Definition - What does Back Pressure mean?
Back pressure refers to pressure opposed to the desired flow of a fluid in a confined place such as a pipe. Back pressure is not pressure traveling in the opposite direction, it is actually the remnants of pressure in the desired direction of movement.
Back pressure has a similar meaning of pressurized obstruction when used regarding drilling, rehabilitation methods, or installing pipe.
Trenchlesspedia explains Back Pressure
Back pressure may be caused by bends in the system, a reduction in diameter, obstructions, or a combination of these factors and others. Due to air resistance and molecule friction, the build-up of pressure reduces flow. This forces any additional pressure to meet a continued back up of pressure. In order to remedy the issue, force must be applied in the same direction.