Compressed Air Dryer Troubleshooting

Dryer problems, what gives field maintenance guys the most headache is dew point exceeding spec and water at outlet. These two often overlap. Refrigerated dryer and desiccant dryer fault logic is quite different. Talking about them separately is clearer.

Refrigerated dryer condenser fin cleaning, drain valve cleaning and replacement, filter element replacement. Desiccant dryer regeneration valve seal replacement. Keep these spare parts in the toolbox year-round, won't go wrong.

Maintenance

Dryer System Inspection

Condenser Fins Are Refrigerated Dryer's Lifeline

Many sites treat refrigerated dryers as maintenance-free equipment. Install it and ignore for years. Fins clogged like a dust cake. High pressure alarms frequently before someone thinks to call for repair. Actually just five minutes with an air gun could solve it. Let it drag into compressor burnout, then it's major repair money.

Dusty shops clean fins every month or two. Normal environment every three to six months. After cleaning, high side pressure noticeably drops, dew point also improves. Some guys like to use water. After hosing off, make sure fins are completely dry before starting up. Otherwise water vapor getting sucked into refrigeration system is more trouble.

Low high-side pressure is less common. Usually refrigerant leak. Put soapy water on fittings and weld joints to find leak. After finding, patch leak, pull vacuum, charge refrigerant per nameplate amount. Can't do this on site, gotta get someone with refrigeration repair license.

This Little Drain Valve Gets Overlooked Most

Refrigerated dryer outlet has water, nine times out of ten it's drain valve problem.

Solenoid type drain valves have a small screen inside. Debris and scale from compressed air block it. Blocked up, solenoid energized but can't open. Condensate can't drain. Accumulates to a certain amount and gets carried away by airflow. Take it apart, soak in descaler, clean screen and spool, put back, usually fixed.

Drain valves, cheap ones are $20-30, expensive ones $50-60. Used over three years, even if cleaning makes it work, won't be long before problems again. Seals aging, solenoid coil insulation degrading, just replace with new one, less hassle.

Timed drain valves also check if timer interval is set right. Interval too long, draining not timely. Interval too short, wastes compressed air. Adjust based on actual condensate volume. Summer when condensate is heavy, set interval shorter.

Filter Element Differential Gauge in Red Zone Is Too Late

Filter elements at dryer inlet and outlet are consumables. When it's time to change, change it.

Differential gauge on element is most direct judgment basis. Needle in yellow zone, time to prepare spares. In red zone means already running past due. Drag it out without changing, pressure drop loss happens every day. Extra electricity compressor consumes over time is way more than element cost.

Desiccant Dryer Valve Problems

Regeneration valves and switching valves are core components of desiccant dryers. High action frequency, high failure rate.

Inspection

Regeneration Valves

Desiccant

Twin Tower System

Simple way to check if regeneration valve is leaking. Wait until regeneration cycle ends, adsorption cycle starts, then feel the regeneration tower top muffler outlet. Normal condition no airflow should come out at this time. Hand on it and feel obvious airflow, valve isn't sealing.

Direct consequence of regeneration valve leak is increased air consumption. Design was 15% regeneration air consumption. Serious leak can be over 20%. A dryer with 350 CFM processing capacity, extra 5% leak is 17.5 CFM every minute. One day adds up to over 25,000 cubic feet of compressed air wasted.

Switching valve problems show differently. Switching valve controls airflow direction between two towers. Not actuating properly causes cross-flow between sides. Dew point fluctuating big, high regeneration air consumption, sometimes two towers unbalanced pressure, all might relate to switching valve. Pneumatic switching valve check air source pressure and cylinder seals. Solenoid valve check coil and spool.

When to Change Adsorbent

Adsorbent failure is gradual process. Won't suddenly fail one day.

Activated alumina or molecular sieve normal service life is 3 to 5 years. Observe granule condition. Color changing to yellow is mild aging. Powdering and clumping is severe aging. Open manhole cover and grab a handful to look, you'll know.

Liquid water also hurts adsorbent. Large amount of liquid water entering tower, short time adsorbent saturates, regeneration releases lots of heat causing granule fracturing. Refrigerated dryer or pre-cooler with drain valve handles liquid water first, then entering adsorption tower is more reliable.

Several Possibilities When Dew Point Can't Meet Requirement

Dryer dew point exceeding spec is most common service call reason. Causes behind it are several.

First rule out simplest possibilities. Inlet temp exceeding design value? Processing capacity exceeded? Either one over, drying effectiveness takes a hit. Nameplate parameters are values under standard conditions. On-site conditions deviating from standard need to recalculate actual processing capacity.

Refrigerated dryer dew point exceeding, refrigeration system is key inspection target. Measure high and low side pressures. Compare to normal condition reference values to judge refrigerant charge and system status. Is evaporator icing? Is condenser heat dissipation good? Is expansion valve blocked? Check these items one by one, cause can usually be found.

Evaporator surface icing causes a contradictory phenomenon: evaporating temperature is very low, but dew point won't come down. Ice layer thermal conductivity is much lower than metal. After evaporator ices, heat exchange efficiency actually drops. Hot gas bypass valve is there to prevent this situation. It gets stuck or mis-adjusted, evaporator temperature goes out of control and ices up.

Desiccant dryer dew point exceeding, adsorbent condition and valve sealing are two main directions. Incomplete regeneration or adsorbent failure, outlet dew point naturally high. Valve internal leak causing dried air and undried air to mix, dew point also rises.

Frequent Start-Stop Really Hurts Refrigerated Dryers

Compressor startup instant current is several times normal running current. Frequent start-stop damages motor windings, contactor contacts, start capacitors.

High pressure protection repeatedly tripping is main cause of frequent start-stop. Condenser poor heat dissipation, ambient temp too high, cooling fan fault, high side goes over then shutdown, temperature drops then startup, round and round.

Solving heat dissipation problem is fundamental. Condenser cleaning is routine. Equipment installed in enclosed space, add exhaust fan to pull hot air out. Installed against wall, keep at least 12 inches from wall, leave space for intake air.

Cooling

Water-Cooled System

Refrigerant

Charge Verification

Water-cooled condenser inspection focus is different. Is cooling water flow enough? Is inlet water temp high? Is condenser copper tube inner wall scaled? These three determine heat dissipation effectiveness. Cooling tower summer overloaded operation, water temp can't come down, refrigerated dryer high pressure alarm is normal.

Refrigerant charge also affects start-stop frequency. Overcharged, high side runs high. Undercharged, low side runs low. Both might trigger protective shutdown. After pulling vacuum, charge per nameplate amount, then observe running current and pressures are normal.

Pressure Drop Economics

Pressure drop issue isn't as obvious as dew point exceeding or water carryout. Easy to overlook.

Dryer inlet-outlet differential each 1.5 psi increase, compressor power consumption increases about 0.7%. A 100 hp compressor, differential from normal 4.5 psi increases to 12 psi, extra electricity per year exceeds $450. That's just dryer one link. Add filter, pipe, valve pressure drop losses, number is more substantial.

Desiccant dryer high pressure drop has another cause: adsorbent powdering. Powder moves with airflow and accumulates at pipes and valves, causing local blockage. Regularly check adsorbent condition. Serious powdering, timely replacement prevents this type of problem.