How to conduct air-tightness and water-tightness tests after HDPE siphon system installation

HDPE (high-density polyethylene) siphonic drainage systems are widely used in modern roof drainage due to their high efficiency, lightweight, and durability. However, the ultimate performance of a system depends not only on superior materials and design; rigorous post-installation testing is crucial for its long-term stable operation. Air and water tightness testing, two crucial acceptance steps, are crucial for verifying system installation quality, ensuring leak-free operation, and ensuring the successful activation of the siphon effect.

1. Air Tightness Testing: The "Detective" for Finding Tiny Leaks

An air tightness test, also known as a negative pressure or vacuum test, is an essential step before commissioning an HDPE siphonic drainage system. Because a siphonic system generates negative pressure when fully flowing, any small leak can prevent the siphon effect from forming or even allow air to be drawn in, compromising the system's drainage efficiency.

Test Principle:

Air is pumped into a closed HDPE piping system to create a certain negative pressure. The change in negative pressure is then observed over a set period of time. If the negative pressure remains stable, the system is airtight. If the negative pressure continues to decrease, a leak may be present.

Testing Steps and Methods:

Preparation:

Ensure all pipe ports, inspection ports, and water traps are securely and temporarily sealed.

Prepare a professional vacuum pump, vacuum pressure gauge, and pipe connection hoses.

Inspect the pipe joints to ensure that the heat-fused or electric-fused connections are smooth and free of burrs.

Performing the Test:

Connect the vacuum pump and pressure gauge to the system's test port via a hose.

Start the vacuum pump and slowly reduce the system's internal pressure to the desired negative pressure (typically -10 kPa to -20 kPa).

Once the desired negative pressure is reached, stop pumping, close the valve, and record the initial pressure reading and the current time.

Keep the system airtight and observe the pressure gauge. After the specified test time (e.g., 1 hour), record the pressure reading again.

Criteria:

If the negative pressure decreases within the allowable range (usually -1.5 kPa) during the test, the system is deemed airtight.

If the negative pressure decreases beyond the allowable range, the system is deemed unqualified. All pipe connections, flange joints, and inspection ports must be carefully inspected. Common inspection methods include applying soapy water to the joints and observing for bubbles to pinpoint the leak.

II. Watertightness Test: Simulating Heavy Rain to Verify Drainage Capacity

The watertightness test, also known as the closed water test, is a crucial step in verifying the HDPE siphon system's leak-free operation and ensuring its stability under full load. This test visually simulates the drainage scenario of heavy rain.

Test Principle:

Water is injected into the HDPE pipe system until it reaches a certain head height. The pipe's outer wall is then observed for leaks within a specified timeframe.

Test Steps and Methods:

Preparation:

Temporarily seal all outlets of the piping system (such as the bottom of a riser).

Ensure the piping system is securely fastened and can withstand the weight of the water.

Prepare an adequate water source and water filling equipment.

Performing the Test:

Slowly fill the system with water from the highest manifold or a dedicated water filling port.

While filling, observe the pipe connections for leaks.

Stop filling when the system is completely filled and the water head reaches the required design height (usually the top of the roof manifold).

Stand still and observe the pipe exterior for visible water seepage or dripping within a specified timeframe (usually 24 hours).

Criteria:

If no leaks or dripping are observed on the exterior of the piping system, at all joints, or at inspection ports during the test, the system is deemed watertight.

If any leaks are detected, the test must be stopped immediately, and the leaks marked and repaired. After repairs are completed, retesting is required until compliance is achieved.

Important Note:

When conducting watertightness testing, pay special attention to areas prone to leakage, such as the joints between the bottom of the riser and the horizontal pipe, elbows, tees, and inspection ports. Additionally, the effects of ambient temperature fluctuations on pipe expansion and contraction should be considered during testing.