Air Compressor Troubleshooting

High Temperature Alarm

Discharge temperature exceeding limit and shutting down, this is the protection that trips most often on compressors. Atlas Copco, Ingersoll Rand machines typically set at 221°F. Fusheng, Kaishan domestic models mostly set at 212°F or 230°F, depends on controller parameters.

Cooling System

Cooler fins clogged up, six or seven out of ten high temperature machines are this cause. Compressor rooms with heavy dust, lots of lint especially bad. Fin gaps packed with stuff, air can't blow through, heat stays trapped inside. Take about 85 psi compressed air, air gun nozzle at 45 degree angle following the fin direction, blow top to bottom, push dust outward. Oil sludge stuck hard, first spray cleaner and soak ten minutes then blow. Fins cleaned up, temperature can drop 25 to 35 degrees.

Fan not turning or turning slow, touch the motor housing and you'll know. Motor hot to the touch means it's seized or has inter-turn short circuit. Motor temperature normal but fan not turning, check relay and contactor. Fusheng machines commonly have fan capacitor failure, swap in a 25μF capacitor and done. Ingersoll Rand VFD machines, cooling fan also VFD controlled. Inverter not giving enough frequency, fan speed can't come up, check inverter output.

Oil Circuit Problems

Can't see oil in the sight glass, or can only see a little at the bottom, oil is low. Screw machine running, oil foams and expands. Oil level looks okay, but actual amount circulating isn't enough. Stop machine ten minutes for oil foam to settle, oil level in middle to upper part of sight glass is normal.

Oil used too long will degrade. Color changes from golden to dark brown. Rub between fingers feels sticky and gritty, means time to change. Atlas Copco OEM oil goes 3,000 hours before change. Using domestic substitute oil, 2,000 hours is safer. Water got into oil will emulsify and turn white, this must be changed immediately.

Oil cooler plugged, oil temperature won't come down. Test method is feel temperature difference between oil cooler inlet and outlet. Normal operation inlet is hot to touch, outlet is warm, temperature difference 35°F or more. Inlet and outlet temperature about the same, means oil cooler internals are dirty, oil flows through without getting effectively cooled. Oil cooler cleaning is troublesome, have to remove it and use chemical cleaner circulating flush.

Thermal valve failure easy to overlook. Thermal valve's job is when oil temp is low, let oil bypass and skip the cooler. Oil temp high, then let oil go through cooler. Valve core stuck in bypass position, oil never goes through cooler, temperature definitely high. Disassemble thermal valve and check valve core movement. Wax thermal element on valve core failed, replace the valve core.

Oil filter differential pressure above 22 psi, time to change element. Differential pressure alarm usually set at 15 psi. Oil filter blocked, oil flow rate drops, airend doesn't get enough lubrication and cooling. Before changing element first release oil circuit pressure. Removing old element, be ready to catch oil that flows out.

Mechanical Failure

Bearing wear generating heat has a characteristic: temperature rises slowly. Not sudden high temperature alarm, but every day a couple degrees higher, after a month or two then exceeds limit. By then noise also gets louder. Put your ear against machine housing can hear abnormal humming or metal friction sound. Use vibration tester on airend bearing location. Vibration value exceeding 0.28 in/s, time to schedule major overhaul.

Screw clearance too large, during compression process high pressure gas leaks back, equals internal idling doing useless work, energy turns into heat. This situation shows as high temperature, current normal to slightly high, insufficient discharge volume all appearing together. Confirming internal leakage needs volumetric efficiency test. Method detailed in discharge pressure insufficient section below.

Sensor Problems

Temperature sensor usually PT100 RTD. Signal wire contact loose or RTD itself drifting, measured reading isn't accurate. Use infrared thermometer gun on discharge pipe surface, if more than 15°F lower than controller display, sensor has problem. PT100 can be removed and resistance measured with multimeter. 32°F is 100 ohms, 212°F is about 138.5 ohms. Deviation too big, replace it.

Discharge Pressure Won't Come Up

Can't build pressure, use points can't get supply, production line affected. This is the most urgent fault.

Inlet Side

Inlet valve not opening or not opening enough, less air going in, less coming out naturally. Pull the inlet pipe off the air filter seat, let machine load, observe inlet valve plate position. Plate should fully retract, intake passage completely open. Plate only half open or opens then closes again, check inlet valve servo cylinder, control solenoid valve, air lines for leaks. Atlas Copco GA series inlet valve servo cylinder seals tend to age and leak. Replace seal kit and done.

Air filter differential pressure gauge needle in red zone, or differential value exceeds 2 inches water, time to change air filter. Open air filter housing and look at element condition. Filter paper black and oily, don't hesitate. Dusty environments one to two months need changing. Low dust can go six months. Cheap domestic elements $5-10. OEM elements $30-50. Filtration precision differs, choose based on site conditions.

Compression Unit

Minimum pressure valve stuck and not sealing, system can't hold pressure. Minimum pressure valve's job is ensure oil separator tank has enough pressure for oil to circulate, also prevents system pressure backflow when machine stops. Valve seat sealing surface worn or spring broken, compressed air escapes through there. Test minimum pressure valve separately: block the outlet, see if machine can build pressure. Can hold pressure means valve is okay. Can't hold, disassemble and check valve core and spring.

Oil separator element damaged lets oil get into compressed air, also affects pressure. Connect a white paper towel after discharge pipe, blow a few seconds, obvious oil marks on towel means oil separator element needs changing. Oil separator severely damaged, pressure builds to 85 psi then can't go higher. Replace with new oil separator element, immediately returns to normal.

System Leaks

Turn off all air-using equipment, let machine fill tank to rated pressure then stop. Watch pressure gauge, within 15 minutes pressure shouldn't drop more than 7 psi. Drops too fast means system has leak points.

Crude method to find leaks is brush on soapy water and look for bubbles. More efficient is ultrasonic leak detector. Leaking spots emit ultrasonic signal. Wearing headphones can hear hissing sound. Where the instrument points and sound is loudest, that's where the leak is.

Common leak locations: pipe threaded fittings with aged thread tape. Flange gaskets deformed and not sealing. Ball valve stem packing leaking. Cylinder seals worn. Pneumatic tools with accumulated wear leak heavily. Go through one production line often can find ten to twenty leak points. Fix them one by one, saves good amount of electricity every day.

Supply-Demand Mismatch

Did you calculate air consumption? Is it enough? Single pneumatic wrench consumes 18 CFM. Spray gun 20-30 CFM. Cylinders calculated by bore and action frequency. Add up all air-using equipment and multiply by 0.7 simultaneous use factor, get actual demand. Demand exceeds compressor rated displacement by 90%, equipment needs expanding.

Low End-Point Pressure

Machine outlet 115 psi, by the time it reaches workshop use point only 70 psi. 45 psi difference lost on the way.

Pipe resistance mainly comes from three places: pipe diameter too small, pipe too long, too many elbows and tees. Fluid dynamics calculations are complicated. Simple estimate method is every 100 feet of pipe loses 1.5 to 3 psi. Each 90 degree elbow equals 10 feet of straight pipe. Each tee equals 20 feet of straight pipe. Calculate out pressure drop exceeds 15 psi, need to go up one pipe size. DN50 becomes DN65, DN65 becomes DN80.

Pipe inner wall rust and scale, cross-section area shrinks, equivalent to pipe diameter getting smaller. Old factory carbon steel pipes used for ten or twenty years, rust layer on pipe wall several millimeters thick. Knock on the pipe and listen, dull sound means thick buildup inside. Cleaning this kind of pipe isn't very meaningful. Replace whole section with galvanized or stainless steel pipe is more thorough.

Filters, oil-water separators, dryers at end points all produce pressure drop. Each stage 3 to 7 psi. Three or four stages in series is 15 psi. Check each filter's differential pressure. Differential gauge exceeds specified value, change element. Precision filter elements are expensive. Some technicians reluctant to change, differential at 30 psi still using it. Wasting pressure and wasting electricity.

Pressure regulator setting problem. Use points usually have pressure regulator in front to adjust pressure to needed value. Regulator setpoint too low, downstream pressure can't come up, that's normal. Regulator valve core stuck, pressure can't be adjusted up. Disassemble and check if valve core is jammed by debris. Clean up and reinstall.

Hose too thin and too long is also a problem. Take a 1/4 inch ID hose from main pipe and run fifteen feet to a pneumatic tool, pressure loss is large. Hose ID at least 5/16 inch, length keep within 15 feet. Need to run far, extend hard pipe over there, then connect hose near the use point.

Measure pressure at every node. Compressor outlet, receiver outlet, workshop inlet, before use point. Draw a pressure distribution diagram. Which two points have big pressure drop between them, problem is in that section. Follow this logic and check, always find the cause.