Just had my rack and power steering pump replaced. Had a screaming pump and a leaking rack. I noticed before my leak got to bad, that after my car had warmed up, then you take the power steering reservoir cap off, there is a little puff of pressure inside. Of course the new pump didn't come with a new cap, so I still have the same condition. The Cap itself has a spring at the top, but I am not sure of its function. Is this system designed to have a small amount of pressure, or Is this cap supposed to vent, and keep the reservoir at 0 psi. I have found many conflicting opinions on this. Any Ideas here?