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Quotes - Engineering - SalesApproach Temperature: 51 vs 59 Series
Approach is the difference between the air leaving the aftercooler and the cooling water entering it.
No exchanger can cool the air below the water temperature, and how close it gets depends on how much tube surface the air passes over. The IPAC 51 Series, at 51-1/8 inches long, brings the air to within 15 to 20°F of the water inlet. The 59 Series, with the same shell diameters at 59 inches, brings it to within 5 to 10°F. Both take the same water and the same air connections size for size.
Side by Side
Same shell, different length.
- 51 Series: 51-1/8" long, 15-20°F approach, W0035-W1500
- 59 Series: 59" long, 5-10°F approach, W0039-W5000
- Small models: 51 Series end in 5, 59 Series end in 9
- Both: 300 PSIG small NPT units, 200 PSIG flanged
Why Ten Degrees Matters
The closer approach matters because the water content of saturated air roughly halves for every 20°F drop in temperature. With 80°F water, a 51 Series unit delivers air at about 95 to 100°F; a 59 Series unit at 85 to 90°F. That 10°F difference means the 59 Series condenses noticeably more water in the separator, and a refrigerated dryer downstream sees a lighter load and a lower inlet temperature - which is usually the limiting figure on its rating.
Which Series to Choose
Choose the 51 Series for general shop air, for plants with cool water, and where the receiver and piping will do the rest of the cooling. Choose the 59 Series where a dryer follows, where the air feeds paint, instruments or a process, where the cooling water runs warm in summer, or where the compressor is large - the 59 Series is the only water-cooled range above 4,785 SCFM.
| RANGE | TYPE | COVERS | RATING |
| Water-Cooled 51 Series | Water-Cooled Aftercooler | Fifteen shell and tube models from 38 to 4,785 SCFM, all 51-1/8 inches long | 200 PSIG (300 PSIG small NPT units) |
| Water-Cooled 59 Series | Water-Cooled Aftercooler | Nineteen close-approach models from 37 to 11,970 SCFM, all 59 inches long | 200 PSIG (300 PSIG small NPT units) |
Common FAQs
No. It costs more and is eight inches longer. For general shop air with cool water and a receiver to do the rest of the cooling, the 51 Series is the right unit. The 59 Series earns its keep ahead of a dryer or a process, and in plants with warm summer water.
No. Size for size they take the same water and the same air connections; the extra length is extra tube surface, which is what closes the approach.
Measure the overall length: 51-1/8 inches or 59 inches. On the small models the last digit also tells you - 51 Series numbers end in 5 (W0035), 59 Series numbers end in 9 (W0039).
Related Pages
Water-Cooled 51 Series
Fifteen shell and tube models from 38 to 4,785 SCFM, all 51-1/8 inches long.
READ
Water-Cooled 59 Series
Nineteen close-approach models from 37 to 11,970 SCFM, all 59 inches long.
READ
Sizing an Aftercooler
The five figures needed to size an IPAC aftercooler, how the catalogue ratings are stated, and how to correct for inlet temperature and cooling water.
READ
