Why think of the rig as a system?
Rig owners often upgrade one part in isolation: a bigger compressor, a new hammer, longer rods. The result is sometimes disappointing because another part becomes the limit. A large compressor cannot help if the hoses and swivel choke the flow. A high-pressure hammer wastes its potential if the compressor cannot hold pressure at depth with water in the hole. Strong rotation torque without feed control damages threads and bits.
Seen as a system, the borewell rig is a mobile production plant. It must travel to site, stand steady against drilling and pull-back forces, rotate and feed the drill string, drive the hammer, clear the cuttings and let the operator see what is happening below ground. The compressor is a primary production unit in this chain, not an accessory bolted on the back.
The main parts and what each one does
| Part | Role | What limits it |
|---|---|---|
| Carrier (truck or crawler) | Moves the rig, carries the compressor and rods, spreads the load | Axle load, terrain, road limits, space for the compressor and rod rack |
| Mast and feed | Holds the string vertical and applies feed and pull-back | Rigidity, feed force, pull-back capacity for the full string |
| Rotary head | Turns the rods at the right speed and torque | Hydraulic flow and pressure; uncontrolled torque damages threads |
| Hydraulic system | Powers rotation, feed, outriggers, rod handling and winch | Oil cleanliness, filtration, cooling and hose condition |
| Air compressor | Drives the DTH hammer and lifts cuttings and water | Flow (FAD), pressure at depth, temperature control in hot weather |
| Air path | Hoses, valves, lubricator, swivel and rod bore carry air to the hammer | Pressure drop, leaks, undersized fittings |
| Drill rods | Transmit torque, thrust, pull-back and air | Wall thickness, thread condition, straightness, weight |
| Hammer and bit | Convert air energy into impact at the rock face | Rated pressure, air consumption, bit wear, flushing |
| Crew and controls | Set feed, rotation and air; watch gauges; respond to ground changes | Skill, instruments, fatigue on long shifts |
How energy flows through the rig
There are two energy paths, and both start with diesel.
The rotation and feed path
The rig engine drives hydraulic pumps. The oil drives the rotary head motor and feed cylinders or chain. The rotary head turns the rods; the feed holds the bit against the rock. On a DTH rig, rotation mainly indexes the bit so each blow strikes fresh rock, so rotation speed is moderate and torque is used mostly to overcome friction and free the string.
The air path
The compressor engine drives the airend, which delivers air through the discharge valve, hoses, lubricator and swivel, down the rod bore to the hammer. The hammer piston strikes the bit, breaking rock. Exhaust air then flows up the annulus between the rods and the hole wall, carrying cuttings and water to the surface.
Every component on the air path costs some pressure. If the compressor delivers 24 bar (348.1 psig) at the outlet but the hose, swivel and rods lose a few bar, the hammer works at a lower pressure than expected. With a column of water above the hammer, back-pressure rises further: roughly 1 bar (14.5 psi) for every 10 metres of water. This is why deep, wet holes need high-pressure compressors.
Matching the compressor to the hammer and hole
The compressor is matched from the bottom of the hole upwards.
- Start with the hammer. Its size and rated pressure set the air consumption. A hammer run well below its rating drills slowly.
- Add the back-pressure. Estimate the water column above the hammer at the deepest expected point and the losses in the air path.
- Check hole cleaning. The air leaving the hammer must move fast enough in the annulus to lift cuttings. Bigger holes and smaller rods need more air.
- Allow for conditions. Heat, dust and altitude reduce what a machine can sustain. Summer ambient of 40–45 °C, and above 45 °C on open sites, is normal in parts of Telangana and Andhra Pradesh.
- Choose the band. Pick a compressor with a margin over the calculated duty rather than one that runs at its limit all day.
| Pressure | Typical flow | Typical rig duty |
|---|---|---|
| 200–250 psig (13.8–17.2 bar) | 600–900 cfm | Shallower holes, smaller hammers, drier ground |
| 250–300 psig (17.2–20.7 bar) | 800–1,200 cfm | Common agricultural and project borewells |
| 300–400 psig (20.7–27.6 bar) | 1,000–1,500 cfm | Deep holes, high water heads, larger diameters |
| Up to about 500 psig (34.5 bar) | Special high-pressure units | Very deep or heavily water-bearing holes |
For the full method, see DTH hammer air requirement and drilling depth and compressor selection.
Matching rods, hoses and the air path
Rods and hoses are often the forgotten parts of the system.
- Rod diameter: a larger rod reduces the annulus, raising up-hole velocity for better cleaning, but adds weight and pull-back load on the mast.
- Rod condition: worn threads leak air, lose energy and risk a dropped string. Inspect and gauge threads regularly.
- Hoses: high-pressure hoses must be rated above the compressor’s maximum pressure, with the right bore so they do not throttle flow. Fit whip checks on every joint.
- Swivel and valves: an undersized swivel or partly closed valve can waste several bar before the air reaches the rods.
- Lubricator: the hammer needs rock-drill oil in the air stream. Too little wears the hammer; too much wastes oil and can foul the bit.
- Booster: for very deep work, a booster can raise pressure from the main compressor. See booster-assisted drilling air.
The crew as part of the system
Two rigs with identical machines can drill at very different rates because of the crew. A good operator reads the ground through the gauges: a rise in air pressure may mean the bit is blocking or water is building above the hammer; a jump in rotation pressure may mean the string is sticking. The operator adjusts feed so the bit stays in contact without overloading the hammer, and blows the hole clean before adding rods.
The crew also keeps the compressor healthy. Daily checks of oil level, air filter, cooler cleanliness and fuel, and attention to the discharge temperature gauge, stop most hot-weather trips. On an oil-injected screw compressor, the discharge temperature normally sits about 75–95 °C; a steady rise is an early warning. Safety shutdowns for high discharge temperature, low engine oil pressure and high coolant temperature should be tested, never bypassed.
Signs the system is mismatched
| What you see | Likely weak link | What to check |
|---|---|---|
| Penetration drops sharply after a water strike | Compressor pressure too low for the water column | Pressure at depth; consider a higher-pressure band or booster |
| Cuttings settle and the bit jams | Not enough air for hole cleaning | Flow, hole and rod sizes, leaks in the air path |
| Compressor trips on high temperature in summer | Compressor running at its limit in heat | Cooler cleanliness, oil, thermostatic valve, margin over duty |
| Fast hammer and bit wear | Wrong pressure for the hammer, poor lubrication, feed too heavy | Hammer rating, lubricator setting, operator feed technique |
| Thread damage and broken rods | Uncontrolled torque, bent rods, mast alignment | Rotation settings, rod inspection, mast condition |
| Hydraulics overheat | Dirty oil or filters, blocked hydraulic cooler | Filtration, oil condition, cooler airflow |
For deeper fault-finding on the air side, see borewell compressor performance diagnostics.
Keeping the whole system working
Downtime on any one part stops the rig. A practical maintenance plan covers all of them:
- compressor oil, filters and separator on a fixed running-hour schedule; on our own hire jobs we change oil and service every 300 running hours;
- engine checks on both rig and compressor engines;
- hydraulic oil sampling, filters and hose inspection;
- rod and thread inspection, with worn rods removed from service;
- hammer servicing and bit regrinding or replacement;
- a simple log of depth drilled, hours, fuel and faults for each hole.
Records make it easier to see which part limits the rig. Our page on borewell rig reliability and drilling records covers this in more detail.
How Reddy Compressors helps
For borewell rig owners we supply all types, all brands and all models of borewell compressors: new sales, used and refurbished machines, rentals, service and spare parts.
Reddy Compressors, at Tarnaka in Secunderabad, focuses on the air side of the borewell rig: the compressor and the air path to the hammer. As an independent multi-brand specialist, we sell, hire and service borewell and DTH compressors from ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic and others, without being an authorised dealer of any one brand.
- Matching: we review your hammer, rods, hole size and water conditions and suggest the compressor band that suits them.
- Sales: new and used borewell compressors, with brand-new machines supplied to site for long-term projects.
- Hire: high-pressure diesel compressors from our own fleet for deeper jobs, peak season or breakdown cover.
- Service and spares: more than 20 service engineers and technicians covering all of Telangana and Andhra Pradesh, and spare parts supplied across India, identified from the nameplate and checked for fit.
What to send us
- Rig make and whether the compressor is truck-mounted or towed
- Hammer make, size and rated pressure; bit and rod sizes
- Typical and maximum depth, and expected water level
- Current compressor make, model, serial and running hours, if any
- The problem you want to solve: slow drilling, overheating, low pressure, a deeper job
Frequently asked questions
What are the main parts of a borewell drilling rig?
The main parts are the carrier, mast and feed, rotary head, hydraulic system, air compressor, air path including hoses and swivel, drill rods, DTH hammer and bit, and the controls. The crew is also part of the system. Each part must suit the others; a weak link in any one of them limits drilling speed and raises running cost.
Watch
A short explainer on this topic
Slide-by-slide engineering explainers from Reddy Compressors. More in the video library.
How do I match a compressor to my DTH hammer?
Start from the hammer’s size and rated pressure, which set its air consumption. Add the back-pressure from water above the hammer, roughly 1 bar per 10 metres, and the losses in hoses and rods. Then check there is enough flow to clean the hole. Choose a compressor with a margin above that duty, not one running at its limit.
Why does my rig drill slowly after hitting water?
Water above the hammer creates back-pressure that the compressor must overcome. As the water column grows, the pressure difference across the hammer falls and so does its impact energy. Cuttings also become harder to lift. The usual remedies are a higher-pressure compressor or a booster, plus checking the air path for leaks and restrictions.
Is a bigger compressor always better for a borewell rig?
No. Extra flow helps only if the hammer, rods and hole need it, and extra pressure helps only if the hammer is rated for it. An oversized machine adds fuel cost, weight and capital cost. The right choice balances hammer rating, hole size, depth and water conditions, with sensible margin for heat and wear.
How often should a borewell compressor be serviced?
Follow the manufacturer’s schedule for oil, filters and separator, adjusted for dust and heat. On our own hire jobs we change oil and service every 300 running hours. Daily checks of oil level, air filter, coolers and discharge temperature matter just as much, because most summer trips come from dirty coolers and low oil.
Can Reddy Compressors supply a compressor for an existing rig?
Yes. Send your rig make, mounting, hammer and rod sizes, depth range and water conditions. We will suggest a suitable new, used or hired compressor in the right pressure and flow band, and the hoses and fittings to suit. We supply across India and service machines throughout Telangana and Andhra Pradesh.
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.
DTH hammer duty against two compressors
Check whether each of two compressors can supply a DTH hammer’s documented air consumption at the pressure the hammer needs, after hose, string and water-column losses, and with what margin.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Hammer working pressure at the hammer (bar g): 21
- Hammer air consumption at that pressure (cfm): 950
- Pressure loss from compressor to hammer (bar): 1
- Water column above the hammer to be lifted (m): 0
- Compressor A: maximum working pressure (bar g): 17
- Compressor A: data-sheet flow at the required pressure (cfm): 1150
- Compressor B: maximum working pressure (bar g): 24
- Compressor B: data-sheet flow at the required pressure (cfm): 1000
- Site derating of delivered flow: heat, altitude, condition (%): 0
Result
- Hammer working pressure: 21 bar g = 305 psig
- Water column allowance: 0 bar
- Required compressor discharge pressure: 22 bar g = 319 psig
- Hammer consumption: 950 cfm = 26.9 m³/min
- Compressor A: Fails: cannot reach 22 bar g (maximum 17 bar g); its flow does not count
- Compressor B: flow available at 22 bar g: 1,000 cfm = 28.3 m³/min
- Compressor B: margin: +5.3 % (covers the duty)
- Result: Only compressor B covers the duty
Method. Required discharge pressure = hammer working pressure + pressure loss from compressor to hammer (hose, swivel, drill string, check valves) + water column to be lifted (0.0981 bar per metre of water). A compressor whose maximum working pressure is below the required pressure fails, whatever its flow. Available flow = data-sheet flow at the required pressure × (1 − site derating). Margin (%) = (available flow − hammer consumption) ÷ hammer consumption × 100. Use the same flow basis (FAD or scfm) for hammer and compressor. 1 bar = 14.504 psi; 1 m³/min = 35.31 cfm. Hole cleaning (annular velocity) is a separate check.
What to take from it. Compare flows at the same pressure. More cfm at a lower pressure does not run a hammer that needs higher pressure.
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.
Annular area and return velocity
In drilling, the air must lift the cuttings up the annulus. Check the return velocity from the hole and rod size.
The worked example below shows the method with fixed numbers. Turn on JavaScript to change the inputs.
Worked example
Inputs
- Hole diameter (mm): 115
- Rod outside diameter (mm): 89
- Free air supplied (m³/min): 12
- Bottom-hole back pressure (bar g): 1
- Target return velocity (m/s): 15
Result
- Annular area: 41.7 cm²
- Return velocity: 24.16 m/s = 4,757 ft/min
- Free air needed for the target velocity: 7.45 m³/min = 263 cfm at 15 m/s
- Assessment: Within the commonly quoted range
Method. Annular area = π/4 × (D_hole² − D_rod²). Actual flow at the back pressure = free air × (P_atm / (P_back + P_atm)). Velocity = actual flow ÷ area. A return velocity often quoted for efficient cuttings lift is around 15–25 m/s; confirm for your material.
What to take from it. Low return velocity leaves cuttings in the hole; very high velocity wears the rods and hammer. Both are warnings, not verdicts.