Pump Head Defined

[Graystar]

I couldn't find a good definition of pump head here so I thought I'd add one.


[size=+1]Head - Defined[/size]
Head is a measure of fluid energy. It is used to describe the Specific Energy of a pump.

Specific Energy is defined as energy per unit of mass. For example, if we lift up a one-pound object by three feet, we say we have three foot-pounds of energy. It doesn’t matter whether it's a pound of lead or a pound of feathers; we still have 3 foot-pounds.

This is why head doesn’t change with the type of liquid being pumped. Whether pumping water, alcohol, or oil, a pump’s head rating is unaffected.

Sometimes Head is described as the resistance that a pump must overcome. While this may describe what’s going on while pumping, it is not technically correct.


[size=+1]Head vs Pressure[/size]
Pressure is not Head. Pressure is a force applied to an Area. For example, PSI refers to Pounds per Square Inch. The “Square Inch” part is the big difference between Head and Pressure. With Head, there is no Area in the calculation.


[size=+1]Types of Head[/size]
There are four types of head; Static Head, Friction Head, Pressure Head, and Velocity Head.

Static Head – Applies only to open systems, such as a waterfall in a manmade pond. It is the difference, in feet, between two water levels. So if the pump is at the bottom of our pond with a waterfall, then the Static Head is measured from the top of the pond water to the top of the waterfall (yes, the TOP of the pond water, not the bottom where the pump is sitting.) A pump's head rating is usually the maximum Static Head the pump can overcome.

In PC watercooling, the Static Head is always 0 because it is a closed system.

Friction Head – Also called Pressure Drop. It is the resistance to flow. When a pump pumps liquid through a component, that component creates a resistance to the flow of liquid. Typical components are tubing, radiators, fittings, and waterblocks. This resistance to flow is usually expressed in feet of head.

In PC watercooling, Friction Head provides 100% of the resistance to flow.

Pressure Head – Refers to the different pressure levels between two vessels. For example, if a pump must pump rainwater (collected in an open tank) to a second tank that is closed and slightly pressurized, then in addition to Static and Friction Head, the pump must also overcome the pressure being exerted on the water in the tank. Exist in open systems only.

In PC watercooling there is no Pressure Head.

Velocity Head – Refers to the energy required to accelerate the fluid. Exist in open systems only.

In PC watercooling, the velocity of the water is constant, so Velocity Head is 0.


The Friction Head of 4 ft of 1/2" tubing, at 2 GPM is 0.58 ft.
The Friction Head of 4 ft of 7/16" tubing, at 2 GPM is 1.141 ft.
The Friction Head of 4 ft of 3/8” tubing, at 2 GPM is 2.5 ft.
The Friction Head of 4 ft of 1/4” tubing, at 2 GPM is 20.58 ft.

This is why it is so important to use 1/2" tubing.


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What is Head
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Definition of Pump Head
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[SiGfever]

Very well done, this should be a "sticky". IMHO

 

[4od]

Thank you very much for a post that will end many arguments

This deserves to be drenched in glue

 

[Charr]

What is the friction head of 7/16" tubing?

 

[Graystar]

What is the friction head of 7/16" tubing?

1.141 ft. Added.

 

[darkcow]

thanks a lot for that information. great stuff.

sticky

 

[raevien]

Very well done, this should be a "sticky". IMHO

Agreed, we need a sticky here.

 

[nikhsub1]

This page describes this better IMO: http://www.ag.ndsu.edu/pubs/ageng/irrigate/ae1057w.htm Pump head can be correlated with PSI - there is a chart on the above page. When you say velocity does not change in the loop, this is incorrect. Water blocks such as the storm (or any impingement block) accelerate the water through jets or restrictions. This DOES increase velocity quite a bit.

 

[Graystar]

Pump head can be converted to PSI for a given liquid. That chart you referenced is for water. It would be different for gasoline or salt water. However, the head rating for the pump remains the same. It’s like trying to calculate how fast a car is going by knowing the RPM only. You can’t do it. You need to pick a wheel and use the circumference in the calculation.

Velocity, as referred to in Velocity Head, involves acceleration due to gravity in the calculation. Since the Static Head of a PC watercooling system is 0, there is no acceleration due to gravity. All velocities are purely a function of geometry and Friction Head.

 

[Sleepy_Steve]

Pump head can be converted to PSI for a given liquid. That chart you referenced is for water. It would be different for gasoline or salt water. However, the head rating for the pump remains the same. It’s like trying to calculate how fast a car is going by knowing the RPM only. You can’t do it. You need to pick a wheel and use the circumference in the calculation.

Methinks that you might want to know the gear teh tranny is using as well... But thats another topic.

The information here is pretty nice. I wish i hadnt taken so much cold meds and could check up on what you are saying. I dont think this in its own right needs to be stickied, but maybe a link from a sticky to help new people get a general feel for things wouldnt be so bad.

 

[speed bump]

Wouldn't the velocity change based upon the equation for continuity of fluids. Area1velocity1=A2V2=contstant throughout your system. So velocity changes however that change is due to cross-sectional area changing not due to gravity. Might put something in there explaining that

Your friction head for tubing comes out exactly were I though it would. However now I am curious about the other half of Cathars explaination about using 7/16" tubing that 7/16" tubing into 1/2" create 3x less turbulence than 1/2" tubing into 1/2" fittings. If thats true then 7/16" is better but 1/2" is almost always better for temps than 7/16". (I know I should calculate this on my own but finals are coming up so the braing is going to be fried soon enough.

 

[Graystar]

Wouldn't the velocity change based upon the equation for continuity of fluids.

You've make the same presumption that nikhsub1 made. Velocity Head isn't referring to any ol' velocity. It is referring to a very well defined occurrence of velocity that involves the acceleration of gravity. In a closed pumping system, such as PC watercooling, this type of head isn't a factor, as it only occurs in open systems. Even then, its effects are usually so small as to be negligible.

 

[(Clanger)(DOA)]

(cough) sticky.

 

[raevien]

This page describes this better IMO: http://www.ag.ndsu.edu/pubs/ageng/irrigate/ae1057w.htm Pump head can be correlated with PSI - there is a chart on the above page. When you say velocity does not change in the loop, this is incorrect. Water blocks such as the storm (or any impingement block) accelerate the water through jets or restrictions. This DOES increase velocity quite a bit.

Even though the block increase velocity I don't think this would negate his claim that a closed loop stays the same velocity since the water loop's overall velocity remains the same.