Does a pump face less back pressure if a vertical pipe is wider?

• Ray F
Ray F
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I've worked at sea for a number of years and now I'm particularly interested in learning more about fluid dynamics in order to find practical solutions to environmental problems. I would be very grateful for any advice people on this forum can give me.
At the moment I want to pump water up to the roof of a house. My question is this: will a pump that pumps water 10 meters up a vertical pipe of 10 mm Inside Diameter face less back pressure pumping the same water 10 meters up a pipe of 20 mm Inside Diameter? Or is the back pressure the same? Thank you for your help.

Ray F said:
How did you find PF?: google search

I've worked at sea for a number of years and now I'm particularly interested in learning more about fluid dynamics in order to find practical solutions to environmental problems. I would be very grateful for any advice people on this forum can give me.
At the moment I want to pump water up to the roof of a house. My question is this: will a pump that pumps water 10 meters up a vertical pipe of 10 mm Inside Diameter face less back pressure pumping the same water 10 meters up a pipe of 20 mm Inside Diameter? Or is the back pressure the same? Thank you for your help.
At the same flow rate in each case?

It depends upon the flow velocity and perhaps the surface roughness of the pipe. Here is a good simple treatment https://en.wikipedia.org/wiki/Friction_loss
The middle part is excellent, in my opinion. Please ask questions as necessary

Welcome to PF.

Ray F said:
Or is the back pressure the same?
To pump water upwards, you must overcome both the hydrostatic pressure, and the resistance to flow in the pipe.

Hydrostatic pressure is a function of height only, not of diameter.

The added back pressure, due to the resistance to flow, is due to wall friction of the water flowing in the pipe. It will be less for a bigger diameter pipe, but that back pressure will be dependent on the flow rate and the pipe details.

Juanda, Rive, russ_watters and 1 other person
The bigger pipe will put less back pressure on the pump for the same flow.

Joe591 said:
The bigger pipe will put less back pressure on the pump for the same flow.
As demonstrated by the fact that central heating (water) central heating often uses large bore pipes (according to a number of rules of thumb) according to the flow of water they need to take. I quote central heating because the system pressure is usually only a bar. Cold water supplies are straight off the mains and tend to use 15mm pipe throughout. Copper is too expensive for plumbing to be over generous with large bore pipes.

1. Does increasing the diameter of a vertical pipe reduce the back pressure on a pump?

Yes, increasing the diameter of a vertical pipe generally reduces the back pressure on a pump. A wider pipe decreases the frictional resistance and allows the fluid to flow more easily, thus lowering the overall back pressure.

2. How does pipe diameter affect the flow rate and back pressure in a vertical system?

A larger pipe diameter typically increases the flow rate and decreases back pressure. This is because a wider pipe reduces the velocity of the fluid for a given flow rate, which in turn reduces frictional losses and back pressure.

3. Are there any limitations to reducing back pressure by widening the vertical pipe?

Yes, there are limitations. While a wider pipe can reduce back pressure, it also requires more material and space, which can increase costs and complexity. Additionally, extremely large diameters may not be practical or necessary for the system's requirements.

4. How does fluid viscosity impact the relationship between pipe diameter and back pressure?

Fluid viscosity plays a significant role in determining back pressure. Higher viscosity fluids experience greater frictional losses, so increasing the pipe diameter can be particularly beneficial in reducing back pressure for viscous fluids. Conversely, for low-viscosity fluids, the impact may be less pronounced.

5. What other factors should be considered when designing a vertical pipe system to minimize back pressure?

Other factors to consider include the length of the pipe, the roughness of the pipe's interior surface, the flow rate, and any bends or fittings in the system. All these elements can contribute to frictional losses and back pressure, so they should be optimized alongside pipe diameter to achieve the best performance.

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