What looks good on paper doesn't always look good in person. I confess straight away that I broke the unwritten law of plumbing engineering; which is: get an honest-to-God person, who knows their way around a plumbing diagram, to review your idea of your pond's pipes.
It is a lot easier to erase a mistake on paper than doing it after the pipes been laid (pun intended) it will become apparent soon). But I didn't listen to my inner self. I was hot on my belief that through my acquisition of pond building knowledge from books and the Internet surfing; I had a good understanding of a proper-plumbing-to-pond-ratio to fit my needs. It all started with a simple piece of paper and a pencil.
My plan called for two 4" bottom drains, one drain near each end of my pond. Then individual 3" BD lines came back to the area (away from the pump) where they met up with an individual 2" line coming from the skimmer box. At this junction, the lines went through individual knife valves, so I could regulate the flow. The lines joined after the valves into a 3-to-1 pipe fitting; cut left; ran six feet to a DIY pre-filter; another eleven feet of pipe; 22.5 degree elbow to access the pump box; a twisting and turning of pipe to line up with the leaf basket / pump. It all looked so good on paper. So I set down to dig, glue, and lay some pipe. Even with one or two setbacks along the way, I still completed the pipe work in good time.
So to recap, I had laid: Bottom Drain #1 Line 40 feet of pipe (actual distance from pump 6 feet). Bottom Drain #2 Line 28 feet of pipe (actual distance from pump 18 feet) Skimmer #3 Line 6 feet to junction; joins to run in main line 22 feet) DIY Pre-Filter - 100 gallon Rubbermaid container (12 feet from pump).
I knew that for each twist and turn that the plumbing took, it degraded the performance of the water to flow. I had read somewhere that for every 10 feet of pipe, it translated in to one foot of head pressure. I figured I would need at least 13 feet of head for the pond to run. The pump I had figured to be rated at 22 feet of head. My figuring was wrong; and it soon showed.
First, I took the DIY pre-filter out because I could never get it to work; period. Then I found the knife valves were useless because I could never adjust them; due to the fact that the pump would lose its prime, in a heartbeat, and run dry; it needed all the water the lines could provide it. And the final straw was the unavoidable fact that the water draw on the skimmer line was weak and/or non-existent. In the end, I learned that what looks good on paper was all wet in actual practice.
In my head, I have redesigned the plumbing numerous times (lowering it will help the draw of water immensely, adding a pre-filter will solve my daily cleaning of the leaf basket and attaching a pump to the skimmer line will increase the draw of water to its filter). Of course all that takes money, and time to fiddle.