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Types of Piston Rings and Their Importance

Some are surprised to learn there are multiple types of piston rings when it comes to PET compressors – and they each serve their own purpose.

Types of Piston Rings in a Compressor - KB Delta

When a PET compressor does not function properly, the rest of the system suffers.

Staff members are not able to perform their functions, productivity takes a hit, and repairs can be costly.

Keeping the piston rings within a PET compressor in good repair, then, is vital.

Preventative maintenance and focus on high quality piston rings will help avoid this frustrating down time.

To fully understand the types of piston rings, it’s important to have a good grasp of how a piston ring works and what its function is within the PET compressor.


What is a PET Compressor?

A PET compressor has a primary role in manufacturing and production.

PET compressors are air compressors that operate under high pressure; they continually raise a gas’ pressure and, at the same time, lowers its volume.

When power is supplied to the PET compressor, it translates it to energy which is then transferred to tightly compressed air that is free of oil.

The compressor then supplies further air into the system; this is stored in nearby tanks.

The stored air forces the system to remain under pressure; when enough air has been collected, the system releases it and returns to a low-pressure status.

The cycle then begins again as the tanks wait to become pressured once more.


How PET Compressors Are Used

What’s happening with all that air?

In a facility which makes plastic bottles out of PET (polyethylene terephthalate), the primary job of the compressor is to control the flow of the liquid PET and PEEK.

The plastic, in this state, is blown into whichever bottle shape the client has decided on.

Although it’s easy to assume the plastic bottles will become water bottles, that’s not always the case.

Plastic bottles can fill many needs in the manufacturing world at a reasonable cost.

You will most likely encounter PET compressors in such industries as:

  • Natural gas
  • Petroleum or oil
  • Perhaps in refineries

With safeguards and careful monitoring, PET compressors can operate at high temperatures at a relatively low cost.

They can also function for long stretches without a lot of finicky maintenance, as long as they are constructed correctly and composed of good quality compressor parts.



What Piston Rings Are Made Of

Most piston rings are made primarily of cast iron, which is strong alloy that adds silicon, manganese, and carbon to the iron for its ability to bear a great deal of weight.

Although steel is used more often in construction applications, cast iron is a popular component for machine parts because it does not demand a great deal of refining work.

If you’re not familiar with cast iron in industrial applications, you may have come into contact with it as cookware or in historical military equipment.

Cast Iron

Cast iron may seem like an antiquated choice of material for something as important as a piston ring, but it’s selected for a specific reason: It also contains graphite.

Graphite, when used in its lamellar form (or in very thin layers which alternate with other materials—kind of like lasagna) acts as a natural lubricant.

Graphite is crystallized carbon, and occurs naturally. If you think of the graphite in a pencil, remember that it’s a soft material that cuts easily.

However, it does not react dangerously with other materials and tends to be heat-resistant.

Other Materials

Piston rings also usually contain coatings to protect the graphite and other materials.

These coatings themselves are usually composed of alloys to provide strength and resistance to corrosion.

The rings can be comprised of:

  • Nickel
  • Chromium
  • Titanium
  • Copper
  • Small amounts of less familiar metals


Different Kinds of Piston Rings Within PET Compressors

PET compressors will not operate properly without the correct piston ring.

Piston rings are essential to efficient operation of the system, as they encounter a great deal of pressure in each work cycle.

Because of this, it’s essential to understand the different kinds of piston rings, and which one is best for you.


1. Pressure/Compression Rings

One of the most common types of piston rings is a pressure or compression ring. These are also called second groove rings.

These have the important role of adding a backup, secondary seal which helps to keep potentially combustible gasses in place.

In some cases, second groove rings can also support the transfer of heat.

These types of piston rings provide an airtight seal of the chamber containing the piston; this prevents the leakage of any gas, which could lead to inefficiency or even danger.

Depending on the role and size of the piston, some engines contain multiple rings.

Wiper Rings

These rings may also contain wiper rings below the piston ring.

The role of the wiper ring is to capture and clean any traces of mineral or oil deposits which might remain from the work cycle, as well as lubricate the surface of the system liner.

This keeps the entire system moving efficiently.


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2. Oil Control Rings

Oil control rings are also an important part of a piston system. These look quite different from the other types of piston rings we have discussed thus far.

They may not look like rings at all, but may be square in shape or even contain a spring.

Within the chamber or casing, oil control rings help to gather oil back to the system for re-use.

The oil control ring also replenishes the oil within the chamber.

Not only do they make the transfer of heat safer and more efficient, it helps to reduce friction when the piston is in the midst of its work cycle.

Oil is regulated and managed when the oil ring isolates a thin layer.

Their Importance

That provides a surface which is slippery enough to allow the upper compression rings to perform their function.

In addition, the oil ring and the compression ring work together to shut the chamber, as well as aid in transferring heat as the work cycle repeats.

Oil control rings might be coated with a covering of chrome.

The oil control ring will also usually operate at high speeds and contain tiny holes or slots to allow for the distribution and draining of oil.



Compression rings and oil control rings are the two most popular types of piston rings seen within compressors.

Now that you know the difference between them, you can better diagnose your compressor and understand which parts you need.

KB Delta is a compressor part manufacturer that offers different types of piston rings and parts. Contact us today if you need compressor repair.

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