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Old 09-27-2013, 5:20 PM   #1
HiImSean HiImSean is offline
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Return plumbing question

I've got a Eheim 1262 for my return pump. It has 3/4" return but the bulkhead on my tank is 1". I've read that it's fine moving up in size in the plumbing but does it matter when you do so? Say will it have more flow if you have the PVC increase directly from the pump versus right at the bulkhead? The only reason I ask is because I got a bunch of 3/4" PVC and fittings laying around.

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Old 09-27-2013, 7:23 PM   #2
Giulianom Giulianom is offline
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There is (a bit) more head pressure with a 3/4" line than there is with a 1", which makes your pump work harder.

So try to do it 1" piping right from the pump if you can.


How high of a vertical run are we talking about here?

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Old 09-27-2013, 9:58 PM   #3
HiImSean HiImSean is offline
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Not high, maybe 30" up and 30" over. I'll just grab some new 1" plumbing.

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Old 09-27-2013, 10:08 PM   #4
Bassett22 Bassett22 is offline
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Quote:
Originally Posted by GiulianoM View Post
There is (a bit) more head pressure with a 3/4" line than there is with a 1", which makes your pump work harder.

So try to do it 1" piping right from the pump if you can.


How high of a vertical run are we talking about here?
Some pumps actually increase in efficiency with some restriction from head pressure or a valve restriction.

And doesn't a larger pipe cause greater head pressure from the added weight of the extra water volume in the larger pipe?

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Old 09-27-2013, 10:12 PM   #5
JDavid JDavid is offline
 
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Originally Posted by leveldrummer View Post

And doesn't a larger pipe cause greater head pressure from the added weight of the extra water volume in the larger pipe?
Great question... No.

This got me thinking, so I decided to do a bit of research. This is what I found.

Quote:
A. The short answer is that the larger pipe would be better because there would be less pressure loss in the pipe. This is due to less “friction loss” as the water flows through the larger size pipe. The larger amount of water in the bigger pipe has no impact on the water pressure. A smaller pipe may create more friction loss however, so it can be worse than a larger pipe. To find out, you need to calculate the friction loss in the different sizes of outlet pipe based on the flow and pipe size. See the Friction Loss Calculators to calculate the friction loss in pipes.

More detailed answer:
One of the really hard to grasp principles of hydraulics is the relation of volume of flow, pressure, and the weight of water. Odd as it seems a larger pipe will actually be easier for the pump. It’s not the volume of water, but the height it is lifted that matters. In a way this is a variation on the old saying “which weighs more, a pound of feathers, or a pound of lead?” Obviously both weigh a pound! This version could be phrased “which is easier for the pump, 5 GPM in a 1/2″ pipe or 5 GPM in a 2″ pipe? Neither because 5 GPM is still 5 GPM regardless of the pipe size! Yes, you would need more power if you were actually lifting more water, also we would need more power to lift the water higher, but neither is not what is happening. The amount of water nor the height we are lifting hasn’t changed.

The other issue here is flow through a pipe. This is the issue that actually makes the smaller pipe potentially worse than the larger. Because the smaller pipe is smaller it is harder to force the water through it. The resistance of the walls of the smaller pipe causes pressure loss as water flows through. this is commonly called “friction loss”. How much friction loss occurs depends on the flow rate and pipe size. Both higher flows and smaller pipes sizes result in greater friction loss. This is the only reason a smaller pipe would be worse than the bigger pipe. How much worse is dependent upon the actual flow rate and pipe size.

As a general rule (ie: not always true, but is most of the time) the pipe size of the pump outlet is almost always smaller than the size of pipe that will provide optimal flow from the pump. In other words, if a pump has a 1″ threaded outlet, it is very likely that a 1 1/2″ pipe would be attached to the 1″ outlet for use as the outlet pipe. Pump manufacturer’s tend to use smaller size inlets and outlets to save money.


More technical answer:
Think about feet of head. As discussed in the Pump Tutorial, the number of feet of water depth determines the water pressure. So 80 feet of water depth equals a pressure of 80 ft. hd. This pressure will be the same regardless of the pipe size. The water pressure at the bottom of an 80′ high 1/2″ pipe is exactly the same as the water pressure at the bottom of an 80′ high 6″ pipe, even though the 6″ pipe holds a lot more water. A pump actually works by creating water pressure. So for the pump there is no difference between pumping into either size pipe, the water pressure required to move the water into the bottom of both pipes is the same. Now the pressure lost as water moves through the two pipes will be different. Assuming a high rate of flow, a lot more pressure will be lost due to friction in the smaller pipe. So for that reason using a larger pipe will be better. Depending on the flow, however, it may be only very marginally better. To find out you need to calculate the friction loss in the outlet pipe based on the flow and pipe size. See the Friction Loss Calculators to calculate the friction loss in pipes or tubes of various types.

Last edited by JDavid; 09-27-2013 at 10:20 PM.

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Old 09-28-2013, 2:15 AM   #6
Giulianom Giulianom is offline
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There's a great pump head loss calculator out there that I found useful.



It takes the pump curve data, pipe diameter and other factors in and outputs your effective head and flow.



For me, with 12' of head and a 20' run it was almost a requirement to do that calculation...



For 30" you should be fine.

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