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The last 7 posts

Tuesday, May 10th 2005, 7:20pm

by Wet_Boots

On pumps and wells, you don't get a 'cushion' per se. You want to draw enough water to keep the pump running continuously. With modern lawn heads, you can change out nozzles to adjust consumption up or down. If the system is an older one, nozzle swapping may not be possible.

It's okay if the water level in the well drops when the pump is running, if it gets to a certain point and goes no lower. When it continues to keep dropping, then there is a real point to the idea of a smaller pump, less capable of running the well dry. But you have to determine whether you can live with less water, based on what adjustments you make with the heads. Also, you need enough water to feed the acreage in a reasonable time period. The drip irrigation won't care about pump capacity, since you can design to fit.

Tuesday, May 10th 2005, 5:52pm

by erikdyba

Wet Boots, Thank you for your response. I have done exactly what you suggested and found that the largest zone has 24 rotors at 3 GPM per head (72GPM). The zone is located approximently 695 feet from the pump and main supply line size is 2.5 inch. Valve sizes is 2.5". The water level in the well is at 770 feet, which is slowly going down and with that said the performance of the pump is going down with the lack of available water.

The reason I ask the question is that I was confronted by the pump/well company and they asked if the existing pump was overkill and if they could replace it with a smaller size. The original pump is a 20 hp that was pushing 80 psi at 93 gpm. (That was what I was told.)

I suggested that the size should be replaced with what was taken out and mentioned if it's not broken don't fix it.

I'm adding about 20 zones mostly drip/netafim and was wondering what kind of cushion/margin should you leave in designing a system in regards to flow/GPM. 75 gpm available ? How many actually used in the field? 10-20 percent under? or is it to max. +/- at 75.

Thank you again for your truely educational information.

Sunday, May 8th 2005, 4:47am

by Wet_Boots

No matter where the pump is located in a well shaft, its performance is based on the actual water level in the well. If you don't know the actual delivery capacity of the well shaft, using other than an original-performance pump risks running the well dry.

If you had time to spend, and were getting paid by the hour, you could get a big air compressor and run the system on air, and inventory the heads, including the nozzles. Then you could get the manufacturers' information on the various heads and nozzles, and do a calculation on what gpm is being used, at a head pressure you select. Then you could calculate the pressure being lost in the pipe and valves between the heads and pump. All that you need from there is the drawdown water level of the well, and you can select a pump.

Is there some particular reason to believe the original pump selection was incorrect? Is there no company that did maintenance on the well or pump, that would have the pertinent information?

Some states have a requirement that for each well drilled, the performance details of the well shaft be filed with the state, including the gallons per minute of replenishment capacity of the well shaft, which is the maximum number of gallons per minute you can draw without lowering the water level in the well. However, don't bet the ranch that the numbers on file are correct.

Saturday, May 7th 2005, 9:49pm

by erikdyba

Thank you for the response although the situation is a little more complex. Depending on the flow requirements of the system the existing well may have to moved down 400-600 feet. Meaning that a new stlye of pump may have to use and a large differnce in price. <u><i>How could a person find the gpm needs of the system?</i></u>

Saturday, May 7th 2005, 9:41pm

by erikdyba

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Wet_Boots</i>
<br />Basically, you'll wind up pulling the existing pump, and replacing it with the same. If it's no longer being made, you'll use a replacement with the same horsepower and number of stages. Usually, the well installation information will be documented somewhere.
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Saturday, May 7th 2005, 6:10pm

by Wet_Boots

Basically, you'll wind up pulling the existing pump, and replacing it with the same. If it's no longer being made, you'll use a replacement with the same horsepower and number of stages. Usually, the well installation information will be documented somewhere.

Saturday, May 7th 2005, 4:42pm

by erikdyba

Pumps and GPM needed

I've taken over the maintanence at a large estate, the pump that was suppling the irrigation has quit working. When talking with the pump contractor he asked me how much flow do you need?

I'm not sure how to figure this out with water to run the system and count number of heads in each zone. Even if I use a compressor to locate the heads and do a take off on the nozzles, Wouldn't I still need to know what the operating/dynamic pressure is, in order to find out what the GPM's needed is?

If anyone could help shed some light on this situation I would be very
grateful.