How deep should a well pump be? This is a question we are often asked, and the answer depends on some specific stats about your well. Submersible well pumps don&#;t have a hard line rule on where they should be installed, it is usually on a case by case basis. A number of factors can play into this, but the main ones will be your well&#;s total depth, the depth of the static water level (how far down the water sits in your well when not being pumped out), and what the flow rate of your well is (usually noted in your well report after a well has been drilled).

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A good rule of thumb is to install it so it is hanging around 10&#; above the bottom of the well. The reason you don&#;t want the pump to sit on the bottom of your well is so that if any sediment or debris were to fall into the well, it will fall to the bottom and there won&#;t be any risk of sucking that debris into the well pump&#;s intake and possibly damaging the pump. So the safest spot to place the pump is a little ways off the bottom of the well. However, if your well is strong and produces a high volume, then you can often place it higher above the bottom of the well. As an example let&#;s say you have a 200&#; deep well with a 30&#; static water level, if the well is producing more gallons per minute than you will be pumping out of it, you can place that pump at 150&#; in the well and you would have no problems. This is because with a high producing well, you will be pumping water out of it slower than the well can put the water back in, so the water level in the well shouldn&#;t change when the pump is running.

Something else you may need to take note of is the submersion limit of the pump, which is how far the pump can be submerged under the surface of the water level. Oftentimes this is not an issue, as many pumps have submersion limits of 600&#;+, but if you have a very deep well then this can become a factor that you will need to consider. If you were to submerge a well pump beyond its submersion limit, the water pressure will start to become so high that the seals on the pump won&#;t be able to handle it. While it may not immediately be a problem, some pumps will work for a bit while submerged beyond the recommended limit, this can cause your pump to fail earlier than it would if it were placed above the manufacturer recommended limit. If you don&#;t know what kind of volume your well is capable of producing, then the safest option will always be to put it close to the bottom so that you can take full advantage of the water column above the pump, so long as that depth is not below the submersion limit of the pump.

What Size of Submersible Pump Do I Need?

by Atlantic Pumps Admin

 

 

What Size Submersible Pump Do I Need?

First of all, to work out the submersible pump size you&#;ll want for the job, let&#;s start with considerations for some of the most common applications for submersible pumps:

Dewatering & Flood Control

The main aim of submersibles for flood or dewatering purposes is to move a high volume of water a sufficient distance so it discharges safely off-site. A good dewatering pump has a reliable, powerful motor with a larger diameter discharge hose to provide a good flow-rate, plus a quick and efficient on/off control. An important consideration in pumping run-off flood water is that its likely to be contaminated with solids; possibly of unknown size and concentration. To achieve the same output, pumps made for &#;dirty-water&#; require a larger motor, plus a gap between the volute chamber and impeller to allow for pebbles, sand, silt, and the like. On the Audex &#;AW&#; range of submersible pumps, an agitator is attached to the shaft to minimise the risk of sand clogging up the pump.

Process Water & Irrigation Pumps

Pumps for delivering water for irrigation or factory processes need to deliver a consistent, measured flow, often with a certain pressure needed at the delivery end. The balance of pressure and flow rate is achieved through the motor&#;s power output and the discharge pipe&#;s diameter. Check the diameter of the inlet on the machine or irrigator used, as a reduction in piping diameter will need factoring in to the size of pump needed.

Electric pumps fitted with a variable frequency drive (VFD) are good for controlling the speed of the motor to fine-tune the flow and pressure requirements to match the system. However, you should ask your pump supplier for the pump curve chart, which will tell you if it will accommodate your flow and head requirements.

Well Pump

Often required to pump water a high vertical distance, head pressure is often more important than flow volume. Well pumps are often designed to fit inside narrow-diameter boreholes. The pressure available is controlled by the motor power in relation to the pipe size. A powerful motor, slim body, and narrow outlet makes a good well or borehole pump configuration.

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Choosing Pump Size For Flow Rate

Depending on region and pump size category, flow-rate is measured in gallons per minute/hour, litres per minute/hour, or sometimes cubic metres per hour (m3/hr) which is the volume that the pump system is capable of moving in a given time. When choosing what size pump you need, consider the maximum peak amount of water that needs to be moved per minute or hour. In the case of dewatering, this might be the maximum rainfall or groundwater seepage within the site&#;s water catchment area, whilst a processing plant might require delivery of a set volume per minute. A pump&#;s outlet (and pipe diameter) sets the maximum flow rate to a large degree. For example, the Audex 20hp motor driving a 4&#; pipe system gives a maximum flow of 1,400 l/min. Compare this to the same pump with an outlet twice the size at 8&#;, whose maximum flow rate is over four times that at l/min, albeit with less head pressure capacity.

Choosing Pump Size For Head Height

What is the vertical distance that the pump needs to lift the water? This elevation difference is measured from the source to the final discharge height, and to get the total dynamic head requirement we need to factor in resistance from friction caused by the pipe lining, bends and valves. Furthermore, if a specified pressure is needed at discharge, then this is added in.

So, the pump supplier might be asked for a pump size that can produce 4 bar of pressure at 35m head height. By specifying the flow volume, head height, and discharge pressure (if significant), the pump designer can configure the correctly sized pump and associated pipework. Pump motor being equal, a high-head pump will often have a narrower outlet/discharge pipe than one designed for high-flow/low head.

The Importance Of Pump Size

Going with a pump that is under-sized or oversized can lead to premature wear and failure, or wasted energy and purchasing costs. Every pump needs to have an adequate supply of fluid &#; known as Net Positive Suction Head available (NPSHa) whenever it&#;s running, to avoid burn-out and cavitation damage, whilst a pump that is straining to handle the system&#;s demands will fail all too soon.

Head Height Vs. Flow Volume

With any given submersible pump, as the head pressure of lift increases, the flow-rate will decrease, and vice-versa. So when the maximum flow rate of a pump is given alongside the maximum head height remember this; you can&#;t have the best of both at once. A pump&#;s best efficiency point (BEP) is somewhere in the middle of these performance maximums. Pump curve charts enable you to see what the flow rate will be at any given head height pressure, or the head at a given flow-rate. Bear in mind that these calculations are made with new, unworn pumps and are usually based on clean water performance, so picking a pump model that is slightly over-sized at new will ensure you&#;ll have the required performance for a good time between maintenance intervals.

Maximum Submerged Depth

Something to be mindful of with submersible pumps is that they are built to withstand the water-pressure of up to a certain depth. In the case of Audex submersibles, these heavy-duty industrial pumps are rated water-proof for immersion at depths of 25 - 30m depending on model size. Other pumps, such as those designed for clean-water boreholes might have a greater immersion depth, whilst domestic model pumps are only suitable for shallow submersion. Suspending a submersible pump by chains (ideally from a floating pontoon), can overcome the risk of over-submerging a pump and this also keeps it clear of dredging up settled solids.

The Size Of The Pump, Vs The Size Of The Solids

Whilst clean water submersibles are designed with narrower tolerances to increase efficiency, submersibles for pumping slurry and solids-laden water need to have wider gaps between the moving parts. Larger motors and abrasive-resistant materials are also used on heavy-duty submersibles, like Audex pumps.

What Is The Power Supply Available?

The different sizes of submersible pumps come in various power ratings, measured in horsepower (HP) or kilowatts (kW), and are made for running on either low voltage 110v (typically used on construction sites), 240v, or three-phase 400v (380v -415v). The higher the kW, the greater the motor's ability to generate pressure and flow rate, for example, the super-capacity 55kW submersible pump from Audex delivers 73HP which can lift 16,000 L/min up to 7m height, or a couple of thousand litres per minute up to 35m height.

What If Power Isn&#;t Available For The Size Of Pump I Need?

As most submersible pumps are electrically driven, generators are used to power them where off-grid use is required, or if it&#;s a 3-phase pump and only single-phase power is available. Bear in mind when sizing your generator that the start-up power draw will be significantly higher than the stated rating (approximately 6 times when starting DOL &#; direct on line). This spike can be reduced by using installing a soft-start, or better still, an inverter. Audex highly recommends using a soft-start or invertor on any pump over 18.5kWh

The Audex Range Of Submersible Pumps

Audex are chosen for their robust design and materials that last longer than standard submersibles, pumping abrasive fluids and slurries in the minerals, metals, waste and recycling industries.

Audex Pump outlet (pipe) size: kWh HP Max head height (m) Max flow-rate (L/min) Max flow-rate in cbm/hr Anti-silt clogging agitator? 2&#; (50mm) 0.4 0.55 12 208 12.5 Yes 1.5 2 22 450 27 1.5 2 20 500 30 Yes 2.2 3 26 550 33 2.2 3 25 500 30 3.7 5 32 550 33 3&#; (75mm) 0.75 1 16 30 18 Yes 2.2 3 19 920 55 3.7 5 34 60 Yes 4 5.5 14 99 Yes 5.5 7.5 34 75 3.7 5 28 833 50 4&#; (100mm) 3.7 5 18.5 90 3.7 5 18 90 Yes 5.5 7.5 23 105 6 8 17 150 Yes 7.5 10 40 84 9 12 21.5 192 Yes 11 15 48 84 15 20 56 84 22 30 68 130 30 40 78 170 6&#; (150mm) 7.5 10 31 125 9 12 21.5 192 Yes 11 15 32 147 11 15 23 234 Yes 15 20 40 156 22 30 50 210 37 50 83 220 45 60 90 220 55 75 105 192 75 100 130 198 90 121 150 150 8&#; (200mm) 15 20 23 372 Yes 22 30 32 360 Yes 30 40 37 390 Yes 37 50 48 330 37 50 42 390 Yes 45 60 53 372 55 74 65 390 75 100 70 408 90 121 90 360 110 148 103 390 10&#; (254mm) 55 74 35 960

 

Hopefully this guide has answered some questions you might have had about pump sizes, however if you&#;re unsure of anything, please submit your question to us via the chat in the right hand corner or us 118 for pump sizing advice to meet your particular industrial application.

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