Flow, pressure, and pipe diameter?

In summary, the conversation discusses the approximate flow rate in gallons per minute (gpm) through two lengths of pipe with different diameters. While the 1.25" pipe generally has a maximum practical flow of 30-40 gpm, the 10" pipe can have a maximum practical flow of 2500-3000 gpm. However, the actual flow rate can vary depending on factors such as inlet and outlet pressure, pipe material, and fluid type. The conversation also highlights the misconception that doubling the diameter of a pipe will result in a flow rate that is 10 times greater.
  • #1
davehans
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If I have water being pumped through two lengths of pipe, both at 50 psi, but one pipe is 1.25" diameter and the other is 10" diameter, approimately how many gpm will be flowing through each pipe? Thanks in advance!
 
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  • #2
There is not enough information for an answer with absolute volume, but only relative volume rate.
 
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  • #3
I can tell you that a 1.25" pipe will generally have a maximum practical flow of ~30-40 gpm and a 10 inch pipe will have a maximum practical flow of somewhere in the range of 2500-3000 gpm. However, each of these pipes can have any flow in between 0 and their maximum practical flow (and beyond, in some/many cases).

If you want to know actual flow, you need to provide more information, at least:
-inlet pressure (check)
-outlet pressure
-fittings? (valves, elbows, meters, etc)
-elevation change?
-Pipe material?
-Fluid type? (water? Syrup?)
 
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  • #4
Thanks guys. Those numbers are close enough for me to have made my point in a discussion... the point being that 10 times the diameter is NOT 10 times the flow... :-) ......especially when we already know that double the diameter is 4x the flow...
 
  • #5


I would approach this question by first understanding the relationship between flow, pressure, and pipe diameter. Flow rate, or the volume of water flowing through a pipe per unit time, is directly proportional to the pressure difference between the two ends of the pipe and the cross-sectional area of the pipe. This is described by the Bernoulli's equation, which states that as the pressure difference or pipe diameter increases, the flow rate also increases.

In this scenario, we have two pipes with the same pressure of 50 psi but different diameters of 1.25" and 10". Using the equation Q = A*V, where Q is the flow rate, A is the cross-sectional area, and V is the velocity of the water, we can calculate the flow rate for each pipe.

For the 1.25" diameter pipe, the cross-sectional area can be calculated using the formula A = π*r^2, where r is the radius of the pipe. This gives us a cross-sectional area of approximately 1.23 square inches. Plugging this value into the equation Q = A*V and rearranging for V, we get V = Q/A. Assuming the flow rate is the same for both pipes, we can set the velocities equal to each other and solve for Q, giving us Q = V*A.

For the 10" diameter pipe, we can use the same process to calculate the cross-sectional area, which is approximately 78.54 square inches. Plugging this value into the equation Q = V*A and rearranging for Q, we get Q = V*A.

Since we have determined that the velocity of the water is the same for both pipes, we can set the two equations for Q equal to each other and solve for Q. This gives us an approximate flow rate of 63.8 gallons per minute (gpm) for the 1.25" diameter pipe and 510.3 gpm for the 10" diameter pipe.

In conclusion, the larger diameter pipe will have a significantly higher flow rate of approximately 8 times that of the smaller diameter pipe, even though both pipes have the same pressure of 50 psi. This highlights the importance of considering pipe diameter in fluid flow systems, as it can greatly impact the flow rate and overall efficiency of the system.
 

1. What is the relationship between flow rate and pipe diameter?

The flow rate through a pipe is directly proportional to the pipe diameter. This means that as the pipe diameter increases, the flow rate also increases, and vice versa. This relationship is described by the Continuity Equation, which states that the product of fluid velocity and cross-sectional area is constant.

2. How does pressure affect the flow rate in a pipe?

The flow rate through a pipe is inversely proportional to the pressure. This means that as the pressure increases, the flow rate decreases, and vice versa. This relationship is described by the Bernoulli's Principle, which states that as the fluid speed increases, the pressure decreases, and vice versa.

3. Why is it important to consider pipe diameter when designing a system?

The pipe diameter plays a crucial role in determining the flow rate and pressure of a system. Using an incorrect pipe diameter can result in either an insufficient flow rate or excess pressure, which can lead to system failures. It is essential to carefully consider the pipe diameter to ensure optimal performance and efficiency of the system.

4. How does the viscosity of a fluid affect flow rate in a pipe?

The viscosity of a fluid has a significant impact on the flow rate through a pipe. Higher viscosity fluids, such as honey, have a lower flow rate compared to lower viscosity fluids, such as water. This is because higher viscosity fluids have a higher resistance to flow, which slows down the flow rate through the pipe.

5. What is the maximum flow rate that a pipe can handle?

The maximum flow rate that a pipe can handle depends on the pipe diameter, pressure, and fluid properties. It is essential to consider these factors when determining the maximum flow rate for a specific pipe. In general, larger diameter pipes with higher pressure can handle a higher flow rate than smaller diameter pipes with lower pressure.

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