• SkillCat Team

Leak Detection

Updated: Mar 16

EPA 608 Type 3 Chapter 5 (Take full course for free)


In this module, we will learn about the methods to detect leaks in low-pressure systems. Skip to quiz!


1. Leak Detection Methods


Vacuum testing is the process of using a vacuum pump to create a vacuum inside the system and test for leaks. Recall that a vacuum pump is the same equipment used during evacuation of a system. We will discuss evacuation in the upcoming topics.


Generally we vacuum a chiller system to 1 mm of Hg. This vacuum is held for a few minutes to see if the vacuum pressure rises. ASHRAE Guidelines 3 states that if the pressure in the system rises from 1 mm Hg to a level above 2.5 mm Hg during vacuum testing, the system should be further leak checked.


A hydrostatic test is a method used to detect leaks in oil pipelines, gas cylinders, boilers, chillers and fuel tanks. In the process of the hydrostatic test, the tube of the chiller is filled with coloured water. The water is pressurized above the operating pressure of the equipment.


The pressurized colored liquid is held there for a set time. Any leaks in the system will cause the water to ooze out of the leaking gaps or holes. The colored dye leaves a mark and helps in detecting the location of the leaks visually.


To summarize the process,

  1. Colored water is pumped into the chiller tubes.

  2. The water is held for some time.

  3. Leaks are detected by searching for colored watermarks outside the tubes.

A leak detector probe is a device used to sense the presence of refrigerant outside the system. It is placed near the opening of the drain valve of the water box of the chiller to check for refrigerant gas leaks. If the refrigerant has leaked into the water system, it can be detected at the drain valve.


Once the water in the system is drained, there should be nothing coming out of the drain valve. If there is a leak, the leaked refrigerant will somehow find its way to the drain valve This can be detected by holding the leak detector probe near the valve.


In this test, the pressure of the chiller is increased while it is working to detect any leaks in the system. To increase the system pressure in a controlled way, we use hot water or electric heating blankets. Recall that as the temperature increases, the pressure increases too.


Electric heating blankets produce warmth by passing electricity through it. The gradual increase in temperature avoid temperature shock to the evaporator. Hot water is circulated throughout the system in a controlled manner to increase the pressure of the system.


The hot water also increases the pressure in the system. The increased pressure causes the liquid to ooze out of the leaking areas if present and they can be detected. The rupture disc on the evaporator may open if the pressures are raised too high so this process must be done in a controlled manner.


An electronic leak detector can then be used to detect any refrigerant leaks outside the system.


Recall that in a nitrogen pressure test, also known as standing pressure test, nitrogen gas is filled in the system to check for leaks. There is a drawback of using dry nitrogen to increase the pressure of the system for leak detection. Recall that nitrogen gas cylinders are highly pressurized.


While leak testing a low-pressure chiller with nitrogen, the maximum pressure should not exceed 10 psig. If it exceeds 10 psig, the rupture disc will burst open. So the nitrogen pressure test has to be done in a very controlled manner that requires highly trained technicians.


2. Conclusion


In this module, we went through the methods of leak detection for a Type 3 system.


Question #1: According to ASHRAE Guideline 3, the system should be checked for leaks if during a standard vacuum test the pressure in a system rises from 1 mm Hg to a level above;

  1. 1.5 mm Hg.

  2. 2.0 mm Hg.

  3. 2.5 mm Hg.

  4. 3.0 mm Hg.

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2.5 mm Hg.

ASHRAE Guidelines 3 states that if the pressure in the system rises from 1 mm Hg to a level above 2.5 mm Hg during vacuum testing, the system should be further leak checked.


Question #2: A hydrostatic tube test kit will;

  1. determine if a tube leaks.

  2. blow all water out of tubes.

  3. remove water from a machine.

  4. vent refrigerant to the atmosphere.

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determine if a tube leaks.

A hydrostatic test is a method used to detect leaks in chiller tubes.


Question #3: A leak detector probe to check gas leaks into the water box with water removed should be placed;

  1. At the rupture disc seal.

  2. Around the vent valve.

  3. Around a test plug

  4. In the drain valve opening.

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In the drain valve opening.

If there is a leak, the leaked refrigerant will somehow find its way to the drain valve. This can be detected by holding the leak detector probe near the valve.


Question #4: Leak testing a low-pressure refrigeration system with nitrogen in excess of ____ psig could cause the ____ to fail.

  1. 30; Condenser tubes

  2. 30; Purge unit shells

  3. 10; Rupture disc

  4. 20; Evaporator tubes

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10; Rupture disc

While leak testing a low-pressure chiller with nitrogen, the maximum pressure should not exceed 10 psig. If it exceeds 10 psig, the rupture disc will burst open.

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