Leak Check and Evacuation) Nuts and Bolts of Evacuation

 

1. Purpose of System Evacuation

• Remove Air and Moisture:
  • Prevents acid and sludge formation.
  • Ensures efficient operation by removing non-condensables.

2. Evacuation Methods

• Single Evacuation (Deep Evacuation):

  • Recommended to pull a vacuum below 500 microns.
  • Requires a two-stage vacuum pump:
    • First Stage: Quickly pulls down the system.
    • Second Stage: Achieves a deeper vacuum.

• Multiple Evacuation:

  • Involves additional steps to further remove moisture and contaminants.

3. Anatomy of a Vacuum Pump

• Components:

  • Intake Flare Fitting: Typically 3/8 flare fitting.
  • First Stage: Initial pull-down.
  • Second Stage: Deep vacuum.
  • Exhaust Port: Releases the air and moisture removed from the system.

• Example Pump:

  • Capacity: Measured in cubic feet per minute (CFM). Example: 6 CFM.
  • Maintenance: Drain port for oil changes, sight glass for oil level, and gas ballast valve for initial vapor removal.

4. Function of the Gas Ballast Valve

• Purpose:

  • Mixes dry air with moist vapors during the initial evacuation.
  • Prevents moisture from contaminating the vacuum pump oil.

• Usage:

  • Open the gas ballast valve for the first 30 seconds of evacuation.
  • Close the valve after initial vapors are removed to continue pulling a deeper vacuum.

5. Vacuum Pump Capacity

• Rule of Thumb:
  • Pump Capacity Squared: Determines the maximum system size.
  • Example: 3 CFM pump is suitable for up to a 9-ton system; 6 CFM pump for up to 36 tons.

6. Proper Vacuum Measurement: Microns

• Micron Gauge:

  • Essential for accurately measuring vacuum levels.
  • Comparison: Refrigeration gauges measure in inches of mercury, not accurate enough for deep vacuum measurement.

• Different Types of Micron Gauges:

  • Basic Digital Gauges: Compact, mounted directly on the vacuum pump.
  • Inline T-Fitting Gauges: Good setup, but extra fittings can create potential leaks.
  • Flexible Cord Gauges: Thermistor-based, accurate, and easy to position.
  • Analog Gauges: Highly accurate, good for teaching and visual confirmation of vacuum progress.
  • Integrated Digital Manifolds: Include micron scale in a gauge manifold, but often limited by smaller port sizes (quarter-inch flare connections).

7. Practical Setup and Use

• Choosing a Gauge:

  • Select based on accuracy and ease of use.
  • Position gauge to minimize potential leaks and ensure reliable readings.

• Evacuation Process:

  • Start Evacuation: Connect vacuum pump, open gas ballast valve for initial vapors, then close for deep vacuum.
  • Monitor Micron Levels: Ensure the system reaches and maintains the target vacuum level (below 500 microns).

• Maintenance Tips:

  • Regular Oil Changes: Use fresh, dehydrated oil for efficient evacuation.
  • Check for Leaks: Ensure all connections are secure to avoid false readings.