Mak 4 gph at 14'

[StirCrazy]

Originally Posted by stephane

pressure in watter calculate in height not in wide, you will have the same pressure 20 feet deep in a pool than 20 feet deep in a 20 mile long lake

thanks Stephane

Steve

[Canadian Man]

So you guys are trying to tell me that if you add 1000x more water in a pipe that extra water weight won't add to the back pressure on the pump?

I understand your point stephane. I do think that at some point it would add more weight to the situation.

Maybe I'm a loonie

[stephane]

Originally Posted by Canadian Man

So you guys are trying to tell me that if you add 1000x more water in a pipe that extra water weight won't add to the back pressure on the pump?

Exacly I know it's hard to understand when a french like me try to learn it to you but it is part of physic.

1/4 inch pipe 10 foot heigh head will have the exact same head or bottom pressure than a 10 mile wide pipe by 10 foot height. Your pump impeler is inside the water so it dont see the ouside weight. In fact it will be a lot easy for the pump to use the 10 mille pipe as it will have absolutly no restriction so you will have more flow than that 1/4 pipe

[stephane]

One last try

if you try to put your finger to stop a leak from the ouside botom of a 2 mille wide x 2 feet deep tank it will be a lot easy but try do the same ting on a 30 foot heigt by 1 inch pipe.

[Canadian Man]

OK OK

[StirCrazy]

Originally Posted by Canadian Man

So you guys are trying to tell me that if you add 1000x more water in a pipe that extra water weight won't add to the back pressure on the pump?

I understand your point stephane. I do think that at some point it would add more weight to the situation.

Maybe I'm a loonie

pressure is determined by the hight of a water column and nothing else. for an example lets say we have a tank that is 24" tall and 5" wide and 5" long that is full of water. to make up a number lets pick that the pressure on the bottom glass is 2psi. the volume of water is ~9L so the weight of water is approximately 21lbs. now take another tank, say 24 tall x 25 wide and 65 long. the volume is 590L and the weight of this tank will be ~1300 lbs, but the PSI on the bottom of the tank will still be 2psi.

the reason increasing the pipe size reduced head is because it reduces the amount of water subjected to shear. because water is composed of molecules that want to stay together when water moves it shears away from the water around it. also water will try to stay to the side of a vessel by a atomic attraction. so to get the water in the pipe to move you have to shear it apart from the water against the edge of the pipe which results in friction. by increasing the diameter of the pipe you are allowing a larger volume of water to exist away from the shear zone while will allow a greater volume to flow while not being in a state of shear and thus lowering the friction inside the pipe.

Steve

[Invigor]

so I assume using the "shear" theory, that is why mag drives recommend you double the pipe size compared to the pump input/output? (ex: my mag 12 has 3/4" inlet/outlet so I should be using 1.5" pipe to maximize the water flow?)

I guess with less pressure my mag would be quieter too!

[Aquattro]

If anyone's interested, the following book is invaluable for this topic of fluid dynamics.

http://www.amazon.com/exec/obidos/AS...660101-0323124

[StirCrazy]

Originally Posted by Invigor

so I assume using the "shear" theory, that is why mag drives recommend you double the pipe size compared to the pump input/output? (ex: my mag 12 has 3/4" inlet/outlet so I should be using 1.5" pipe to maximize the water flow?)

I guess with less pressure my mag would be quieter too!

this is part of it but you are also incorporating laminar and turbulent flow to the equation.

now this is just off the top of my head so if I have some terms wrong for give me.

OK one assumption to make, the law of conservation of mass (meaning a given mass put in in a period of time must come out in the same period of time)

if you have a small pipe it will cause high shear stresses which will lead to turbulent flow. this is because if you look at the conservation of mass you are putting in 200 gph from a 3/4" pump outlet into a 1/2" line so the result will be a increase in pressure so it can keep the same volume of water coming out the end. this increase in pressure makes the pump work harder but it also reduces the efficiency of the pump by making it have to work harder to achieve the same result. inside the pipe as the amount of water put in increases you fine the shear stresses between the boundary layer and the rest of the water increase until the water flow becomes turbulent and requires even more work out of the pump to push the water through.

by going to a larger pipe you are slowing down the water flow and creating a laminar flow of water through the pipe. you are also dropping the back pressure allowing the pump to work more efficiently.

Steve