Pipeline (C-34) · Lesson 6 of 6

Pressure Testing a Trenched Supply Line (Method A)

"Pressure Testing a Trenched Supply Line (Method A)" is lesson 6 of 6 in the Pipeline (C-34) Learning Hub. It opens with "Set Up the Test Before You Backfill" and works through 5 short steps, then a worked example you can check yourself against.

Open the free trialSee pricing

One-time purchase, no subscription. Law & Business included.

Steps in this lesson

  1. Set Up the Test Before You Backfill
  2. Method A: 125 psi, 1 Hour, 5 psi Drop
  3. Method B and Special Cases
  4. Water Supply Lines on a Structure
  5. The Building-Code Version

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Pressurize" through "Respond to a failure".

What you'll be able to do

  • Explain the main idea of "Pressure Testing a Trenched Supply Line (Method A)" in plain language you can use on the exam.
  • Apply this step with confidence: "Method B and Special Cases".
  • Apply this step with confidence: "Water Supply Lines on a Structure".
  • Apply this step with confidence: "The Building-Code Version".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Pressure Testing a Trenched Supply LinecapcapOPEN TRENCH: TEST BEFORE BACKFILLSTART125psiAFTER 1 HR121psi1 hourdrop = 4 psiOTHER PRESSURE TESTS IN THE BOOKSSupply line in conduit: 0.5 hr, no drop allowedBridge water line (4 in+): 120 psi min, 4 hr, no dropCPC 609.4 building water: at least working pressure, 15 minMETHOD A TESTFill line, set 125 psiRemove the pressure sourceHold for 1 hourStart 125 psi, end 121 psiDrop = 125 - 121 = 4 psi4 psi is not over 5 psi: PASSSecond line ends at 117 psi:Drop = 125 - 117 = 8 psi8 psi is over 5: FAIL.Locate leaks, repair,then repeat the 1-hour testuntil the drop is 5 psi or less.Notify Engineer 48 h ahead.A 4 psi drop in 1 hour is within the 5 psi limitTest before backfilling, gate valves open, ends cappedCaltrans Std Specs 2025 sections 20-2.01A(4)(b), 20-2.13A(1)(d)(iii); CPC 2025 section 609.4CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Set Up the Test Before You Backfill

The 2025 Caltrans Standard Specifications, section 20-2.01A(4)(b)(i), require a pressure test for leakage on irrigation supply lines, run in the Engineer's presence on business days from 8 a.m. to 5 p.m. unless authorized. The test is done before backfilling the supply line trench, with the system gate valves open and the open ends of the supply line and fittings plugged or capped. You must notify the Engineer at least 48 hours before the test. A new supply line connected to an existing line must be isolated from it and tested on its own.

Step 2: Method A: 125 psi, 1 Hour, 5 psi Drop

Method A (section 20-2.01A(4)(b)(ii)) starts with a pressure gauge calibrated from 0 to 200 psi in 5 psi increments and accurate to within 2 psi. Fill the supply line with water, connect the gauge, and bring the line to a pressure of 125 psi. Remove the source of pressure and leave the line under that pressure for 1 hour, with the gauge staying in place until the period is over. If the gauge shows a drop of more than 5 psi, locate and repair the leaks, then repeat the 1-hour test until the drop is 5 psi or less.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

More lessons for this trade

Browse all lesson previews

Ready to practice for real?

Try the real classroom free, no sign-up, or get the full course for your trade.

Open the free trialSee pricing

Independent exam preparation. Contractors Classroom is not affiliated with the Contractors State License Board, and no course can guarantee a passing result.