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Just as with other types of air compressors, timely and thorough maintenance of your centrifugal compressor can help increase performance, reduce the incidences of breakdown and subsequent downtime caused, while also helping your centrifugal compressor become more energy-efficient.
If you would like to learn more about centrifugal compressors, visit our Centrifugal Compressors Explained guide! This article will provide you with a number of useful preventative maintenance tips for centrifugal compressors along with an example of a preventative checklist, to keep on top of things!
Table of Contents
- Centrifugal Air Compressor Maintenance Tips
- Centrifugal Air Compressor Maintenance Checklist Example
- The Importance of Proper Preventative Maintenance Checks
- FAQs (Frequently Asked Questions)
Centrifugal Air Compressor Maintenance Tips
Although centrifugal air compressors have fewer internal components than other types of compressors, there are two areas in particular that require special attention when it comes to their maintenance. These two areas are the rotors and the cooler components.
The cooler performance must be checked regularly by measuring the CTD, or cold temperature difference, which is the difference in temperature between the water entering the cooler and the air leaving the cooler. The CTD should be around 15 degrees Fahrenheit or more.
It’s as crucial, to be inspecting the compressor for debris and condensate. Look for debris or any sign of corrosive acids. Contaminated compressors can result in fouled cooler tubes, which can then lead to elevated temperatures and have other impacts on the running performance.
It’s important to ensure condensate is removed so that diffusers, impellers, rotors, and other crucial components are protected from damage.
Let’s take a look at the following components and checks of a centrifugal compressor in more detail:
- Intake filter
- Control panel
- Bypass valve
- Inlet valve
- Checking vibrations
- Discharge check valve
- Oil filter
- Oil suction screens
- Oil cooler
- Condensate trap
All filtration systems have a maximum recommended pressure drop at which the filter element should be cleaned or replaced. It can be very difficult to predict the life of a given filter element due to the varying atmospheric conditions possible. To counter this, it is recommended to take a weekly pressure drop measurement for both the primary and final stage filter elements to help determine the usefulness of the filter element.
Filter maintenance is a very important part of the centrifugal compressed air system. If you properly maintain your inlet air filter, you will be able to have your compressor running at its optimum operation. You will know when your intake filter is performing as it should as you will see an increase in filter differential pressure.
The control panel checkout procedure is designed to verify that the control panel is functioning as it should. This task can be carried out with regular maintenance checks. Typically centrifugal compressors will have control drawings and a checkout procedure included in the instructions manual so that you can ensure proper calibrations and adjustments.
Periodically stroke the bypass valve to help with the optimum performance of the compressor. Stroking instructions will typically be available in the user’s manual of the centrifugal compressor.
In addition to this stroking, the bypass valve should also be removed from the air piping system once a year to inspect the seals for damage. You should replace damaged seals as required before reinstalling the valve.
Just like the bypass valve, you should periodically stroke the inlet valve to aid in the optimum performance of the compressor. Instructions on how to do so will be described inside the user’s manual.
The vibrations on the shaft should be monitored on both sides of the coupling using a vibration analyzer. In normal operation, you should not run the unit when the vibration levels exceed 2 mils on 3000-3600 RPM and 2.5 mils on 1500-1800 RPM drivers.
If the vibration is measured using a non-contacting probe, add .5 mil to the above levels. Of course, these are just some recommendations from a manual, so I would recommend you refer to yours for exact guidance for your centrifugal compressor model.
Discharge Check Valve
The discharge check valve must be removed from the compressed air system so that it can be inspected. You should inspect the valve for rust, broken strings, damaged seals, and freedom of movement. Repair or replace as necessary before reinstalling the discharge check valve.
If the check valve is mounted in a horizontal run of piping, the valve should be oriented so that the stem is vertical. To learn more about check valves, visit our Air Check Valves Explained guide here!
Filter elements within oil filters should be replaced when the pressure exceeds around 8 PSI from when the filter was new. When changing the oil filter, you should discard the filter element and clean all parts, before lubricating the two rubber seals received with the new element.
Oil Suction Screens
Every time the oil reservoir is drained, the suction screens should be removed and cleaned if your centrifugal compressor has them. The screens are typically open type located within the reservoir and are provided for the pre-lubricate pump and the main oil pump. Rinse these screens in solvent to be able to clean them.
Oil coolers must be inspected by removing the bonnets and checking the zinc anode for erosion or any oxide deposits. It is generally recommended to replace if more than half is corroded away. Carefully examine the tubes for scale and clean if needed.
The shell side of the oil cooler generally will not need to be cleaned, but flushing a high-velocity stream of water through the cooler may clean the tube side of the cooler, otherwise, a wire brush may be needed. After conducting either maintenance or cleaning on the oil cooler, both the shell and tube side should be carefully vented and full of liquid.
The condensate trap will typically need periodic inspection and cleaning to ensure that it is operating properly. The trap should have an intermittent discharge, a semi-continuous discharge, or a constant discharge flow or liquid to know that it is in working order.
If there is no discharge then this will indicate a potential problem. You should open the condensate bypasss valve. If a small amount of condensate discharge appears then this indicates a light condensate load to the trap, while a large amount of condensate discharge indicates the trap has failed and must be repaired or replaced.
When cleaning the trap, the bolts should be removed that hold the body together followed by carefully removing and cleaning the internal parts. While there, inspect orifice seats for any corrosion or undesirable conditions and inspect the leverage system for freedom of movement.
It is very important to only perform maintenance on a condensate system when the air compressor is shut off.
Centrifugal Air Compressor Maintenance Checklist Example
I have picked out this example of maintenance guidelines, or a checklist, provided by Ingersoll Rand in their centrifugal air compressor manual!
Scheduled preventative maintenance and inspection are essential for continuous optimum system performance of an air compressor, and a greater life span. The following are a general requirement and schedule checklist for routine maintenance on a centrifugal compressor.
Daily/Each Start-Up Maintenance
- Check compressor reservoir oil level.
- Check and record the oil temperature to the compressor.
- Check and record the compressor oil supply pressure.
- Check the main driver oil level.
- Check the vibration level on each compressor stage.
- Inspect tubing and fittings for signs of leaks.
- Check and blow down the condensate traps.
- Check air intake filter differential pressure.
- Check to make sure the air coolers are continuously venting. Vent valves are located on top of the casing.
- Drain the condensate from the inlet air line drip leg. Do not open the valve while the compressor is operating.
- Drain the condensate from the discharge header and bypass air line drip legs.
- Drain the drip legs on any other horizontal run of air piping.
- Check for oil leaks and fix if necessary.
- Inspect gasket/o-ring for leaks.
- Check the air line filter and drain any moisture.
- Check and record the oil filter differential pressure and replace the filter if necessary.
- Inspect air filter, drain and clean it and replace the filter element if necessary.
- Inspect condensate traps, remove and clean them and replace any parts as necessary.
- Grease the motor bearings using the correct type and amount of grease. Use hand-pump grease gun only. Bearings should be greased with the motor stopped.
- Visually inspect the intake filter, clean the filter element and replace if necessary. Inspect the seams of the filter element for cracks and potential bypassing.
- Change oil mist arrestor element, add oil to the U-tube, clean the element housing.
- Inspect control panel and look for loose wiring, wrong line filter, damaged line filters and adequate arc suppressors. Clean the control panel fan filters and panel, disconnect and tie back all unused wires from terminal strips.
Every 6 Months Maintenance
- Repeat quartely maintenance
- Lubricate the main driver coupling and inspect
- Change oil filter
- Test the air coolers for leaks
- Change the driver bearing lubrication
- Check the control system
- Check the inlet and bypass valve calibration
- Inspect the main driver
- Visually inspect the coupling. Align and lubricate as required and replace any components that have excessive wear
- Inspect and clean the oil reservoir suction screens
- Visually inspect the oil cooler tubes and clean the water side if necessary
- Inspect the inlet throttle valve
- Inspect the bypass valve
- Inspect the discharge check valve
The Importance of Proper Preventative Maintenance Checks
Carrying out regular preventive maintenance can help your centrifugal air compressor and all the inline equipment to run at their optimum performance. If you were to let your centrifugal air compressor wear down, eventually shutting down, then so would your projects.
Regular preventative maintenance will also help direct you to any issues before they’re able to propagate into more serious long-term damage. Each compressor manufacturer will provide specific maintenance schedules and maintenance kits that are recommend for your model’s proper service; like in the checklist example provided above.
Following a regular maintenance schedule will not only reduce service calls but it will also ensure that you have an efficient centrifugal air compressor performance, along with extending the life of your centrifugal air compressor. Read our guide on Air Compressor Maintenance – How to Guide – Preventative & Ongoing here!
FAQs (Frequently Asked Questions)
Yes, though there are many steps you can take yourself with preventative maintenance, it is possible to get your centrifugal compressor professionally serviced by a technician. The technician will have the in-depth knowledge and experience required to successfully service your centrifugal air compressor.
The daily maintenance check on a centrifugal air compressor includes checking compressor reservoir oil level, checking and recording the oil temperature to the compressor, checking the vibration level on each compressor stage, inspecting tubing and fittings for any signs of leaks, checking air intake filter differential pressure, checking for oil leaks and draining all moisture.
How often you should service your air compressor depends on how frequently you’re using it. If you’re running the air compressor continuously then it is recommended that you service the compressor quarterly to ensure you avoid issues. While if you’re only using your compressor occasionally, then an annual service should be adequate.
If you have any questions regarding centrifugal air compressor maintenance, please leave a comment below, with a photo if applicable, so that someone can help you!