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#431277 - 12/11/15 12:08 AM Gasoline powered water pump question
John Fitzgerald Offline


Registered: 10/27/15
Posts: 1992
Loc: S. end of Elkins, Arkansas
For those of you experienced in pumping water:
Would a three inch pump have any advantage over a two inch pump if my discharge pipe is limited to two inches? I have a good length of 2 inch poly.
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#431283 - 12/11/15 07:05 AM Re: Gasoline powered water pump question [Re: John Fitzgerald]
Cecil Baird1 Offline
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Registered: 08/08/02
Posts: 20043
Loc: Northeastern Indiana
It might pump more even with the restriction, but my trash pump is 2 inches discharge all the way and it pumps plenty of water.

How much water do you want to pump and how fast? What's the price difference between a 2 and 3 inch pump?


Edited by Cecil Baird1 (12/11/15 07:07 AM)
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#431285 - 12/11/15 07:30 AM Re: Gasoline powered water pump question [Re: John Fitzgerald]
Bill D. Offline


Registered: 10/19/14
Posts: 5586
Loc: Boone County Illinois
I would think the 2 inch discharge hose would increase the back pressure on the 3 inch pump which, IMHO, is not a good thing as it will lower pump efficiency and might make it difficult to prime the pump, depending on type of pump and length and depth of inlet hose.


Edited by Bill D. (12/11/15 09:21 AM)
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#431286 - 12/11/15 08:18 AM Re: Gasoline powered water pump question [Re: John Fitzgerald]
snrub Offline


Registered: 10/05/13
Posts: 4926
Loc: SE Kansas
You could operate it at lower engine RPM to extend both the life of the pump and engine.

Centrifugal pumps operate most efficiently at low head pressures. At low back pressure they pump lots of water, as the back pressure increases the GPM drops off. So reducing the size of the outlet, especially if the run is long (more friction), will drastically reduce maximum output. But if you are satisfied with how much water will flow through 2" pipe, the larger pump can be run much less aggressively (lower RPM) and still see maximum water output through said 2" pipe.

We run 1" gas powered cent. pumps to pump chemical and for many years run 2" pumps (trash type pumps) to fill water tanks and spray tanks. Since we went to a 1600 gallon sprayer that replaced two sprayers (800 and 1200 gallon) we have exclusively went to 3" pumps to replace the 2". Even running at half throttle we can fill a 1600 gallon sprayer in just a few minutes (3" hose). But we also have 2" adapters around (quick disconnect) for when we need to hook something 2" up. The 3" pumps work fine with a 2" outlet hose, but we need to run them only at about a third throttle. You can get more water output at higher throttle, but only marginally and use a lot more gas as the pump runs at higher RPM and pump pressure levels. Like breathing through a straw. Breathing is ok as long as you are at rest but try and do some activity and the straw creates too much resistance for enough air to pass.

We use 3" electric start pumps, one in the tender to fill the sprayer, and another on the ground for the semi-truck tender to refill it. And we keep one on the shelf as a spare because we can not afford field downtime because of a pump failure. So far after two years and quite a few hours on both pumps, the new one is still on the shelf.

You ask if there would be any advantage to a 3" over a 2". The only one I can think of is longer life of the pump for a given amount of gallons pumped. If you ever had the need for full 3" output into a 3" hose it would be there. If long life is not an issue, then likely the 2" pump will be cheaper and serve your purpose adequately.

My experience with these small single cylinder air cooled four cycle engines is if you don't have to run them balls to the wall all the time they can last a lot longer. That and change the oil once in a while. We put the cheap electronic digital hour meters on them so remember they get serviced. I think they are about 15 bucks on Ebay and you just run a wire near the spark plug. Drain the gas and/or use fuel conditioner between uses if it is going to sit without use for a long time. We have a fuel supplier deliver premium fuel to a barrel here on the farm and we use it exclusively in all our small engines including chain saws. I don't know that it is needed in the summer, but we have found the engines we need to start in the winter (especially the China ones some of our portable air compressors use) start so much better on a better grade of gas when it is cold. So we just started running it year round.


Edited by snrub (12/11/15 08:40 AM)
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#431288 - 12/11/15 09:57 AM Re: Gasoline powered water pump question [Re: John Fitzgerald]
John Fitzgerald Offline


Registered: 10/27/15
Posts: 1992
Loc: S. end of Elkins, Arkansas
Thanks for the information. I really appreciate it. With the price difference in both pumps and fittings, it might be better for me to stick with the two inch pumps. My pipe is two inch poly, and that is heavy enough to drag around. The next commonly available size is four inch, and it would be impossibly heavy. I don't have a tractor or such.
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#431289 - 12/11/15 10:06 AM Re: Gasoline powered water pump question [Re: John Fitzgerald]
DonoBBD Offline


Registered: 06/13/12
Posts: 1900
Loc: Ontario, Canada, Eh.
I use expandable for discharge and rigid for intake. Its very easy to roll up. I do get some pin holes in it but it works great for transfer.

As said above always use gas stabilizer or sea foam in your fuel. It will save your self allot of aggravation. All my small engines use it. I just always grab some when its on sale and have the stabilizer on the shelf.

Cheers Don.
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#431292 - 12/11/15 10:46 AM Re: Gasoline powered water pump question [Re: John Fitzgerald]
sprkplug Offline
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Registered: 06/02/08
Posts: 6945
Loc: Freedom, Indiana
A note of caution concerning rpm on air-cooled engines. The name says it all - air cooled. And that air comes from vanes or fins mounted on the flywheel. The faster the flywheel turns, the more cooling air flows over the engine. Engine manufacturers will tell you, (and I will also), to crank it up while working. If full throttle powers the equipment too fast for your liking, you need a reduction somewhere in the drivetrain....never use engine rpm to vary equipment speed on an air-cooled unit. Full throttle is what you want.

In the old days of cast iron flathead engine designs, you could get by with some variance while under operation. Not so anymore. The OHV aluminum engines are epa mandated to run as lean as possible, which means they run even hotter than their predecessors. I wish I knew how many valve/valve guide/cylinder head issues I've seen over the years caused by overheating.
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"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.

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#431293 - 12/11/15 10:47 AM Re: Gasoline powered water pump question [Re: John Fitzgerald]
Kelly Duffie Offline
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Registered: 04/19/02
Posts: 1475
Loc: Cypress, TX (Helena A-E LLC))
This was an interesting question - as were the responses....
I'll add one more quirk regarding the various types of pumps.
The "work load" on centrifugal pumps; unlike piston or diaphragm pumps, decreases as downstream pressure (or restrictions) increase.
Using a pressure-washer (piston pump) as an example; when the pump is running and the wand-trigger is activated, the engine comes under a noticeable "load" to produce pressure; but when the trigger is released, the pump's bypass dumps pressure and the engine-load is significantly reduced.
Centrifugal "trash pumps" are quite different, since they operate under maximum engine-load when no downstream back-pressure is encountered; which is also when they produce maximum volume.
I found an interesting info on centrifugal pumps HERE.

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#431298 - 12/11/15 12:09 PM Re: Gasoline powered water pump question [Re: John Fitzgerald]
snrub Offline


Registered: 10/05/13
Posts: 4926
Loc: SE Kansas
Three inch flexible plastic pressure hose is definitely a bear to drag around. Especially when filled with water if you have a valve on the end.
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#431299 - 12/11/15 12:13 PM Re: Gasoline powered water pump question [Re: sprkplug]
snrub Offline


Registered: 10/05/13
Posts: 4926
Loc: SE Kansas
Originally Posted By: sprkplug
A note of caution concerning rpm on air-cooled engines. The name says it all - air cooled. And that air comes from vanes or fins mounted on the flywheel. The faster the flywheel turns, the more cooling air flows over the engine. Engine manufacturers will tell you, (and I will also), to crank it up while working. If full throttle powers the equipment too fast for your liking, you need a reduction somewhere in the drivetrain....never use engine rpm to vary equipment speed on an air-cooled unit. Full throttle is what you want.

In the old days of cast iron flathead engine designs, you could get by with some variance while under operation. Not so anymore. The OHV aluminum engines are epa mandated to run as lean as possible, which means they run even hotter than their predecessors. I wish I knew how many valve/valve guide/cylinder head issues I've seen over the years caused by overheating.



Interesting. Thanks for the input. I've never had any trouble from valves in a small engine save an old Wisconsin about 40 years ago that I had to replace an exhaust valve. I can't recall ever having trouble with the inside of a small engine since then. Usually other things give up the ghost first for me. I guess I will keep running them part throttle as needed until I run into problems. Then I'll think back and say to myself "sprkplug told me so". Sometimes I just have to learn things the hard way.

We do run full synthetic oil in all gas engines (air or liquid cooled) and have for probably 20 years. I think it stands up to high temps better so maybe that is our saving grace.
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#431300 - 12/11/15 12:21 PM Re: Gasoline powered water pump question [Re: Kelly Duffie]
snrub Offline


Registered: 10/05/13
Posts: 4926
Loc: SE Kansas
Kelly, a person can prove that to themselves for their own satisfaction very easily. A shop vac has a centrifugal air pump (or vacum, same thing). Hold your hand over the intake or exhaust and the electric motor speeds up. Rather than the impellers engaging air and doing work, the same air contained in the chamber just goes round and round.

I remember discovering this on my own when in grade school and could never convince my older brother there was less load on the motor when the intake was covered. But I heard the motor increase in speed so figured it had to be.

But I was a strange child. I was reading "Implement and Tractor" when most kids were reading, correction, looking at the girls in "Hot Rod" magazine.


Edited by snrub (12/11/15 12:26 PM)
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#431308 - 12/11/15 02:10 PM Re: Gasoline powered water pump question [Re: snrub]
sprkplug Offline
Ambassador
Lunker

Registered: 06/02/08
Posts: 6945
Loc: Freedom, Indiana
Originally Posted By: snrub


Interesting. Thanks for the input. I've never had any trouble from valves in a small engine save an old Wisconsin about 40 years ago that I had to replace an exhaust valve. I can't recall ever having trouble with the inside of a small engine since then.


Wish I could say that. Then again, I did see 1400 engines or so in an average year. wink

Oil changes make a huge difference. In an air-cooled engine the oil doesn't just function as a lubricant, but as a coolant also. When it gets dirty its ability to carry heat away diminishes also. Synthetic is good stuff and most major small engine manufacturers offer it through their parts channels, but conventional oils are just fine when recommended oil change intervals are followed. Interestingly, the manufacturers I am familiar with do not specify an extended service interval when using synthetic....supposedly one of it's major benefits. But I look at that like I do with 3000 mile oil changes in an automobile....there's no need under most circumstances, but if it makes you feel better, do it.

I well remember a few years ago when Cub Cadet introduced a new model year's tractors. Every one we got in that spring would idle around 2300 rpm. Those old farmers HATED that. They would bring those tractors back, complaining about such a high idle speed. I tried everything to slow them down, but finally resorted to calling Cub and asking for help. I ended up with an engineer from Kohler Engines, who let me know in no uncertain terms that if it were up to him, he would set the engines at 3600 rpm and remove the throttle levers from the dash altogether. "It's an air cooled engine!" he said. "I don't care if they're mowing grass, or just riding down the driveway to get the mail, you tell em' wide open, no exceptions!"

Ah, the good ole days.
_________________________
"Forget pounds and ounces, I'm figuring displacement!"

If we accept that: MBG(+)FGSF(=)HBG(F1)
And we surmise that: BG(>)HBG(F1) while GSF(<)HBG(F1)
Would it hold true that: HBG(F1)(+)AM500(x)q.d.(=)1.5lbGRWT?
PB answer: It depends.

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#431323 - 12/11/15 05:15 PM Re: Gasoline powered water pump question [Re: John Fitzgerald]
DonoBBD Offline


Registered: 06/13/12
Posts: 1900
Loc: Ontario, Canada, Eh.
Still to this day with our one air cooled 440 arctic cat sled we run one cooler plug on the far side from the fan. The fan side sees the cool air first then the second cylinder sees the warm air to cool it. 99% of the time one cylinder go's down its that side.

Been running one cooler temp with the gap the same to balance the motor for years. Works well and no stuck pistons/rings. I like to run the lowest resistance plug I can in them too. Helps with cold starts. I think they are NGK EIX or EXI solid core. Great cold start plugs.

Cheers Don.
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#431341 - 12/11/15 08:24 PM Re: Gasoline powered water pump question [Re: John Fitzgerald]
John Fitzgerald Offline


Registered: 10/27/15
Posts: 1992
Loc: S. end of Elkins, Arkansas
What pipes do you guys use to pump into your ponds? It seems to me that a long run even slightly uphill with the lay flat type hose would cause a lot of restriction due to the hose always wanting to collapse. I use one 25 foot length of 2" red lay flat that unions onto my 2" slick lined poly pipe that goes about 450 more feet to the pond. The poly is too stiff to connect directly to the pump.
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#431379 - 12/12/15 09:10 AM Re: Gasoline powered water pump question [Re: John Fitzgerald]
snrub Offline


Registered: 10/05/13
Posts: 4926
Loc: SE Kansas
I've only been involved in one pond pumping (most of our pumps are used for other purposes) and we have the plastic flex hose on hand so use it. Have never used the thin, flat, collapsable hose.

But I can not see where it would make much difference. If you are pumping up a rise of 10' then you are pumping a head pressure of almost one third of an atmosphere or about 5 psi. So the hose is going to expand to reflect 5 psi at the pump outlet (and less as it would measured up along the pipe to the ultimate outlet where the pressure drops to zero).

I may be wrong. That is just how I see it in my minds eye. But I don't see where it would make measurable difference using either pipe type (unless you have a kink or some other cause of obstruction).


Edited by snrub (12/12/15 09:12 AM)
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#431386 - 12/12/15 09:34 AM Re: Gasoline powered water pump question [Re: John Fitzgerald]
Diver Cody Offline


Registered: 11/11/14
Posts: 95
Loc: Louisiana, Evangeline Parish
How far uphill are you running this when I was looking at and eventually bought my pump most can do a ~25' draw and a ~90' uphill elevation change. Otherwise if it is really far uphill, you might need to do two engines, one at bottom and one halfway to help keep your GPM's higher.

Also, the hose prices as you go up in size was why I decided to settle on a 2" model that and I have access to old worn 2" hoses from my company.
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#431397 - 12/12/15 01:19 PM Re: Gasoline powered water pump question [Re: Diver Cody]
John Fitzgerald Offline


Registered: 10/27/15
Posts: 1992
Loc: S. end of Elkins, Arkansas
I am pulling about 5 feet uphill on the suction end and pushing about 16 feet uphill over a total distance of about 475 feet. Total lift about 21 feet more or less. I estimate I am getting about 3,500 gph out of a pump rated at zero head 9,060 gph. I have been running at 3/4 throttle. Full throttle gets me very little water gain, and is much louder and uses more gas. Friction losses in the pipes I suppose. However, my pipe is very slick and looks like teflon lined on the inside, and there are four non restrictive splices due to the fact that the pipe was scrap and pieced together. My estimates are based on how much it raises the pond, and may be off somewhat. I have about 50 hours on this 2 inch Harbor Freight pump now, and it has performed flawlessly. The gas tank is too small is my only complaint. I paid just under $200 total for it new including a one year full replacement plan.
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#431400 - 12/12/15 01:34 PM Re: Gasoline powered water pump question [Re: Bill D.]
catmandoo Offline
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Registered: 08/08/06
Posts: 5680
Loc: Hampshire Co., WV
Originally Posted By: Bill D.
... and might make it difficult to prime the pump ...


I mostly use my 2-inch semi-trash pump for watering the garden. I leave the hoses connected most of the summer. A FOOT VALVE like this saves me from having to prime the pump if I leave the intake hose in the pond. It also makes it a lot easier to prime the pump without getting a shower when the pump finally starts to pump while pouring priming water into it.
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#431406 - 12/12/15 02:14 PM Re: Gasoline powered water pump question [Re: catmandoo]
snrub Offline


Registered: 10/05/13
Posts: 4926
Loc: SE Kansas
That is a GREAT idea catmandoo.
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#431407 - 12/12/15 02:30 PM Re: Gasoline powered water pump question [Re: John Fitzgerald]
snrub Offline


Registered: 10/05/13
Posts: 4926
Loc: SE Kansas
Originally Posted By: John F
I am pulling about 5 feet uphill on the suction end and pushing about 16 feet uphill over a total distance of about 475 feet. Total lift about 21 feet more or less. I estimate I am getting about 3,500 gph out of a pump rated at zero head 9,060 gph. I have been running at 3/4 throttle. Full throttle gets me very little water gain, and is much louder and uses more gas. Friction losses in the pipes I suppose. However, my pipe is very slick and looks like teflon lined on the inside, and there are four non restrictive splices due to the fact that the pipe was scrap and pieced together. My estimates are based on how much it raises the pond, and may be off somewhat. I have about 50 hours on this 2 inch Harbor Freight pump now, and it has performed flawlessly. The gas tank is too small is my only complaint. I paid just under $200 total for it new including a one year full replacement plan.


The big deal with the higher RPM is it will generate more head pressure if you were trying to push the water higher up a hill. For example, if your lift would be 33' that would be one atmosphere or about a 15 psi differencial in pressure from the pond level. But at current throttle setting, if you raised the pipe up to say 66 ft lift (almost 30 psi, water might barely come out of not at all. At some point in the lift height water flow would stall out, but increased throttle would increase the potential pressure output of the pump and make the water go higher.

Cool weather, I personally would not worry about engine overheating, but that is just me. What do I know.

When water is drawn into the center of a centrifugal pump, the impellers sling the water to the outer surface creating centrifugal force. As the tip of the impeller pushed the water out the exit, that impeller vane passes the exit point and there is a void till the next vane gets there. During that time the water tries to come back into the pump via the output port. The faster the impeller runs, the less time between vanes for the water to return and the more force the impeller has to send the water out the output. That is why you are not seeing a lot of extra capacity for the extra engine speed and fuel used. If your head pressure was much higher (higher lift) you might see an overall less water pumped but a greater portion increase by the increased engine speed. Although the increased speed will get you a little more volume, the main thing it would do is give you the ability to push to a higher head pressure.

If that makes sense. The pump we use to fill our sprayer we just run the throttle enough to fill the tank in the amount of time it takes our hot mix tank (with 1" cent. pump) to pump into the water stream. If we ran it faster, it would either just fill our tank before we got the chemicals in or we would have to throttle the flow with an inline valve and create unneeded pressure within the system. Like you said, lots less noise, less fuel and the water lines do not look tight as fiddle strings with unneeded pressure.

That was a great article Kelly linked to above. The one thing it did not address was what changing the pump speed would do. That is because it was using an electric motor driven pump as an example, where the speed of the impeller could not be varied. Similar calculations are involved when using an air pump to pump air down into the water for aeration systems.


Edited by snrub (12/12/15 02:49 PM)
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#431426 - 12/12/15 04:33 PM Re: Gasoline powered water pump question [Re: John Fitzgerald]
John Fitzgerald Offline


Registered: 10/27/15
Posts: 1992
Loc: S. end of Elkins, Arkansas
Honda has a pump calculator program that will give expected discharge rates. If I could handle four inch pipe, I could almost double my discharge rate with the same pump, due to less friction in the pipes.
Four inch rolled poly is so stiff that for me it would be unmanageable. I suppose four inch PVC could be glued together and buried to the pond, but very expensive to do so.
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