TEST YOUR SKILLS
Understanding Supply-Side
Air Preparation
As air is compressed, the temperature of the air increases significantly. The compressor discharge air temperature is typically over 200°F (93°C) for a system operating at 120 psi (830 kPa). Compressed air must be cooled from this high temperature or it would be hazardous. Various coolers are utilized to reduce the air temperature. Air compressors that have two or more stages will have an intercooler between the stages to eliminate some of the heat before the air is fed into the next stage of compression. This improves efficiency. An aftercooler is used to reduce the compressed air temperature. A properly sized aftercooler will reduce the compressed air discharge temperature from 5 to 20°F (2.7 to 11°C) above the ambient air or cooling water. On small compressors, the aftercooler may be a finned tube placed in the airstream of a fan that is an integral part of the compressor drive pulley. On larger systems the aftercooler can be either an air-to-air cooler or an air-water cooler. The aftercooler should be located as close as possible to the discharge of the air compressor(s). The air-to-air aftercooler is commonly a traditional radiator style or a plate cooler. Sizing the cooler must consider the maximum expected ambient air temperature at 100% humidity. The heated ambient air will need to be vented out of the compressor area. In the next phase of the conditioning process, the dryer or filter are typically designed to operate at 100°F (37.7°C) or less. If the cooler cannot be sized to lower the discharge air to those temperatures, an air-water cooler or other type of device should be considered. Shell and tube style aftercoolers, consisting of a series of tubes that the hot air flows through with the cooling water flowing around the outside of the tubes in the shell, are commonly used. A water modulating valve is recommended to maintain a constant water temperature and to reduce water flow. The aftercooler will need to be inspected regularly to insure that passageways remain clear. A dirty aftercooler will be less effective, allowing a higher discharge temperature and creating increased pressure drop. The higher the discharge temperature of the aftercooler, the higher the remaining water content, causing the dryer to work harder to achieve the required relative humidity.
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AUGUST 2021
MAXIMUM PARTICLE SIZE PARTICLES
CLASS
By particle size (maximum number of particles per m3) See note 1 0.10-0.5 μm
0 1 2 3 4 5 6 7 8 9 X
WATER
0.5-10.0 μm
By mass
1.0-5.0 μm
mg/m3
OIL
Pressure dew point
Liquid
°C
g/m3
°F
Liquid, aerosol, vapor See note 2 mg/m3
As specified by the equipment user or supplier and more stringent than class 1 ≤400 ≤10 ≤-70 ≤-94 ≤6,000 ≤100 ≤-40 ≤-40 ≤90,000 ≤1,000 ≤-20 ≤-4 ≤10,000 ≤+3 ≤+37 ≤100,000 ≤+7 ≤+45 0 - ≤5 ≤+10 ≤+50 5 - ≤10 ≤0.5 0.5-≤5 5 - ≤10 > 10 > 10
≤20,000 (3) ≤40,000 (3) -
≤0.01 ≤0.1 ≤1 ≤5
>5
Note 1: For Particle Class 1 and 2 (0.1-0.5 µm range only), a laser particle counter is required. Note 2: ISO 8573 Oil includes aerosol, vapor and liquid oil. Liquid oil is typically sampled when wall flow is present, contamination is suspected, or results are greater than 5 mg/m3.
WATER CONTENT OF AIR IN GALLONS PER 1,000 CUBIC FT. Temperature °F % RH 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
35 0.0019 0.0039 0.0058 0.0078 0.0098 0.0117 0.0137 0.0156 0.0176 0.0195 0.0215 0.0235 0.0254 0.0274 0.0294 0.0313 0.0333 0.0353 0.0372 0.0392
40 0.0024 0.0047 0.0071 0.0095 0.0119 0.0143 0.0166 0.0190 0.0214 0.0238 0.0262 0.0286 0.0310 0.0334 0.0358 0.0382 0.0406 0.0430 0.0454 0.0478
50 0.0035 0.0069 0.0104 0.0139 0.0174 0.0209 0.0244 0.0279 0.0314 0.0349 0.0384 0.0419 0.0454 0.0490 0.0525 0.0560 0.0596 0.0631 0.0666 0.0702
60 0.0050 0.0100 0.0150 0.0200 0.0251 0.0301 0.0351 0.0402 0.0453 0.0503 0.0554 0.0605 0.0656 0.0707 0.0758 0.0810 0.0861 0.0913 0.0964 0.1016
70 0.0071 0.0142 0.0213 0.0284 0.0356 0.0427 0.0499 0.0571 0.0644 0.0716 0.0789 0.0861 0.0934 0.1007 0.1081 0.1154 0.1228 0.1302 0.1376 0.1450
80 0.0099 0.0198 0.0298 0.0398 0.0498 0.0599 0.0700 0.0801 0.0903 0.1005 0.1107 0.1210 0.1313 0.1417 0.1521 0.1625 0.1730 0.1835 0.1940 0.2046
90 0.0136 0.0273 0.0411 0.0549 0.0689 0.0828 0.0969 0.1110 0.1251 0.1394 0.1537 0.1681 0.1825 0.1970 0.2116 0.2263 0.2410 0.2559 0.2707 0.2857
100 0.0186 0.0372 0.0561 0.0750 0.0940 0.1132 0.1325 0.1519 0.1715 0.1912 0.2110 0.2310 0.2511 0.2713 0.2917 0.3122 0.3328 0.3536 0.3745 0.3956
110 0.0250 0.0501 0.0755 0.1012 0.1270 0.1531 0.1794 0.2060 0.2328 0.2598 0.2871 0.3146 0.3424 0.3705 0.3988 0.4273 0.4562 0.4853 0.5147 0.5443
120 0.0332 0.0668 0.1007 0.1351 0.1699 0.2051 0.2407 0.2768 0.3133 0.3502 0.3876 0.4254 0.4637 0.5025 0.5418 0.5816 0.6219 0.6627 0.7041 0.7460
Water removal As the compressed air is cooled, the excess water vapor will precipitate out, along with small particulates and residual oil from the compressor. The aftercooler, filters, receiver, and additional dryers will have a sump to collect all the condensate. The condensate is primarily water, but because it will also contain particulate contaminants from the free air and residual lubrication oils from the compressor, it cannot be simply drained into a waste-water drain without additional treatment. The sumps
will need to be drained periodically to insure proper operation. The simplest drain is a ball valve that maintenance personnel periodically open to collect the condensate for disposal. For systems that have cyclical demand or require frequent draining, an automatic drain can be used. Automatic drains can be simple float valves that open when the sump fills to a preset level, have electrical sensors that open a solenoid valve or use a timer to open on a regular interval, or operate based on air compressor cycle time. WWW.FLUIDPOWERJOURNAL.COM • WWW.IFPS.ORG
