Basics of Pump Pressure/Velocity 2

[tbarkerjr]

The numbers I'm giving below are totally made up and are being asked for fundemental understanding only:

Say I want a pump that can pump a fluid 5 ft/s with a pressure of 5 psi;

1. I understand that the 5 ft/s is a direct result of how fast the blades of the impeller are pushing the water along on a macroscopic scale. Is this correct?

2. Is the 5 psi actually the pressure that gets "put into" the fluid or is it more the pumps potential capability to overcome a back pressure? Can you provide me with an analogy of how this happens? For example, is this dependent on the speed or torque of the motor?

Sorry if this question seems "out of left field"


Regards,

Tom

 

[tbarkerjr]

Basically given a specific size pump, pump velocity and pressure are dependent on one another? I.E. if you want to have 30 ft of head, but you want to make sure you are at 3 fps, you spec out a pump that has say 40 ft of head and is at 6 fps under normal operating conditions. Would you be able to get the motor to pump exactly at 30 ft of head and 3 fps? If so, is there a formula that proves this? How would it be done? Is that what VFDs are for?

 

[nickelkid]

Pumps add energy to the fluid flowing through it, how much is dependent on the efficiency of the pump.

You should take some time and study the extended Bernoulli equation to better understand pressure and velocity relationships.

http://en.wikipedia.org/wiki/Bernoulli's_principle

 

[Artisi]

5ft/s - is this a velocity thru the pump or the pipeline - it is a nonsense measure without clarification.
A trip to the library or a search on the net for pump terminology wouldn't hurt you.

 

[Artisi]

Start your learning at this site.

http://www.mcnallyinstitute.com/index.html

 

[MrNiceGuy3082]

quote: "2. Is the 5 psi actually the pressure that gets "put into" the fluid or is it more the pumps potential capability to overcome a back pressure? Can you provide me with an analogy of how this happens? For example, is this dependent on the speed or torque of the motor?"


A pump creates head (ft, m, whatever), not PSI. The pump ALWAYS runs on the pump curve. Basically the pump is just reacting to the TDH of the system. If you have 30ft vertical pipe on the discharge, and the pump dead-heads at 30ft, then you have 0 flow, and 30ft of head (/2.31 = psi). If you have 0ft of pipe on the discharge, then the pump is producing no head, and at 'run-out' flow (i.e. 25gpm)

As far as impeller diameter, pump speed, pipe diameters... You need to look up the Affinity Laws.

 

[BigInch]

Let me take a stab at this,

2.) A pump adds energy to the fluid. That energy can be converted to either potential energy , static head, head with no flow, "dead head", or kinetic energy, velocity head at full flow, "runnout", or any point inbetween those two extremes, such as, by judicious use of a discharge control valve.

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"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic (Note: Make that 99.99% for pipeline companies)

http://virtualpipeline.spaces.live.com/