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newSchoolWorks.com › VoTechWorks › Building & Construction › Plumbing & Pipefitting › Brazing, Soldering, and Mechanical Joining for Plumbing Systems › Lesson 7
BLD-PLUM06-07 · Lesson 7 · 10 clock hours · lab

Hydrostatic and Air Pressure Testing of Solder Joints

Objective. Students will assemble a solder-joined copper test manifold, connect it to a hand pump or compressed-air source, pressurize to the code-specified test pressure for potable water systems, and document the result on an official-format pressure-test report.

Why Pressure Testing Matters

Every solder joint you make carries the reputation of your work and the safety of the building's occupants. A joint that looks clean on the outside can still harbor a pinhole leak or a cold-solder void that will weep the moment water pressure is applied. Pressure testing is the industry's way of proving a system is sound before walls are closed and the system is put into service. It is also a code requirement: both the International Plumbing Code (IPC) and the Uniform Plumbing Code (UPC) require new potable water piping to be pressure tested before concealment or connection to fixtures. Inspectors expect a completed, signed pressure-test report as part of the inspection package.

Two Types of Pressure Tests

Hydrostatic testing fills the system with water, then uses a hand pump to raise the pressure to the code-specified level. Water is essentially incompressible, so if a joint fails the energy released is very small—the system weeps or drips rather than ruptures violently. This makes hydrostatic testing the safer and preferred method for most potable water piping.

Air pressure testing pressurizes the system with compressed air or nitrogen. Air is compressible, which means a failed joint under air pressure releases stored energy suddenly—a risk of injury from projectile fittings, water spray, or loud noise. Because of this hazard, air testing demands strict pressure limits, safety glasses are mandatory at all times during pressurization, and no one should put their face near a pressurized joint. Many jurisdictions restrict air testing to situations where water cannot be used, such as freezing conditions.

Code-Specified Test Pressure and Duration

The IPC and UPC specify the minimum test pressure and hold time for new water supply piping. You must look up the current edition adopted in your jurisdiction, because exact numbers can vary between code editions and states. As a general guide, codes commonly require the system to be tested to a pressure not less than the system's working pressure—and in no case less than a stated minimum—held for a defined duration while every joint is inspected. Your instructor will identify the specific numbers from the code edition your state has adopted. During this lab you will use those exact figures; do not substitute other values.

Setting Up the Test Loop

Before connecting any pressure source:

1. Verify the assembly. Confirm all end caps are fully soldered and cooled. Check that the pressure gauge and ball valve are installed on the manifold and that all threaded connections are wrench-tight with appropriate thread sealant.

2. Inspect visually first. Under good lighting and before any pressure is applied, look at every joint for flux residue, drips of solder, or obvious gaps. A visual failure before the test saves time.

3. Fill and bleed (hydrostatic test). Open the highest point of the loop and connect the hand pump at the lowest. Slowly introduce water until it flows from the high-point opening, then close that opening. This bleeds trapped air. Air pockets in a hydrostatic test give false gauge readings.

4. Connect and zero the gauge. Record the gauge identification number and its calibration status. With the valve closed and the pump not yet stroked, note the gauge reads at or near zero. If it does not, the gauge may be faulty—swap it before proceeding.

Conducting the Test

Slowly pump pressure up to the code-specified test pressure. Do not overshoot; release pressure if you go past the target value and re-pressurize to the correct level. Once at target:

A gauge reading that holds steady (within the gauge's resolution, typically ±2 psi) with no visible leakage is a passing test. A drop beyond gauge resolution, or any visible moisture at a joint, is a failure.

Safety Rules During Pressurized Testing

Handling Failures and Repairs

If a joint weeps, mark it with a marker or tape flag, depressurize the system completely, drain it, and allow it to dry. Cut out the failed joint, clean and re-fit the pipe and fitting, and re-solder. After the repair cools, repeat the entire test from the beginning. A pressure-test report that documents a failure must also document the repair before a passing result is recorded. Inspectors will reject a report that shows only a passing test if they know a prior test was run and failed—document everything honestly.

Completing the Pressure-Test Report

The report is a legal document. Fill in every field: date, location/system description, test medium (water or air), gauge ID and range, the required test pressure, start pressure, end pressure, hold duration, pass/fail result, and your printed name and signature. Incomplete reports are rejected. File the original with the inspection package; keep a copy for your own records.

Key terms8

Hydrostatic testA pressure test that uses water as the test medium; because water is nearly incompressible, a joint failure releases very little energy, making this the safer method for potable water piping.
Air pressure testA pressure test that uses compressed air or dry nitrogen; air is compressible, so a failure releases stored energy suddenly—requiring strict pressure limits and full PPE at all times.
Test pressureThe pressure, specified by the adopted plumbing code, to which a system must be raised and held during inspection; it must not be exceeded by the test operator.
Hold periodThe code-required length of time the system must remain at the test pressure without a detectable drop while every joint is visually inspected.
Gauge resolutionThe smallest pressure change a gauge can reliably indicate; a pressure drop within the gauge's resolution (commonly ±2 psi) does not automatically indicate a leak.
Pressure-test reportThe written record of a pressure test, including date, system description, test medium, gauge ID, start and end pressures, duration, pass/fail result, and technician signature; required by inspectors before a system is approved.
Air bleedThe process of removing trapped air from a hydrostatic test loop by filling from the lowest point and allowing air to escape from the highest point before sealing the system.
Cold-solder jointA defective solder joint in which the filler metal did not flow properly due to insufficient heat, leaving voids or weak bonding that may not be visible externally but will fail under pressure.

Worked examples4

1. Your pressure gauge reads 152 psi at the start of the hold period. At the end of the required hold time it reads 149 psi. The gauge is rated ±2 psi resolution. Is this a passing or failing result, and why?
  1. Calculate the observed pressure drop: 152 psi − 149 psi = 3 psi.
  2. Compare the drop to the gauge resolution: the gauge can only reliably distinguish changes of ±2 psi, so any apparent change of 2 psi or less cannot be called a real drop.
  3. Since 3 psi exceeds the ±2 psi gauge resolution, this drop is outside the uncertainty of the instrument and must be treated as a real pressure loss.
  4. Inspect every joint visually for any sign of moisture. Even without visible weeping, a drop of 3 psi on a gauge with ±2 psi resolution is a failing result that requires investigation and repair before the test is accepted.
Answer: Failing result. The 3 psi drop exceeds the gauge's ±2 psi resolution, meaning it cannot be explained by instrument uncertainty alone. The test must be repeated after identifying and repairing the source of the loss.
2. You are filling a test loop to bleed air before a hydrostatic test. The loop holds approximately 0.35 gallons of water. Your hand pump delivers about 0.02 gallons per stroke. Roughly how many strokes does it take to fill the loop if you start from empty?
  1. Identify the volume to fill: 0.35 gallons.
  2. Identify the pump delivery per stroke: 0.02 gallons per stroke.
  3. Divide total volume by delivery per stroke: 0.35 ÷ 0.02 = 17.5 strokes.
  4. Round up to the nearest whole stroke, since you cannot do a half-stroke: 18 strokes.
Answer: Approximately 18 strokes to fill the loop. Additional strokes will then be needed to raise the pressure to the required test pressure after the loop is full and air has been bled.
3. During a hydrostatic test you notice the gauge climbs from 0 psi to the target test pressure over 10 pump strokes, then slowly drifts back down 5 psi in two minutes even though you can see no water at any joint. What is the most likely cause, and what should you check first?
  1. Recognize that a pressure drop with no visible leak suggests a small leak that has not yet produced visible moisture, or a component that is not fully sealed.
  2. Check all threaded connections first—the gauge fitting, the valve stem packing, and any end-cap threads—because threaded connections can weep slowly without dripping visibly.
  3. Check the ball valve itself: if the valve is not fully closed during the test, pressure can bleed off through it.
  4. If all connections and the valve check out, dry every solder joint with a clean rag and re-inspect under a flashlight for a fine mist or slow wicking of water along the pipe.
Answer: The most likely cause is a small leak at a threaded connection or valve rather than at a solder joint, because solder joint failures typically produce visible weeping. Check all mechanical connections before assuming a solder joint has failed.
4. A test loop is made of 3/4-inch copper tube. You need to calculate the approximate internal volume to decide how much water to have ready. The loop has a total tube length of 8 feet. The internal diameter of 3/4-inch Type L copper tube is approximately 0.785 inches. What is the approximate volume in gallons? (Use π ≈ 3.1416; 1 gallon = 231 cubic inches.)
  1. Find the internal radius: 0.785 in ÷ 2 = 0.3925 in.
  2. Calculate the cross-sectional area: π × r² = 3.1416 × (0.3925)² = 3.1416 × 0.1541 = 0.484 in².
  3. Convert length to inches: 8 ft × 12 in/ft = 96 in.
  4. Calculate volume in cubic inches: 0.484 in² × 96 in = 46.5 in³.
  5. Convert to gallons: 46.5 ÷ 231 = 0.201 gallons, approximately 0.20 gallons.
Answer: Approximately 0.20 gallons of water is needed to fill this section of 3/4-inch Type L copper tube. Have at least 0.5 gallons on hand to allow for filling, bleeding, and priming the pump.

The math in this lesson2

Learners compute test loop internal volume from tube length and inside diameter.
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Brush up in the math halls at newSchoolWorks.com:
In class: Assemble a solder-joined copper test loop (minimum six joints, incorporating a tee, two 90s, and two couplings) from tube and fittings soldered during Lessons 5 and 6; cap all ends and install a pressure gauge and a valve. · Fill the loop with water (hydrostatic test), bleed air, and pressurize with a hand pump to the required test pressure specified in the IPC/UPC for new potable water systems; hold for the code-required duration while visually inspecting every joint with a flashlight; record pressure at start and end of hold. · Complete a pressure-test report form (date, system description, test medium, gauge ID, start pressure, end pressure, duration, pass/fail, technician signature); discuss what an acceptable pressure drop (if any) looks like and how temperature changes affect readings.
Materials: Completed copper solder assemblies, end caps, pressure gauge (0–200 psi), hand hydrostatic pump or regulated compressed air source with pressure regulator, ball valve, flashlight, pressure-test report forms, IPC/UPC pressure-testing section, PPE (safety glasses mandatory during pressurized testing)
Check: Pressure must hold at the code-specified test pressure for the full required duration with no detectable drop beyond gauge resolution (±2 psi); the completed pressure-test report must be fully filled in and signed; any joint that weeps or fails is cut out, remade, and the test is repeated—no report is accepted for a failed test without the documented repair.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

NCCER Plumbing – Safety and Tools
1. Why is hydrostatic testing preferred over air pressure testing for potable water copper piping?
NCCER Plumbing – Safety and Tools
2. Which PPE is mandatory for all personnel in the work area from the moment a pressure source is connected to a test loop until the system is fully depressurized?
NCCER Plumbing – Plumbing Systems
3. When filling a test loop for a hydrostatic test, where should water be introduced, and where should air be allowed to escape?
NCCER Plumbing – Plumbing Systems
4. At the start of a hydrostatic hold, the gauge reads 150 psi. After the required hold period, it reads 148 psi. The gauge has a resolution of ±2 psi and no visible moisture is present at any joint. What is the correct conclusion?
NCCER Plumbing – Plumbing Systems
5. A solder joint weeps during a hydrostatic test. After the technician depressurizes and drains the system, what is the required next step before a new pressure-test report can be accepted?
NCCER Plumbing – Safety and Tools
6. Which of the following gases is NEVER acceptable as a pressure-test medium for copper plumbing?
State Journeyman Plumber – Inspection and Documentation
7. Which field on a pressure-test report form establishes that the gauge used in the test was a known, identified instrument—not an unmarked or uncalibrated tool?
State Journeyman Plumber – Plumbing Systems
8. A journeyman plumber is pressure-testing a new potable water system on a cold morning. The system was pressurized when the pipe temperature was 40 °F; two hours later the sun has warmed the pipes to 70 °F and the gauge reads slightly higher than the starting pressure. What is the most likely explanation?
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