Applied Methods and Techniques Flashcards

How is a low-pressure chiller usually pressurized for leak testing?

Answer: By heating the refrigerant with hot water or a heating blanket, not exceeding 10 psig

Controlled heat raises the pressure without going over 10 psig, which keeps the 15 psig rupture disc intact.

When charging an evacuated low-pressure chiller, why add vapor first instead of liquid?

Answer: To raise the pressure above the saturation pressure for 32°F so water in the tubes does not freeze

Liquid flashing at low pressure gets cold enough to freeze water in the tubes and possibly rupture them.

Why should chilled and condenser water be circulated while recovering refrigerant from a low-pressure chiller?

Answer: To prevent the water in the tubes from freezing

As pressure drops during recovery, the refrigerant gets cold, and moving water keeps the tubes from freezing.

Low-pressure equipment made after November 15, 1993 must be evacuated to what level before opening?

Answer: 25 mm Hg absolute

Low-pressure appliances require 25 mm Hg absolute (about 29 in. Hg vacuum) with post-1993 recovery equipment.

In a low-pressure chiller, what does a purge unit that runs too often most likely indicate?

Answer: A leak letting air into the system

Low-pressure systems run below atmospheric pressure, so frequent purging means air is leaking in.

After removing liquid refrigerant from a large low-pressure chiller, why does a lot of refrigerant remain?

Answer: A large amount stays as vapor in the system's large volume

Low-pressure refrigerants have low vapor density, but a chiller's big internal volume can still hold a lot of vapor, which must be recovered too.

Where is the rupture disc on a low-pressure chiller usually located?

Answer: On the evaporator

The 15 psig rupture disc sits on the evaporator to protect the shell from overpressure.