About a year ago, when I started my system, I received ample criticism for using 1.5" PVC on my return pump. Many experienced hobbyists told me that using the wider pipe would increase head pressure and actually lower the GPH of my return pump, thus 1" was preferable. I was also advised that using flexible nylon tubing was preferred to PVC because it reduces sound and also head pressure. Having a little extra time on my hands this weekend, I upgraded my system taking these considerations to mind. I replaced my PVC return using 1" braided nylon tubing.
My return seems to be running much slower as the water line in my sump is higher (with the same amount of water) and I had to turn the ball valve in my overflow to keep it from gurgling. The pressure on the loc-line return feels lighter and I think my pump is actually louder now. Does anybody have any idea what's going on?
What kind of pump is it? That can make a difference. Generally you need only up-size the pipe one size above that of the actual pump outlet size to see around a 2/3 reduction in friction loss. This is common (or should be) practice, and a part of Centrifugal Pumps 101, or "How To Install and Run Centrifugal Pumps."
The one exception to this rule are the Mag Drive pumps 9.5 and larger. They are supposed to be "positive displacement" pumps, and are advertised as such. However, positive displacement pumps are not affected by pressure head, E.G. the flow curve is a "straight" vertical line (in a perfect world; friction loss is converted and added to the pressure head.) However, the Mag Drive pumps are poorly designed, and due to the design flaws, it requires the use of 1.5" pipe on the outlet to get any flow out of them. This is stated, not obviously, but very clearly in the directions for the pumps. It is certainly an impeller/volute design flaw, and it is with the impeller/volute design, that causes variations in pump performance. (all else being equal.)
Still, in reading this thread, I see some things that are amiss. One of them concerns weight of water. Weight is a function of mass and the acceleration due to gravity. It is not the same as pressure. You will see weight (in reference to an aquarium) measurable below the water column; inside the water column the pump will see pressure, not weight. The pressure or "pressure head" is a function of depth + atmospheric pressure (hydrostatic pressure as absolute pressure opposed to "gauge pressure" which ignores atmospheric pressure.) This pressure will vary with elevation above sea level. Just general information.
The pump will not see weight, only pressure. Pressure at a given point in a water column will be equal in all directions, and at every single point at the same depth as the "original" point. E.G. the pressure up is equal to the pressure down, sideways, around & through, and measuring weight at that point, will = 0. What this says is that in a water column of any volume, at the same depth the pressure will be the same. It also means that regardless of the relative diameters concerned (pipe id and pump outlet id) at the same depth, the pressure will be the same.
So if you have a 3/4" pump outlet with 2" pipe above it, the pump will see "x" pressure; if the pump outlet is 2" with 2" pipe above it, the pump will see "x" pressure. If the pipe is 3/4" sitting on a 3" pump outlet, at the same depth as the other two, the pump will see "x" pressure. Weight is irrelevant. Although what you will get out of the pump in the last "what if" will be nothing more than a dribble.
A great many hobbyists are not aware of these principles, and a portion that are aware, have trouble believing it, and don't up-size their pipe. Or they up-size the pipe, and then negate the increase in flow by splitting their return line, and using loc-line fittings, or "gyro" type things. However it is not something to be believed, it is physics. It is unfortunate, but a good thing, that you have seen these principles in action, in the dynamic context. Increasing pipe size does make a positive difference and that difference is very noticeable.
