300–375 cfm compressors

What a 300–375 cfm compressor is

This band sits in the middle of the 250–400 cfm portable class, the workhorse size for construction, plant maintenance, standby air and light drilling across India. Most machines are towable diesel units with an oil-injected screw airend, rated around 7 bar (101.5 psig) or 8.6–10 bar (124.7–145 psig), with some electric skid versions for plant use.

In metric units, 300 cfm is about 8.5 m³/min and 375 cfm about 10.6 m³/min of free air delivery (FAD), measured at the outlet to ISO 1217. As with every compressor, the flow belongs to a pressure. A machine listed at 360 cfm at 100 psig and another at 320 cfm at 125 psig are not simply “bigger” and “smaller”: the second gives less flow but at a higher pressure, and the right one depends on the tool.

Typical loads for 300–375 cfm

The step up from the 250–300 cfm band is usually driven by a third tool, a larger blasting nozzle, or the need for margin on long hose runs. If demand passes about 375 cfm, look at the 375–450 cfm band rather than running at the edge.

Why the hammer figure alone can mislead

Drilling enquiries often start with the hammer’s air consumption because that is the number on the hammer data sheet. But on many rigs the compressor also supplies rotation and feed motors, flushing air, a lubricator and a dust collector. The complete rig demand can be two or three times the hammer figure.

One published drilling-rig brochure illustrates the point for a specific DTH arrangement at a hammer pressure of 10.3 bar (149.4 psig):

On the hammer figure alone, this rig appears to fit a 300–375 cfm compressor easily. On the complete rig figure it falls well outside the band, and the brochure notes that extra flushing air may be needed depending on depth and formation. This is one example, not a rule for other rigs, but it shows why the full equipment list must be checked before choosing a size. Removing the dust collector to make the numbers fit is not an acceptable answer.

Convert units before comparing

Rig and hammer makers often publish air demand in litres per second or m³/min; compressor data is often in cfm. Comparing the numbers without converting causes large errors. Useful conversions are:

• cfm ≈ litres/second × 2.119
• cfm ≈ m³/min × 35.31
• m³/min ≈ cfm × 0.0283
• psig ≈ bar(g) × 14.5

So 208 litres/second is about 441 cfm, and 10 m³/min is about 353 cfm. These conversions change only the unit. They do not correct between different reference conditions; if a rig figure and a compressor FAD rating use different reference temperatures or pressures, ask for clarification. Keep the original value and unit next to the converted figure so that anyone checking later can trace it.

How to screen a drilling enquiry against this band

1. Identify the rig model and its installed options, including the hammer or drifter, dust collector and any foam or water injection.
2. Find out which functions use compressed air from the external compressor and which are hydraulic or engine-driven.
3. Take the maker’s total air requirement for that configuration at the working pressure. If only component figures exist, add them without double counting.
4. Convert everything to the same unit and pressure basis.
5. Add allowances for depth, formation and water, which can raise flushing air requirements.
6. Compare with the compressor’s FAD at the required discharge pressure, allowing for hose losses.
7. If the total exceeds the band, move up a size; for deep borewells, the 600–1,500 cfm high-pressure class is the right starting point.

Choosing between 7 bar and 10 bar versions

Many models in this band come in a 7 bar (101.5 psig) and a 10 bar (145 psig) version, or as a variable-pressure machine. A 10 bar machine is useful for rock drills that like higher pressure, for long hose runs and for some blasting set-ups. But it uses more fuel for the same air: about 7% more power is needed for every extra bar. If the tools only need 7 bar, a 7 bar machine with higher flow is usually the better buy or hire.

For plant standby, match the plant’s normal pressure band. A standby unit set well below the plant pressure will not take load; one set far above it wastes energy and can upset the plant’s controls.

Faults to watch for in this size

• Pressure drops under load: demand exceeds delivery, or hoses are undersized.
• High discharge temperature shutdown: clogged oil cooler or radiator, low oil, or recirculating hot air. Normal oil-injected discharge temperature is about 75–95 °C.
• Low engine oil pressure or high coolant temperature shutdown: check levels, belts and radiator cleanliness first.
• Oil in the air: separator element due, scavenge line blocked or oil overfilled.
• Water at the tools: missing or failed aftercooler and separator drain.
• Hard starting: battery, charging system or fuel issues; dusty sites also clog fuel and air filters quickly.

On our own hire jobs we change oil and service every 300 running hours, with filter checks more often on dusty drilling sites.

Rent, buy new or buy used in this band?

Contractors who keep a 300–375 cfm machine busy most of the year usually buy, either new or a refurbished used unit with a known service record. For a single project, a shutdown or work whose size is uncertain, hire avoids capital outlay, includes servicing and lets you move up a size if the rig or tool list changes. Many fleets own a base machine and hire for peaks.

When buying used, ask for the running hours, the engine and airend service history and a loaded run at rated pressure and flow. A machine that reaches pressure but cannot hold it with full demand may have a worn airend, a sticking intake valve or a control fault, and each has a very different repair cost.

How Reddy Compressors helps

We sell (new and used/refurbished), rent and service portable compressors of ELGi, Atlas Copco, Ingersoll Rand, KAESER, Chicago Pneumatic, Doosan and other makes as an independent multi-brand specialist, not an authorised dealer of any brand; brand names and trademarks belong to their owners. We have tie-ups with all major and reputed brands.

In the 300–375 cfm band we sell new and used/refurbished diesel and electric portables, rent from our own fleet with hoses, aftercoolers and moisture separators, and provide service, AMC, overhaul, breakdown repair and spares identified from your machine’s nameplate. For drilling enquiries we check the complete rig demand before recommending a size, and we will tell you if the job belongs in a larger class.

Our office is at Srinilayam, 12-13-200, First Floor, Street No. 1, Tarnaka, Secunderabad 500017, and we have served industry since 2002. Call +91 99590 60718 or +91 92468 88812, WhatsApp +91 99590 60718, or email reddycompressors@gmail.com. Our service teams cover the whole of Telangana and Andhra Pradesh, and we supply compressors, rentals and spare parts across India.

What to send us

• Tools or rig model, with installed options such as dust collector
• Air demand from the maker’s data, with unit and pressure
• Pressure required at the tool or rig inlet
• Hole depth, diameter and expected formation for drilling work
• Hire period or purchase plan and site location
• For service or spares: make, model, serial number and nameplate photo

Frequently asked questions

How many rock drills can a 375 cfm compressor run?

Rock drills typically use about 85–145 cfm at 7–10 bar (101.5–145 psig), so a 375 cfm compressor usually runs two medium drills with margin or three lighter drills. Check the maker’s figure at your working pressure and allow for hose length and wear. Running at the limit leaves no headroom for leaks or a worn drill.

Is 350 cfm enough for a DTH drilling rig?

Sometimes for small, shallow rigs, but often not. Check the complete rig demand, including rotation, feed, flushing and dust collection, not just the hammer. One published rig example needs about 201 cfm for the hammer but about 578 cfm in total with its dust collector. Deep borewells normally need the 600–1,500 cfm high-pressure class.

How do I convert litres per second to cfm?

Multiply litres per second by about 2.119 to get cfm. For example, 208 litres/second is about 441 cfm. To convert m³/min to cfm, multiply by about 35.31. These conversions change the unit only; they do not adjust for different reference conditions. Keep the original value alongside the converted figure for checking.

Should I choose a 7 bar or 10 bar compressor in the 300–375 cfm range?

Choose by the pressure your tools need at their inlet, plus hose losses. A 10 bar machine helps rock drills and long hose runs, but uses roughly 7% more power for each extra bar. If your tools run well at 7 bar (101.5 psig), a 7 bar machine usually gives more air for less fuel.

Why does my 350 cfm compressor shut down on high temperature in summer?

In summer ambient of 40–45 °C, and above 45 °C on open sites, the cooling system has little margin. Common causes are dust-blocked oil coolers and radiators, low oil level, a slipping fan belt or hot air recirculating into the cool-box. Clean the cores, check oil level and park the machine with its cooling air intake away from exhaust and walls.

Do you rent 300–375 cfm compressors outside Hyderabad?

Yes. Our service teams cover all of Telangana and Andhra Pradesh, and we supply rentals, equipment and spares across India. Rentals come from our own fleet of diesel and electric machines, with hoses and moisture separators as needed, and operators on request. We service hire machines every 300 running hours.

Related pages

• 250–300 cfm compressors
• 375–450 cfm compressors
• cfm, psi and bar conversion and selection
• DTH drilling compressors
• Diesel portable compressors
• Temporary air for construction work zones