• SkillCat Team

Leaks in Low-Pressure System

Updated: Mar 16

EPA 608 Type 3 Chapter 4 (Take full course for free)


In this module, we will learn about leaks in low-pressure systems. We will see the different indicators of a leak and the common areas that can leak in a Type 3 system. Skip to quiz!


1. Leaks


Recall that any matter flows from a high to low pressure. If you come across a leaking water pipe, you can see the water coming out of it from an opening. But, this is not the case with low-pressure appliances.

Recall that a low-pressure system operates below atmospheric pressure under a vacuum. The vacuum in Type 3 appliances wants to suck everything inside it like a vacuum cleaner. This is why Type 3 appliances need to be sealed tight to avoid the sucking of outside moisture into the system.


Recall that there is water flowing in the chiller systems’ evaporator and condenser. This water leaks into the refrigeration system to mix with the refrigerant. Apart from this leak, the outside air that contains non-condensables can also leak into the system.


Moisture is an impurity and is known as non-condensable in the system. Recall that air, moisture, and nitrogen are considered non-condensable gases in any system. Any problem in sealing low-pressure systems causes the outside air and moisture to leak inside the system.


2. Leak Indicators


Head pressure is also called high side pressure or discharge pressure. Recall that the discharge side of a system consists of liquid refrigerant. We can confirm the presence of non-condensable gases if the discharge side pressure in the refrigeration system is higher than normal.


The reason for a higher discharge pressure is;

  1. The gases remain in the vapor phase and do not convert to liquid.

  2. This exerts pressure on the refrigerant liquid, increasing its pressure on the discharge side of the appliance.

Recall that the purge unit performs the purge unit's function is to remove the moisture collected in the refrigeration cycle. Excessive moisture collection in the purge unit or excessive running of a purge unit could act as an indicator that the system is leaking.


Excessive moisture collection in the purge unit could indicate that the condenser or the chiller barrel tubes are leaking and drawing water into the system. Recall that there is water flowing in the chiller barrel and condenser. Water tubes in the chiller that suffer from leaks may need extensive repairs.


3. Common Leak Areas


In a belt-driven non-hermetic system, the compressor motor and the compressor are in different structures and connected by a rubber belt. Unlike the hermetic type, it does not have its components in a single shell. This type of system can be seen mostly in industrial refrigeration systems.


A Rotating shaft seal is used at the junction where the metallic shaft connects to the compressor. Rotating shaft seals have rubber seals for the purpose of sealing. If a system is non-working for several months, the rubber seals become hard and cannot perform sealing, causing leaks in the system.


To reiterate the whole concept:

  1. A Rotating shaft seal is used at the junction where the metallic shaft connects to the compressor.

  2. In a belt-driven non-hermetic system, that has not been used for many months, the rotating shaft seal is most likely to leak.

Fittings generally mean any part of the piping that is joined to the refrigerant tubing. All nuts, joints, bends, elbow joints, etc., pieces of refrigerant pipings are called fittings. Leaks can be due to improper assembly of the fittings or timely damage to the fittings.


A gasket is a ring of rubber or other material. Common examples of gaskets are those seen in pressure cookers. Gaskets seal the joint between two surfaces in any appliance and can leak if they are worn out.


A water box is generally fixed to the chiller barrel, and gaskets are used to seal them perfectly. Also, the compressor parts use gaskets to provide sealing. Gaskets and fittings are common components that can cause a leak.


4. Conclusion


We went through the definition of leaks in a low-pressure system. We also learned about the indicators of leaks and the common areas that can face leaks in Type 3 systems.


Question #1: Continuous excessive moisture collection in which component of a low-pressure refrigeration system could indicate a leak?

  1. Water Box

  2. Purge Unit

  3. Drain Valve Outlet

  4. Pressure Relief Valve

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Purge Unit

Excessive moisture collection in the purge unit could indicate that the condenser or the chiller barrel tubes are leaking and drawing water into the system.


Question #2: Which part of a belt-driven non-hermetic compressor is most likely to leak if the compressor has not been used for several months?

  1. Suction service valve

  2. Rotating shaft seal

  3. One or both of the king valves

  4. Head gasket on discharge side

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Rotating shaft seal

If a belt-driven non-hermetic compressor has not been used for several months, rubber seals in the rotating shaft seals become hard. A hard seal cannot perform its function of sealing the system. Insufficient sealing will let the refrigerant oil leak out of the system.


Question #3: On low-pressure chillers, water is most like to leak into the refrigerant system through;

  1. air leaks in the rupture disc assembly.

  2. tube leaks in the evaporator.

  3. leaks from areas with gaskets or fittings.

  4. leaks from the charging service valve.

Scroll down for the answer...











leaks from areas with gaskets or fittings.

Gaskets and fittings are common components that can cause a leak.

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