physics question

[Capt. Vulcan]

I've got a random physics question. I've got a pump in the backyard for a water fountain. As I understand it every ft up hill I need to push the water decreases the output of the pump significantly because it has to fight gravity and the weight of the water. But what if the pump pushes the water say 4 ft up hill then 3 ft back down hill before exiting the pipe appx 1ft higher than where the pump is drawing water? Will the reduced pressure on the other end from the falling water decrease the strain on the pump pushing the water up hill on the front end? Would it be a similar gallons per hour as a pump pushing water up to 1ft?

 

[sojourner]

Only the 4ft going uphill matters in the pipe arrangement listed, when doing the math. Everything after the drop off is free flowing with gravity. If it where 3ft down, then 4ft up, that 3ft would cancel out 3ft of the up segment.

 

[Capt. Vulcan]

Ah, ok thanks. So really what matters is the total elevation between where the water is being picked up and the highest point in the piping, and probably the horizontal distance the water is travelling. I was hoping the final downward section would relieve some pressure on the pump because of the siphon effect, but I guess that's not how it works. Ugh there must be some physics principal that will help me move water up a 4ft incline without needing a new pump.

 

[farmkid]

Actually, I think the siphon effect just might factor in here and negate those three feet. If the end of the pipe is under water or otherwise sealed from air (perhaps by flowing out through a flexible rubber tube or something), then the downward-flowing water will exert a vacuum on the system. If that downward pipe isn't full, so that the water is just running down a hill, then there would be no such vacuum. To get the whole thing started, however, the pump will need to be capable of pushing the water 4 ft high or you'll have to find some other way to fill the system with water before starting the pump.

I suppose you could just pump the water into a container just over 1 ft higher, then use a siphon to pull it out of that container and over the hill.

 

[Tiberius]

I'm going to vote for siphon effect too. Provided that the set up allows for it.