What can cause back pressure in a plumbing system?

Back pressure occurs when the pressure in a plumbing system exceeds the pressure of the fluid being moved through it, often caused by mechanical means. This can happen when pumps or other mechanical devices exert pressure in the system, creating a situation where fluids are forced in the opposite direction or where they can't flow freely due to increased pressure. Essentially, mechanical devices can actively push against the natural flow of water, leading to back pressure situations.

Additionally, while improperly installed vents, excessively high water temperatures, and low water levels in tanks can create various plumbing issues, they do not specifically generate back pressure in the same way that mechanical means do. For example, improperly designed vent systems primarily lead to inadequate drainage or siphoning effects rather than directly causing back pressure. High water temperatures might impact the pressure within a system, but it doesn't fundamentally create back pressure like a mechanical pump or compressor would. Low water levels can affect the flow rate but do not inherently create pressure that would push against the flow. Hence, the mechanical means creating pressure is the most accurate answer in the context of causing back pressure in a plumbing system.