What is the difference between hydrotest & pneumatic test

How long should hydrotesting/pneumatic testing be

Please keep similar questions or related ones on one question, I have merged your questsions

It means testing with Fluids or gas. It also depends on what your testing. Sewer, plumbing, hvac, hi vacuum systems, chiller loops and code requirements.

in hydro we r using fluid for making pressure
bt in pneumatic we r using gas/air

generraly hydrotest is carried out for checking integrity of job as well as leaks
bt pneumatic is only for leak detection here we can't check integerity

if u want to know more details refer ASME section III NB 6112.1

How long should hydrotesting/pneumatic testing//

Dats depend upon the manufacturer spec
Otherwise follow your CODE