Pump sizing concern

[tolind]

Not working with pipes and pumps all that often I would like someone to verify this.

I have a process system that needs 75gpm and 60psi at two seperate points along a system. One point is 90 ft from the pump and the other is 130 ft. The pump sits 15 ft below the outlet points of this equipment.

I'm being told that I need a pump that can handle 150gpm at 200 ft of head. Does this jive. If I do the calcs myself I come out with this being only associated with the 60psi at one location.

Do pressures add together to render the design value? Do you only concern yourself with the last fixture on the circuit?

Thanks,
Cautious

 

[sathanasiou]

I agree with the pump selection. In any similar case, you add the flows needed and take the pressure of the last fixture of the circuit, or the fixture in the most disfavored position (by the means of pipe length, curves, orifices, etc). If you consider the equivalent electrical circuit, flow is the current, while pressure is the voltage.

As a guideline only, you can calculate the pressure drop on a circuit using the following formula:

pressure=(length*1.5*0.005)+1,5 meters of water
lenght= the distance from the pump to the last fixture and back to the pump

Hope this is useful!

 

[DesignerMike]

What line size are you planning?

I imagine you would prefer to have output pressures on both use points very similar. Since pressure drop is dependant on line size you should over size the line slightly to minimize the pressure drop.

4" tubing would give you less than 7 psi pressure drop, and then your pump would only need 170 ft of head. BUT 2" tubing will be closer to 28 psi of drop which means 200 ft of head is not adaquate.

If use point #1 is a little distance from the main feed line, you should use smaller tubing for this drop than the line continuing to point #2. A 5 ft section of 1" tubing will produce the same pressure drop on point one as 45 ft of 1.5" tubing going to point 2.

 

[TBP]

Is this a loop, or is the liquid on a one-way trip? How critical is the supply pressure? If it really matters, you may need to consider delivering a higher pressure to the points of use, then using a pressure reducing valve at each point.

 

[tolind]

This pump only does one way. The main is a 6" pipe and the individual to the equipment is a 2 1/2". Supply pressure is pretty critical but I would rather not use a reducing valve.

Thanks to the help.