Larger suction pipe to pump - better?
All inside tubes, inlets on the pump, and suction tube from fresh tank are 1/2". 3GPM pump, 40 PSI on the push side, self-priming up to 10ft (I think). Now, imagine fresh tank 6ft away, sitting on...
Forum Discussion
mobeewan wrote:
With the tank sitting on the ground part of the water in the tank is going to have to be lifted higher than the water that would normally be in the onboard tank. The pump will have to work harder then it normally would to lift it that distance. The Shurflo pumps are designed to lift water about 12 feet using 1/2 inch ID tubing so your tank on the ground is well within the operating parameters. However, keep in mind when switching to three quarter inch pipe (1.066 OD/.824 ID for standard schedule 40) your internal diameter will be significantly larger and your volume and weight of water in that pipe that the pump is lifting will more than double and the pump will be working harder especially while self-priming to lift that amount of water.
The weight of the water in the pipe is larger, but the pressure at any given height is the same because the weight is spread out over a larger area (ignoring the frictional resistance from flowing along the pipe wall). The pump doesn't "see" how big the feed pipe is, only what the pressures are, be they positive or negative (with respect to air pressure).
You can demonstrate this by comparing how hard it is to drink a beverage through a skinny straw and a fat straw. You don't need to suck more strongly with the larger straw. If you try to slurp rapidly, the skinny straw is harder to use because of the frictional losses.
