What is an analysis register and why does a borewell project need one?
A borewell project produces many numbers: drilling depths, water strike levels, compressor pressures, air-lift discharges, drawdowns, recovery times and pump settings. Decisions are built on calculations that combine these numbers. When those calculations sit in scattered notebooks and spreadsheets, nobody can later tell which reading supported which conclusion, or whether a unit was converted correctly.
An analysis register solves this with a disciplined record. It is not paperwork for its own sake. It is the shortest route to answering three practical questions when something is questioned: what was calculated, from which readings, and is the result still valid after something changed?
- A drilling contractor can show why a given compressor pressure and flow was chosen for each stage.
- A well owner can see how the safe pumping rate was derived from the yield test.
- A pump supplier can check the duty point against the measured drawdown, not a remembered figure.
Organise the evidence in layers
Keep four layers distinct: observations, assumptions, calculations and decisions. Mixing them is the usual source of confusion.
Each decision should point back to the calculations it relies on, and each calculation back to its observations and assumptions. When a reading is later corrected, you can trace forward to every result that must be rechecked.
What should each formula entry contain?
A formula register entry needs enough context that a competent engineer who was not on site can reproduce the result. A bare equation is not enough.
- Reference – a short identifier for the calculation, so other records can refer to it.
- Purpose – what question the calculation answers.
- Formula – written out, with each symbol defined.
- Units – for every input and the result.
- Inputs – the actual values used and where each came from.
- Validity limits – the conditions under which the formula applies.
- Result – with sensible rounding and the date calculated.
- Checked by – who verified it, and how.
Verify units before interpreting results
Unit errors are the most common and the most damaging mistakes in borewell calculations. Flow appears in litres per second, cubic metres per hour, litres per minute and, for compressors, cubic feet per minute. Pressure appears in bar, psig, kg/cm² and metres of water. Levels may be measured from casing top, ground level or a reference mark.
| Quantity | Common conversion | Typical trap |
|---|---|---|
| Water flow | 1 L/s = 3.6 m³/h | Mixing L/min and L/s in one table |
| Air flow | 1 m³/min ≈ 35.3 cfm | Comparing free air delivery with flow at pressure |
| Pressure | 1 bar = 14.5 psi | Mixing gauge and absolute pressure |
| Water head | 10 m of fresh water ≈ 0.98 bar (14.2 psi) | Ignoring the head when sizing air-lift start pressure |
| Levels | State the datum (casing top or ground) | Subtracting readings taken from different datums |
A quick dimensional check, writing the units through the formula, catches most errors before they reach a decision.
Keep a groundwater-analysis register
The groundwater part of the register covers the yield test and the operating decisions that follow. Typical entries include static water level, pumping water level, drawdown, specific capacity, recovery and daily volume.
Specific capacity and its limits
Specific capacity is discharge divided by drawdown, often stated in m³/h per metre. If a well delivers 12 m³/h with 8 m of drawdown, its specific capacity is 1.5 m³/h per m at that rate and duration. It is a useful comparison between tests on the same well at similar rates. It is not a constant: it usually falls as the rate rises and as pumping continues, so it should never be used alone to predict the yield at a much higher rate.
Daily volume from a time series
When discharge varies during a day, integrate it rather than multiplying one reading by total hours. Record the method used: meter totals, timed readings with average flow per interval, or logged data. State how gaps and stoppages were treated. Two people using different methods on the same data can arrive at different daily volumes, and both need to be traceable.
Keep a compressor and drilling-air register
Drilling, development and air-lift testing all depend on compressed air, and those calculations deserve the same discipline. Typical entries are:
- Pressure budget for each drilling stage: hammer working pressure, line and string losses and water head above the bit.
- Annular velocity: free air delivery divided by annular area, with bit and rod diameters stated.
- Air-lift start pressure: the submerged length of the air line converted to head, plus losses.
- Site correction: the effect of high ambient temperature or altitude on the mass of air delivered.
- Running hours: hour meter readings that tie the air duty to service intervals.
Worked example: air-lift start pressure
For air-lift development or testing, the compressor must first push the water out of the submerged air line. If the air line foot is 60 m below the standing water level, the start pressure is about 60 × 0.098 ≈ 5.9 bar (85.6 psi), plus hose and fitting losses. Once lifting begins, the working pressure usually falls. The register entry should state the submerged length, the datum used and that the figure is a start-up estimate. Practitioners commonly aim for a reasonable submergence ratio, often quoted around 60%, so that air-lift works efficiently; lower submergence lifts water poorly.
Separate calibration from validation
Where a model or rule of thumb is fitted to measured data, keep the data used to fit it separate from the data used to check it. A relation tuned on the first day of a test and then “confirmed” on the same day proves little. Use a later period, a different rate or an independent reading to test whether it predicts well.
Simple ratios need the same care. A ratio that holds well at moderate rates may break down at high rates or in a different season. Record the range over which it was checked and refuse to extrapolate far beyond it without fresh evidence.
Make uncertainty usable
Uncertainty should change what people do, not sit in a footnote. For each key result, note the main sources of doubt and their likely direction. If a flow meter was not verified, say so beside the yield figure. If the static level was taken before full recovery, mark the drawdown as possibly understated.
Then link uncertainty to action: a conservative pump setting, a repeat reading, an independent check measurement or a scheduled review. A register that records uncertainty but never changes a decision is not doing its job.
Control changes to formulas and models
When a formula, spreadsheet or method is changed, record the old version, the new version, the reason and the date. Rerun a short set of reference examples with known answers to confirm the change works. List the decisions that used the old method and decide whether each must be reviewed. Never overwrite an earlier result silently; keep it, mark it superseded and show what replaced it.
How Reddy Compressors helps
We supply all types, all brands and all models of borewell compressors: new, used and refurbished, rentals, service and spare parts. As an independent multi-brand specialist, we handle ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Doosan and others, and we are not an authorised dealer of any one brand. We have tie-ups with all major and reputed brands.
On the compressed-air side of a borewell project, we help you set up the calculations that matter: stage pressure budgets, annular velocity, air-lift start pressure and site corrections for heat and dust. We can supply compressors for drilling, development and air-lift testing from our rental fleet of 50–2,000 cfm and 2–30 bar, with hour-meter records and servicing every 300 running hours on hire. Groundwater interpretation and well design remain with your hydrogeologist or consultant; we provide the air duty and the records that support it.
Our team of more than 20 service engineers and technicians covers all of Telangana and Andhra Pradesh, and we supply across India from our office at Tarnaka, Secunderabad.
What to send us
- Bit and rod sizes, hammer details and planned depth stages
- Static water level and expected air-line submergence for air-lift work
- Present compressor make, model and nameplate photo
- Your existing calculation sheet or drilling log, if you have one
- Site location, ambient conditions and duration of work
Frequently asked questions
What is a formula register in borewell engineering?
It is a controlled list of every calculation used in a borewell project. Each entry gives the purpose, formula, units, input values and their sources, validity limits, the result and who checked it. It allows a later reviewer to reproduce a yield figure, pump setting or compressor duty and to see which results need rechecking when a reading is corrected.
How do I calculate specific capacity of a borewell?
Divide the steady pumping discharge by the drawdown at that discharge. For example, 12 m³/h with 8 m of drawdown gives 1.5 m³/h per metre. State the rate, the pumping duration and the level datum. Specific capacity usually falls at higher rates and longer pumping, so use it for comparison, not to predict yield at much higher rates.
What pressure does an air-lift compressor need to start?
Roughly the submerged length of the air line converted to water head, plus losses. About 0.98 bar (14.2 psi) is needed for every 10 m of submergence, so 60 m of submergence needs around 5.9 bar (85.6 psi) to start. The working pressure normally falls once the water begins to lift. Choose a compressor with margin above the start figure.
Why do my borewell calculations give different answers?
The most common causes are mixed units, different level datums, readings taken at different stages of recovery, and different methods of averaging a varying discharge. Write units through each formula, state the datum for every level and record how daily volumes were integrated. A register with these details usually shows exactly where two answers diverged.
Should I correct compressor output for summer heat?
Where mass of air matters, yes. Free air delivery is a volume at inlet conditions, and hot air is less dense: at about 45 °C intake air carries roughly 8% less mass than at 20 °C. For tight drilling or air-lift duties, record the ambient temperature and allow margin, rather than selecting a machine that only just meets the duty on paper.
Who should verify borewell calculations?
Someone other than the person who did them, ideally an engineer familiar with the method. The checker confirms units, datums, input sources and the formula, and reproduces at least the key results. Recording who checked each entry and how gives the well owner, pump supplier and compressor supplier confidence that the numbers behind their decisions are sound.
Related pages
Calculators and worked examples
These tools give indicative figures for screening, comparison and for preparing an enquiry. They run in your browser and send nothing. No prices or tariffs are assumed: enter your own to see costs. Efficiencies and other figures shown are example values: replace them with your own. Results are not a performance guarantee or a design certificate; final selection is confirmed by a service engineer against the machine data sheet and the site.
Borewell air-lift start pressure and submergence
Estimate the pressure a compressor needs to start an air-lift (development, testing or redevelopment), the submergence ratio, and the effect of hot intake air on the mass of air delivered.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Submerged length of the air line below standing water (m): 60
- Lift from the water level up to the discharge point (m): 40
- Hose and fitting losses (bar): 0
- Compressor rated pressure, to check margin (bar g; 0 to skip): 0
- Compressor intake temperature (°C): 45
Result
- Air-lift start pressure: 5.89 bar g = 85 psig = 6 kg/cm² (60 m × 0.0981)
- Submergence ratio: 60% of the air-line length below the discharge point
- Air mass at this intake temperature: -7.9% compared with 20 °C intake air
Method. Start pressure ≈ submerged length of the air line × 0.0981 bar per metre of fresh water (10 m ≈ 0.98 bar ≈ 14.2 psi) + hose and fitting losses. The submerged length is measured from the water level at the time of starting to the air-line foot; once lifting begins the working pressure usually falls. Submergence ratio = submerged length ÷ (submerged length + lift from the water level to the discharge point); about 60% is commonly quoted as a target, and lower submergence lifts water poorly. Free air delivery is a volume at inlet conditions, so hot intake air carries less mass: mass ratio = (20 + 273.15) ÷ (intake °C + 273.15).
What to take from it. Choose a compressor with clear margin above the start pressure, and record the datum and submerged length with the result.
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 17 October 2026. How our engineering content is reviewed.
Pumping test: Drawdown, specific capacity and pumped volume
Work out drawdown, specific capacity and pumped volume from a pumping test, with every level measured from the same datum.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Static water level below datum (m): 30
- Pumping water level below the same datum, stabilised (m): 50
- Discharge: 600
- Discharge unit: L/min
- Pumping duration at constant discharge (h): 24
Result
- Drawdown: 20 m
- Discharge: 600 L/min = 10 L/s = 36 m³/h
- Specific capacity: 30 L/min per m of drawdown, at 600 L/min after 24 h
- 1.8 m³/h per m
- 0.5 L/s per m
- Pumped volume at constant discharge: 864 m³ = 8,64,000 litres
Method. Drawdown s = pumping water level − static water level (both as depths below the same datum, e.g. top of casing). Specific capacity = discharge Q ÷ s, quoted with the rate and the pumping duration, because it usually falls as the rate rises and as pumping continues. Pumped volume V = Q × t, valid only while the discharge is constant; for a varying discharge add the measured interval volumes. 1 L/s = 3.6 m³/h = 60 L/min.
What to take from it. Choose the operating rate from the constant-rate and recovery tests with headroom for the dry season and nearby pumping, not from the airlift figure or the maximum tested rate.