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Need Help Choosing the Right Compressor?
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Choosing the Right Air Compressor

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First and foremost, the compressor must be big enough to do the job of handling peak loads without undue strain and waiting for the compressor to build up to the required pressure. Select the compressor that will do the job and allow time between pumping cycles to permit ample cooling. Do not buy a compressor that is too small!

The following series of charts will be helpful in selecting the proper size air compressor for the job and are important in checking and installing the compressor. If you have additional questions as to which air compressor is most appropriate for your needs, please feel free to email J-Air at support@cfmair.net.


Step #1: Single-Stage vs. Two-Stage Compressor
Single stage compressors take air into their cylinders at atmospheric pressure and compress it with a single stroke of the piston directly to the desired pressure. The air is then passed through a cooler, called an aftercooler, which removes some of the heat of compression. This type of compressor is most commonly used for applications where the pressure requirements are not in excess of 150 psi.

Efficiency varies with pressure, being lower at higher pressures. At high pressure or above 130 psi the efficiency of a single stage compressor falls off rapidly and a two-stage compressor should be used.

Note that single stage efficiency (55% to 70%) is lower than two-stage (75% to 80%).

Step #2: Control Description
Automatic Operation : In automatic (or stop-start) operation, the compressor stops when the pressure in the storage tank reaches the pre-determined maximum pressure (called the cut-out pressure) and starts when the pressure in the tank falls to a pre-determined minimum pressure (called the cut-in pressure).

Continuous Operation(or constant running control) : The compressor continues to run without pumping air after the cut-out pressure has been reached. This is accomplished through either a suction valve unloader, which opens the suction valve or a discharge unloader valve and prevents pumping during compression. This type of control is most widely used where the requirements for air are constant for a long period of time, or if automatic control would require motor starts more than 12 times per hour.

Dual Operation : The dual operation is a combination of automatic and continuous controls in conjunction with a method of changing from one control to another. This option is available only on electric models, for situations such as limiting high start-up amps on the motor, or applications requiring frequent starts/stops.

Step #3: Approximate Cubic Feet per Minute (CFM) Required to Operate Various Pneumatic Equipment
CFM free air is a volume of air at a given pressure expressed as its volume at intake conditions (normally 14.7 psi ABS. and 70° F). The actual delivered free air (CFM FA) is the CFM displacement, multiplied by efficiency.

Whenever possible, use actual ratings.

Equipment Air Pressure Range
Type of Device
Avg Free Air Consumption (CFM)
70-100 Air Filter Cleaner 3.0
70-100 Body Polisher* 2.0
70-100 Body Sander* 6.0
70-100 Brake Tester 3.6
70-100 Carbon Remover* 3.0
120-150 Car Rocker* 6.75
70-100 Car Washer* 2.5
70-100 Dusting Gun (blow gun) 2.5
120-150 Grease Gun (high pressure)* 3.0
70-100 1/8" & 1/2" Impact Wrench 2-7
70-100 3/4" Impact Wrench 10-20
70-100 1-1/4" Impact Wrench 20-40
70-100 Pannel Cutter 13
70-90 1/4" Screw Driver 9
70-90 1/4" Drill 7-13
70-90 2" Medium Duty Grinder* 10-20
70-90 6" Medium Duty Grinder 20-40
70-90 Laundry Press 2
70-90 Dry Cleaning Press 3
70-90 Sander 7-10
     
Hammers    
70-100 Air Hammer - Light* 4-8
70-100 Air Hammer - Medium* 10-20
70-100 Fender Hammer* 8.75
70-100 Cement Breaker* 75
     
Lifts    
70-100 Hoist (one ton) 1.0
145-175 Hydraulic Lift* 6.25
120-150 Pneumatic Garage Door 2.0
70-100 Radiator Tester 1.0
70-100 Spark Plug Cleaner 5.0
70-100 Spark Plug Tester 0.5
     
Spray Guns    
70-100 Engine Cleaner* 5.0
70-100 Paint Spray Gun (production)* 8.5
70-100 Paint Spray Gun (touch-up)* 2.25
70-100 Paint Spray Gun (undercoating)* 19.0
70-100 Spring Oiler 3.75
70-100 Trans. & Diff. Flusher 3.0
     
Tire Tools    
70-100 Tire Hammer 18
70-100 Bead Breaker 18
120-150 Rim Stripper 5.0
120-150 Tire Changer 1.0
120-150 Tire Inflation Line 1.5
120-150 Tire Spreader 1.0
120-150 Vacuum Cleaner* 6.5

* These devices are to be considered as continuously operating devices when operating normally. All other devices listed are to be considered as intermittently operated when operating normally.

Step #4: Using Compressed Air for Blowing

Pressure
(psi)
CFM of Free Air for Orifice Diameter
1/32"
1/16"
3/32"
1/8"
1/4"
50
0.91
3.64
8.2
14.5
58.2
70
1.19
4.76
10.7
19.0
76.0
80
1.33
5.32
11.9
21.2
85.0
100
1.61
6.45
14.5
25.8
103.0
120
1.90
7.58
17.0
30.2
121.0
150
2.33
9.20
20.7
36.7
147.0

Step #5: Air Storage Tank Capacity

Capacity in Gallons
10
20
30
60
80
Capacity in Cubic Feet
1.25
2.7
4.0
8.0
10.8
Cubic Feet Free Air @ 100 psi
10.5
21.0
31.0
62.1
84.0
Cubic Feet Free Air @ 150 psi
15.0
30.2
45.0
89.5
120.8

Note: 1 cubic foot = 7.48 gallons

       

Step #6: Motor Loads / Recommended Wiring

Single Phase
115V HP
1/2
3/4
1
1-1/2
2
3
Motor Amp
10
14
16
19
22
34
Line Fuse
30
45
50
60
80
110
Min. Wire Size
14
14
12
10
8
6
 
230V HP
1/2
3/4
1
1-1/2
2
3
5
Motor Amp
5
7
8
9
12
17
23
Line Fuse
15
25
25
30
40
60
70
Min. Wire Size
14
14
14
14
12
10
8

Three Phase
230V HP
1
1-1/2
2
3
5
7-1/2
10
15
20
25
Motor Amp
4
5
6
9
15
22
27
40
52
64
Line Fuse
15
15
20
30
45
70
90
125
175
200
Min. Wire Size
14
14
14
14
12
10
8
6
4
3
 
460V HP
1
1-1/2
2
3
5
7-1/2
10
15
20
25
Motor Amp
2
2.5
3
4.5
7.5
11
14
20
26
32
Line Fuse
15
15
15
15
25
35
45
60
80
100
Min. Wire Size
14
14
14
14
14
14
12
10
8
8

Step #7: Compressed Air Lines
(based on approx. 100 psi initial pressure)

Air pressure loss, psi, per 100 ft. length:

Volumn Air
CFM
5
10
20
30
50
70
100
Pipe
1/2"
3/4"
1"
1-1/4"
 
 
 
 
0.38
0.09
0.03
0.01
1.42
0.34
0.10
0.03
3.13
0.74
0.23
0.06
8.65
2.00
0.60
0.15
3.85
1.12
0.28
7.80
2.21
0.55
Air Hose (ID)
5/16"
3/8"
1/2"
3/4"
3.0
0.5
8.0
2.0
30.0
10.0
63.0
31.0
4.6
70.0
16.0
36.0
4.0
7.5