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Scroll Air Compressors Explained

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Scroll air compressors, otherwise known as spiral compressors, are one of the types of positive displacement air compressors readily available in today’s oil-free compressed air market.

This article will provide you with all the relevant information on scroll air compressors to help you better understand them, including how they work, their advantages vs disadvantages, applications, and more!

Table of Contents

What Is a Scroll Air Compressor?

Scroll air compressors are positive-displacement type compressors that work by internal compression. Air is drawn in from the atmosphere and trapped, before being reduced in volume, and then finally, discharged at an outlet port.

The concept of a scroll-type air 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.

Scroll Air Compressors Explained

How Do Scroll Compressors Work?

A scroll compressor actually consists of two scrolls, 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 formed 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 air pockets, both its temperature and pressure are increased as its volume decreases.

Therefore, this motion of the compressor scrolls results in 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 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 increases the efficiency of the compressor.

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, and will subsequently hinder the efficiency. Hence these types of valves are normally not preferred.

Scroll Compressors 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.

If you were to compare a scroll compressor vs a screw compressor, scroll compressors are considerably quieter in operation, not only compared to a rotary screw compressor but also other types of compressors 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 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 of 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

  • Food and fruit refrigeration
  • Production facilities
  • Vacuum pumps
  • Marine containers
  • Truck transportation

Since their introduction, scroll compressors have been successfully used in many various applications. On top of those listed above, you will find them being employed as superchargers in automobile applications, and in small to medium-scale commercial air-conditioning applications.

Scroll Air Compressor Manufacturers & Where to Buy

The 3 brands above are examples of the most common scroll compressor manufacturers, the best place to purchase these will be by visiting the manufacturers’ websites and contacting them directly.

When selecting a compressor from any of these manufacturers you will typically have a decision between going for a single-phase or 3-phase motor for the orbiting scroll compressor. This will completely depend on what kind of electrical connection you have available. In most cases, single-phase connections are available. However, if a 3 phase connection is available, then the three-phase motor is deemed considerably more efficient.

After that, you should be considering the differential pressure and flow rate parameters. Given that there are various scroll compressors available in the market, having various combinations of differential pressure and flow rate values. You should ensure you select the one which covers your requirements of certain minimum differential pressure at a given flow rate.

FAQs (Frequently Asked Questions)

Are scroll air compressors better?

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 makes the scroll compressor more efficient, reliable, and less likely to undergo mechanical failure. However,

Are scroll compressors more efficient?

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.

Why are scroll compressors so expensive?

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.

Which compressor is better rotary or scroll?

Depending on how you compare them, either can be better. For instance, scroll compressors are better in the sense that they create less noise compared to rotary, but, rotary compressors are far more easily repaired compared to the complex design of scroll compressors.

Who makes the best scroll compressor?

The best scroll compressors are manufactured by the most common brands in the air compressor industry, some notable names are Ingersoll Rand, DeWalt, and Atlas Copco.

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:

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!

By Aidan Weeks

A passionate Mechanical Engineer with endless enthusiasm for fluid power - building off the back of over 18 years of high quality contribution and discussion stimulated by Bill Wade here at About Air Compressors. With both practical and theoretical experience in pneumatics and hydraulics, I'm putting my knowledge to work - and working my grey-matter through my research, assistance and publishing work here at About Air Compressors. Feel free to reach out any time! P.S. A HUGE shout out to Doug who really offers such great value to all visitors to About Air Compressors - once again, feeling like I'm standing on the shoulders of GIANTS by getting to work alongside such a great community

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