3 Evacuating Low-Pressure Systems Free Online FlashCards

How do refrigerant recovery and dehydration evacuation differ?

Refrigerant recovery removes refrigerant before the system is opened; dehydration evacuation removes air and moisture after the system is sealed and leak-tested.

Why can leaks draw air into a low-pressure chiller?

Because low-pressure chillers can operate below atmospheric pressure, leaks may draw air and moisture into the system.

What damage can moisture cause inside a chiller?

Moisture can freeze, corrode components, or contribute to acid and sludge formation.

How does a vacuum help dehydrate a chiller, and what can slow drying?

A vacuum lowers water’s boiling point so moisture can vaporize and be removed. Pooled water, cold surfaces, oil, and moisture trapped in materials can make drying slow.

Where should the micron gauge be placed during evacuation?

Place the micron gauge at the chiller, or as close to it as practical, so it measures the system’s actual vacuum rather than a potentially better reading at the pump.

Why is a compound gauge unsuitable for measuring deep vacuum?

A conventional compound gauge cannot reliably measure deep vacuum; use an electronic micron gauge.

What must be completed before dehydration evacuation?

Recover the refrigerant and complete the required leak test before dehydration evacuation.

Why must the valves connect all sections requiring evacuation?

Connect all sections requiring evacuation to the pump as directed. A closed valve can leave part of the system undried.

What is the basic sequence of a triple evacuation?

Triple evacuation means evacuating to an intermediate vacuum, isolating the pump, breaking the vacuum with dry nitrogen, and repeating at progressively lower pressures. One example uses 1,500, then 1,000, then 500 microns; these are not universal targets.

What gases must not be used to break a vacuum?

Use dry nitrogen safely and follow equipment instructions. Never use oxygen or compressed air to break a vacuum, and never exceed allowable system pressure.

What does a micron gauge measure, and what indicates a deeper vacuum?

A micron is one-millionth of a meter of mercury pressure. The micron gauge measures absolute pressure, and lower absolute pressure means a deeper vacuum.

How is a standing-vacuum check performed?

Reach the specified final vacuum, close the isolation valve between the chiller and pump, keep the gauge sensing the chiller, and observe pressure rise over the specified hold period.