How much resistance does one 3" 90-degree elbow have in equivalent length of 3" pipe?

The concept of equivalent length is crucial in understanding how different fittings, such as elbows, impact the flow resistance in a piping system. For a 3" 90-degree elbow, industry standards provide a way to quantify this resistance by equating it to a straight section of pipe of the same diameter.

When discussing equivalent lengths, what we are attempting to do is express the resistance of a fitting (in this case, a 90-degree elbow) in terms of a length of straight pipe. This is particularly important for accurate calculations in fluid dynamics and piping design, particularly when assessing the overall pressure loss due to fittings.

A 3" 90-degree elbow typically has an equivalent length of about 5 times the diameter of the pipe, which in this instance translates to 5 inches. Therefore, expressing the resistance of the elbow in terms of straight pipe length leads us to conclude that a 3" 90-degree elbow has an equivalent resistance of 5 inches of straight 3" pipe.

The other available choices do not align with commonly accepted values in the industry for resistance involving a 90-degree elbow, which is why they are not the correct answer. Choosing 5 inches accurately reflects the significant impact that such a fitting can have on the hydraulic