What a borewell air supply record should prove
Rig owners and drilling contractors judge a compressor supplier on one thing: whether the machine kept the hammer working and the hole clean, shift after shift. A useful project record answers that question with facts rather than adjectives. It should show:
- What the drilling job needed: hole diameter, planned depth, hammer size, ground conditions and expected water ingress.
- What was supplied: compressor type, rated pressure and flow, drive (diesel or electric), hoses, booster or lubricator where used.
- How it was set up: hose length and size, manifold, valves and the connection to the rig.
- What was observed: discharge pressure, pressure at the rig where gauged, running hours, fuel use as logged, alarms and stoppages.
- How it was maintained: oil and filter changes, checks done on site, any repairs.
- What the record does not show, stated plainly.
A record does not prove that a bore struck water, how much water it yields or how fast every hole will drill. Yield and penetration depend on the formation, the bit, the hammer and the driller as much as on the air. We never present a drilling result as something the compressor guaranteed.
We supply all types, all brands and all models of borewell compressors: new machines, used and refurbished units, rentals, service and spare parts. The records on this page are how we explain that work honestly.
Pressure and flow are different jobs
A DTH hammer needs pressure to strike with enough energy, and the hole needs air volume to lift cuttings to the surface. Both must be right, and one does not stand in for the other.
- Pressure governs hammer impact energy within the hammer maker’s limits. As the hole deepens and water enters, back-pressure in the annulus rises, so more compressor pressure is needed to keep the hammer firing.
- Flow governs uphole velocity in the annulus between the drill pipe and the hole wall. Too little flow and cuttings settle, regrind and can jam the string.
- Pressure at the hammer is always lower than at the compressor because of losses in hoses, swivels, valves and the drill string.
- Free air delivery (FAD) in cfm is quoted at reference intake conditions; actual flow at line pressure is a much smaller volume. The two must not be mixed in a record.
Our borewell rig as an integrated system page explains how compressor, rig, hammer and hole work together.
Typical borewell compressor bands
The table shows the pressure and flow bands we commonly see on borewell and DTH work. They are typical working ranges, not a selection rule; the right machine depends on hole size, depth, hammer, water and ground.
| Pressure band | Typical flow band | Where it is usually seen |
|---|---|---|
| 200–250 psig (13.8–17.2 bar) | 600–900 cfm | Shallower agricultural and domestic bores in stable ground |
| 250–300 psig (17.2–20.7 bar) | 800–1,200 cfm | Medium-depth bores, larger hammers, moderate water |
| 300–400 psig (20.7–27.6 bar) | 1,000–1,500 cfm | Deep bores, heavy water ingress, hard rock |
| Up to about 500 psig (34.5 bar) | Special units | Very deep or special drilling duties |
Overall, borewell compressors usually fall between 600 and 1,500 cfm at 200–400 psig (13.8–27.6 bar), with special high-pressure units up to about 35 bar. A record should state which band the job needed and which machine was supplied.
Define the drilling duty
Depth alone is not a compressor specification. Before a job is recorded we note:
- Hole diameter and planned depth, and the depth actually reached.
- Hammer and bit size, and the hammer maker’s stated pressure range, where the driller shares it.
- Ground conditions as observed: overburden, weathered rock, hard rock, fractured zones.
- Water ingress depth and approximate volume as observed by the driller.
- Casing plan and drilling method.
- Whether figures are measured, estimated or reported by the operator.
In Telangana and Andhra Pradesh, many agricultural bores pass through weathered rock into hard granite, and summer ambient temperatures of 40–45 °C, and above 45 °C on open sites, put real strain on compressor cooling. A record that notes ambient temperature and dust conditions is far more useful to the next rig owner than one that only states depth.
Measure at the right points
A single gauge on the compressor panel cannot tell you what the hammer is receiving. Where practicable we record pressure at three points:
| Measurement point | What it shows | Limits |
|---|---|---|
| Compressor discharge | What the machine is producing and whether it is loading fully | Says nothing about losses downstream |
| Rig inlet, after the hose | Hose and fitting losses | Needs a calibrated gauge fitted for the job |
| Hammer feed, at the top of the string | The best surface indication of hammer supply | Downhole pressure still differs because of string losses and back-pressure |
Each reading should carry the unit and whether it is gauge pressure, the time, the hole depth at that moment, and whether the hammer was drilling or blowing clean. We do not write that a machine “delivered” a flow to the hammer unless that flow was actually measured.
Equipment identity and condition
The record identifies the compressor by make, model and serial number or an anonymised fleet number, with its nameplate pressure and FAD. It notes the engine, the hours at start and finish, the oil grade used, and the condition of air and oil filters at delivery. For a used or refurbished machine it notes what was overhauled before delivery.
Hoses, safety whip checks, clamps and valves are listed too. A burst high-pressure hose is one of the most serious hazards on a borewell site, and the record should show that hoses were rated for the working pressure.
Service on site
Borewell compressors work in heat, dust and long shifts. The service log is often the most valuable part of the record. It should show:
- Air filter cleaning or replacement intervals, which shorten sharply in dusty conditions.
- Oil and oil filter changes, with hours. On our hire jobs we change oil and service at every 300 running hours.
- Separator differential pressure and any element changes.
- Cooler cleaning; radiator and oil cooler fins clog quickly with drilling dust.
- Safety shutdowns: high discharge temperature, low engine oil pressure, high coolant temperature, and what caused each one.
- Repairs carried out and parts fitted.
Our borewell compressor service and repairs and rig reliability and drilling records pages go further into these checks.
What we will not publish
- Customer or rig owner names, unless they have given written permission.
- Groundwater yield, bore success or penetration rates presented as a result of our equipment.
- Depths, yields or costs for particular villages or districts.
- Prices or rates of any kind.
- Photos whose date, place and machine cannot be confirmed.
We add borewell project records to this page as rig owners and contractors agree to publication. Until a record has passed these checks, we describe our borewell work in general terms on our service, rental and sales pages rather than presenting it as a verified project.
Record template: field by field
The sections above explain what a record should prove. The table below sets out the individual fields, the units to use and what counts as acceptable evidence. It follows the rule stated at the top of this page that every figure gives its unit, where it was measured and who confirmed it. You can apply the same standard to any supplier’s records. A field left blank is better than a field filled with a guess. If a figure was estimated and not measured, the record should say so.
| Field | What to record | Units | Acceptable evidence |
|---|---|---|---|
| Job identity | Month and year, state or region, and whether the customer agreed to publication; the exact location is kept on file, not published | Not applicable | Written consent from the customer; dated job sheet |
| Hole design | Bit diameter for each section, casing depth and diameter, final depth | mm (or inches with mm stated), m | Driller’s log |
| Hammer and string | Hammer size, drill pipe outside diameter, total string length | Inches or mm, m | Rig equipment list |
| Compressor | Make, model, serial or fleet number, rated flow and pressure from the nameplate | cfm, psig and bar(g) | Nameplate photograph |
| Pressure readings | Compressor discharge pressure and rig inlet pressure at stated depths | psig or bar(g), m | Log sheet with time, depth and gauge position |
| Flow | Rated free air delivery; whether the machine ran at full load or was unloading | cfm (free air) | Nameplate, plus the controller or regulator state noted on the log |
| Ground and water | Formation changes, depth of each water strike, whether returns were wet | m | Driller’s log |
| Conditions and running | Ambient temperature, discharge temperature, engine hours at start and finish, fuel added | °C, h, litres | Log sheet; hour meter photographs at start and finish |
| Faults and service | Each stoppage, its cause and the work done | Time and hours | Service report |
| Verification | Who took the readings, who checked them, and the date checked | Not applicable | Name and role of the person who checked |
How to evaluate any supplier’s borewell references
A rig owner or drilling contractor comparing suppliers should test every reference the same way, including references from us. Use this checklist:
- Can the reference be traced? Is there a month, a general location and a person you can call with the customer’s permission? A reference with no date and no contact is only a claim.
- Is the compressor identified? Look for model and nameplate rating, not “a 1,000 cfm machine”. Nameplate flow is free air delivery in cfm at a stated pressure. Check that the rating matches the duty described.
- Are the pressures in their units and at a stated gauge position? “300” means little. “300 psig at the compressor discharge at 150 m” can be checked.
- Do the figures make physical sense? Rig inlet pressure cannot be higher than discharge pressure. The pressure should rise as the water column above the hammer grows. Fuel used should fit the engine hours worked.
- Does the record separate air supply from water yield? A record that promises water because of the compressor is not an engineering record.
- Are faults included? A real field record usually shows a clogged filter, a hose change or a stoppage. A record with no problems at all needs a second look.
- Is field data kept apart from brochure data? Ask which figures were measured on site and which were copied from a datasheet.
- Does it match your job? A reference from shallow, dry ground says little about a deep, wet bore. Compare hole size, depth band and water conditions.
How to read a drilling air log
A drilling air log is a time and depth sequence. Read it as a set of trends, not as single readings. The log below is illustrative. It is not a project record, and it does not describe any customer or site. It assumes a 165 mm (6.5 in) hole below casing, 114.3 mm (4.5 in) drill pipe and a compressor rated at 1,000 cfm at 350 psig (24.1 bar(g)).
| Time | Depth (m) | Discharge (psig) | Rig inlet (psig) | Note |
|---|---|---|---|---|
| 08:10 | 12 | 230 | 218 | Casing set; drilling 165 mm, dry returns |
| 10:00 | 60 | 240 | 227 | Hard rock, steady dust return |
| 11:20 | 95 | 290 | 276 | First water strike; returns wet |
| 13:40 | 150 | 315 | 301 | Second water at 140 m; heavy wet returns |
| 15:30 | 200 | 330 | 315 | Penetration slowing |
| 17:20 | 240 | 335 | 319 | Final depth; hole blown clean |
Pressure. Discharge pressure rises slowly in dry rock, from 230 to 240 psig. It then steps up by about 50 psig at the first water strike. A column of water above the hammer adds back-pressure: 10 m of water is about 0.98 bar, or 14.2 psi. A 50 psi step is therefore about 35 m of solid water column. Aerated returns weigh less than solid water, so the real column is usually longer than that. The point is that the step lines up with the water note. A pressure step with no change in ground or water would point to a blocked bit, a collapsing hole or a hammer fault. See wet-hole drilling and water ingress.
Hose and fitting loss. Discharge minus rig inlet stays between 12 and 16 psi. That is steady, so the hose and couplings are not getting worse. A difference that suddenly grows points to a kinked hose, a partly closed valve or a damaged coupling.
Margin to rating. At 240 m the discharge pressure is 335 psig against a 350 psig rating, which leaves 15 psi. Any deeper or wetter, and the compressor starts to unload or modulate, and delivered flow falls. A credible log notes whether the machine was still at full load.
Cuttings lift. The annular area is π ÷ 4 × (0.1651² − 0.1143²) = 0.01115 m². 1,000 cfm is 1,000 ÷ 35.315 = 28.32 m³/min of free air. At atmospheric pressure the up-hole velocity would be 28.32 ÷ 0.01115 ÷ 60 = about 42 m/s. Near the bottom of the hole the annulus pressure is higher. At 3 bar(a) the actual velocity is about 42 × 1.01325 ÷ 3 = 14 m/s. A minimum of about 15 m/s (about 3,000 ft/min) is often quoted for dry cuttings, and wet or heavy cuttings need more. So in this illustration, cleaning at depth in wet ground is marginal. See cuttings transport and borehole cleaning.
Fuel. Suppose the log shows 9.5 engine hours and 513 litres of diesel for 228 m drilled below casing (illustrative). That is 513 ÷ 9.5 = 54 litres an hour and 513 ÷ 228 = about 2.25 litres a metre. The hourly figure is an average of loaded drilling and unloaded running during rod changes. Litres per metre is the figure to compare between jobs. See drilling productivity and cost per metre.
Site conditions and the air figures a credible record should show
Different ground and weather put different demands on the compressor. A credible record shows the figures that matter for its conditions. The table below lists them, with the warning signs to look for.
| Site condition | Figures that should appear | Warning signs in a record |
|---|---|---|
| Dry hard rock, moderate depth | Steady discharge pressure; small, constant hose loss; litres of fuel per metre | Large pressure swings with no ground change noted |
| Soft overburden with casing | Bit and casing diameters, casing depth, larger-diameter section noted separately | Annular velocity worked out for the small hole and applied to the large one |
| Heavy water ingress | Depth of each water strike, the pressure step at each, full-load or unloading state | Wet returns logged with no change in pressure |
| Deep bore, near the pressure rating | Discharge pressure against rated pressure; any booster use stated | Pressures at or above the nameplate rating with no booster recorded |
| Summer ambient of 40–45 °C | Ambient and discharge temperatures; any high-temperature trips | No temperature data from a summer job |
| Dusty site | Air filter restriction readings, filter changes with engine hours | No filter entries on a long dusty job |
Why temperature belongs in the record. A compressor delivers a fixed volume of air, but hot air weighs less. Air at 45 °C has 298.15 ÷ 318.15 = 0.937 of the density it has at 25 °C. So the same cfm delivers about 6% less mass of air for lifting cuttings and driving the hammer. The discharge temperature is also closer to the trip setting. Two jobs with the same cfm and psig can perform differently in April and in December. A record without temperature cannot show why. For fault-finding from these readings, see borewell compressor performance diagnostics.
How Reddy Compressors helps
Reddy Compressors, at Tarnaka, Secunderabad, has served industry since 2002. We supply borewell compressors of all brands, including ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Doosan and others, as an independent multi-brand business, not an authorised dealer. We have tie-ups with all major and reputed brands. For rig owners and drilling contractors we:
- Sell new borewell compressors and supply used and refurbished units.
- Rent borewell and high-pressure compressors from our own fleet.
- Service, repair and overhaul borewell compressors with our team of over 20 service engineers and technicians across Telangana and Andhra Pradesh.
- Supply spare parts across India, identified from the make, model, serial number, nameplate photo or old part, with fit confirmed before quoting.
- Help you match pressure and flow to your hammer, hole and ground before you buy or hire.
What to send us
- Hole diameter, typical and maximum depth, and hammer size.
- Ground conditions and expected water ingress.
- Rig make and model, and your current compressor’s nameplate photo if you have one.
- Whether you need to buy new, buy used, hire or repair.
- Your working location and the expected duration of the work.
Frequently asked questions
What size compressor do I need for borewell drilling?
Most borewell compressors fall between 600 and 1,500 cfm at 200–400 psig (13.8–27.6 bar). The right size depends on hole diameter, hammer size, depth, ground and water ingress. Deep bores with heavy water need more pressure; larger holes need more flow to lift cuttings. Send us your hole size, depth and hammer details and we will recommend a range.
Why does my DTH hammer stop working at depth?
As the hole deepens and water enters, back-pressure in the annulus rises and the compressor may not have enough pressure left to fire the hammer. Other causes are hose and string losses, a worn hammer, a compressor not loading fully, or a blocked air filter. Measuring pressure at the compressor and at the rig helps find which one it is.
Does a bigger compressor guarantee more water from a borewell?
No. Water yield depends on the geology and the aquifer, not on the compressor. The right compressor lets the hammer drill efficiently and keeps the hole clean so the driller can reach and test the water-bearing zones. That is why our project records describe the air supply only and never claim a bore success or yield.
How often should a borewell compressor be serviced?
Follow the maker’s schedule as a minimum and shorten intervals in dust and heat. On our own hire jobs we change oil and service at every 300 running hours. Air filters may need daily cleaning on dusty sites, and coolers need regular cleaning to prevent high-temperature shutdowns in summer.
Can I hire a borewell compressor instead of buying one?
Yes. We rent borewell and high-pressure compressors from our own fleet for short jobs, seasonal peaks or while your own machine is under repair. Hiring makes sense when work is irregular or you want to try a pressure and flow class before buying. For steady year-round drilling, buying new or used usually works out better.
Do you supply spare parts for all borewell compressor brands?
Yes. We supply spares for all brands and models of borewell compressors across India. We identify parts from the make, model, serial number, nameplate photo or the old part, and confirm fit before we quote. That avoids the delays and costs of a wrong part reaching a remote rig site.
How do I check a borewell compressor supplier’s references?
Ask for references with a month, a general location and a contact you may call with the customer’s permission. Each should give the compressor model and nameplate rating, and pressures with units and gauge positions at stated depths. Check that the figures make sense. Rig inlet pressure should be below discharge pressure, pressure should rise with water ingress, and fuel used should fit the engine hours. Be careful with any reference that links the compressor to water yield, or that has no dates and no faults at all.
What should a drilling air log record?
At each depth reading, record the time, depth, compressor discharge pressure and rig inlet pressure. Note whether the compressor was at full load or unloading. Record formation changes and the depth of every water strike. For the whole job, record engine hours at start and finish, fuel added, and ambient and discharge temperatures. Note any stoppage, its cause and the repair. Readings must have units and gauge positions. A log with these entries lets anyone check hose losses, back-pressure and fuel per metre.
What up-hole air velocity is needed to clean a borewell?
A minimum of about 15 m/s (about 3,000 ft/min) is often quoted for lifting dry cuttings. Wet or heavy cuttings need more. To estimate it, divide the free air flow by the annular area between the hole and the drill pipe. Then correct for the pressure in the annulus, because air at 3 bar(a) takes up about one third of its free volume. For example, 1,000 cfm in a 165 mm hole with 114.3 mm pipe gives about 42 m/s at atmospheric pressure, but only about 14 m/s at 3 bar(a).
How do I calculate diesel used per metre of borewell drilling?
Divide the litres of diesel added over the job by the metres drilled in the same period. Use engine hour meter readings at start and finish to get litres per hour as well. For example, 513 litres over 228 m is about 2.25 litres a metre, and over 9.5 engine hours it is 54 litres an hour (illustrative figures). Compare litres per metre between jobs in similar ground and depth. A rise often points to clogged filters, a worn hammer or the compressor running near its pressure limit.
Related pages
Technical content reviewed by D. Srinivas Reddy, Managing Partner and service engineer, Reddy Compressors. Last updated 7 November 2026. How our engineering content is reviewed.