Pumping distance and height for newbie.... 2

[jdumont]

Good day all, i know very little in the pump world so my question may seem trivial but here goes. We currently have a 1/4hp, 1725rpm pump which removes a watery material from a ultrasonic sump to an evaporator unit. The piping goes from 3" off the floor up to 5 or 6 feet high and over a foot before dropping into the evap unit. What I want to do is relocate the evap unit to a better location (logistically) but am worried about the pump being powerful enough to get the material there. In the new location I would need to run the PVC piping up about 12 feet and across the room about 40 feet. I know the across part isnt very difficult its the going up part. Does this sound feasible using the current pump setup?

 

[Artisi]

Without having the manufactures performace data, it is difficult to give you good advice.

However, as you are talking about such a small unit - why not run an experiment on the unit.
1. Fit the discharge with a shut-off valve and connect a pressure gauge between the pump and the valve - and run the pump momentarily to see what pressure is developed.
Or
2. Fit the pump discharge with a vertical pipe of 12 - 14 ft high and run the pump to see if the pump can deliver to that height.

This then tells you if you can achieve what you need.


Naresuan University
Phitsanulok
Thailand

 

[Ashereng]

Empirical experimentation. I like it.

 

[jdumont]

Thats kind of what I was thinking of doing. Just hooking a flex line in quick and dirty like. Thanks for the advice.....

 

[Artisi]

That's the way to go - quick,easy and direct.

Naresuan University
Phitsanulok
Thailand

 

[vpl]

jdumont

Actually, the elevation really only has a role if the modification leaves the evaporator higher in the system than it is now. If you run the pipe up and then back down then the heights cancel each other out. What does have a significant effect is the new length of piping added: going up, going across, and coming down. That piece would be fairly significant as the friction head loss increases linearly with length of pipe, unless you go to a larger diameter pipe.

Remember Bernoulli's equation? (The total head loss = the change in elevation plus the change in system pressure head, plus the change in velocity head) where the change in the velocity head is a function of the friction factor times the pipe length times the velocity squared and divided by the pump diameter (with the gravity constant thrown in to keep units straight)

You can use the pump affinity laws to do a rough estimate of the effect, assuming you don't change pipe size. Specifically: for a given change in speed, the flow rate changes linearly, the head loss changes with the square root and the horse power changes with the cube root. If you hold speed constant, you can also define the change in head loss in terms of its effect on either pump horsepower or capacity.

Given the above, I did some rough calculations that assumed that the evaporator ended up on the same level as it was originally (i.e., that the relative elevation of the sump and evaporator to each other did not change). Working in whole numbers for simplicity, I took the current piping length as 6' up, 1' across, and 6' down for a total of 13'. For the new design, I used 12' up, 40' across, and 12' down for a total of 64'. Thus the length increased by a multiple of 5. Since the head loss is proportional to the length, I assumed the head loss would also increase by 5. If I assume that the pump speed can vary, but that capacity and hp are fixed, then the speed would need to increase by the square root of 5 or by 2.2. If I assume that the capacity and pump speed are fixed, then the hp needed would increase by 11 (5^1.5). Based on these rough estimates, I doubt your pump will handle the change, unless you go to a bigger pipe diameter.

Using the Bernoulli equation and the affinity laws, you could work this out on paper before you make any physical changes.

Patricia Lougheed

Please see FAQ731-376 for tips on how to make the best use of the Eng-Tips Forums.

 

[Artisi]

As it appears there isn't any performance curve, first of all it needs to be established if the pump can actually generate the static head of approx. 12ft. all the other factors can be looked at once the 1st point is clear.

Naresuan University
Phitsanulok
Thailand