CIT cheat sheet

Static pressure conversion: 1 psi = 2.31 ft of water head; 1 ft of head = 0.433 psi.

Flow equation: Q (gpm) = 2.448 × d² (inside diameter, in) × V (ft/s); keep laterals at or below 5 fps and mainlines at or below 7 fps.

Nozzle discharge varies with the square root of pressure: Q₂ = Q₁ × √(P₂/P₁); doubling pressure raises flow about 41%, not 100%.

Total dynamic head = static lift + suction lift + friction loss through pipe and fittings + required operating pressure at the farthest head.

Precipitation rate (in/hr) = 96.25 × head gpm ÷ area covered (ft²); matched rates across a zone prevent wet and dry spots.

Typical head operating pressures: spray heads about 20–30 psi, rotors about 40–65 psi, per manufacturer optimum.

Zone sizing rule: sum of head flows in a zone must not exceed available safe flow, commonly kept at or below 75% of meter capacity.

Hazen-Williams friction loss rises with flow^1.852 and falls with diameter^4.87, so upsizing pipe sharply reduces loss.

Elevation change of 10 ft changes line pressure by about 4.3 psi (0.433 psi per foot of rise or drop).

Backflow is reverse flow of nonpotable water into the potable supply; causes are backsiphonage (negative supply pressure) and backpressure (downstream pressure exceeds supply).

An air gap provides the highest protection; separation is typically at least twice the pipe diameter and never less than 1 inch above the flood-level rim.

RPZ assembly: two independent check valves plus a differential relief valve; protects against both backpressure and backsiphonage at high-hazard connections.

Double check valve assembly (DCVA) uses two check valves with no relief valve; approved for low hazard only.

Pressure vacuum breaker (PVB): low hazard, not for backpressure, installed at least 12 inches above the highest downstream outlet per manufacturer and code.

Atmospheric vacuum breaker (AVB): no downstream shutoff valve and no continuous pressure over 12 hours; mounted at least 6 inches above the highest outlet.

Hose-threaded outlets require hose bib vacuum breakers to prevent cross-connections from hoses and attachments.

Backflow assemblies are tested annually by a certified tester, tagged, and results reported to the local water authority.

A cross-connection is any actual or potential link between the potable system and a nonpotable source.

Controllers supply 24 VAC to solenoid valves from a transformer with a 120 VAC primary; station and common terminals form the circuit.

Healthy solenoid coil resistance is typically about 20–60 ohms; infinite resistance means an open coil, near-zero means a short.

Keep voltage drop on valve wiring below about 10% of supply (5% preferred); long runs or undersized wire prevent valves from opening.

Voltage drop = 2 × length × current × resistance per unit length; use larger gauge wire (14 or 12 AWG) for long runs.

Most rain sensors are normally closed and wired in series with the common wire; rainfall opens the circuit and stops irrigation.

Master valve and pump relay terminals energize only while a station is running, providing hydraulic or pump control.

Ohm's law (V = I × R) and power (P = V × I) underpin valve and transformer troubleshooting; a 24 V valve drawing 0.3 A has roughly 80 ohms impedance.

Decoder (two-wire) systems use addressable decoders on a single path, reducing wire runs but requiring correct polarity and addressing.

120 V outdoor circuits, including controller receptacles, require GFCI protection.

Spray heads typically throw 10–15 ft at 20–30 psi; rotors throw roughly 15–100 ft and operate best at 40–65 psi.

Use matched precipitation rate (MPR) nozzles or heads within a single zone to keep application uniform.

PVC pressure ratings depend on schedule and class; Class 200 is rated 200 psi at 73°F, and ratings drop as temperature rises.

PVC joints are solvent welded with primer and cement; apply both, insert with a quarter turn, and cure fully before pressure testing.

Built-in check valves in heads prevent low-head drainage and puddling at the lowest heads on slopes.

Swing joints or flexible funny pipe let heads be adjusted for height and grade without stressing the lateral.

Valve types include globe, angle, and anti-siphon; anti-siphon valves must sit at least 6 inches above the highest downstream head.

Drip emitters typically deliver 0.5–2 gph; pressure-compensating emitters hold constant flow, and drip zones require filtration, commonly 100–200 mesh.

Pumps are selected from a pump curve relating flow and head; adequate NPSH and a foot valve or prime protection are required.

Call 811 (utility locate) before digging in the US; wait the required period and hand-dig near marked utilities.

Typical burial depths: mainlines 12–18 inches and below the frost line; laterals 6–12 inches.

Hydrostatic test piping at about 1.5 times design pressure or at least 50 psi above working pressure, held per specification before backfilling.

Flush mainlines and lateral ends thoroughly before installing heads, nozzles, and valves to clear debris.

Bed pipe in sand or fine soil, remove rocks against the pipe, and compact backfill in lifts to prevent settlement.

Install drain valves at low points and air relief valves at high points of the system.

Use direct-burial-rated wire, buried below grade alongside piping, and leave slack at valve boxes and splices.

Head spacing: sprays are commonly spaced head-to-head; rotors often at 50–60% of their diameter, tightened for wind.

On slopes, use heads with check valves and pressure-regulating stems to control drainage and pressure.

Valve will not close: debris in the seat, torn diaphragm, solenoid plunger stuck open, or manual bleed left open.

Valve will not open: no 24 VAC at the solenoid, open coil, stuck plunger, clogged filter, or insufficient pressure.

Low pressure or dry heads: check clogged nozzles, leaks, partially closed valves, undersized pipe, and pump performance before replacing heads.

Solenoid diagnosis: measure coil resistance, then confirm 24 VAC at the solenoid terminals while the station is active.

Controller faults: verify fuse, transformer output, rain sensor state, and station output under load.

Winterization: blow lines out with compressed air at moderate pressure, one zone at a time, and drain or remove the backflow device.

Water hammer: caused by fast-closing valves, high flow velocity, or missing air chambers and shock arrestors.

Seasonal tune-up: straighten and adjust heads, replace worn nozzles, repair leaks, and confirm the backflow test date.

Drip system clogs: flush laterals, clean or replace filters, and check emitter flow at the end of the line.

Call 811 or the local utility locate service before digging and wait the required time before excavation.

OSHA requires a protective system (sloping, shoring, or trench box) for trenches 5 ft deep or more and an exit within 25 ft for trenches 4 ft or deeper.

Keep spoil piles and equipment at least 2 ft back from the trench edge to reduce collapse risk.

Outdoor and wet-location circuits require GFCI protection; follow lockout/tagout before servicing controllers or pumps.

Backflow prevention assemblies must be tested annually by a certified tester, with results reported to the water authority.

EPA WaterSense labels water-efficient controllers and heads; smart controllers schedule irrigation from evapotranspiration data.

Local watering restrictions commonly govern day-of-week and time-of-day irrigation; permits are often required before installation.

PVC primer and cement are flammable and emit vapors; use ventilation, gloves, and eye protection and keep them away from ignition.

Never enter an unsupported excavation, and never work alone in a deep trench.