Air Compressor Spare Parts Buying Guide – Air Compressor Manufacturers

Screw compressor spare parts fall into two categories: consumables and repair parts. Consumables get changed on schedule, repair parts wait until they break.

Consumables

Air Filter and Oil Filter

Consumable

Air & Oil Filters

Maintenance

Filter Change

Monitoring

Pressure Differential

These two discussed together because in practice they get changed together.

Air filter catches dust, oil filter catches debris, similar principle, similar replacement judgment too: look at differential pressure. Air filter differential to 25mbar, oil filter differential to 1 bar, about time to change. Older machines without differential pressure display, changing every 2000 hours is safe.

Dirty environments mean air filters change more often. Customer doing cement grinding, air filter clogs dead at 800 hours, added a pre-filter before the intake, can stretch to 1500 hours. Can't skimp on this, air filter clogged means intake is restricted, main unit draws higher vacuum, seals get damaged easier.

Oil filter incidents are rare, clogged at worst means insufficient oil supply and high temp alarm, won't directly damage main unit.

These two items have small price gap between OEM and aftermarket, want convenience use OEM, penny-pinching then Donaldson aftermarket elements pass quality, lots of service shops use them.

Oil Separator Element

Oil separator is the most expensive filter element in a screw machine.

What makes it expensive? The filter media. Oil separator uses ultra-fine glass fiber, has to catch oil mist particles around 3 microns, precision requirements high. Cheap stuff uses filter media that's not dense enough, barely works when new, run two to three thousand hours and separation efficiency tanks, discharge oil carryover shoots up.

How to tell oil separator needs changing? Most direct indicator is differential pressure, over 0.8 bar need to watch, at 1 bar must change. Another way is watch oil consumption, normal machine running 1000 hours tops up a liter or two of oil, if top-up frequency noticeably increases, mostly oil separator issue.

This part recommend OEM or first-tier aftermarket brands. Saving $40-70, in exchange for discharge oil over spec, downstream equipment contaminated, not worth it.

Lubricating Oil

Oil selection is more complicated than filters.

Mineral oil is cheap, synthetic oil is expensive, everyone knows this. Question is which to use?

Simple answer: normal conditions mineral oil is totally adequate, just change oil more frequently, every two thousand hours. High temp environment, long-term high load operation, or wanting to extend service intervals, go synthetic. Synthetic has stronger oxidation resistance, six to seven thousand hours between changes no problem.

People ask can you mix them, answer is better not to. When switching from mineral to synthetic, drain old oil completely, flush oil circuit then add new oil.

Brands, OEM oil is safest, Shell, Mobil compressor oils also work. Definitely don't use hydraulic oil or machine oil as substitutes to save money, additive formulas are different, won't be long before problems appear.

Oil quantity depends on model, 37kW machine takes about 15-18 liters, stock one 20-liter pail is enough.

Belts

Only belt-drive models need to worry about this, direct-drive models skip.

Belts nothing much to say, cracked, worn thin, aged, then change. OEM belts or Gates, Optibelt all fine, don't buy no-name products.

Repair Parts

Repair parts characteristic is non-scheduled replacement, change when broken. Whether to stock, how much to stock, depends on how likely this part breaks, how serious the impact when it breaks, whether you can get it quickly.

Repair Part

Intake Valve Assembly

Repair Part

Minimum Pressure Valve

Intake Valve and Minimum Pressure Valve Repair Kits

These two valves are the most frequently actuating components on a screw machine, seal wear is just a matter of time.

Intake valve problems usually show as: pressure still rising during unload (won't close tight), or slow to load (won't open cleanly). Minimum pressure valve problems are opening pressure not right, too low and oil circulation has issues, too high and wastes power.

Around 20,000 hours do preventive maintenance, replace all the wear parts like seals and springs, better than waiting for failure. Repair kits aren't expensive, OEM ones around $100-150, downtime losses cost way more than that.

Stock one of each.

Thermostatic Valve Element

Thermostatic valve failure has two presentations: one is oil temp won't come down, high temp alarm; two is cold start oil temp won't come up, water in oil.

This part has long life, over 20,000-30,000 hours, low failure probability. Can stock one, can also not, depends whether you can quickly get one locally.

Solenoid Valves, Sensors and Such Small Parts

Cheap, don't take up space, recommend stocking several. Solenoid valve dies and compressor may not load/unload normally, sensor dies and display goes crazy or false alarms. These small things fail without warning, having them on hand is peace of mind.

Bearings

Don't need to stock.

Bearing life over 40,000 hours, before failure there's noise, vibration, can catch it early. When it really needs changing, it's not work regular maintenance can do, need to pull main unit and send for repair. Bearings are expensive and need special storage conditions, no need to stock yourself.

Procurement Channels

OEM parts from manufacturer or authorized distributor, expensive, quality stable.

Aftermarket from specialty parts dealers, cheaper, quality varies. Filters have a few brands with good reputation: Donaldson, Mann+Hummel been doing air and oil filters for years, stable QC. Oil separator aftermarket is murkier waters, get from suppliers you're familiar with, don't go cheap buying random stuff online.

Critical parts use OEM, common consumables use aftermarket, this is what most users do.

Rebuilt parts use cautiously, unless it's a rebuilder you trust.

What to Watch When Buying

First is model number. Compressor parts model numbers don't just interchange, same brand different series, same series different power, even same model different years, parts may differ. Before ordering send machine nameplate info to supplier to verify, best to provide old part photos or OEM part numbers.

Second is incoming inspection. When goods arrive compare dimensions and appearance, filters check pleat count and workmanship, seals squeeze to feel elasticity, obviously wrong stuff send back.

Third is supplier. Long-term partnership beats shopping around. Find two or three reliable suppliers, one primary, one or two backup, prices can be negotiated, delivery is guaranteed, problems can be exchanged.

How Much Inventory to Keep

Consumables stock one year's usage. Air filters and oil filters two to four each, oil separator one to two, lube oil one to two pails.

Repair kits stock one set. Solenoid valves, sensors stock several extra.

Rubber parts have shelf life, two to three years unused they age, don't buy too many at once to sit and expire. Lube oil once opened use up promptly, unopened store in cool place, shelf life three to five years.

Costs

Still using 37kW machine as example.

$700-850

All OEM + Synthetic

~$400

Mixed + Mineral

2×

75kW Cost Ratio

All OEM parts plus synthetic oil, annual maintenance cost $700-850. Critical parts OEM, consumables aftermarket plus mineral oil, around $400.

Can't skimp too hard on this money. Seen people use garbage oil separators to save money, clogs in six months, oil consumption shoots up, downstream treatment filters all toast, total loss is more than saved.

Higher power machines scale proportionally, 75kW roughly double the 37kW.

When to Buy

Month before service check inventory, order what's short in advance. Don't wait until service day to discover no parts, machine sitting waiting for delivery.

Facilities with multiple units can negotiate annual agreements with suppliers, volume gets better pricing, delivery also prioritized.