How to size a deep well submersible pump from the pump test: pumping level and drawdown, total head, setting depth, check valves, cable voltage drop, protection, solar pumping and an RFQ checklist.
Choose a submersible borehole pump from the well, not the catalogue: find the flow the well can sustain and its pumping water level from a pump test, add the lift to the surface, pipe friction and the pressure you need at the outlet to get total head, then pick a pump that fits the casing and a motor, cable and check valves that suit the setting depth. The submersible pump suppliers in the UAE listed on ListGCC can quote once you have those figures.
This guide is for farm owners, well contractors, compound managers and procurement teams buying deep well pumps. Our main guide to water pumps in the UAE and Saudi Arabia already covers motor cooling flow and flow sleeves, start limits, saline water materials and the Saudi groundwater licence; here we go further into the well itself: yield and drawdown, head, setting depth, check valves, drop cable, protection and solar drives.
Three numbers describe a well for pump selection. The static level is the water level when nothing is being pumped. The pumping level is the level while the well is pumped. Drawdown is the difference: the fall in water level caused by pumping. Specific capacity, the well yield per metre of drawdown, tells you how hard the well can be pushed.
These come from an aquifer test (pumping test), in which the well is pumped at a controlled rate while the water level is measured. Ask the drilling contractor for the test record: pumping rate, static level, pumping level at each rate and how long the level took to stabilise. Without it, any pump size is a guess.
Total dynamic head (TDH) is the sum of four parts at the design flow:
These are illustrative assumptions to show the arithmetic. A farm well has a pumping level of 80 m at the required flow. Water goes to a ground tank whose inlet is 5 m above the wellhead, and the rising main and surface pipe lose 6 m at that flow. TDH = 80 + 5 + 6 = 91 m. If the same pump fed a drip system needing 1.5 bar instead of the tank, TDH would rise to about 106 m. That 15 m difference can mean several more stages, and it is the reason many farms pump to a tank and boost from there; our guide to booster pump sizing covers the second stage.
A borehole set is a pump end (the stack of impellers and diffusers) coupled to a submersible motor below it. The outside diameter must pass down the casing with clearance for the drop cable and its guard. Makers name ranges by nominal well size: Pedrollo, for example, lists 3-inch, 4-inch and 6-inch borehole pumps, some in precision-cast stainless steel, and Franklin Electric lists 4-inch, 6-inch and 8-inch submersible motors. Check three things when a supplier pairs a pump end from one maker with a motor from another:
Franklin Electric recommends that one or more check valves always be used in submersible installations. Its rules, from the 50 Hz application, installation and maintenance manual:
The manual explains what goes wrong without them. With no valve, water in the riser flows back and spins the pump backwards, and starting during backspin can break shafts and impellers. With a leaking or drilled valve, every start is at zero head, causing upthrust. If the lowest valve sits more than 9.1 m (30 ft) above the static water level, or a lower valve leaks while the one above holds, a vacuum forms in the riser and the next start produces a hydraulic shock that can split pipes and damage the pump and motor.
Deep settings put a long cable between the panel and the motor, and voltage drop in that cable is a common reason for overheating and nuisance trips. Franklin's 50 Hz cable tables are built to keep motor voltage at no less than 95 percent of supply voltage at maximum rated running current, while keeping starting voltage and cable temperature acceptable. Points from the manual worth putting in a specification:
Ask the supplier to state the cable size and length used in their selection, and the voltage they assumed at the panel. If the supply at the panel runs below nominal voltage at peak times, that margin shrinks, so measure it.
| Power option | Suits | What to check |
|---|---|---|
| Grid, fixed speed with starter | Wells with steady demand pumping to a tank | Start limits, voltage at the motor, surge arresters |
| Grid with variable frequency drive | Direct supply to irrigation or a pressure system with changing demand | Motor maker's drive rules and filters, minimum speed for cooling flow and thrust |
| Diesel generator | Remote wells without grid | Generator sized on locked rotor current; voltage swings when the load changes |
| Solar (PV array, controller, pump) | Remote farms and livestock wells pumping into storage | Seasonal output, storage tank volume, array sized to the pump |
A solar pump system has three main parts: one or more PV panels, a controller and the pump. The controller matches the pump's power to what the panels deliver and switches off outside the pump's voltage range. DC motors suit small to medium systems up to about 4 kW; AC pumps need an inverter. Output varies with sunlight and season, so the usual design stores water in a tank rather than storing energy in batteries, which avoids an extra conversion step. Pedrollo's catalogue includes a 4-inch solar submersible series (FLUID SOLAR), and Franklin Electric runs a separate solar product site. Size the array from the pump, the daily water need and local sunlight, and size the tank to carry the farm through the hours or days the array cannot.
New wells should be developed until the water runs clear before the permanent pump goes in. Ask the supplier for the maximum sand content the pump is rated for and the material of the impellers and diffusers: Pedrollo's filters list brass, stainless steel and precision-cast stainless impellers across its ranges. For brackish groundwater, the main guide covers corrosion-resistant options; send a full water analysis with the RFQ.
Well drilling and groundwater use are licensed by MEWA, and the pump should be sized to the licensed abstraction; see the main guide for the permit details. Browse submersible pump suppliers in Saudi Arabia and irrigation pump suppliers in Saudi Arabia; drip and pivot equipment is listed under drip irrigation systems and center pivot irrigation.
Before drilling or deepening a well, confirm with the competent authority in your emirate whether a permit is required and what abstraction it allows. Surface motors and controls fall under the UAE motor efficiency rules described in the main guide; IEC 60034-30-1 itself excludes submersible motors.
Franklin Electric makes 4, 6 and 8-inch submersible motors, well pumps and controls, and publishes the detailed 50 Hz application and installation manual quoted throughout this guide. Its motors are often paired with other makers' pump ends.
Pedrollo lists 3, 4 and 6-inch borehole pumps (4HR and 6HR in precision-cast stainless steel, 6ST in stainless steel), borehole motors and a 4-inch solar submersible range.
For dewatering and drainage duties rather than wells, see our sump and sewage pump guide. Then post your borehole pump requirement on ListGCC with the pump test attached so suppliers quote on the same well.
More in this series: Fire Pumps and Jockey Pumps, Types of Pump.
Get the pump test first: the flow the well sustains and the pumping level at that flow. Choose a design flow no higher than the well yield or the licensed abstraction. Add the lift from the pumping level, the elevation to the delivery point, pipe friction and any outlet pressure to get total head. Pick a pump whose curve passes that flow and head near its best efficiency, in a diameter that fits the casing.
The static level is the water level in the well when nothing is pumped. The pumping level is the level while the pump runs, and it is always lower. The difference is the drawdown. Pump head must be calculated from the pumping level, otherwise the pump will deliver less water than expected once the level falls.
Below the lowest expected pumping level with a margin for seasonal decline, and at least 3 m above the bottom of the well to allow for sediment, as Franklin Electric's installation checklist states. If the pump sits in or below the screens, fit a flow inducer sleeve so the motor still gets cooling flow.
Yes. Franklin Electric recommends one or more check valves in every installation, with the first within 7.6 m of the pump if the pump has none built in. Use spring-loaded or internal valves, never swing check valves, and never drilled valves. Missing or leaking valves cause backspin, upthrust and water hammer.
It depends on motor rating, voltage and cable length. Franklin Electric's tables keep motor voltage at 95 percent or more of supply voltage at full running current and give a maximum length for each copper conductor size. Long settings often need a larger size than the motor leads; two sizes can be combined if their fractions of allowable length add up to no more than 100 percent.
Often, for wells pumping into storage. A solar system has panels, a controller and a pump, and output follows the sun and the season, so the design stores water in a tank rather than energy in batteries. DC solar motors suit systems up to about 4 kW; larger duties use AC pumps with an inverter. Size the array to the pump and the daily water need.
Featured image: Photo: Joydeep, CC BY-SA 3.0, via Wikimedia Commons
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