A smaller diameter pipe will not increase pressure at the output or head height. You get more back-pressure from a smaller pipe, which will ultimately reduce your flow at maximum head height.
putting sump 20ft away from dt?
- Thread starter hdrob
- Start date
A smaller diameter pipe will not increase pressure at the output or head height. You get more back-pressure from a smaller pipe, which will ultimately reduce your flow at maximum head height.
In my old house my sump was 10 feet below my display tank (in the basement). When we built our house I placed the sump (300G Rubbermaid) in the crawl space. The main tank (210G) sits just a few feet behind the sump and a couple feet above it. I also have two tanks (135G &55G) in the garage about 25 feet away from the sump.
The main thing is to properly grade your horizontal drain line. 1/4" drop per foot is standard up to 3" pipe, 1/8" per foot for 4" and up. Your plans for a 4" drain and 3" return seem a bit overkill, but it does leave plenty of room for upgrading you pump in the future.
The main thing is to properly grade your horizontal drain line. 1/4" drop per foot is standard up to 3" pipe, 1/8" per foot for 4" and up. Your plans for a 4" drain and 3" return seem a bit overkill, but it does leave plenty of room for upgrading you pump in the future.
I agree with you, but I think it can be argued both ways here:
1. Smaller pipe means that the water flowing through it encounters more friction/resistence which increases head pressure.
2. Larger pipe increases the weight of water the pump is pushing vertically so that will also increase head pressure.
I'm thinking there has to be an efficient frontier.
In order to maximize flow, I have always heard that you should use the maximum sized plumbing possible. But there has to be an efficient frontier. I'm guessing you would actually lose flow if you go with too large of pipe. For example, say you use 12" pipe for a return, would that really give you more flow than using 2" pipe? I would think the weight of all that water in a 12" pipe (and the head pressure that creates at the pump) would offset the reduction in friction that you would get by using the 12" pipe versus the 2" pipe.
Interesting stuff. I wonder if there are any Fluid Mechanics PhDs on the site.
The pressure ("head" or "head height" are just products of pressure) is calculated in pounds per square inch. It is the "per square inch" part that is being overlooked here. It doesn't matter if it is a 1/2" pipe or a 12" pipe, the pressure will be the same.
Back-pressure (better stated as frictional loss) is dependent on the diameter and length of piping, pressure, and flow rate. Constrictions such as valves and fittings also figure in. There are tables that engineers use to do these calculations on water systems, but they mostly deal with higher pressures and longer runs than we deal with while plumbing our tanks. If you want to maximize the flow and pressure of your pump bigger piping is always better, although the gains diminish very quickly after you get above the optimum pipe size.
So, the 12" pipe probably wouldn't give you an appreciable gain over the 2" until you get into many thousands of GPH. It wouldn't flow any less, though, regardless of flow rate.
I'm not a fluid engineer, but I am an ex-plumber turned science teacher.
