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Scroll air compressors, or otherwise known as spiral air compressors, are one of the types of positive displacement air compressors readily available in today’s compressed air market.
This page will serve as an overview of scroll air compressors, providing you with all the relevant information to help better understand them!
Table of Contents
- What Is a Scroll Air Compressor?
- How Does a Scroll Air Compressor Work?
- Scroll Air Compressor Advantages vs Disadvantages
- Scroll Air Compressor Applications
- Other Types of Air Compressors
- FAQs (Frequently Asked Questions)
What Is a Scroll Air Compressor?
Scroll compressors are positive-displacement type compressors that work by internal compression. Air is drawn in from atmosphere and trapped, before being reduced in volume, and then finally, discharged at an outlet port.
The concept of a scroll compressor has been around for way longer than a century, but it took significant advances more recently in manufacturing technology to make the product viable and commonly found.
The two main components of the scroll air compressor are a stationary scroll and an identical moving scroll. Each of these is a precisely machined or cast part in the shape of an involute spiral for sheer accuracy.
The slow speed of the scroll compression elements ensures a relatively quiet operation and as little vibration as possible, making it suitable for installations at the point of use, and there are few moving parts, so reliability is high and service interventions are minimal.
How Does a Scroll Air Compressor Work?
A scroll compressor actually consists of two scrolls, or otherwise known as spirals. The first scroll is moving, whereas the second one is fixed or attached to the compressor body. The first scroll is attached to the compressor’s crankshaft which makes it orbit/rotate in a path defined by its mating fixed scroll.
Gas pockets are then form between the two scrolls as a result of the scroll’s movement. At the outer part of the spirals, the pockets suck in gas and then move it towards the center of the spiral, where the compressed gas is discharged. As the gas moves into the continuously smaller internal pockets, both its temperature and pressure are increased as its volume is decreasing.
Therefore, this motion of the compressor scrolls results in a desirable discharge pressure. The compression cycle lasts for around 2.5 turns, which allows a continuous flow of pulse-free compressed air to leave the scroll element through the outlet port.
Scroll compressors are fully hermetic, meaning that they’re enclosed in the compressor’s shell, which is usually a cylindrical welded steel shell. The majority of scroll compressors used in refrigeration and HVAC services are of vertical orientation, with the scroll sets typically installed on the upper part of the motor shaft.
Normally, scroll compressors to do not tend to use suction or discharge valves. They prefer dynamic discharge valves at the compressor discharge only when operating at high differential pressure values. In such scenarios, having a dynamic valve at the discharge increased the efficiency of the compressor’s efficiency.
For example, scroll compressors operate at high differential pressures, and in the case of refrigeration applications for instance, the dynamic discharge valves will be utilized.
But in other cases, for example – in air conditioning units, having a discharge valve actually results in pressure losses, will will subsequently hinder the efficiency. Hence these type of valves are normally not preferred.
Scroll Air Compressor Advantages vs Disadvantages
Scroll Air Compressor Advantages
Scroll type compressors are inherently more efficient compared to other types of compressors and this is due to many reasons.
First of all, the absence of pistons for gas compression compared to reciprocating air compressors enables scroll compressors to reach 100% volumetric efficiency, leading to significantly reduced energy costs.
Each piston stroke encounters re-expansion losses in reciprocating models, and scroll compressors eliminate these. In addition, any losses at valve ports are eliminated, since suction and discharge valve ports do not exist in their design.
Scroll compressors are considerably quieter in operation compared to other types of compressors, like for example rotary screw type ones due to the absence of several moving parts. Scroll compressors typically make 5 to 15 dBA lower noise than other compressor types which can be a very desirable trait.
The fewer moving parts, lead to lower vibrations and less friction which means that scroll compressors are more durable. Due to lower vibration and noise, they do not need spring suspensions. Scroll compressors weight and footprint are considerably smaller compared to other bulkier types of compressors in use nowadays.
Scroll Air Compressor Disadvantages
Due to the fact that scroll air compressors are fully hermetic, perhaps the biggest disadvantage of scroll compressors is that they are generally not easily repairable. If anything goes wrong they cannot be disassembled for maintenance.
Many reciprocating compressors are tolerant on rotating in both directions. This is usually not the case for scroll compressors. The incremental capacity control on systems that use several scroll compressors has proven at times to be significantly problematic as well.
Scroll Air Compressor Applications
Since their introduction, scroll compressors have been successfully used in many various applications. Some of these examples involve food and fruit refrigeration, truck transportation, vacuum pumps, marine containers as well as residential and small to medium scale commercial air-conditioning applications.
Other Types of Air Compressors
If you’re interested in finding out more information on other types of air compressors please visit our specific pages:
- Reciprocating Air Compressors Explained
- Rotary Compressors Explained
- Rotary Vane Compressors Explained
- Centrifugal Compressors Explained
- Axial Flow Compressors Explained
- Oilless Air Compressors vs. Oil Compressors
FAQs (Frequently Asked Questions)
Scroll air compressors run quieter and smoother than reciprocating air compressors as they only have two moving parts, the fixed and orbital scroll. The reduced number of parts make the scroll compressor more efficient, reliable and less likely to undergo mechanical failure. However,
Scroll air compressors are deemed to be around 10% to 15% more efficient than reciprocating compressors due to their reduced number of parts. They have higher volumetric efficiency compared to other types of compressors.
Due to the precision and accurate technology needed when manufacturing the scroll elements of scroll compressors, they are typically more expensive than other types of air compressors.
If you have any questions regarding scroll air compressors, please leave a comment below, with any photos if applicable, so that someone may help you!