I'm thinking this is homework. It looks just like the rest of your posts. All of which are very elementary questions about pressure vessels. My guess is that the term started about 3 weeks ago. That would roughly coincide with the date of your first question.
It's interesting to note that at least one of your posts was closed by admin. and labeled as homework!
Ok you are honest. Pressure Vessel does not generate pressure but pressure is introduced into it to with stand. Go to your mom's kitchen and take out the "pressure cooker" - thats an elementry vessel if you say. By itself it will not generate pressure unless you put inside something and give heat. Similarly an industrial pressure vessels can be something to take in heat steam(direct/indirect)/ or thermal oil(indirect) inside can be any product and the vessel is designed to with stand the input pressure.
A Compressor or a Pump Receiver can be also pressure vessels where they are pressure tested 1.5 times the operating pressure and stamped for safety.
Now please read your books.
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ya thnx a lot ....... i was also thinking on same lines.......... Pressure vessels are used to store many components i.e LPG , CNG , Liquids ......... Pressure Vessels can have high internal pressures and can have low internal pressure depending upon the type of fluid in it ............ Some pressure vessel have very low internal pressure becoz they are just stored in ambient temp............and are called Storage tanks...................