required a good example for this

Take an ordinary water faucet. Open it just a little bit (that, is, the orifice is small) and notice the water sprays out at a fairly high pressure.

Now, without changing the faucet, connect a water hose to the faucet and go look at what comes out the end. What is the pressure?

volume increase but force (or pressure) is decreased.

Depends on the flow.

If there is NO flow, the pressure (ignoring head pressure) will be the same throughout the pipe system regardless of size!

If there IS flow, the pressure will vary dependant on local orifice size (of pipe). Generally, the higher the velocity, the lower the pressure!

Why aren't there Bad Answer points? I should get one for mixing up pressure and velocity heads. Duh! Anyway, OP, ignore my answer. 'Twere completely wrong.

The larger your pipe, the less restrictions there will be on the fluid. Pipe works depends on what you need in flow and mass of your fluids. If you have a 6"/ ~150mm ID pipe, your are moving 150 glns/ ~567ltr per minute, depending on the actual pump being used, you will have XX amount of flow pressure.

Now take this very same amount of fluids and it moves to another part of your production feed line, this fluid is now diverted to a larger pipe, lets say a 12"/ ~300mm ID pipe as a final feed line to your processing. Your feed line has other smaller pipes entering at various points too. This is a batch feed line with all the chemical lines converging into one final pipe before entering the batch vessel.

The pressure from the 6" line will only be the same up to the conversion of the two lines, being 6" to 12". Once it reaches this point, the volume will be the same in the 6" pipe as a constant, then when it reaches the 12" pipe, the pressure will drop due to volumetric space change. The flow rate will still remain constant, but the pressure will drop because there is no constraints on the fluid being moved in your process.

Now if you were to take this very same fluid feed and reduce the line from 6" to 4", your head pressure will increase and the rate of feed will change as well. This is the cause and effects of reducing your line size, which in turn bottle necks the fluid flow at this very junction. There is a formula for differential pressure calculations and I am still half asleep while writing this blurb.

Overall answer; if you change size of pipe only, the transition from small pipe to larger pipe area, your flow remains the same at the pump with the volume, but once it enters the larger space the pressure will drop from less constrictions.

And the opposite is the same from large pipe to smaller pipe. The constriction of ID will increase the volume pressure on the same flow rate. Which in turn, over a period of time, will ware your pump down sooner when forcing your fluids through a smaller pipe then the actual size of the pump head.

Good luck, its like putting your thumb on the end of a 1/2" garden hose, you block the output oriface to raise the out-put pressure.

Maximo

I have written a response to a similar question earlier regarding the pipe into which a pump is pumping. The link below will take you to that thread and my response was #10. It is of interest to this thread as well for the following reason:

The piping and valves and related items into which a pump delivers its medium is called the "system". Every pipe, valve, strainer, elbow, tee, etc. through which the medium passes exerts its own "backpressure" (expressed as feet of head) on the pump's attempts to deliver its medium. So, when you say that a pump is pumping into a "system" that consists of, say, 275 feet of 4" PVC pipe entering a 6" Ductile iron pipe that is 750 feet long, and there is a gate valve in the 4" line and a strainer in the 6" line and there are 3, 90º elbows in the 4" line, this describes the "system". The only remaining consideration is the elevation difference; the "static head".

So a close and not concise answer can now be drawn from the instructions I used in the link, although I did not reference the strainer, elbows and valves. However, using the information that IS contained in my example, one can determine the flow that will be discharged from the end of the 6" pipe using a certain size centrifugal pump whose characteristic curve is available and can be consulted.

A whole new set of parameters arises if the pump happens to be a gear pump, lobe pump, plunger pump, diaphragm pump or any number of other "positive displacement" pumps whose discharge ability is unchanged with changes in the "system" head as long as sufficient horsepower is supplied to maintain the pump speed and flow. These, too, can be calculated using the information in my thread, except, in the case of these positive displacement pumps, it is necessary to consult the engineering data for the proposed pump and determine the flow you want and the head you anticipate and the manufacturer's literature will tell you which pump and the SPEED that the chosen pump must run to accomplish the task.

You see, this is not a short and easy answer to a short and easy question. What I have stated here still leaves many unanswered questions, but it may trigger some investigation by the questioner to find the correct answer to HIS question. As some have said, the pressure as the medium enters the larger pipe will be less than in the smaller pipe. However, let's assume the lengths I have used above. The conjunction of the two pipes is 275 feet away from the pump. So, according to what I just said, the pressure at 276 feet would be less than in the 4" pipe. That is true, but if the 4" pipe is 285 feet long, the pressure at 276 feet would STILL be less than at 275 feet. That is because there is additional friction loss at the next foot mark, and the next, and the next, etc. That is due to the increase friction loss.

It only gets worse. There are more considerations, but you get the idea, and the question is answered without explanation YES. The pressure decreases. Whew!!!

So Sorry. In my haste, I forgot the link.

http://cr4.globalspec.com/thread/22443?frmtrk=cr4sd#newcomments

in gases this is called the joules thomson effect, and is what happens in the nozzle of a Co2 fire extinguisher, as sophomore chemistry students we employed this to good effect to chill warm beer.

http://www.earlham.edu/~chem/chem341/c341_labs_web/joule_thomson.pdf

http://www.chem.arizona.edu/~salzmanr/480a/480ants/jadjte/jadjte.html

http://encarta.msn.com/encyclopedia_761563758/cryogenics.html

Essentially the same thing in liquids well, cryogenic liquids... poster didn't specify...

(I'm feeling a bit frisky to day)

milo

Is it gravity feed or pumped liquid.

Gravity feed will remain constant.

Pumped liquid will depend on the pump switching or pressure setting.

The pressure reduces along any piece of pipe in the direction of flow, due to friction at the pipe wall. Change the pipe size at any point and it introduces some turbulence, which manifests itself as a loss of energy from the fluid. So the simple answer is, "yes, a little more than would be the case if the pipe size remained constant".

What about Bernoulli???