Head loss?

[nightanole]

Ok i had a brain fart. Head is how high you can pump water, aka 6-10 foot on average. Now you dont want to have to pump water up, you want the pump level with your system. Now imagin lets say a 6 foot tall 4" pvc pipe filled with water with the pump at the bottom. The pump would have to pump the water up a tube (say 1/2" clearflex) to the top of the water line of the pvc pipe. Now would The 6 feet be considered the 6 foot max of the pump? Or since its just at the water line, would this be considered zero foot and the pump would consider the 6 foot of tube to just be horizontal? Using that thery try this.

Could a pump, pump almost infinite height ( less loss from tubing) if it was a closed cercuit? Think about it. A giant vertical ring of water in a tube, with the pump in the bottom. In my head it shouldnt matter where the pump was located in the ring, since the pressure change is only due to the pumps force. The "head" pressure would be directly pushing on the inlet, so there should be no head loss. There would be no more effort to push the water up , then if it was horizontal.


Ok Heres where im getting at. Putting the pump on the floor ( say 6 feet from the very top water level) and not having any head loss due to the pump not being horizontal with the pc case. It would be a closed loop ( ring thery).

I know that the head of the pump is 6-10 foot up, but thats if it has to over come the pressure of the 6 foot collom(sp) of water pushing its way back into the impeller. In a closed loop there shouldnt be any pressure change between the intake and exaust to cause the pump to have to "force" the water back up the tube.

 

[Deadlierchair]

I'm not 100% on the physics and how you're figuring these things (someone else with more knowledge can help with that part), but even with you closed circuit theory, you won't be able to get the pump to pump up 10 feet because it's not powerful enough. It will not have that suction force of coming back down at the beginning point, so you'd have to assist it in the start.

 

[TheArchitect]

Consider the case which is basically identical to the closed loop scenario (pressure wise):
You have two columns of water 6 feet tall each. At the bottom of each column tubing connects one to the inlet of pump and the other to the outlet. Without the pump the water levels would be equal, or if one was less than the other it would reach an equilibrium anyway. The pump can be simply modeled as a pressure source, in which case the approximate difference between the two water levels when the pump is on would be the amount of pressure head the pump has.

This means that it wouldn’t matter where u put the pump as long as it is a closed circuit the only head the pump "sees" is the head loss through the system.

Although, the pump really needs to be the lowest thing in your system for cavitation reasons or have a reservoir at the inlet.

 

[deeppow]

It isn't really clear what your question is but I'll have a go.

Head represents the amount of pressure that is available to push water. The head height times the density of the water (or whatever fluid) tells you the pressure available for pushing. More pressure loss than this pressure and you can't push the water thru the system.

That is really a statement of Newton's second law, F=ma (force = mass * acceleration) where F is the sum of the forces on the system. In this case if the pushing force (pressure * flow area) is exceeded by the losses due to resistance and elevation, the sum of the forces is negative which in turn means that acceleration wants to be negative. Since the flow can't go backward is this particular case then it really means no flow.

For a closed loop (assuming no pressure loss due to the tubing) if you raise the highest point in the loop above the head available, flow stops. In truth the flow will stop before you reach that height due to the pressure loss in the tubing and any other equipment present.

 

[TheArchitect]

It isn't really clear what your question is but I'll have a go.
For a closed loop (assuming no pressure loss due to the tubing) if you raise the highest point in the loop above the head available, flow stops. In truth the flow will stop before you reach that height due to the pressure loss in the tubing and any other equipment present.

I guess what i said wasn't clear to some people. Lets say a pump your using is capable of 2 feet of head pressure, and lets bring back the two columns of water that are 6 feet tall each.

If i understand what your trying to say correctly, you think that if these columns of water are greater than 2 feet tall the pump will not do anything... i.e. the water levels would remain even.

so lets analizes this. For what your saying to make any sense no matter what the inlet presure is of the pump the oulet pressure is always 2 feet of head.

In realality you will add the pressure head of the pump to the inlet pressure, which would mean the column of water on the outlet would be 2 feet higher than the column of water on the inlet.

gravity is not just working one way here, it works against you when you are pushing water up (against gravity) and it helps you when your pushing water down (with gravity).

 

[nightanole]

Man we are getting /. smart here. So it looks like there will not be any head loss due to gravity if:

Its a closed loop.

For the 2nd guy, yes it will not work if there is air in the system, so ill put the T line at the top, so there will be no air inbetween the front and the back of the pump, So it will not have to prime.


In thery im not pumping water up, but just moving it in a loop, like a chain, it doesnt matter how long or high the chain is, as long as its connected in a loop, it will always be in equalibrum

 

[zer0signal667]

For a closed loop (assuming no pressure loss due to the tubing) if you raise the highest point in the loop above the head available, flow stops. In truth the flow will stop before you reach that height due to the pressure loss in the tubing and any other equipment present.

This is not true. In a closed loop, and assuming there is no pressure loss due to tubing, you could techincally have infinite tubing length. However, tubing itself does impose a restriction, as water has some positive viscosity and shears against the tubing and itself. So really in a closed loop, frictional losses are all that you need to account for.