Tube ID vs Pump head

[Andrew]

How does tube ID change the head flow of a pump?
Or to put it another way:
If I have two pumps both of which have a 3/4" discharge. On one I put a 3/4" tube going straight up and on the other I reduce it to 3/8" and put a 3/8" tube also going straight up. Which tube would have the highest water level?

Does the amount of water (alot more water in 3/4" vs 3/8") that I am trying to push up change the height that can be achieved?

[moonlightcheese]

head flow? i think you mean head pressure? as the ID gets smaller the restriction increases. therefore the pressure increases and decreases flow.

the 3/8" will have the highest discharge because the velocity of the water is higher than that of the 3/4" tube. the 3/4" tube will have higher flow because there is less to restrict the amount of water going through the tube. that help?

[Andrew]

Very true, I misspoke. I did mean head pressure.

So the water will be higher in the 3/8" tube? The reason that I ask is because of the massive bong that hooter'Tbc is building.
http://www.xtremesystems.org/forums/attachment.php?attachmentid=39772

Would it be better to have 3/4" tubing going up and out of the bong or 1/2"? Which would work better with that much vertical rise? It just got me thinking and that is always a bad idea ;) so I figured I would ask.

[moonlightcheese]

i see no reason to restrict the loop simply to add height to the discharge of the water. if you just run the tube up the side of the bong i would think that'd be sufficient. but then i'm not the expert on bongs. NoL should chime in here anytime now lol.

[Andrew]

The water blocks are going to all be 1/2" so there will be restriction anyway. The real queston is what does 3/4" vs 1/2" tubing do to the pumps ability to push the water up from the floor?

[Cathar]

Tubing ID has no impact on static vertical pushing capability.

It will impact how much resistance the pump encounters when trying to push flow through the tubing, and this resistance is independent of the orientation of the tubing (flat/vertical/angled/whatever).

[Andrew]

So the extra weight of the water in a 3/4" pipe vs a 1/2" pipe does not impact the pump? Hmm.. that doesn't seem right. I think I am missing something. Can you explain a bit more? Maybe a definition of static vertical pushing capability as opposed to flow, etc.

[Andrew]

Any enlightenment for me?

[MaxxxRacer]

theoreticall your tube could be 1 foot diameter or 1mm diameter and the pump would get the waater to the same height.. granted it would take alont longer to fill up the 1 foot diameter tube than it would to fill the 1mm, but u get the idea.

this is assuming that there are no frictional forces from the tubing itself. In real world apps, the surface of the tubing has friction and it will degrade ur flow the smaller u go.

so if u want the best flow, just slap a gigantic 5/8" ID or even 3/4" ID tubing on the bong.

the laminar flow of the water in the tubing gets more prominent as the diameter gets larger, thus lowering the friction from the walls (the water at the inside of the walls of the tubing is moving at a much lower rate)

anyway thats the jist of it. there are some more details that i wont go into merely because i dont feel that its neccesary, nor do u really care (i dont think anway)

[PorkchopExpress]

theoreticall your tube could be 1 foot diameter or 1mm diameter and the pump would get the waater to the same height.. granted it would take alont longer to fill up the 1 foot diameter tube than it would to fill the 1mm, but u get the idea.


That isn't true (at least not in the context it sounds like you meant). In your example, the water would reach the same height in both sizes. That isn't true because the pressure from the larger diameter tube would affect the pump differently. The same volume would amount to the same pressure (taking account for the different shaped tubes), but not the same height (in fact the height is irrelevant.)

EDIT: after reading the ENTIRE thread, I have a feeling of what was meant. If your entire loop stayed the SAME length but the tubing size increased, the flow rates would decrease (as volume increased)... However, this is irrelevant of tube placement, as pointed out by Cathar.

[Andrew]

Thanks guys. That clears up my questions quite a bit. Still not sure why the weight of the water in the larger pipe is not a factor but I will take your word for it.

Maybe I should go and brush off the cobwebs on one of my old physics books. They have not been opened in many years ;)

[PorkchopExpress]

It is the volume of the water that is a factor. A 10ft loop with 3/8" tubing is going to have less water than a 10ft loop of 1/2" tubing. This means the flow rates for the 1/2" tube is going to be slower because the pump can only move a set amount of water (in practice, pumps are powerful enough to make it negligible).

The "weight" of the water WOULD be a factor if you were simply firing water into a vertical tube (not a closed loop)

If you had 2 vertical tubes going 10 feet in the air, one 2" and the other 1" diameter, the head pressure would remain constant, meaning there would "appear" to be less in the 2" tube (when realistically the volume would remain the same because its wider).

So, if you wanted to get 10ft high in both the 2" and the 1" tubes, you'd have to have a more powerful pump on the 2" tube.

Remember that water cooling entails a closed loop, meaning whatever the position of the components, the volume of water stays the same.

Hopefully that clears it up a tad.

[MaxxxRacer]

pork chop you are completely wrong.

if a pump has a head pressure of 7ft, it could fill up a lake full of water 7 feet high, or a 1/2" piece of tubing 7ft high.. that is a principle of phsyics. it may seem a bit wierd, but that is FACT.. u can try it urself (with more reasonable sizes of course)



If your entire loop stayed the SAME length but the tubing size increased, the flow rates would decrease (as volume increased)...

this is FALSE!!!. The water VELOCITY in the tube would decrease but the overall flowrate at a given point would NOT decrease, infact it would INCREASE due to their being less restrction... please get your facts straight before you open ur mouth.


http://www.mcnallyinstitute.com/CDweb/p-html/p033.htm

if u look at those calculations you will see absoltuely no consideration for tubing size as it doesnt f'ing matter.



It is the volume of the water that is a factor. A 10ft loop with 3/8" tubing is going to have less water than a 10ft loop of 1/2" tubing. This means the flow rates for the 1/2" tube is going to be slower because the pump can only move a set amount of water (in practice, pumps are powerful enough to make it negligible).

completely false!! this is a closed loop system. so the same volume of water is coming "down" as is going up.. its balanced.


The "weight" of the water WOULD be a factor if you were simply firing water into a vertical tube (not a closed loop)

again, the weight of the water does NOT NOT NOT matter...

[shimmishim]

lol, this discussion reminds me too much of my fluid dynamics class.. ugh...

:)

[MaxxxRacer]

well thats what this is...

[Bloody_Sorcerer]

actually, maxxx, this particular system is an open loop; its a bong. Less water is coming down than is going up :)

[PorkchopExpress]

First off, calm down down there, cowboy :)

I never insulted you or anything like that, so no reason to get angry.

Secondly, the example I used was an open system, where water pressure would have a direct impact on the on pump performance. You'd have to imagine that the pump is getting the water without any additional pressure from behind the pump. The pumps performance does not increase. It has a set amount for flow rate. The gravity of the water would affect the backpressure on the pump.

Third, as for the flow rates in a static system with different sized tubing, you are correct. That was wrong of me to post. Larger surface area of tubing, more volume of water, however the actual FLOW rate of the water remains constant, and is only affected by the friction of the tubing. It was late when I posted that. I should have clarified the difference and not lumped the different variables into one "this would happen".

[MaxxxRacer]

lol bloody.. u got me there. but i was speaking of regular w/c'ing systems.


the example I used was an open system, where water pressure would have a direct impact on the on pump performance.

I am not following. which pressure do u mean? the back pressure on the inlet of the pump (which will generally be 0 or negative unless something other than the pump is feeding the water back into it)


The gravity of the water would affect the backpressure on the pump.

again to clarify, which water do u mean?



btw, sorry i snapped. I just cant stand it when ppl post false information on the forums. Most people think almost anything they read is fact and will then go off the false information, thus confusing the hell out of them when they talk to someone who does know the facts. And then the person wtih the facts will have to reteach it to them. To make matters worse this person who is confused will fight to the death for their previous beliefs.. I have encountered this time and again on the forums... drives me nuts.

[PorkchopExpress]

NP man... These forums are a great place to learn. Another thing, if I've posted something that I have believed correct, but is actually false(which almost never happens, :P ), I'll be the first to admit I was wrong... That's simply how we learn.

As for clarification, in my first post to OP, I was simply trying to illustrate the difference that would be encountered with an open pool of water (without a vacume or equal pressure behind the pump) to a closed water cooling system (PC, car, whatever), and how gravity (what he was referring to as "weight") no longer has affects on the performance of the pump, since the entire loop is equal (IE there is as much force behind the pump as there is in front of it).

Somewhere around my 2nd or 3rd post we completely got off the OP's topic. In my 2nd post I posted this-

"The "weight" of the water WOULD be a factor if you were simply firing water into a vertical tube (not a closed loop)"

I should have qualified my statement additionally by saying there was no vacume behind the pump, and it was simply the pressure of the volume of water vs. the pressure put out of the pump.

We were simply speaking in different contexts.

The one thing I am still not quite certain on, however, it this- The water VELOCITY in the tube would decrease but the overall flowrate at a given point would NOT decrease, infact it would INCREASE due to their being less restrction...

How would the water velocity descrease, yet the overall flowrate increase when it's a static system so the overall rates have to stay constant?

[MaxxxRacer]

The one thing I am still not quite certain on, however, it this- The water VELOCITY in the tube would decrease but the overall flowrate at a given point would NOT decrease, infact it would INCREASE due to their being less restrction...

How would the water velocity descrease, yet the overall flowrate increase when it's a static system so the overall rates have to stay constant?

The flow rate would increase as the tube diameter increases merely becuase there is less friction from the tube walls.. thats all. The velocity in the tube would decrease becuaes the cross sectional volume of a n lenght section of tube would be larger than that of a smaller tube. hence lower velocity.

think of a garden hose.. an unrestricted garden hose doesnt shoot the water very far.. this is because the cross sectional area the water is flowing out of is relatively large.

now imagine the same garden hose with a sprayer attachment. the water will now shoot upwards of 20 feet. this is ude to the decrased diamtere of the tube. the overall flow rate will decrease due to the higher restrciction, and the water velocity at the output of hte sprayer will dramatically increase due to the smaller diameter.





"The "weight" of the water WOULD be a factor if you were simply firing water into a vertical tube (not a closed loop)"

I should have qualified my statement additionally by saying there was no vacume behind the pump, and it was simply the pressure of the volume of water vs. the pressure put out of the pump.

in this scenario, the water would reach the height of the max head pressure of the pump. this is assuming that we are at sea level as at higher altitudes there is less gravity and thus less pressure bearing down on the pump from the water.

BUT what i dont think you understand is this. at a 10 foot depth, the water presssure is the same weather your in a 10 foot tall cylinder of water that is 1 foot in diameter, or at 5 foot depth of a swimming pool. so you see the volume of water does not matter with regards to pressure, only the depth. this can easily be shown with a little calculus. (which i dont happen to remember off hand)

[PorkchopExpress]

think of a garden hose.. an unrestricted garden hose doesnt shoot the water very far.. this is because the cross sectional area the water is flowing out of is relatively large.

Cool, got it.




BUT what i dont think you understand is this. at a 10 foot depth, the water presssure is the same weather your in a 10 foot tall cylinder of water that is 1 foot in diameter, or at 5 foot depth of a swimming pool. so you see the volume of water does not matter with regards to pressure, only the depth. this can easily be shown with a little calculus. (which i dont happen to remember off hand)


That wasn't the example I was using for the OP, but I got what you're saying... and I do understand pressures brought on by depth.

Again, I was referring to the pressure that would have been placed upon the pump in a vertical situation with no pressure behind the pump. The more water, the more pressure... That was my point, and that is correct. :)

[MaxxxRacer]

Again, I was referring to the pressure that would have been placed upon the pump in a vertical situation with no pressure behind the pump. The more water, the more pressure... That was my point, and that is correct.

yup... just need to stipulate that the pressure is coming from the vertical height of the water, and not by the actual amount of water.

[Andrew]

Wow! Thanks guys. Your talking has brought back my physics memories. I had never actually thought about the factors in an open system (even though I had created a couple). The only things that really get talked about here are closed loop systems since they are in the majority. It is all clear now.

Thanks again

[hooter`Tbc]

HHMM. It is kind of odd to find pics of my den in places I didn't put them, although from reading the argument it caused, its worth it. Making people think is fun.

Looking at that pic again, I can see one of my case fans is going out. The fan right below my PSU is spinning like mad but the next one down isn't. So, I will run my tubes through that spot when I take it out.

I picked up some copper fittings to make a reducer, I am thinking of putting the reducer in the case wall and running 3/4 to the case, and 1/2 from there on. I think that will be easier than drilling and retaping the Swifty Apogee for 3/4 inlet and 1/2 outlet... unnless someone has a link to a reducer fitting that will work with that block... :stick:


::EDIT:: Just to be clear, is pump head in a submersible system measured from the pump, or from the surface level of the water it is under? My pump is gonna have almost 3 feet of water over it's outlet but that won't help the measurable head will it? :confused:

[Andrew]

The pump head is measured from the pump, and having the pump submerged will help. You don't want to starve the pump. The more water you can get into the pump the better... up to a point. On my current system I am only using 3/8" tubing from the pump to the blocks but I have 3/4" feeding the water to the pump. It almost acts as a res.