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Semi-Hermetic Compressors: Why They’re Ideal For Refrigeration

Semi-Hermetic Compressors | KB Delta

With so much new technology entering the field of engineering since the turn of the century, it is one of the simplest products that continues to be the most popular choice.

Working in a similar way to the engine in your car, semi-hermetic compressors offers many advantages for refrigerating and air cooling systems that make it unbeatable for this purpose.

First manufactured in the late 1940’s and with a design that has only altered greatly through the materials used to produce it, the semi-hermetic compressor has established itself as an industry standard in the field of refrigeration and for good reason.


What Is A Semi-Hermetic Compressor

With a broad range of compressors now existing in the engineering world, one common way to differentiate them is by the way in which they are designed.

The word hermetic is derived from the word hermit, meaning to be isolated from the outside world and similarly, hermetic means to be tightly sealed. Hermetic seals in engineering terms therefore refer to airtight seals used to maintain a closed system of operation.

A hermetic compressor, by definition, is when the main compressor and the engine are both sealed inside the outer casing so that they can operate in an isolated environment. As such, this term is used to categorize compressors into three distinct types:

  • Hermetic
  • Semi-hermetic
  • Open

An open compressor unit is the most common type, as the engine and the compressor are separate entities and a semi-hermetic compressor is a unit that therefore features elements of both designs. With the body of the compressor along with the engine sealed inside the casing during operation, but in such a way that it can be opened for inspection and maintenance if and when needed.


Advantages Of The Hermetic System

One major benefit of having the mechanical process sealed during operating conditions is the protection from contamination of the closed system. By preventing air into the system, dust particles are unable to dirty the lubricant and the moving parts which would in-turn cause increased deterioration of the components and a shorter lifespan.

Often incorporating a simple design, hermetic compressors are often able to run at a lower level of running cost, although this is often at the price of increased noise and vibration compared to open compressors. As such, they’re suitable for non-intensive purposes, such as the circulation of gas and liquids around a closed system that makes them ideal for use in temperature control equipment. As a fully hermetic system can’t be opened, this does limit them to a short to medium term lifespan, as they need to be completely replaced if a problem occurs to them.


Applications for Semi-hermetic Compressors

Similarly, semi-hermetic compressors are also typically used in appliances like refrigeration and air conditioning units, but the fact that they can be serviced and upkept means that they’re the preferred choice of compressor systems for larger scale units, as they can provide a more financially efficient option.

As all refrigeration systems work on the same principle of pumping a refrigerant gas between the evaporator and the condenser to control temperature as needed, the same system that’s used in a regular household refrigerator is also applied to larger walk-in industrial cold rooms, bar cooling equipment or air conditioning systems used for the environmental control of buildings.

As a result, this type of compressor is the most common compressor you will encounter throughout your day.


Common Faults With Semi-Hermetic Compressors

As compressors are subject to general wear and tear of components like any other type of machine, the advantage with the semi-hermetic system is that they can be serviced or even re-built if a fault occurs in the system. There are several reasons for compressor valve problems, including:

  • Oil leakage resulting in too little lubrication
  • Insufficient coolant or oil within the system
  • Slugging of oil or coolant into the compressor
  • Overheating of the compressor
  • By-products or contaminants inside the system which erodes valves and seals
  • Thermostatic expansion valve set incorrectly


With a number of problems that can affect their performance added to the fact that they operate on the same mechanical model, it’s possible to apply the same troubleshooting strategy across all types of semi-hermetic compressors.

One of the most common problems encountered is for either the coolant liquid or an outside contaminant entering the closed system and flooding the compressor. This reduces the effectiveness of the compressor and as such, measuring the compressors performance level over a period of time will help provide an insight into the inner workings of the machine, without needing to dismantle the unit for inspection.


Maintenance And Servicing

As the systems have become larger and more complicated in bigger temperature control applications, the methods of detecting problems have also become more refined to locate and eliminate performance problems.

However, there are still common techniques that you can apply to help prevent repeat failures, such as monitoring temperatures and performance output against optimum specifications. This will help you understand if the equipment is working under increased stress, which can result in accelerated component deterioration or in a worst case scenario, the motor burning out due to being overworked.

Technicians now have a variety of different tests that they can perform on the equipment to prevent a problem escalating to this point. It is worth noting that prevention is always a much cheaper alternative than a cure. However, as the semi-hermetic compressor is so widespread across all areas of the world, there’s many compressor valve repair components and kits alike available to remedy an emergency situation.

With customized repair and parts for rebuilds also available, this makes the long term prospect of these compressors not only an incredibly financially viable solution, but also a product that can be returned to full working order, with less downtime than a fully hermetic system that would require a complete replacement.

Coupled with its increased time needed between servicing due to the protection provided by the sealed casing, there’s little surprise that there has been no need for a redevelopment of this compressor.


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