Wide tubing for pumps inlet - does it realle metters?

Wide tubing for pumps inlet - does it really metters?

I plan my 1st WC. I hate doing things without understanding, so I started reading basic literature on hidraulics.
Vikers "Industrial Hydraulics Manual" by Sperry Rand, 'velocity in pipes' (1-19):
"Friction creates turbulence in the oil stream and of course resists flow, resulting in an increased pressure drop through the line. Very low velocity is recomended for the pump inlet line becasue very little pressure drop can be tolerated there."
I searched the explanation for why "very little pressure drop can be tolerated there", but couldn't find it in the book.

1) Why very little pressure drop can be tolerated at pumps inlet?
2) If i use 3/8'' tubing in the system, will using a 3/4'' tubing from reservoirs outlet to pumps inlet increase the flow rate in the system? (edited: i'm planning to use eheim 1250 which has 3/4'' inlet)

yes it will

there is an article somewhere around here that explains why intake benifits from larger tubes , just have to look around for it . if i find it ill link it

You can read up on "net positive suction head" and its effect on flow here:

http://www.procooling.com/articles/html/maximizing_flow_rates_with_h2o1.php

yeah thanks cpufan that was the one i was thinking of

thorilan, cpufan:
Thanks. Just what i need.

Please also take note that while it is interesting to read about centrifugal pumps and what NPSH is and how the inlet diameter can effect pressure drops you have to realize that all of these "articles" are taking about

1) more expensive pumps
2) pump for "usually" different applications
3) pumps on a much larger scale

I am going to suggest that if you have, for example, an eheim 1250 that has a normal inlet of 5/8" that if you use a 1/2" barb for the sake of easily connecting up you system that you are really not going to loose any performance.

If you look at this artical that is referenced http://www.cepmagazine.org/pdf/050252.pdf and by looking at the 2 graphs on it you will see that our little Hydors and Eheims are practically at the 0,0 gridpoint.

Meaningful data on curves for centrifugal pumps do not even start till you hit 300 feet of head and that is 290 feet higher that what the watercooling world uses.

When you look at ASME B73.1, "specifications for horizantal end suction centrifugal pumps..." that they say from the tank/source of liquid, in our case a res, that the pipe sholud be shourt and straight to the pump inlet. Once again you have to realize this is meant for pumps on a much larger scale that what we use in the watercooling world. It is like you speedometer, it is good when you are travelling 60kph or mph but when you are going 1 or 2 kph or mph it is almost useless.

You also have to realize that a whole system has to be designed for a pump. For example in the real world you will have a pump that has a 3" inlet and a 2" discharge. The 2" discharge travelles "somewhere", lets say to a storage tank and connects to a 2" inlet on that tank. From the tank you travel back to the pump through a 3" flange on the tank, 3" pipe and a 3" inlet on the pump. In our watercooling world it is ALL 1/2" (in a 1/2" system). Just because you put a 6" piece of 5/8" I.D. tubing from your res or rad to the inlet of your pump really will not make much of a differnce.

Don't get me wrong, it is great that people are learning something about pumps but it has to be applied in the correct context.

Anyways if you think I am way out of whack let me know in a civilized responce.

themodguy

heh ive got a hydor L30 .. all i did is use 3/4 inch tubing on the way back from the rad.. and use jubille clips to fix it to a 1/2 inch barb.. does make a slight difference eg. my output now needs to be jubileecliped and sealed on with silcon beacuse the damm pressure its under!

themodguy:
I'm a total zero in hydraulics, but i do think that the principles by which big and small pumps work are the same.
Why do you claim that "low velocity is recomended for the pump inlet" is not appliable for small-aquarium-like-pumps? Please explain in details.

I will agree that to a point that the principals in which pumps work are the same.

I am not claiming that low velocity is a recommendation, not saying that at all. The general consensus is that higher flow in a system in better, in most situations and depending on what your watercooling system is build to do.

What I am questioning is the fact that people are going head over heals to put in 6" of 5/8" tubing between the rad(or res) and the pump inlet. They are doing this because the pump inlet is bigger AND that is what it says to do for larger pumping systems, ie gas plants and such.

I am mearly suggesting that for such a small system as a watercooling system that it really is not going to make a difference. In a gas plant you have 3" inlets all the way up to 24" inlets on pumps. Is these cases you have to design the system properly or your pump will not work at its proper place on the pump curve. You need the correct diometer of pipe and propper lengths. Is these systems you are talking about 30 to 300 feet of piping and this is where NPSH really comes into play.

I am not saying don't do it, just that you sholud not expect any real difference. It is akin to saying that a 80 cfm fan is going to cool better that a 79 cfm fan. In theory it will, but the difference is very small.

I just wanted to give someone a little more depth other that the common, "ya it will work".

Anyways thanks for the reply.

themodguy