Back pressure

From Wikipedia, the free encyclopedia
Jump to: navigation, search

Back pressure refers to pressure opposed to the desired flow of a fluid in a confined place such as a pipe. It is often caused by obstructions or tight bends in the confinement vessel along which it is moving, such as piping or air vents.

Because it is really resistance, the term back pressure is misleading as the pressure remains and causes flow in the same direction, but the flow is reduced due to resistance. For example, an automotive exhaust muffler with a particularly high number of twists, bends, turns and right angles could be described as having particularly high back pressure.[1]

Back pressure in automotive (four-stroke engine) exhaust[edit]


Back pressure in two-stroke engine exhaust[edit]

In a piston-ported two-stroke engine however, the situation is more complicated due to the need to prevent unburned fuel/air mixture from passing right through the cylinders into the exhaust. During the exhaust phase of the cycle, back pressure is even more undesirable than in a four-stroke engine due to the shorter time available for exhaust and the lack of pumping action from the piston to force the exhaust out of the cylinder. However, since the exhaust port necessarily remains open for a time after scavenging is completed, unburned mixture can follow the exhaust out of the cylinder, wasting fuel and increasing pollution, and this can only be prevented if the pressure at the exhaust port is greater than that in the cylinder.




Back pressure in information technology[edit]

The term is also used analogously in the field of information technology to describe the build-up of data behind an I/O switch if the buffers are full and incapable of receiving any more data; the transmitting device halts the sending of data packets until the buffers have been emptied and are once more capable of storing information. It also refers to an algorithm for routing data according to congestion gradients (see Backpressure Routing).[2] [3]

See also[edit]


  1. ^ Muffler at How Stuff Works
  2. ^ L. Tassiulas and A. Ephremides, "Stability Properties of Constrained Queueing Systems and Scheduling Policies for Maximum Throughput in Multihop Radio Networks, IEEE Transactions on Automatic Control, vol. 37, no. 12, pp. 1936-1948, Dec. 1992.
  3. ^ L. Georgiadis, M. J. Neely, and L. Tassiulas, "Resource Allocation and Cross-Layer Control in Wireless Networks," Foundations and Trends in Networking, vol. 1, no. 1, pp. 1-149, 2006.