Air Compressors Capacity Horsepower Pressure Duty Cycle

Air Compressors Compressors can be classified into two types: Positive Displacement Reciprocating (piston type) Vane Rotary Screw Lobe Dynamic

Positive Displacement Compressors Reciprocating Compressors Single Stage, Single Acting

Positive Displacement Compressors Reciprocating Compressors Single Stage, Single Acting

Positive Displacement Compressors Reciprocating Compressors Single Stage, Double Acting

Positive Displacement Compressors Reciprocating Compressors Single Stage, Double Acting

Positive Displacement Compressors Intake and Discharge Valves Work very similar to check valves Can open and close 720,000 time a day The number 1 reason for compressor downtime is valve failure Check the temperature of the valves regularly

Positive Displacement Compressors Reciprocating Compressors Multi Stage Piston Compressors

Multi – Stage Piston Compressors

Cooling Reciprocating Compressors Heat is generated when air is compressed With air-cooled compressors, ambient air is circulated around the housings of the finned cylinders With water-cooled units, water is circulated through passages that are cast into the cylinder housings

Cooling Reciprocating Compressors Air-Cooled Intercoolers Use finned tubing that is connected from one stage to the other A fan mounted on the flywheel is commonly used to blow air over the fins.

Cooling Reciprocating Compressors Water-Cooled Use a shell and tube type heat exchanger to transfer the heat from the air to the water. More efficient than air – type heat exchangers

Lubrication There are 2 areas that require lubrication in a reciprocating compressor. Compressor Housing Main cross head, connecting rod and motor bearings Cylinder Area Valves, packing and compression rings

There are 2 different methods of lubrication. Splash Lubrication Most common in small compressors. Use “dippers” on the connecting rod to scoop oil out of the crankcase. Pressurized Lubrication Usually used on very large compressors. A gear pump is used to force oil through orifices in the connecting rods.

Unloading Valves

Unloading Valves Small Reciprocating Compressors A pressure switch is used to turn the compressor on and off When the pressure switch is actuated, a mechanical lever shifts the unloading valve open. This allows the compressed air in the compressor pistons to vent to atmosphere. When the low setting is reached, the unloading valve closes and the compressor is started.

Unloading Valves Larger Reciprocating Compressors Air Pilot Operated Control Once the pressure in the receiver reaches the “A” valve’s spring setting, the valve shifts to direct pilot pressure to open the intake valve. No compression will occur so long as the intake valve is open. When the pressure in the receiver drops below the “A” valve’s spring setting, the cycle will repeat.

Unloading Valves Larger Reciprocating Compressors Solenoid Valve Unloading When the compressor is first started, the solenoid is energized and a 10-30 second timer is started. Pilot air is directed to shift and hold the intake valve open. No compression will occur so long as the intake valve is open. This allows the compressor to start up at little or no load.

Unloading Valves Larger Reciprocating Compressors Solenoid Valve Unloading When the timer elapses, the solenoid is de-energized and the intake valve is closed. When the pressure reaches the high setting of the pressure switch, the solenoid is energized and the compressor is unloaded. When the pressure drops below the low setting of the pressure switch, the solenoid is once again de-energized.

Rotary Vane Compressor Vanes Drive Shaft Rotor

Rotary Vane Compressor

Rotary Screw Compressors May be of the “dry” or “wet” design.

Dry Rotary Screw Compressor Has a male and female screw. The male screw is driven by the electric motor. Timing gears synchronize the rotation of both screws .

Dry Rotary Screw Compressor Limited to approximately 50 PSI unless a multi stage design is used . Driven at high speeds between 3,000 and 12,000 RPM.

Wet Rotary Screw Compressor

Wet Rotary Screw Compressor No timing gears are required. Oil is injected into the compression chamber. Lubricates the screws. Acts as a sealant between the screws. Absorbs the heat of compression

Wet Rotary Screw Compressor

Wet Rotary Screw Compressor The outlet air flow first flows through an air/oil reservoir, which removes 95% of the oil. The air then passes through an oil separator to remove the remaining oil.

Wet Rotary Screw Compressor

Wet Rotary Screw Compressor A check valve (minimum 36 PSI) is installed in the outlet line of the separator to build back pressure so that adequate lubrication is provided at all times.

Wet Rotary Screw Compressor

Wet Rotary Screw Compressor Thermostatic Valve Regulates the oil flow through the oil cooler

Wet Rotary Screw Compressor

Wet Rotary Screw Compressor The air is ported through an aftercooler before being directed to the system.

Wet Rotary Screw Compressor

Wet Rotary Screw Compressor Solenoid Unloading Valve

Rotary Lobe Compressors High Volume Low Pressure

Rotary Lobe Compressors

Dynamic (Centrifugal) Compressors

Dynamic (Centrifugal) Compressors Advantages Smooth air flow Very high volume Disadvantages More horsepower per CFM is required High drive speeds required (3000 – 50,000 RPM). Cannot achieve high pressures without using multiple stages.

Dynamic (Centrifugal) Compressors Air Flow Control Speed Variation Suction Throttling This is the most common method, but the compressor becomes inefficient at slower speeds. A butterfly valve or other device is used to restrict the inlet air flow. Discharge Throttling Recirculation The outlet air is restricted with a throttling valve. The outlet air is directed back to the inlet port. Lubrication A separate pump is used to supply lube oil through a filter and heat exchanger.

Compressor Horsepower and Energy Savings For every 10 PSI, 5% more electrical horsepower is needed. 100 HP will be required to drive a compressor that delivers 520 CFM at 110 PSI If the pressure is reduced to 100 PSI, then only 95 HP is required. 1 HP = 746 Watts 5 HP = 3,730 Watts or 3.73 kilowatts If the compressor operates 24 hours a day, 7 days a week (8,760 hour per year): Kilowatt hours = 3.7 kilowatts X 8,760 hours Kilowatt hours = 32,412 Electrical Cost = 32, 412 kilowatt hours X .10 (10 cents per kilowatt hour) Electrical Cost = $3241 per year

Troubleshooting Air Compressors Checking the Compressor Output Close the valve in the receiver outlet line to block flow to the system. Turn the compressor off and bleed the air in the receiver tank to 30 PSI. Turn the compressor on and record the amount of time it takes for the pressure to build from 50 to 100 PSI. Oc = .45 X VR / T VR = Receiver volume in gallons T = Time (in minutes) required to build from 50 to 100 PSI OC = Actual compressor output in CFM

Troubleshooting Air Compressors Checking the Compressor Output If the receiver tank volume is 400 gallons and the time required to fill it is 30 seconds (.5 minutes) then the actual flow can be found. OC = .45 X VR / T OC = .45 X 400 / .5 OC = 360 CFM If the original flow rating of the compressor is 450 CFM, then we can find the current capacity. Present Capacity = Current CFM Flow / Original CFM Flow Rating Present Capacity = 360 / 450 Present Capacity = .80 or 80%

Troubleshooting Air Compressors Common Compressor Problems Low Pressure at the Compressor Outlet Dirty intake filter Defective intake valve Worn or broken valve, vane or screw Improper adjustment or failure of unloading control Improper pressure switch setting Large leak in the system

Troubleshooting Air Compressors Common Compressor Problems Compressor Overheating Restricted air flow through the intake filter Dirty fins on an air type intercooler Restricted water flow through water jackets or an intercooler. Low oil Level Thermostatic valve not working Restricted oil flow due to contamination High ambient temperature

Troubleshooting Air Compressors Common Compressor Problems Oil in Compressed Air Oil separator saturated (rotary screw) Oil level too high or viscosity too low High temperature (reduces oil viscosity) Worn piston rings or cylinder (reciprocating)

Compressor Reliability Checks Oil Analysis The condition and performance of the oil has the greatest effect on compressor cost and reliability! Particle Count (ISO Cleanliness Code) Water Content Usually .4 - .6% PH Level TAN (Total Acid Number) 4.50 or below is considered normal Only used for polyglycols and synthetic fluids. Represents the amount of oxidation in the oil. Viscosity Low viscosity can be caused by high temperature or adding the wrong type of oil.

Compressor Reliability Checks Fluid Levels Levels should be checked regularly Flow rates to cylinder injectors must be monitored Accumulated water must be drained regularly System Pressures Pressures should be checked / monitored daily. Differential pressure of the inlet air filter Bearing, seal and filter pressures Suction, discharge and intercooler pressures Pressures should be compared to the manufacturer’s recommendations. Temperature Temperatures should be checked daily. Suction line, compressor discharge, intercoolers and aftercoolers Inlet & outlet water temperatures of coolers Lube system and crankcase Compressor valves, bearings and cylinder heads

Work Exercises 1. The amount of air flow that a compressor delivers is rated in: A. GPM B. CFM C. HP D. HP 2. If 60 CFM is required at 100 PSI, how much horsepower is required? ___________ HP 15 3. A centrifugal compressor is considered what type of compressor? A. Reciprocating B. Dynamic C. Positive Displacement D. Rotary Screw 4. True or False: A single stage compressor is normally used with pressures above 100 PSI. True False

Work Exercises 5. True or False: Single stage compressors usually run relatively cool with temperatures rarely exceeding 200°F (90°C). True False 6. What is the number one reason for downtime of a reciprocating compressor? _______________________________________________________________ Intake and discharge valve failure 7. What happens to air when it is compressed? A. The air is heated B. The pressure increases C. A vacuum is created at the inlet port of the compressor D. All of the above E. None of the above 8. True or False: The intercooler reduces the horsepower required to drive the compressor. True False

Work Exercises 9. The incoming water in a water cooled intercooler should: A. Be cooler than the inlet air temperature B. Flow the same direction as the air C. Be cool enough to turn the water vapor to condensate. D. Flow in the opposite direction of the air 10. What two areas require lubrication in a reciprocating piston compressor? 1. ________________________ 2. ________________________ Compressor housing Cylinder Area 11. What happens if the check valve fails open in a reciprocating compressor system where a pressure switch and unloading valve are used? __________________________________ Air will back flow into the compressor

Work Exercises 12. What will happen to a reciprocating compressor if the air operated unloading valve fails in the shifted position? A. Pressure will not build up at the outlet port B. The electric motor will trip out C. Pressure will build until the relief valve on the receiver tank opens D. The compressor will continue to operate normally 13. Where would you most likely use a rotary vane compressor? A. When flow rates over 5,000 CFM are required B. When pressures below 80 PSI are required C. When a compressor is needed that is more efficient than a rotary screw type D. When the surrounding air is dirty 14. True or False: In a rotary screw compressor, the male screw drives the female screw. True False

Work Exercises 15. What 3 purposes does the injected oil serve in a wet rotary screw compressor? 1. ____________________________________________________ 2. ____________________________________________________ 3. ____________________________________________________ Provides a lubricant between the male and female screws Acts as a sealant between the screws, preventing blow by Absorbs the heat of compression 16. What is the purpose of the minimum pressure check valve in a wet rotary screw compressor system? A. To dump the air to atmosphere if the outlet pressure builds too high B. To allow the air to flow through the oil cooler C. To make sure the air pressure doesn’t build over 36 PSI D. To make sure that adequate lubrication is provided to the screws at all times

Work Exercises 17. What happens if the oil return filter element in a rotary screw compressor system becomes contaminated? A. The oil will flow through the bypass check valve inside the filter housing B. The filter housing will be destroyed C. The thermostatic valve will port all the oil exiting the air/oil reservoir through the oil cooler D. The compressor will shut down on overload 18. True or False: You would normally use a rotary lobe compressor when 80 PSI is required. True False 19. You would normally use a centrifugal compressor when _______ CFM or more is required. 3,000

Work Exercises 20. What 3 components require lubrication in a centrifugal compressor? 1. ______________ 2. ______________ 3. ______________ Bearings Gears Seals 21. If 50 horsepower is required to operate a compressor at 90 PSI, how much horsepower will be required if the pressure is increased to 110 PSI? A. 100 B. 60 C. 25 D. 55 22. You are called in to troubleshoot a low pressure problem at the compressor. What is the most likely problem? A. Improper pressure switch setting B. Dirty oil filter C. The fins on the air cooler are dirty D. The outside air temperature is too high

Work Exercises 23. A reciprocating compressor with a water intercooler has shut down due to over temperature. Name three checks you would make. 1. ___________________________________________ 2. ___________________________________________ 3. ___________________________________________ Check the intake filter Check for restricted water flow through the cooler Check the oil level 24. Oil is showing up in the outlet air of a wet rotary screw compressor. The oil level and temperature are normal. What’s the most likely problem? A. Worn piston rings B. Bad aftercooler C. The thermostatic valve is bad D. The oil separator is saturated