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Overhauling an Air Compressor: Cost Control, Rigorous Testing and Quality Parts

By David Grabau, Ingersoll Rand Compression Technologies and Services

When an air compressor needs to be overhauled, you hope the experience will be as pain free as possible. There are different approaches to overhauling an air compressor, and each has different implications related to cost, parts, service and performance.

Knowing when to overhaul a unit is important, and there are certain signs that indicate a unit needs attention. Performing routine fluid checks, taking oil samples, and routinely checking for bearing vibration can unveil indicators that suggest an upcoming failure. Oil contamination with metal fragments usually indicates parts are wearing. It’s also important to take notice of airend temperature increases. If internal compressor temperatures go up, that’s a good indicator that the cooler may be failing.

It is important to take notice of airend temperature increases. If internal air compressor temperatures rise, it is a good indicator the cooler may be failing.

The rebuild approach to overhauling an air compressor typically takes place in the field, at the customer site, where the compressor is already installed.  The product testing after the rebuild occurs in the field and may include checking discharge pressure, vibration levels and testing for oil leaks. During a non-OEM rebuild, existing parts are either refurbished or replaced with rebuilt or third-party parts. 

A remanufactured air compressor is overhauled within the original equipment manufacturer’s (OEM) factory. In this scenario, the factory will have all of the design drawings and specifications to bring the unit back to the original factory specifications. The manufacturer may also build the replacement airend with in-house parts, replacing bearings, seals, gaskets, pumps and more with new or OEM-certified parts. They will also conduct a complete mechanical and performance test before the unit leaves the factory.

The bid for an overhaul often starts with a low initial price that includes basic parts and services. However, as the disassembly and inspection process gets underway, additional items are often found to be worn or broken. The price and scope of the overhaul can change with the addition of each item. Without a fixed-price guarantee, additional parts and labor can quickly add up.

A successful overhaul can be evaluated by assuring the unit makes discharge pressure, the vibration levels are reasonable and the unit isn’t leaking. These standard measurement protocols include: delivering the rated capacity at the specified discharge pressure with “as new” efficiency and ensuring the surge pressure meets new equipment standards. The unit can be tested to determine it is leak free and that the stage and bull gear vibration levels meet new equipment specifications. The air cooler performance should match new equipment requirements. While these are good things to measure, there are many other things that can be tested to ensure a high standard of quality and reliability.

A company with in-house stock units allows the customer to plan in advance for their air compressor overhaul. For example, they can overhaul a unit within their factory, while the customer leaves their existing compressor running until the exchange unit arrives. This eliminates downtime and disruption.

Testing overhauled air compressors to meet rigorous specifications and standards is a crucial step in the process because it will ensure the unit meets the original quality benchmarks.

Benefits from testing air compressors include:

·       Validation of the mechanical integrity of the machine
·       Proof that the machine was returned to like-new efficiency
·       Minimization of uncertainties and field issues

Without completely testing the unit before it’s started up at the customer site, it is impossible to know if the air cooler performance meets new equipment standards. You won’t know if the unit will have the correct oil pressure or even if the compressor is completely air, oil and water leak-free. This is a particular challenge when an overhaul is completed at the customer site, as they may not have the necessary testing equipment to ensure the unit is returned back to the original specs and tolerances.

The following is an example of the importance of testing. A large U.S.-based equipment manufacturer had an air compressor rebuilt by a company that did a field overhaul. They were curious to see if the unit still met the original performance and efficiency rating, so they contracted a company to test the unit. The testing revealed the throttle range of the trim compressor had decreased by over 80 percent from factory specifications. This resulted in unwanted bypass and wasted energy consumption. Based on the test findings, the customer had the original manufacturer overhaul the compressor back to its original performance capabilities. In doing so, the customer was able to reduce their operating costs and energy consumption.

When comparing two quotes, there is an expectation that the lower quote will ultimately save money. But without a fixed price, there is no way to control costs and no guarantees. It’s not uncommon for overhaulers to quote an initially low price. Unfortunately, and all too often, the costs increase as additional issues are discovered during the teardown and inspection process. Of course, this results in more repairs, parts and service labor that were not part of the original quote.

With a fixed, upfront quote and complete scope of work, there are no additional costs to take into account, including the typical added cost overruns, potential customer downtime and possible onsite productivity loss, which can easily make up the cost differences. With a fixed price and scope of the compressor overhaul, there is no need to go back and forth with purchase order revisions or additional purchase order requests.

There are many advantages to a comprehensive contingency plan in the event something unforeseen happens.

A contingency plan should cover many areas, such as a risk assessment that identifies potential interruptions, ranking them according to cost impact, probability of occurrence and system downtime.  A financial risk analysis can review all areas of the facility and their dependence on compressed air equipment to determine the financial impact of a failure. An air compressor overhauler should be able to help plan for future emergencies. Having a contingency plan can help:

·       Reduce the risk of financial loss
·       Eliminate the risk of production downtime and loss
·       Reduce delivery time by completing paperwork ahead of time
·       Make employees aware of their roles
·       Identify weaknesses in the compressed air system
·       Plan for scheduled maintenance and new equipment installation

Non-OEM air compressor rebuilders rely on rebuilt or third-party parts; thus, the reliability and performance of the overhauled compressor may adversely impact production. This can occur when an inferior part fails or if the compressor exhibits inefficient performance that can slow productivity.

Recently, tests conducted on compressor coolers supplied by an aftermarket part supplier found many deficiencies in the product’s design and performance.Most notably, the Cold Temperature Difference (CTD) performance. It’s important to remember that Ingersoll Rand manufactures, designs and tests their own coolers to ensure performance and build integrity. Third-party coolers offer no control over product quality or adherence to specifications and tolerance requirements.

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