I have not seen U-571, but let me take a shot at answering your question. I am not sure what you are referring to when you say "salvage system". Compressed air was stored in tanks on a U-boat for the purpose of blowing sea water out of the ballast tanks. Replacing the water in the ballast tanks with air makes a submarine lighter and causes it to rise toward the surface while submerged. There is only so much compressed air available for blowing water out of ballast and other tanks. The U-boats (like virtually all other submarines) had air compressors on board which were used to replenish the compressed air supply while they ran on the surface. The main air compressor was manufactured by Junkers and was operated by its own diesel engine. There was also an electric powered air compressor. In addition to blowing water out of the ballast tanks, compressed air was also used to start the main diesel engines and to launch torpedoes.
Hope this helps.