Maintenance & Reliability · SOP

Air Compressor Tank Blow Down And Moisture Drain

Standard operating procedure for manually draining accumulated condensate and performing a full tank blow down on stationary industrial reciprocating and rotary screw air compressors. Proper moisture removal prevents corrosion, emulsification of lubricant, and pneumatic system contamination.

Estimated Time
15 min
Difficulty
Basic
Regulation
CSA B52 / ASME BPV
Version
1.0
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Purpose

To establish a standardized, safe, and repeatable method for the manual removal of accumulated water condensate and moisture-laden air from the air compressor storage tank. This procedure prevents internal tank corrosion, water carryover into the distribution piping, lubricant degradation in oil-flooded rotary screw compressors, and potential for automatic drain valve failure.

Scope

This procedure applies to all stationary industrial air compressors equipped with manual or automatic tank drain valves located in Mechanical Room 101, 102, and the South Plant Annex. It covers both reciprocating piston and rotary screw compressor types operating at pressures up to 150 psig. This is a preventive maintenance task scheduled weekly or as dictated by humidity conditions.

Safety Precautions
  • LOTOEnsure compressor is isolated from the electrical supply and the automatic start circuit is locked out in accordance with CSA Z460. Depressurize the distribution header. Verify zero energy state before approaching the drain valve.
  • PPEApproved safety glasses or face shield are mandatory to protect against airborne debris and moisture spray. Wear hearing protection (minimum NRR 22 dB) during the rapid depressurization phase. Use chemically resistant gloves (e.g., nitrile) to handle condensate which may be acidic.
Required Tools & Materials
  • Floor drain or 5-gallon bucket for condensate capture
  • Chemically resistant gloves (Nitrile, or equivalent)
  • Safety glasses / face shield
  • Lockout/Tagout kit (lock, hasp, tag)
  • Adjustable wrench or specific drain valve key (if equipped with ball valve)
  • Lint-free rags

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Procedure: Step-by-Step
1 Preparation & Lockout: Place the compressor in "Off" mode. Disconnect electrical power and apply a personal lockout/tagout device per site LOTO procedure (CSA Z460). Verify zero pressure on the tank pressure gauge.
2 Header Depressurization: Close the isolation valve between the compressor tank and the plant distribution header. Open a downstream drip leg or manual vent valve to verify zero pressure on the downstream side.
3 Position Condensate Container: Place a suitable container (e.g., 5-gallon bucket) directly under the tank drain valve outlet or route a hose to the nearest industrial floor drain. Ensure the hose is secured to prevent whipping.
4 Slow Open Drain Valve: Standing to the side of the drain valve, slowly crack the valve open to release any trapped pressure and initial condensate. Proceed slowly to control the discharge rate and avoid splashing.
5 Full Blow Down: Once initial pressure is released, fully open the manual drain valve. Allow the tank to completely depressurize and all accumulated condensate to drain. Continue until only dry air is expelled.
6 Inspect Discharge: Visually inspect the discharged condensate for signs of excessive oil carryover (oil sheen or emulsified milky liquid) or particulate debris. Note any anomalies in the PM log for maintenance scheduling.
7 Close and Repressurize: Close the drain valve firmly, but do not overtighten. Remove the LOTO device. Reopen the header isolation valve. Restore power and restart the compressor. Allow the system to return to normal operating pressure.
8 Log the Task: Record the completion date, time, pressure readings, and any observations regarding condensate volume or quality in the preventive maintenance log or CMMS (e.g., ServiceGrid).

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