Subject: Fluid pressure in a tube of variable diameter

When sending a pressurized fluid through a tube that begins with a small 
diamter, is increased and then reduced, is the exiting pressure/volume the same 
as the input volume/pressure?

Working example: 
Tube begins as 3mm ID, pressure is 150psi After a length of 5 cm the tube 
becomes 5mm ID for a length of 100 cm Then the tube thins back to 3mm ID for a 
length of 10cm.

This is not a homework question. But to help I wil clarify what I don't 
understand.

If a fluid enters a tube with a fixed velocity and pressure, why is it possible 
to leave the tube with a different pressure if no fluid loss has occured? 
further by having a variable diameter tube as I understand it I cause the 
pressure/volume to switch from hi/low to low/high and then back again. If this 
tube was a part of a machine pumping a fluid with lets say .50 microsecond 
bursts. What would be the difference between a 1m pipe of constant 3mm diameter 
against a pipe of 3 and 5mm diamaeter, so long as the in and outlet were of the 
same internal diameter? 

I have tried to follow Bournellis equation but I get confused with changing the 
diameter, further in my research I came across mention of pressure waves 
tavelling backwards in a pressurized fluid when the diameter of the tube it is 
travelling through changes. It was at this point that I raised the question as 
I became then totally confused and worried I was trying to make the problem too 
difficult.


Thanks in advance

Tim Russell

Re: Fluid pressure in a tube of variable diameter