The aftercooler cools compressed air from discharge temperature (typically 40–60°C on a water-lubricated machine; 150–200°C on a dry oil-free screw) to near-ambient temperature. This causes the bulk of the moisture in the air stream to condense. The aftercooler separator or moisture trap immediately downstream is typically the highest-volume condensate point in the system — 60–80% of total condensate generated is collected here.

The receiver provides further thermal equilibration — compressed air that entered the receiver slightly above ambient temperature cools to full ambient as it sits. The resulting condensate collects at the bottom of the receiver. The receiver drain is one of the most frequently neglected drain points — a receiver without a functional drain fills with condensate, which is then carried downstream in slugs when demand spikes.

The refrigerated dryer cools compressed air to its target pressure dew point (typically +2°C to +10°C), causing substantial moisture condensation. The dryer’s internal separator and drain handle the largest single volume of condensate in systems with refrigerated drying. A failed refrigerated dryer drain is the single most common cause of downstream moisture contamination in refrigerated dryer systems.

Coalescing filters and particulate filters collect condensate in their bowls as liquid water and oil aerosol coalesce onto the filter medium. Filter bowl drains must operate correctly for the filter to function — a full filter bowl causes re-entrainment of collected liquid back into the air stream. Filter bowl drains are typically the smallest volume but largest number of drain points in a complex filter train.

In any distribution system that is not perfectly dry (i.e., not desiccant dried to −40°C or better), condensate forms at low points in the distribution pipework — particularly in long horizontal runs and at the bottom of vertical legs. These points require periodic manual drain valves or automatic drain traps to prevent water slugs from reaching tools and processes.

Desiccant dryers regenerate by passing a dry purge air stream through the saturated desiccant bed, desorbing moisture and discharging it as a warm, humid exhaust. For heatless desiccant dryers, this purge is vented to atmosphere and produces no liquid condensate. For heated desiccant dryers with cooled regeneration, the exhaust passes through a cooler and separator that produces a smaller volume of concentrated condensate.

Opens on a timed cycle (e.g., 30 seconds every 30 minutes). Simple, low-cost, reliable. The primary disadvantage is that it releases compressed air with the condensate — wasting energy and creating noise. Also, the timer is set for expected condensate volume; if condensate generation is higher than expected (humid day), the bowl may fill between cycles; if lower, the drain releases compressed air for part of the open period unnecessarily.

Uses a capacitive sensor to detect liquid level in the bowl, opening the drain valve only when liquid is present and closing as soon as the bowl empties — releasing no compressed air with the condensate. More expensive than timer drains but eliminates energy waste and adjusts automatically to variable condensate generation rates. The best solution for high-pressure systems and any drain point where energy efficiency matters.

A ball float rises with condensate level and mechanically opens the drain valve, closing again when the bowl empties. No electrical power required. Reliable in steady-state conditions. Vulnerable to fouling by debris or sludge that prevents the float from seating correctly — causing either continuous air loss (float stuck open) or condensate overflow (float stuck closed). Requires periodic cleaning.

Operator-opened valve at condensate collection points. Reliable when operated but entirely dependent on operator discipline. In practice, manual drains are frequently neglected — the receiver fills with condensate, the aftercooler separator overflows, and moisture carries over into downstream systems causing quality and corrosion problems. Acceptable as a backup or for very low condensate volume points only.