To speed up evacuation on a large system, a technician removes the schrader valve cores and connects large diameter hoses directly to the service ports. Why does that make such a difference?
Correct Answer
B) Narrow passages choke the flow of vapor at deep vacuum, so removing restrictions lets the pump move what it is actually rated to move
At deep vacuum there is very little gas left, and what remains moves lazily. The pressure difference available to push it through a hose is tiny, so every restriction matters enormously. A schrader core is a small opening with a spring behind it, and a quarter-inch charging hose is a narrow pipe. Replacing them with large-bore hoses connected straight to open ports can cut evacuation time dramatically on a large system. The pump was always capable; the hookup was the bottleneck.
Why This Is the Correct Answer
Flow at deep vacuum is limited by the conductance of the path, and conductance falls off sharply with small openings and long narrow hoses. The pump's rated capacity is measured at its inlet, so a restricted hookup means the system never sees that capacity no matter how long the pump runs.
Why the Other Options Are Wrong
Option A: It lets the vacuum pump motor turn at a higher speed than it can reach while the schrader cores are still in place restricting the flow
Pump speed is fixed by its motor and does not change with what is hooked to it, since the shaft turns at the same rate against an open port or a valve core. What the restriction limits is flow, not speed.
Option C: It keeps vacuum pump oil from being drawn backward through the hoses and into the system when the pump stops
Oil backflow is prevented by valving the system off before the pump stops and by the pump's own check valve. Larger hoses and open ports would if anything make backflow easier rather than harder.
Option D: It allows the vacuum pump and the recovery machine to remain connected to the same service ports at once
Connecting both machines at once is a hookup arrangement that has nothing to do with hose size or valve cores, and the two are used at different stages of the job in any case.
Memory Technique
Big pump, little hose, slow job. At deep vacuum the hose is the bottleneck.
Reference Hint
40 CFR 82.156 sets evacuation requirements; hose sizing and core removal are the accepted practice for reaching those levels in reasonable time.
More epa-608-type-2 Questions
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A data sheet for an unfamiliar refrigerant lists a boiling point of about fifty-five degrees Fahrenheit at atmospheric pressure. What does that tell a technician holding Core and Type II certification?
A technician holds Core, Type I and Type III certification and is sent to recover the charge from a twenty ton rooftop unit charged with R-410A. What does that combination of sections allow on this job?
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