DTH hammer duty comparison tool

What does the hammer duty comparison tool do?

The tool sets two hammers, or a hammer and a candidate compressor, side by side using documented data. For each case it records the exact hammer model and bit, the working pressure and air consumption from the hammer maker’s data, the flow basis, and the compressor flow available at that same pressure. It then shows whether the duty is covered, the margin, and the site factors that still need an engineer’s judgement.

The calculator panel on this page performs the comparison. The notes below explain the inputs and why each one matters.

Why pressure and flow must stay paired

A DTH hammer is a pneumatic piston machine. Its air consumption rises with supply pressure: the same hammer passes more air at 24 bar than at 17 bar, and strikes harder and faster. A maker’s data sheet therefore gives consumption at stated pressures, not a single figure. Equally, a compressor’s delivered flow is stated at a rated pressure; many machines can be set to several pressure points with different flows.

• Comparing a hammer’s consumption at 24 bar (348.1 psig) with a compressor’s flow at 17 bar (246.6 psig) is meaningless.
• Pressure at the hammer is lower than at the compressor by the losses in hose, swivel, drill pipe and any check valves.
• Below the pressure the hammer needs, penetration falls sharply and hole cleaning suffers.
• Deep holes with standing water need extra pressure to lift the water column before the hammer can work effectively.

Inputs the tool needs

Use the unit conversion tool where data comes in different units. 1 bar ≈ 14.5 psi, and 1 m³/min ≈ 35.31 cfm.

Typical borewell compressor bands

For water-well and borewell drilling in India, compressors are typically chosen within these bands. They are general working ranges, not a substitute for the hammer maker’s data.

How the comparison works

1. Choose the hammer operating case: the working pressure you intend to use at the hammer.
2. Read the hammer’s air consumption at that pressure from the maker’s data.
3. Estimate the pressure losses from compressor to hammer and add them to get the required compressor discharge pressure.
4. Read the compressor’s delivered flow at that discharge pressure, on the same flow basis.
5. Apply site derating where the compressor maker gives it, for altitude and high ambient temperature.
6. Calculate margin (%) = (compressor flow available − hammer consumption) ÷ hammer consumption × 100.
7. Check hole cleaning: annular velocity between drill pipe and hole wall must lift the cuttings.
8. Record the result and the assumptions; mark any missing data as unresolved.

Worked example

A rig owner plans 6½-inch holes with a hammer that, according to its data sheet, consumes about 950 cfm at 21 bar (304.6 psig) at the hammer. Losses through hose and string are estimated at about 1 bar. Two compressors are offered. The figures are illustrative.

Compressor A has more cfm on paper but cannot deliver the hammer’s pressure, so it fails the comparison. Compressor B meets the duty with a small margin. Because the margin is thin, the rig owner should consider site temperature, altitude and the effect of water in deep holes before committing; a larger unit or a booster may be justified where heavy water is expected.

Hole cleaning and annular velocity

Airflow that powers the hammer also flushes cuttings up the annulus. Annular velocity depends on the free-air flow, the pressure in the annulus and the area between drill pipe and hole wall. A larger bit with the same drill pipe increases the area and reduces velocity; cuttings then regrind at the bottom, slowing penetration and wearing the bit. The annular velocity tool on this site calculates this separately, and the result should be checked against the hammer or bit maker’s guidance and local drilling practice.

Site derating: heat, altitude and machine condition

Data-sheet flow is stated at reference inlet conditions. On a Deccan plateau site in May, inlet air may exceed 40 °C, and hot, thinner air carries less mass per cubic metre, so the hammer receives less effective air. High-ambient packages are designed for this, but older machines run closer to their high discharge temperature shutdown and may unload or trip in the afternoon. Use the compressor maker’s derating guidance where it exists, and keep a margin when the comparison is close.

Machine condition matters as much as the rating. A compressor with a worn airend, a sticking inlet valve, choked air filters or a fouled oil cooler can deliver noticeably less than its nameplate. Before blaming a hammer for slow penetration, check the compressor’s delivered pressure under load, its discharge temperature and its filter and cooler condition. Our borewell service teams carry out these checks during routine visits and breakdown calls.

Common mismatches in the field

• Choosing by cfm alone and finding the compressor cannot hold the pressure the hammer needs.
• Comparing data on different flow bases without converting.
• Ignoring high summer ambient temperature, which reduces delivered air and causes high-temperature shutdowns.
• Changing to a larger bit without rechecking airflow and annular velocity.
• Long or undersized hoses that lose pressure before the hammer.
• Worn airend or unloader valve on an older compressor delivering less than its original rating.

How Reddy Compressors helps

Reddy Compressors supplies all types, all brands and all models of borewell compressors: new sales, used and refurbished machines, rentals, service and spare parts. We work with machines of ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Doosan and others as an independent multi-brand specialist, not an authorised dealer. We have tie-ups with all major and reputed brands.

• Matching compressors to hammers and bits using the hammer maker’s pressure-flow data.
• Rental high-pressure diesel units from our own fleet for drilling seasons and project work.
• Service, overhaul and breakdown repair by over 20 service engineers and technicians, covering Telangana and Andhra Pradesh.
• Spare parts identified from the compressor nameplate and fit confirmed before quoting, supplied across India.

Our office is at Tarnaka, Secunderabad, and we have served industry since 2002.

What to send us

• Hammer make and model, bit size and shank, and the hammer data sheet if available.
• Typical hole depth, rock type and expected water.
• Compressor make, model, nameplate photo and running hours, if you already have one.
• Drill pipe size and hose length.
• Whether you want to buy new, buy used, rent or repair.

Frequently asked questions

What size compressor do I need for a DTH hammer?

One that delivers the hammer’s documented air consumption at the hammer’s working pressure, plus the pressure lost in hose and drill string. Read both figures from the hammer maker’s data sheet, then check the compressor’s flow at that same pressure. For borewells in India, compressors typically fall between 600 and 1,500 cfm at 200–400 psig (13.8–27.6 bar).

Can a higher cfm compressor run any DTH hammer?

No. If a compressor cannot reach the pressure the hammer needs, extra flow at a lower pressure does not help. The hammer will strike weakly, penetration falls and hole cleaning may suffer. Always compare compressor flow at the hammer’s required pressure, after allowing for hose and drill string losses, rather than comparing nominal cfm ratings.

Why does my borewell compressor lose pressure in deep holes?

Deep holes add pressure losses in the drill string and, where water enters, a water column that the air must lift. A compressor working near its pressure limit then cannot keep the hammer at full pressure. Worn airends, faulty unloader or minimum-pressure valves and blocked filters also reduce delivered pressure and flow and should be checked.

Does hammer air consumption change with pressure?

Yes. A DTH hammer passes more air as supply pressure rises, and its blow energy and frequency increase too. That is why makers publish consumption at several pressures. Use the consumption figure at the pressure you actually plan to run, and match it with compressor flow at that same pressure.

What happens if I change to a bigger drill bit?

A bigger bit increases the annular area between drill pipe and hole wall, so the same airflow gives lower upward velocity and poorer cuttings removal. The hammer configuration may also change. Recheck both the hammer’s air requirement and the annular velocity before drilling, and consider a larger compressor or larger drill pipe.

Can I rent a borewell compressor for a drilling season?

Yes. We rent high-pressure diesel compressors from our own fleet for seasonal drilling and project work in Telangana, Andhra Pradesh and further afield. Tell us the hammer, bit size, expected depth and site location so we can propose a machine that matches the duty, with service support during the hire.

Related pages

• Borewell and DTH compressor library
• DTH hammer air requirement
• DTH hammer and bit selection
• Annular area and velocity calculation tool
• Borewell compressor rentals and hire
• New borewell compressor sales