Reciprocating compressors are generally used for compressing air, fuel, coolant, and other gaseous substances. This is the primary objective for most compressors, though they achieve this result in unique ways and for different reasons. One factor that remains constant, however, is volumetric efficiency. In other words, when it comes to the operation and control of a reciprocating compressor, the primary goal is efficiency, i.e., compressing the largest volume of gas/air for the least cost.
Volumetric efficiency plays a highly essential role in the overall productivity of a reciprocating compressor. But only a few within the industry understand this area. This article highlights this concept, why it is crucial in the grand scheme of things, and much more.
What is Volumetric Efficiency?
It can be said to be the ratio of a gaseous substance – like air or gas – entering a cylinder to the volumetric displacement of a piston. It represents the overall efficiency of a reciprocating compressor cylinder to compress the gas.
Every compressor, especially a reciprocating compressor, comes with a cylinder. This cylinder is usually injected with coolant, fuel, air, or any other gaseous substance.
Causes of Poor Volumetric Efficiency in Reciprocating Compressors
The most significant factors the compressor cylinder fails to deliver the piston displacement capacity include:
- Heating of the gas during admission or injection into the cylinder
- A throttling effect on the compressor valves
- Leakage past piston rings and valves
- Re-expansion of the gas trapped within the clearance-volume space from the previous stroke
- This has the greatest effect on the volumetric efficiency of a reciprocating compressor
- Old, cracked, or poorly designed seals
- Excessive angles or unevenness that effectively prevent gas from advancing without deviation from the cylinder
To have efficiency within the mid-to-high 70-percent range, a reciprocating compressor must have an excellent cylinder design with minimal base clearance.
When volumetric efficiency is in the mid-40 percent range, the machine exhibits what is referred to within the industry as ‘valve flutter.’ Valve flutter is when the compressor valve plates within the valves fail to fully close or open upon impact.
Valve flutter is one of the primary contributors to the poor performance of a reciprocating compressor. It significantly lowers the unit’s reliability, boosts the stress applied to the compressor valve, and severely damages it over time. This results in the additional wear of the springs and plates of the equipment.
The overall financial impact of poor volumetric efficiency can be significant. For example, valve flutter is known to cost up to 2 days of downtime every year. This incurs a massive cost through lost revenue to the manufacturer or producer.
Therefore, increasing your machine’s volumetric efficiency rating is crucial. It will boost gas flow by 1 percent to 2 percent and even extend the overall life span of the equipment.
Why Is Volumetric Efficiency in Compressors So Important?
You can find compressors in several engines since this is one of the most efficient ways of generating potential energy. But when the volumetric efficiency of any compressor is low, they perform less compression than desired.
Therefore, you must consider the volumetric efficiency of compressors to achieve the desired results. When you eliminate the factors negatively impacting the machine, there will be quicker compression of gaseous substances. As a result, your appliance will be more efficient and healthy.
How to Measure Volumetric Efficiency in Compressors
You can measure the volumetric efficiency in your reciprocating compressor by comparing the precise amount of gas or gaseous substance entering the cylinder against the gas or gaseous substance that exits.
The gas or gaseous substance exiting the cylinder has already been compressed. This means it will have a different volume that can be measured based primarily on the amount of escaped gas.
Every given cylinder has a theoretical maximum volume. For instance, the cylinder of a compressor can be 1 liter after you measure it. Of course, this is the theoretical maximum since a cylinder may not hold an entire litter during compression due to several factors and cannot be efficient.
To measure the volumetric efficiency of a compressor accurately, the gas or gaseous substance that enters must fill up the cylinder in its entirety. All the gas that enters the cylinder must also exit into the system where it is utilized. This will make the compressor 100 percent efficient, which is practically impossible.
Maximizing the Volumetric Efficiency in Reciprocating Compressors
Here are two effective methods of maximizing the volumetric efficiency in reciprocating compressors
Utilizing Large, Insulated Valves
The most efficient reciprocating compressors with maximized volumetric efficiencies come with large, often insulated valves. These valves allow the appropriate amount of gas to pass directly into the cylinder without undue expansion or friction.
Therefore, finding and maintaining highly effective compressors hinges on the ability of the equipment to work as perfectly as possible. However, some compressors aren’t designed or manufactured well. As a result, such machines will only attain maximum efficiency
If you own one of such machines, all hope is not lost. Having the ideal components and applying correct compressor maintenance can make your compressor unit more efficient in the long run.
For instance, your compressor unit can achieve maximum efficiency by consistently replacing seals before they become old and wimpish and smoothing out the intake valves.
Varying the Operating Speed of the Compressor Unit
Another efficient way of improving a compressor unit’s volumetric efficiency is by varying its operating speed. This can significantly boost the unit’s volumetric efficiency while minimizing the equipment’s wear and tear since the piston’s speed is slower.
Although varying the operating speed of your compressor unit addresses a subpar volumetric efficiency, your machine needs to be the appropriate size for maximum effectiveness.
The truth is that no compressor can achieve 100 percent efficiency, irrespective of the quality of its design. Although several methods of pre-compressing air or turbo-charging fuel exist to maximize potential energy, it is practically impossible to capture each molecule of a gaseous substance within a compressor, especially with today’s prevailing technology.
One cannot overstate the importance of volumetric efficiency in reciprocating compressors – or any other compressor, for that matter. The lower the volumetric efficiency of your equipment, the greater the volume of gas you need to compress time and again.
Therefore, you should do everything possible to boost or maximize the volumetric efficiency of your equipment considerably. This reduces the overall cost of production and resources during production.
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