rain Bird’s design manual) recommend keeping velocity at or below 5 feet per second (≈1.5 m/s). Above that, friction loss climbs quickly and water hammer (pressure surges when a valve closes) can crack fittings and blow apart glue joints.

Velocity (ft/s) = 0.408 × GPM ÷ (inside diameter in inches)²

Rough maximum flows at 5 ft/s from the calculation above: Class 200 PVC — ¾ in ≈ 10.6 GPM, 1 in ≈ 17.3 GPM, 1¼ in ≈ 27.6 GPM; PE (SIDR 15) — ¾ in ≈ 8.3 GPM, 1 in ≈ 13.5 GPM, 1¼ in ≈ 23.3 GPM.

Module 1 · Lesson 4

Elevation and the pressure budget

Elevation: 0.433 psi per foot

A column of water 1 foot tall exerts 0.433 psi at the bottom (≈ 9.8 kPa per metre of height). Put another way, 1 psi lifts water 2.31 ft. Heads uphill from the valve lose pressure; heads downhill gain it. In hilly neighbourhoods of Kamloops or on Nicola Valley acreages this matters a lot.

Field calculator

Run the two calculations you’ll use on almost every job. The formulas are the same ones in the lessons — this just does the arithmetic.

Height difference (feet)

The head is

8.7 psi lost

20 ft × 0.433 psi/ft = 8.66 psi.

Rule: 0.433 psi per foot, or 9.8 kPa per metre. 1 psi lifts water 2.31 ft.

Line chart showing pressure change rising in a straight line with elevation: 10 feet equals 4.3 psi, 50 feet equals 21.7 psi, 80 feet equals 34.6 psi. — Figure 1.2 — Pressure change with elevation (0.433 psi per foot).

Putting it together: a pressure budget

A pressure budget starts with the static pressure and subtracts each loss on the way to the last head. If what’s left is below the head’s required operating pressure, the zone will under-perform. The chart below is a worked example with sample numbers — on a real job use measured pressure and chart values.

Waterfall chart of an example pressure budget: 75 psi static at the hose bib drops through meter, backflow, mainline, valve, lateral and elevation losses to about 47 psi at the farthest head. — Figure 1.3 — Example pressure budget: 75 psi static drops to about 47 psi at the farthest head (sample values for teaching).

Field tip. Spray heads are generally designed to work around 30 psi at the nozzle, and rotors at higher pressures — check the nozzle chart. When static pressure is high (common in some lower-elevation neighbourhoods), pressure-regulating spray bodies such as the Rain Bird 1800 PRS series, or a pressure-regulating valve, stop the misting.

Module 1 · Lesson 5

Key terms and field scenarios

Tap a card to flip it. Then work the two Kamloops and Merritt call-outs the way you would on a job — pick an answer, then read the walkthrough.

Key terms

Try it

Try it · 1 of 2

Fogging spray heads on a hillside

Upper Sahali, Kamloops — single-family home

The homeowner says the front lawn spray heads “make a cloud” and the lawn edges are brown. Your gauge on the hose bib reads 95 psi static. What is the most likely cause?

Try it · 2 of 2

Will a new zone work?

Merritt — new build on the bench

The builder wants “one more zone” of rotors for the back lawn. You do a bucket test: a 5-gallon bucket fills in 25 seconds. The proposed zone has rotor nozzles that add up to 14 GPM on the nozzle chart. What should you tell the builder?

Module 1 · Lesson 6

Module 1 quiz

Five questions. You’ll see whether each answer is right as soon as you pick one. You need 4 out of 5 to pass and mark the module complete. You can retry if you don’t pass.