Size matters

[Shdwdrgn]

My pond liners and pump were given to me by a friend, who in turn received them from a friend of his. Needless to say, it's been around the block for awhile. The pump is a 3000gph submersible with about a 3' head, all piped with 3/4" sprinkler pipes. Other than building my own skippy filter, this is all set up the way I originally received it. The flow rate has been pretty questionable for a supposed 3000gph pump, but since this was my first setup, I assumed everything was as it should be.

Yesterday I noticed the basket or rocks around the pump had accumulated a fairly heavy layer of debris, so I decided to pull everything apart and clean it up. In doing so, I found a small split in the flex tubing that drops the pump into the bottom of the pond and went to replace it. I was unable to find a suitable 3/4" replacement, but they had 1" in stock, so I got that. A quick bit of work on the lathe with a 1"-to-1.25" pipe adapter, and I was able to make a new fitting for the pump with a 1" outlet.

Now keep in mind that I have only replaced about 20" of pipe here. The rest of the run up to the filter is still the original 3/4" pipe. Despite this, as soon as I plugged in the pump, there was a noticeable difference in the water flow! So I grabbed some scrap 1" sprinkler line and jury-rigged it up to the filter, and there is now so much flow that my outlets *barely* keep up. Just that small difference of 1/4" diameter in pipe nearly doubles the output from my pump.

Keep this in mind when you do the plumbing for your pump... use at least the largest pipe that your pump has fittings for, or you'll be disappointed in the final flow rate.

 

[RSFish1]

The following table is not exact for all piping. But it is an eye opener to how quickly the flow rate can be diminished. The friction of the piping/tubing has a lot to do with the output also.
Volume of flow is at one foot per minute velocity in Pipe or Tube.

Schedule 40 pipe
Dia. inches Cubic ft/min Gallons/minute
1/8 0.0004 0.003
1/4 0.0007 0.005
3/8 0.0013 0.010
1/2 0.0021 0.016
3/4 0.0037 0.028
1 0.0062 0.046
1-1/4 0.0104 0.078
1-1/2 0.0141 0.106
2 0. 0233 0.174

 

[hewhoisatpeace]

Shoot. 3000 gph I wouldn't go less than 2". Use an adapter to scale it up from your pump output. Makes a difference.

 

[Shdwdrgn]

I'm nearly finished with the planning stage and will start buying pieces over the Winter for my next pond... will be ripping up the plastic liners and laying down a much larger pond with a rubber liner, so there's no point in making changes to the current setup. Thanks to what I was reading last night, I've settled on a pair of Laguna max-flo 2900's (has a 1.5" output), each with its own 2" pipe. The main pond volume will only be around 1000 gallons, but I also will have a 12" wide stream going to a second smaller pond, and I want there to be a little bit of current.

...So yeah, I've become aware of the pipe diameter issue, but was still surprised by such a change in flow even from only changing a short section of my return line.

 

[hewhoisatpeace]

You also fixed the split, sure that increased flow too.

 

[Shdwdrgn]

That was actually pretty minor. It only showed when I pulled the hose back at an angle. Plus the poor flow rate has been pretty consistent throughout the past four years I've been running this setup.