oil cooler question

[tmontague]

Quick question that I couldn't find answered anywhere on the internet.

How does an aftermarket oil cooler have oil flow through it if a sandwich plate is use to access the oil?

Both holes in the adapter would be equal pressure so would the oil not just fill the oil cooler and then stay stationary? From my understanding one side would have to have higher pressure then the other for the oil to continuously flow through and for it to be effective.