# Thicker pipe, more pressure?

1. Aug 2, 2012

### eddiej90

Can someone explain to me why a thicker pipe would have a higher pressure than that of a thinner pipe with the same mass flow rate?

Surely the thinner pipe would have a higher pressure?

2. Aug 2, 2012

3. Aug 2, 2012

### HallsofIvy

What do you mean by a "thicker pipe"? If pipe "B" has the same outer radius as pipe "A", but thicker, then it will have smaller inner radius and, by Bernoulli's principle (voko's link), have greater pressure. Of course, if a thicker pipe will withstand a greater pressure before bursting.

4. Aug 2, 2012

### eddiej90

Sorry, my bad terminology letting me down there. One pipe has a larger inner diameter than the other.

Thanks

5. Aug 2, 2012

### Staff: Mentor

There is no fixed relation between pressure and flow. If you combine both and let the same stuff flow through both pipes, you can see a pressure difference.

Think of it like this, with a flow thick pipe -> thin pipe: The material has to increase its velocity at the boundary (as you have the same flow in both pipes). This requires an overpressure in the thick pipe. In the reversed flow direction, the material does slow down, this corresponds to a higher pressure in the thick pipe, too.

What you probably mean is the pressure drop per length in the pipes: This is lower in the thicker pipe, as the resistance to flow is lower there.