Air compressor filter, drain and air dryer maintenance

⚙Care and inspection

• Clean the intake filter and replace it on scheduleIntake filter (air filter)

  Clean with a brush or air, and replace it if it is badly clogged. For screw types: clean every 6 months and replace every year (ANEST IWATA)

  When it clogs, intake pressure drops, the compression ratio rises, and power is wasted (J-Net21). It can also cause higher temperatures in the unit and discharge air, and a lower discharge volume. A JSIM document gives an example where a clogged filter, as in the photo, cuts the air volume by about 4 %^[1][2][3][4]

• Replace the separator element periodicallyOil separator element

  Replace every 2 years (8,000 hours) (ANEST IWATA example)

  When it clogs or deteriorates, oil separation worsens, the oil content of the compressed air rises, and oil consumption goes up (ANEST IWATA). Clogging is one cause of the safety valve blowing under load (Atlas Copco). Carbon buildup also creates a risk of ignition (JSIM)^[1][5][4]

• Replace the oil filter periodicallyOil filter

  Replace every 2 years (8,000 hours) (ANEST IWATA example)

  Keeps the oil clean and protects sealing and cooling performance. Dirty oil leads to wasted power and shutdowns from abnormal temperature^[1][5]

• Check the auto drain discharge every day, and disassemble and clean (or replace) it periodicallyAuto drain (drain trap)

  Check every day that condensate is coming out and that there is no air leakage. Disassemble and wash every month (example: dryer supplied with an ANEST IWATA reciprocating unit). Replace the auto drain trap of a screw unit's built-in dryer every year (example: ANEST IWATA LRS)

  If it clogs, condensate does not come out and water mixes into the downstream air. Causes include a clogged discharge pipe and a faulty float valve (Atlas Copco). JSIM lists disassembling and cleaning the auto drain among the dryer inspection items^[5][6][1][4]

• Do not discharge oil-containing condensate as isTreating condensate (drain water)

  Separate the oil with a condensate treatment unit, or contract an industrial waste disposal company

  The condensate from oil-lubricated units contains oil. ANEST IWATA gives an oil discharge standard of 5 mg/L or less and recommends checking with the pollution-control desk of your city, ward, or town office, since standards differ by prefecture. JSIM's installation pamphlet also lists the Water Pollution Prevention Act as a relevant law^[7][8]

• Manage intake temperature, ambient temperature, throughput, and refrigerant to keep the pressure dew pointRefrigerated air dryer

  Check that the dryer inlet air temperature, the temperature of the installation site, and the air flow rate are within specifications. Clean the condenser fins. Have a specialist check refrigerant pressure and leaks

  When the pressure dew point rises, condensation forms downstream. Causes include high intake or ambient temperature, low intake pressure, exceeding capacity, and low refrigerant (Atlas Copco). Never attach an intake duct to the exhaust port of a refrigerated dryer to force exhaust: overcooling freezes the condensate inside the dryer and breaks it (ANEST IWATA)^[7][4][9][5]

• Check the tank inside and out for rust and wall thinning, and do not modify itAir tank (Class 2 pressure vessel)

  Drain it every day. At least once a year, clean the inside and outside surfaces of the vessel and carry out the periodic voluntary inspection. Keep the Class 2 pressure vessel specification sheet (original)

  Wall thinning or pinholes from rust create a risk of serious accidents: air leaks, damage, and rupture (JSIM). A regulated vessel must not be modified, and its main components cannot in principle be replaced (replacing consumable parts such as gaskets with the same material and dimensions is allowed). The specification sheet cannot be reissued after 2 years from the inspection date, and if it is lost the vessel can no longer be used or transferred (ANEST IWATA). In one case, a tank homemade from plastic pipe without strength calculations ruptured within 3 weeks (MHLW)^{[5][10][11][12]}

• Check the safety valve setting and operation, and never remove it or raise the settingSafety valve

  Adjust it to operate at or below the maximum allowable working pressure. If there are two or more, one can be set at or below the maximum allowable working pressure and the others at no more than 3 % above it (Boiler and Pressure Vessel Safety Regulations, Article 86). Check that it blows when you pull its lever near maximum pressure (Meiji Machine)

  In one case, a leaking safety valve was removed and plugged, the other valve did not work because of poor maintenance, the pressure regulator was also broken, and the air tank ruptured (MHLW). Many vessels have ruptured because a safety valve was stuck. JIS B 8342, the standard for small reciprocating air compressors (single-acting, air-cooled, single- and two-stage, rated output up to 11 kW), also has a section on the performance of the safety valve on the attached air tank (from the standard's table of contents)^{[11][13][14][15]}

• Check the pressure gauge for error and protect it from freezing and high temperaturePressure gauge

  With the tank pressure at zero, check that the needle reads zero (Meiji Machine). Put an easy-to-see mark at the maximum allowable working pressure

  Article 87 of the Boiler and Pressure Vessel Safety Regulations requires measures to keep the inside of the gauge from freezing and from reaching 80 °C or more, and a marking at the maximum allowable working pressure. ANEST IWATA recommends a gauge whose full-scale value is 1.5 to 3 times the maximum allowable working pressure^[11][10][13]

• Choose filters to match the required air quality, connect them from coarse to fine, and replace the elementsLine filters (filtration order and element replacement)

  Check the purity class required by the equipment (JIS B 8392-1 / ISO 8573-1), and install filters from coarse to fine, for example line filter (3 µm) → submicron filter (0.3 µm) → micro mist filter (0.01 µm) (ANEST IWATA's suggested example)

  Installing a fine filter first makes it clog sooner and causes a pressure drop (ANEST IWATA). Replacing the elements of the line oil filters is one measure that allows the discharge pressure to be lowered (J-Net21)^[16][3][17]

• Keep piping pressure loss low, and fit shutoff valves and drains correctlyShop air piping

  Aim for a total pressure loss of 0.05 MPa including the dryer, and keep it to about 0.1 MPa at most. Fit a shutoff valve on each line (branch), using ball valves (full bore) or butterfly valves that are used fully open or fully closed (globe valves are unsuitable) (J-Net21). Provide drains partway along the piping, with a separate drain line for each machine (JSIM)

  Piping pressure loss is inversely proportional to the 5th power of the bore (J-Net21). Dirt and rust inside the piping also increase pressure loss, so inspect and clean it regularly (ANEST IWATA). Be careful with the position of the check valve at the compressor outlet: it can cause abnormally high pressure and frequent switching between load and unload (JSIM)^[3][8][18]

• Secure the required ventilation volume and keep exhaust air from returning to the intakeCompressor room ventilation

  Take intake air from the lower part of the building and exhaust from the upper part of the opposite wall. Fit an exhaust duct to each compressor (do not combine them). For a guideline ventilation volume, see the calculation section

  A higher room temperature lowers performance and service life and causes failures (JSIM, ANEST IWATA). Insufficient or recirculated cooling air raises the discharge temperature (Atlas Copco)^[8][9][4]

• Check the magnetic switch contacts, loose wiring, dust inside the panel, and groundingElectrical parts and wiring

  Check the magnetic contactor for contact roughness and terminals for looseness. Remove dust from inside the panel. Check the earth leakage breaker and the grounding (Class D grounding)

  Roughened or damaged contacts can weld or ignite. Dust buildup on electrical components can lead to malfunction or fire (JSIM). Provide a power supply of sufficient capacity and keep temporary voltage drops within −10 %. For inverter units, watch for harmonic noise and keep power lines and signal lines apart (JSIM). Electrical work is done by qualified personnel such as licensed electricians^[5][8][13]

▦Guide to parts replacement for a screw compressor (ANEST IWATA LRS-220BD, based on 4,000 operating hours a year)

Replacement criteria are separate from the warranty period. Where operating hours exceed the standard, follow the hours; in harsh environments, service earlier. Safety valves, cooling fan motors, compressor motors (insulation resistance, SPM), air coolers, and oil coolers are parts to inspect, in addition to the replacement parts^[1](1 source, for reference)

▦Guide to inspection and servicing of an oil-lubricated reciprocating compressor (packaged) (ANEST IWATA CLP37EF-8.5(D), based on 2,500 operating hours a year)

If the unit runs 24 hours a day for 200 days a year, do the work at half the intervals in the table (ANEST IWATA). Do it at whichever comes first, the number of years or the operating hours. Some of the work is to be left to the dealer or manufacturer^[6](1 source, for reference)

▦Compressed air purity classes (JIS B 8392-1:2012 = ISO 8573-1:2010)

Classes are written in the order [solid particles:water:oil]. Example: [3:6:4]. The values come from the class table published by ANEST IWATA (in that table, the pressure dew point and oil entries for classes 7–9 are blank). The outlet of a refrigerated dryer (pressure dew point 10 °C or lower) corresponds to water class 6 (ANEST IWATA's suggested example)^[16][17]

÷How to find the air leak rate, and an energy-saving estimate for eliminating leaks (J-Net21)

1. Close all the ends of the piping (the equipment in use) and run the compressor
2. Measure the time t1 for the pressure to rise from the lower limit P2 of the working range to the upper limit P1
3. After the compressor stops at the set pressure, measure the time t2 for the pressure to fall from the upper limit P1 to the lower limit P2 because of leakage
4. Leak rate Lp (%) = t1 ÷ (t1 + t2) × 100 (the ratio of leakage to the compressor's discharge volume)

Leak rate

Lp (%) = t1 / (t1 + t2) × 100

Derivation

Let V be the internal volume of the piping. Leakage during pressure drop: Q = (P1−P2)V ÷ (t2·P0). During pressure rise: (Qc−Q)·t1 = (P1−P2)V ÷ P0. From the two equations, Q ÷ Qc = t1 ÷ (t1+t2) (Qc is the compressor discharge volume, P0 is atmospheric pressure, and pressures are absolute)

Power reduction

Power reduction (kWh/year) = rated output (kW) ÷ overall efficiency × (power consumption ratio before improvement − power consumption ratio after improvement) × annual operating hours

Worked example: conditions

55 kW inverter-controlled screw compressor, 6,000 hours a year, average load factor 70 %, leak rate 8 %, motor efficiency 94.5 % × inverter efficiency 95 % = overall efficiency 90 %, electricity price 20 yen/kWh

Worked example: result

From the part-load performance chart: at a 70 % load factor the power consumption is 60 %; with zero leakage the load factor becomes 62 % and the power consumption 53 %. 55 ÷ 0.90 × (0.60 − 0.53) × 6,000 ≈ 25,700 kWh/year, about 510,000 yen/year

The power consumption ratio varies with the part-load performance of the model (the J-Net21 chart compares inverter units, intake-throttling units, and load/unload units). A manufacturer survey says 10–20 % of the compressed air in factories is leaking^[19](1 source, for reference)

÷How much power falls when the discharge pressure is lowered (theoretical adiabatic power)

1. Express intake pressure Ps and discharge pressure Pd as absolute pressure (MPa-abs) (gauge pressure + 0.1013)
2. Calculate the theoretical adiabatic power Lad at Pd before and after lowering it (specific heat ratio of air k = 1.4, number of stages m)
3. Power reduction rate = 1 − Lad (after) ÷ Lad (before)
4. Leakage is proportional to pressure, so add the reduction in leakage (leak rate × pressure reduction ÷ original pressure)

Theoretical adiabatic power

Lad (kW) = m·k / (k−1) × Ps·Qs / 0.06 × {(Pd / Ps)^((k−1)/(m·k)) − 1} [Qs: discharge volume converted to intake conditions, m³/min]

Reduction in leakage

Leakage reduction rate = pressure reduction ÷ original absolute pressure. Energy saving from it = that reduction rate × leak rate

Worked example: conditions

Lower the discharge pressure from 0.8 MPa-abs to 0.7 MPa-abs. Single stage, intake 0.1013 MPa-abs, leak rate 20 %

Worked example: result

Theoretical power falls by about 8 %. Leakage falls by 0.1 ÷ 0.8 = 12.5 %, and 12.5 × 0.2 = 2.5 %. Together about 10 % (J-Net21)

Atlas Copco's FAQ says “lowering the pressure by 0.1 MPa generally saves 6–7 % energy”, which is smaller than J-Net21's theoretical value (about 8 %). The actual effect varies with the model and control method. The working pressure of air cylinders and the like is around 0.4 MPa, and the required discharge pressure is that plus the piping losses (J-Net21). The Energy Conservation Center also names reducing consumption, reducing leaks, and lowering pressure as the pillars of pneumatic energy saving^[3][20][21]

÷Estimating the condensate volume (ANEST IWATA's calculation method)

1. Water content of intake air (g/m³) = saturated water vapor content at the intake temperature × relative humidity
2. Water content the compressed, cooled air can hold, converted to atmospheric pressure: saturated water vapor content at that temperature (tank surface temperature, or the dryer's pressure dew point) ÷ {(gauge pressure + 0.1013) ÷ 0.1013}
3. Condensate volume (L/h) = discharge air volume (m³/min) × duty ratio × 60 × (value of step 1 − value of step 2) ÷ 1000

Condensate volume

Condensate volume (L/h) = discharge air volume × duty ratio × 60 × (water content of intake air − water content remaining in the compressed air) ÷ 1000

Worked example: air tank

Intake 25 °C, 60 % (23.0 × 0.6 = 13.8 g/m³); discharge 1.285 m³/min at 1.0 MPa; duty ratio 50 %; tank surface 55 °C (103.9 g/m³ → 9.56 g/m³ converted to atmospheric pressure) → 1.285 × 0.5 × 60 × (13.8 − 9.56) ÷ 1000 ≈ 0.16 L/h, about 60 L over 12 hours × 30 days

Worked example: refrigerated dryer

Discharge 1.215 m³/min at 0.85 MPa; duty ratio 70 %; pressure dew point +15 °C (12.8 g/m³ → 1.36 g/m³ converted to atmospheric pressure) → 1.215 × 0.7 × 60 × (13.8 − 1.36) ÷ 1000 ≈ 0.63 L/h, about 100 L over 8 hours × 20 days

With a manual drain valve, drain it every day if possible (ANEST IWATA)^[22][7](1 source, for reference)

÷Guideline ventilation volume for the compressor room

1. Simple formula (JSIM): for air-cooled units, ventilation volume (m³/h) = 700 × compressor output (kW); for water-cooled units, 110 × compressor output (kW). For general ventilation with a 5 °C room temperature rise
2. Heat-balance formula (ANEST IWATA): heat release Qc (kcal/h) = 860 × motor output (kW)
3. Required ventilation volume (m³/min) = Qc ÷ (air specific weight 1.2 kg/m³ × allowable temperature rise Δt °C × specific heat at constant pressure 0.24 kcal/(kg·°C) × 60)

Simple formula

Air-cooled: 700 × kW (m³/h); water-cooled: 110 × kW (m³/h)

From heat release

Ventilation volume (m³/min) = 860 × kW ÷ (1.2 × Δt × 0.24 × 60)

Worked example: conditions

Air-cooled 3.7 kW, room temperature rise 5 °C

Worked example: result

Heat-balance formula: 860 × 3.7 = 3,182 kcal/h, 3,182 ÷ (1.2 × 5 × 0.24 × 60) ≈ 36.8 m³/min (about 2,200 m³/h). Simple formula: 700 × 3.7 = 2,590 m³/h

The simple formula gives the larger figure. Choose the fan capacity with the building's static pressure (50 Pa, for example) in mind, and confirm the ventilation method and volume with each manufacturer (JSIM)^[8][9]