MRO Today - 23 steps for starting a rebuilt rotary compressor airend

23 steps for starting a rebuilt rotary compressor airend

by Dan Wise

The airend on your oil flooded, rotary screw compressor is not going to run forever. It will eventually need repairs, and may even need to be replaced with a new or a rebuilt exchange airend.

Repairing or exchanging an airend will easily be the most expensive maintenance project for your rotary screw compressor. You can manage this cost by handling the installation and startup process with your in house Maintenance Staff.

Here are procedures for starting an oil-flooded, rotary screw compressor after the airend has been removed for repairs.

Clean and inspection phase
a) Always follow safety precautions outlined in the manufacturers manual as well as general safety rules for working with machinery.

b) Always make sure electrical power is not connected to the compressor package. Everyone involved should personally verify that the electrical power is disconnected, and all should follow proper lock out, tag out procedures.

c) Verify the compressor has been isolated from the air system, and all pressure has been relieved from the compressor package.

d) Drain all lubricant from the sump tank, oil coolers and all oil lines.

e) Remove fluid filters and separator elements.

f) Inspect filters, separators and the lubricant for causes of the unit failure, such as varnish, metal and foreign material. Inspect the air intake system for leaks or contamination.

g) The sump tank must be thoroughly cleaned with a pressure washer, or flushed with a cleaning agent compatible with your compressor lubricant.

h) The oil cooler or coolers must also be back flushed and cleaned.

i) If the compressor was varnished, before the airend repairs, ask us for the proper varnish clean up procedure.

l) Inspect the thermal valve, oil stop valve, the oil filter head(s) and control components for proper operation or contamination from the prior failure. Repair or replace any defective components.

j) Check all shutdown devices for proper function, and settings.

Assembly phase
a) After the cleanup procedure is completed, install the repaired
airend.

b) Make sure all piping has been restored to its proper location.

c) It is important to prime the airend with your lubricant, which prevents you from starting a dry airend. The actual process will depend on the type of compressor:
(1) Some units have a way to safely spin the drive shaft after the airend is assembled on the compressor, but without applying electrical power. Examples would be an airend with a coupling or one that is belt driven. If you have this type of compressor, you can pour a small amount of oil into the air intake port on the airend. Then, spin the drive shaft until the action feels less resistance, which means the oil has exited the airend. Remember to keep track of how much oil you pour into the assembled airend. Then, subtract that amount from the fill capacity of the sump, to avoid overfilling.
(2) Some units do not have a way to spin the drive shaft without electrical power. These include the newer compressors, those that are gear driven and the direct drive types. If you have this type of compressor, you can prime the airend before it is connected to the drive mechanism. Pour a small amount of oil into the air intake on the airend. Then, spin the drive shaft until the oil pours out the discharge port, and onto the floor.

d) Fill the sump tank with your lubricant.

e) Make sure the drive coupling is properly installed, and torqued. The coupling alignment should be within +/- .005 inches, both in parallel and angular, total indicator reading.

f) Make sure the compressor turns freely, before connecting electrical power to the unit.

Start up phase
a) Connect electrical power to the compressor package.

b) Jog the unit, and check the compressor for proper rotation.

c) Start the compressor and check for leaks, noise, vibration and anything that would appear abnormal.

d) Reset the controls, and check for proper operation of the control system, correct discharge temperature and normal amperage draw.

e) Allow compressor to run one hour, check for fluid leaks, and recheck coupling alignment. Operate the compressor in the load profile normally used for the unit.

f) Inspect the filter to make sure there is no foreign matter present. The oil filter should be changed after the first 50 hours of operation. The separator need not be changed at this time, unless there is a high differential pressure across the element or there is an indication of damage to the separator element (i.e., oil carryover).

An extra tip
You or your Maintenance Staff may be tempted to open the rebuilt or exchanged airend, just to look inside. Airends are interesting, but this action is the fastest way to void the airend warranty.

If you would like to learn more about rotary screw compressors, send your questions to us at airends@compressorwise.com.