Hypothetical Plumbing Question

[marcmen]

Hi all

I have a hypothetical plumbing question.
Let’s say you have two pipes with the same pumps running at 100%

The first pipe is 10’ long and is then reduced 3/4” for 1’. It produces 100 gph. So the total length is 11’

The second pipe is 11’ of all 3/4 pipe. Will the second pipe maintain the 100 gph or will it drop?

What I am trying figure out is if running 1 inch pipe from my return when the tank has a 3/4 inlet has any flow advantages over all 3/4 pipe.

 

[Red_Beard]

That is a good question and i am going to watch and see what others say. But, from the way i understand it, pump flow/ head is a property of velocity, and that the 11 feet of 3/4 is going to create more drag and reduce velocity. That said, my fluid dynamics studies were more focused on air and ducting.

 

[Red_Beard]

Found a quick read if you are interested:
https://www.marchpump.com/blog/pipe-length-diameter-requirements/

"""
Pipe Diameters for Different Pump Systems

Friction loss rises or falls based on a number of factors. For instance, let’s say that you have three sections of pipe that all share the same diameter, but they all have different lengths. As you might expect, the required PSI rises as the length of the pipe grows. That’s because the friction increases as the liquid comes into contact with more surface area over time.

That makes sense to a lot of clients. However, sometimes the rules that govern pipe diameter surprise them. Many seem to think that a smaller pipe requires less energy when it comes to moving a fluid. The opposite, though, is true. Pipes with larger diameters lead to lower PSIs, whereas smaller pipes generate far greater PSIs.

Let’s illustrate this with an example. Suppose you have two different pipe systems, both seeking to move 15 GPM through 200 feet of pipe. One system uses 1.5” PVC and requires a PSI of 2.2 to achieve its goals. But the second system that employs a pipe with a half-inch diameter? Its PSI would be a whopping 610.

It’s not hard to see why this is the case once you reconsider the idea of friction loss. In a pipe with a smaller diameter, more of the liquid comes into contact with the pipe’s interior surface area, slowing it down. That requires more output from the pump to make up the difference. In a larger-bore pipe, less of the fluid rubs up against the pipe and thus drops in velocity, requiring less energy.

Of course, you can alter the pipe diameter flow rate, and trying to calculate pipe size from flow rate always makes sense when attempting to construct the most efficient pump system for your end use. In fact, there are several rough rules of thumb that you ought to consider when determining pipe diameter, length, and arrangement. """

 

[marcmen]

Found a quick read if you are interested:
https://www.marchpump.com/blog/pipe-length-diameter-requirements/

"""
Pipe Diameters for Different Pump Systems

Friction loss rises or falls based on a number of factors. For instance, let’s say that you have three sections of pipe that all share the same diameter, but they all have different lengths. As you might expect, the required PSI rises as the length of the pipe grows. That’s because the friction increases as the liquid comes into contact with more surface area over time.

That makes sense to a lot of clients. However, sometimes the rules that govern pipe diameter surprise them. Many seem to think that a smaller pipe requires less energy when it comes to moving a fluid. The opposite, though, is true. Pipes with larger diameters lead to lower PSIs, whereas smaller pipes generate far greater PSIs.

Let’s illustrate this with an example. Suppose you have two different pipe systems, both seeking to move 15 GPM through 200 feet of pipe. One system uses 1.5” PVC and requires a PSI of 2.2 to achieve its goals. But the second system that employs a pipe with a half-inch diameter? Its PSI would be a whopping 610.

It’s not hard to see why this is the case once you reconsider the idea of friction loss. In a pipe with a smaller diameter, more of the liquid comes into contact with the pipe’s interior surface area, slowing it down. That requires more output from the pump to make up the difference. In a larger-bore pipe, less of the fluid rubs up against the pipe and thus drops in velocity, requiring less energy.

Of course, you can alter the pipe diameter flow rate, and trying to calculate pipe size from flow rate always makes sense when attempting to construct the most efficient pump system for your end use. In fact, there are several rough rules of thumb that you ought to consider when determining pipe diameter, length, and arrangement. """

Wow, that was a great reply. Thank you.

 

[KStatefan]

At 100 gph it will not make much difference since the velocity is low in both sizes. As you increase flow the difference will grow. You can use a headloss calculator to get some estimates.

 

[Red_Beard]

should ask also though, what is the output size of the pump? And how many of those feet are vertical? That is also going to make a big difference, as oversizing (especially)a vertical pipe also has a negative impact on velocity. From the flow calc @KStatefan posted the velocity of the 3/4 is 1.02fps and the velocity of the 1 is only .63fps. Velocity is a big part of what makes up max head height for your pump.
usual quick dirty pipe sizing method, especially in reef returns because they are pretty strait forward is match pipe diameter to pump discharge diameter.