Backpressure
ahd-5
noun.
Residual pressure opposing the free flow of a gas or liquid, as in a pipe or an exhaust system.
Wiktionary, Creative Commons Attribution/Share-Alike License
noun.
pressure
that is opposed to the
flow
of a
fluid
Word Usage
"Often such well head units do not have a condenser, and are called backpressure units."
suggests
acupressure