02:30 PM
SE KansasSsnrub
S
SE KansasOriginally 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.
Last edited by snrub;
02:49 PM
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John
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Hi all,I am trying to understand if it is possible to use a gasoline powered water pump to fill a pressure tank. I have an off grid camp on a lake in northern Maine. For decades we have used a gasoline pump to fill a 50 gallon tank that sits on a slight hill above the cabin. The pump sits on the shore of the lake, less than 15 vertical feet above the water, and pushes the water another 60 or 70 vertical feet up to the holding tank, which then feeds our sink via gravity. Our pump is a 3.5hp Koshin/Honda: https://www.koshinamerica.com/shopproductdetail.asp?prodID=14 This has worked well, but we recently hooked up a small tankless water heater, and the gravity from the holding tank does not provide sufficient water pressure to activate the heater. I have temporarily fixed this by installing a small 12v RV pump to pressurize the line, run off a car battery, but what I would really like to do is replace the holding tank with a big pressure tank (maybe 86 gallon, which would give me about 26 gallons of drawdown at 20-40 psi). My question is, can a gas pump like the one that I have be used to fill a standard pressure tank? The specs on my pump say that it can manage 42 psi maximum. So in theory, I could put a pressure gauge on the line above the pump, and run the pump until it reaches about 40 psi, and shut it off. Does that make sense? Suggestions appreciated!