Formulas

Instrument Quality Air Requirements


In accordance with the Instrument Society of American Standards (ANSI/ISA-57.3-1975)(R1981) are:


  1. Maximum Particle Size-3 micron
  2. Oil content-1PPM w/ w/ or v/ v or less under normal operating conditions.
  3. Pressure Dew Point-At least 10C or 18F below the lowest ambient temperature.
  4. Air shall be free of all corrosive contaminants and hazardous substances.

How to Estimate Compressed Air Capacity


Generally, the compressed air capacity of an air compressor is related to its horsepower (HP). A good rule of thumb is: 4.5CFM per HP@100PSI.


Correction Factor for Sizing a Dryer



C1-Inlet Air Pressure Correction Factor


Pressure
(PSIG)C1

40 60 80 100 120 140 150 180 200
.67 .83 .94 1.00 1.03 1.05 1.08 1.09 1.11

C2-Inlet Air Temperature Correction Factor


TempF

60 70 80 90 100 110 120
2.73 1.94 1.50 1.21 1.00 0.84 0.69


C4-Pressure Dew Point Correction Factor


P.D.P.
C4

35° F to 39° F 45° F to 50° F
1 1.2

You Can't Afford Water In Compressed Air


Ambient air at 75F and 75% relative humidity carries 18 gallons of water/day into a compressor of 100 SCFM at 100 PSIG. An after-cooler will remove approx. 50% of that amount or 9 gallons. A properly sized dryer will remove the balance.


Low Pressure Calculation For Equivalent At 100 PSI


Blower at 200 CFM @ 15 PSI.


Step 1

Calculate the atmosphere at 15 PSGI

Calculate the atmosphere at 15 PSGI

Step 2

Calculate the atmosphere at 100 PSGI

Calculate the atmosphere at 100 PSGI

Step 3

Determine ratio between pressures

Determine ratio between pressures

Step 4

Convert volume to its equivalent at 100 PSI

200 SCFM x 3.86 ratio = 722 SCFM

Step 5

Size dryer/filters/equipment for that which is rated for 775 CFM @ 100 PSI


Comp. R.P.M. =


MOTOR PULLY p.d. =


COMP. PULLY p.d. =


MOTOR R.P.M =


PISTON DISPLACEMENT IN CU. FT. MIN. =


CU. FT. COMPRESSED AIR =



CU. FT. FREE AIR =


CU. FT. FREE AIR REQ'D. TO RAISE REC. FROM 0 GUAGE
TO FINAL PRESSURE =


GALLONS =



CU. FT. =



LOSS OF AIR THROUGH AN ORIFICE

In cubic feet of free air per minute at standard atmospheric pressure of 14.7 lb per square in. absolute and 70 F.


Gauge
Pressure
before Orifice in Pounds per sq in.
DIAMETER OF ORIFICE
1/64"
1/32"
1/16"
1/8"
1/4"
3/8"
1/2"
5/8"
3/4"
Discharge in cubic feet of free air per minute
6
7
9
12
15
.068
.073
.083
.095
.105
.272
.293
.331
.379
.420
1.09
1.17
1.32
1.52
1.68
4.34
4.68
5.30
6.07
6.72
17.4
18.7
21.2
24.3
26.9
39.1
42.2
47.7
54.6
60.5
69.5
75.0
84.7
97.0
108
109
117
132
152
168
156
168
191
218
242
20
25
30
35
40
.123
.140
.158
.176
.194
.491
.562
.633
.703
.774
1.96
2.25
2.53
2.81
3.10
7.86
8.98
10.1
11.3
12.4
31.4
35.9
40.5
45.0
49.6
70.7
80.9
91.1
101
112
126
144
162
180
198
196
225
253
281
310
283
323
365
405
446
45
50
60
70
80
.211
.229
.264
.300
.335
.845
.916
1.06
1.20
1.34
3.38
3.68
4.23
4.79
5.36
13.5
14.7
16.9
19.2
21.4
54.1
58.6
67.6
76.7
85.7
122
132
152
173
193
216
235
271
307
343
338
366
423
479
536
487
528
609
690
771
90
100
110
120
125
.370
.406
.441
.476
.494
1.48
1.62
1.78
1.91
1.98
5.92
6.49
7.05
7.62
7.90
23.7
26.0
28.2
30.5
31.6
94.8
104
113
122
126
213
234
254
274
284
379
415
452
488
506
592
649
706
762
790
853
934
1016
1097
1138