Question on Pump Strength and pipe size

[crsublette]

Just a quick side note.... I noticed that Engineering toolbox mentions 2.5 inch PVC...

2.5 inch PVC is tough to find and you will probably have to order it online, which can be expensive when shipping pipe... 2.5 inch PVC seems to be only used for specialized projects...

I was doing a project where I was using 2.5 inch PVC... I could not find it anywhere... I had to order it online. Last time I did that!!

 

[Meyer Jordan]

...so... technically.... the centrifugal water pumps used in our hobby do not push nor pull... they simply create pressure to move the water...

Not so, according to:

http://www.onestopfire.com/head.htm

http://www.irrigationtutorials.com/pumps-page-2-types-of-water-pumps/

www.explainthatstuff.com/pumpcompressor.html

http://www.robinsons1874.com/Honda/pumps/Honda_pumps_principles.html

http://www.atlanticwatergardens.com/public/uploaded/media/Pump.pdf

 

[crsublette]

...so... technically.... the centrifugal water pumps used in our hobby do not push nor pull... they simply create pressure to move the water...

Not so, according to:

http://www.onestopfire.com/head.htm

http://www.irrigationtutorials.com/pumps-page-2-types-of-water-pumps/

www.explainthatstuff.com/pumpcompressor.html

http://www.robinsons1874.com/Honda/pumps/Honda_pumps_principles.html

http://www.atlanticwatergardens.com/public/uploaded/media/Pump.pdf

Be nice if you elaborated... but since ya didn't want to... I will do it...



http://www.onestopfire.com/head.htm#elevations

Makes zero mention of how centrifugal pumps move water... The best I can find that is applicable states..

"Typically, atmospheric pressure limits vertical suction lift of pumps to 25 feet at sea level (see chart below). This does not mean that you are limited to 25 feet of pipe, you could use upwards of 200 feet of suction pipe, so long as the liquid source is not lower than 25 feet below the pump center line."

"The vertical distance that a pump may be placed above the water level (and be able to draw water) is determined by pump design and limits dictated by altitude."


If our pumps were designed to "push" water rather than move water according to created pressure by the impeller, then sea level altitude would not have an impact.

Since our pumps are utilizing pressure (created by the impellers) to move water, this hyperlink makes much sense and I actually learned something new from this one.

Thank ya!



http://www.irrigationtutorials.com/pumps-page-2-types-of-water-pumps/

"Centrifugal Pumps"

"This spinning action moves the water through the pump by means of centrifugal force. Centrifugal pumps may be “multi-stage”, which means they have more than one impeller and casing, and the water is passed from one impeller to another with an increase in pressure occurring each time."

"End-Suction Centrifugal Pump"

"As a general rule guideline, they perform very poorly if they are more than 5 feet above the water surface. Just remember, end-suction centrifugal pumps are great for pushing water, but they suck at sucking it!"


That is quite interesting... and appears the pumps we use are considered to be "end-suction centrifugal pumps"... The "perform very poorly 5 feet above the water surface" makes me skeptical considering not everyone actually has their pumps close to their pond nor at the same altitude.

Very interesting though... I learned something.. Thanks!



www.explainthatstuff.com/pumpcompressor.html

"Angled blades mounted on the impeller draw water (for example) through an inlet pipe, spin it around at speed, and then force it out through an outlet pipe, usually pointed in the opposite direction. Devices like this are sometimes called centrifugal pumps because they fling the fluid outward by making it spin around"

I failed to find how this negates what you quoted me...



http://www.robinsons1874.com/Honda/pumps/Honda_pumps_principles.html

This one actually supports what I wrote... direct quote from the article...

"CENTRIFUGAL FORCE
The centrifugal pump works in the same way as sucking on the straw. As the engine starts, the impeller turns which forces the water around it out of the pump's discharge port. The partial vacuum created, allows the earth's air pressure to force water up the suction hose (straw), and into the suction (inlet) side of the pump to replace the displaced water. When the water hits the rotating impeller, energy of the impeller is transferred to the water, forcing the water out (centrifugal force). The water is displaced outward, and more water can now enter the suction side of the pump to replace the displaced water."


That is where my understanding of my quote was coming from.



http://www.atlanticwatergardens.com/public/uploaded/media/Pump.pdf

"On the other hand,
using high head pumps at low head heights doesn’t give them enough work to do,
causing “cavitation”, a low pressure condition which can destroy both motor and impeller.
If the pump you want to use will be happier at a higher head height, installing a ball valve
and pressure gauge on the discharge line to restrict the flow will raise the head and
ensure it is within the recommended operating range."

Don't know how they figured this.... I never heard of a pump cavitating due to lack of discharge head...

Their head calculations are incomplete as well... that is only half of the formula... they left out calculating the total suction head.

...the actual formula is... (referenced in the 2nd hyperlink from my first post here)

Total System head = total discharge head - total suction head

 

[crsublette]

@Meyer Jordan , the hyperlinks I found quite interesting have the ...

...especially the one below...


http://www.onestopfire.com/head.htm#elevations

Suction Lift at Various Elevations
Altitude: Suction Lift In Feet
Sea Level 25.0 ft
2,000 ft. 22.0
4,000 ft. 19.5
6,000 ft. 17.3
8,000 ft. 15.5
10,000 ft. 14.3


That actually sounds applicable to our pumps since atmospheric pressure, created by the impellers, is responsible for the movement of water in our centrifugal pumps....

...Thus, the change in sea level changing our atmospheric pressure would impact our pump's suction capabilities.

Very very interesting.

 

[Meyer Jordan]

Be nice if you elaborated... but since ya didn't want to... I will do it...

I prefer not to clutter the Forum with data that is non-essential at the time.

 

[crsublette]

@Meyer Jordan , I think we are splitting hairs here... playing semantics... which I am responsible for starting...

 

[crsublette]

@texmaster , my apologies for cluttering your thread with non-essential information.

 

[crsublette]

Well, since @Meyer Jordan doesn't want to "clutter up the thread" anymore... ...

Thought I would share some info for ya, @texmaster, that ya might find interesting....


I learned something here as well...


Here is a good article....

http://petrowiki.org/Pumps

"Theoretical lift
A pump that develops a perfect vacuum at its suction end can lift a column of water 34 ft. This vertical distance is called theoretical lift. The pressure to lift the liquid comes from atmosphere pressure. At sea level, atmosphere pressure is approximately 14.7 psia.

Actual suction lift
Because a perfect vacuum is never achieved and because some lift is lost to friction in the suction line, the maximum actual suction lift for a positive-displacement pump is approximately 22 ft. The maximum actual suction lift for a centrifugal pump is approximately 15 ft when pumping water from an open air tank"

...and our pumps are centrifugal pumps....

 

[crsublette]

So I'm redoing the pipe from my bottom drain to the pump. The bottom drain is 3.5 feet down and its about 5 feet to the edge of the pond. Right now its reduced to 1.5 which is obviously too low. The pump is about 20 feet away. Right now my plan is to bring the 4inch pipe to the surface so another 3.5 feet directly up then once on the surface after a check valve only reduce it to 3 inches for maximum flow until the basket then reduce again to 2 inches which is what the pump is rated for.

This is the basket I'm considering

http://www.calponds.com/Evolution-Pu...ap-p-6719.html

My question is can this pump handle a 4 inch 9 foot piple + 20 foot 3 inch pipe and still maintain decent flow?

The "20 feet away" is not a big deal at all if you will use 3 inch pipe.... 20 purely horizontal feet, 5400gph, in 3 inch pipe... this is only 0.36 feet of suction head... A 90 degree 3 inch adapter adds 0.144 feet of suction head... Not a big deal at all...

The 3 inch priming pot would also be much better providing lower friction loss...

A minimum of 3 inch is what you should use if ya want to pump more than 5000 gph...


I am guessing your 9 foot of pipe is coming from... bottom drain is in the center of pond, 5 feet from the wall... then takes 3.5 feet vertically up to the surface.. equals 8.5 feet...Is this correct?


@texmaster How much of that 3.5 feet "up to the surface" is actually under the pond's water level elevation?

...i'm asking because... if your pond is actually 3 feet deep... and are actually only raising 0.5 feet above the pond's water level... then just that 0.5 feet is what matters... the footage below the water level does not matter...

Vertical feet (above the pond water line) equals to the same amount of feet in head... so... if your pipe is actually only raising 0.5 feet above your pond's water level... then that is 0.5 feet of head...


...so... with a couple 90 degree 3 inch adapters, 20 horizontal feet of 3 inch pipe, only 0.5 feet of actual vertical pipe above the pond water level... then..


....that is only 1.148 feet of suction head... which is nothing...


...I think the type of check valve you are using (whether it is swing or spring/tension) and whether you get the 2 inch or 3 inch priming pot will add most of the head feet on your pump's suction....


... I bet you will be pumping 5000 gph easy... just as I mentioned in my first post in this thread...

...but all this can change dependent on how your water flows after the pump's discharge...

...remember, ya add suction head to the discharge head to determine your final head... and this final head is what you use, with your pump's flow chart, to find your actual pump flow rate.

 

[crsublette]

Their head calculations are incomplete as well... that is only half of the formula... they left out calculating the total suction head.

Quick correction on myself here...

...after reading more closely... when the Atlantic Water Garden PDF file said... "Vertical Head, the height in feet from the surface of the water the pump will be sitting in, to the highest point the water is pumped to."... the PDF is conflating "Vertical Head" to be both discharge and suction head... which is confusing and why I overlooked it on my first read....