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Pump Ratings - Head Pressure vs Flow Rate

post #1 of 12
Thread Starter 
when evaluating the relative "power" of a pump, which is the better indicator - Head pressure (expressed in feet or meters) or flow rate (expressed in Gallons or liters per minute)? I've been under the impression that head is a better number. You don't know under what conditions the flow rate was derived, and it may not match real world conditions.

However, I note that the MCP355 head far exceeds the MCP655s, but the latter has a much greater GPM rating. Both are accepted as excellent pumps. Other factors (quality, longevity, etc) aside, what's the best camparitive measure?
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post #2 of 12
Head pressure > flow rate.

They are both good pumps and have their uses. The 355 is a champ in a restrictive loop. The 655 in a freer flowing loop. Also the 655 is slightly quieter.
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post #3 of 12
Thread Starter 
Quote:
Originally Posted by Kaldor View Post
Head pressure > flow rate.

They are both good pumps and have their uses. The 355 is a champ in a restrictive loop.

That's kinda how I was thinking - head pressure would be an indicator of how well a pump can overcome restictions. Right?
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post #4 of 12
Correct. IE more restrictive blocks like an EK Supreme or a multiple block (CPU and GPU/s) setup.
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post #5 of 12
Quote:
That's kinda how I was thinking - head pressure would be an indicator of how well a pump can overcome restictions. Right?
More or less, you have to balance them out. Like you've already noticed the 18W DDC has a lower flow rating but higher head then a D-5, the D-5 has lower head but higher flow. When you get them in a loop they are comparable for actual performance. With the DDC you have to have a after-market top to perform as well as the D-5, but with one its just a tad better. And with a high restriction loop it may do a little better also.
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post #6 of 12
as long as you stick to cetrifugal pumps lik those generally used in watercooling, a high head pressure usually automatically comes with a suffient flowrate. so when shopping for one, mainly look at the head rating, the flow for all pumps available on watercooling webshops is sufficient anyway.
post #7 of 12
How big of a flow would you need? At 1200LpH that the D5 has, thats 20L/minute or .33L/sec. How much water do most systems contain? Judging my reservoir sizes, its around 1-1.5 liters and that might be a high estimate, especially for reservioir less systems. At that flow rate does the ratiator have enough time to disipate the heat from the water? Every 3-6 seconds the water in the system has made a complete loop.

That just seems to quick to me. Where is my mistake in my thinking?
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post #8 of 12
When you can actually hear your water screaming like it's on a roller coaster then you need just oonneee more pump. I want that water terrified not having fun!

Kidding

Get yourself either a D5/MCP-655 or a MCP-355+XSPC top(or XSPC Res Top)

Whichever one you like the looks of better because all will serve VERY well.
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post #9 of 12
Thread Starter 
Quote:
Originally Posted by MobAttack View Post
Every 3-6 seconds the water in the system has made a complete loop.
It's more rapid than that in a typical loop. The linked calculator has fluid in a 7/16" tube (.4375 incehs) with a 1.5 GPM flow rate travling 38.4"/sec (3.2ft/sec). In a 5ft loop, that's a complete cycle in less than 2 secs. That's one of my main reasons for beliving that loop order doesn't matter that much. The "coolest" water from the rad is clear on the other side of the loop just like that.

****Oops. Here's the link:

http://www.1728.com/flowrate.htm
Edited by TonyL222 - 1/15/09 at 11:25am
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post #10 of 12
Quote:
Originally Posted by TonyL222 View Post
It's more rapid than that in a typical loop. The linked calculator has fluid in a 7/16" tube (.4375 incehs) with a 1.5 GPM flow rate travling 38.4"/sec (3.2ft/sec). In a 5ft loop, that's a complete cycle in less than 2 secs. That's one of my main reasons for beliving that loop order doesn't matter that much. The "coolest" water from the rad is clear on the other side of the loop just like that.
That all just seems to quick for the water to disipate its heat to the radiator to cool it down. Would moving the water slower be better? Giving it more time to pick up heat from the heatsinks and drop it off at the radiator?
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