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Someone else has asked this question but the answer just says that it regulates the pressure of hot air, and I don't understand what that means. Does "hot air pressure" just mean "hot air"?

So I've been learning about an Airbus A320 and its air conditioning system and I'm wondering what's the point of the hot air pressure regulating valve? Why can't bleed air, which is hot compressed air, be used as hot air? Send some of the hot compressed air to the packs and some hot compressed air to the trim air valves to heat the air from the mixing unit.

Please explain what is the purpose of the hot air pressure regulating valve and even what it is. What's even the purpose if you have bleed air? Please don't tell me that the hot air pressure regulating valve regulates the pressure of hot air, I already know that. I just want to know why it is generating hot air pressure, why not just hot air? Or is hot air pressure the same thing as hot air?

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  • $\begingroup$ "Why can't bleed air, which is hot compressed air, be used as hot air?" Because bleed air comes directly from the compressor section, at temperatures around 250°C (482°F). Turning the cabin heat on would result in 100+ passengers experiencing the face-melting scene from Indiana Jones Raiders of the Lost Ark. $\endgroup$
    – Ron Beyer
    Apr 19, 2017 at 19:00

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The hot air pressure regulating valve does not generate hot air. The hot air is generated from the engine bleed air.

But that air does not go straight from the engines into the cabin, it would be too hot. If you want to adjust the temperature, you need a way of limiting the amount of hot air going into the cabin. That is what the regulating valve does (in conjunction with a couple of other components).

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  • $\begingroup$ So what would happen if Hot Air regulating valve is inoperative in closed position? How does the system adjust the temperature? Does the pack control its outlet temperature? $\endgroup$
    – dingdingdong
    May 15, 2020 at 6:13

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