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Compressors have bleed (unloader) valves to remove pressure over the piston to facilitate easier motor start when the low pressure set point turns the compressor back on. Turbine compressors have a bleed function to eliminate back pressure and pressure fluctuation, similar in concept to the unloader valve of piston compressors.
The Air Brush industry seems to use the term bleeder valve to refer to the ability of the air pressure regulator to bleed off any downstream pressure back through the regulator should that downstream pressure ever exceed the regulator set point. Most general purpose regulators are set up to bleed to atmosphere anytime there’s back pressure to the regulator from the end tooling.
You can purchase compressed air regulators that don’t bleed. These are commonly used when the compressed gas being used is expensive (you don’t want it voiding to atmosphere ever) or when the compressed gas if flammable or toxic. You don’t want them bleeding to atmosphere through any orifice for obvious reasons.
Since your question is a bit general, I’m not quite sure if I’ve targeted the question correctly, or provided the right answer.
I think what they are talking about is the on off switch. Internal would be fully automatic and self is you turn on the unit to use it and turn off when you are done. But don’t walk away and leave as the compressor might not shut off.
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