The 9-Point Checklist I Use Before Ordering a Rotary Screw Air Compressor for DTH Drilling

Who this checklist is for (and why I made it)

I handle equipment orders for drilling contractors. I've been doing it for 7 years. In that time, I've personally made (and documented) 3 significant purchasing mistakes that totaled roughly $11,400 in wasted budget, emergency repairs, and one very awkward phone call with a project manager. Now I maintain our team's pre-order checklist.

This checklist is for anyone ordering a screw air compressor, down hole drilling equipment, or a silent diesel generator for a DTH project. It has 8 steps. It won't make you an expert, but it will keep you from repeating my worst errors.

Step 1: Match the compressor to the DTH drilling machine, not the price tag

The first thing most buyers do is compare quotes. That's backwards. Start with the dth drilling machine spec sheet. You need to know required CFM and PSI at the hammer. For a typical 5-inch DTH hammer, you're looking at roughly 750–1,100 CFM at 150–250 PSI (this varies by altitude and temperature). If you order a rotary screw air compressor that's 20% under spec, the hammer will run sluggish, and you'll blame the bit. I did exactly that in 2019. Cost me $2,100 in unnecessary bit replacements before a technician pointed at the pressure gauge.

Checkpoint: Write down the required CFM/PSI and the maximum altitude. Then add 15–20% buffer for leaks and filter loading.

Step 2: Confirm whether you need a screw air compressor or a rotary screw air compressor

They're the same thing. Screw air compressor is the short name; rotary screw air compressor is the full name. Don't let a supplier confuse you into buying a reciprocating unit because it's cheaper. For DTH rotary drilling, you want a rotary screw—they handle continuous duty better. I once approved a reciprocating compressor for a short job. It worked for two days, then overheated. The rebuild cost $1,800 and we lost a week.

Checkpoint: Confirm the duty cycle. If the compressor runs more than 6 hours a day, go rotary screw.

Step 3: Check compatibility with your existing down hole drilling equipment

This is the step most people skip. Your new compressor might have perfect CFM, but if the discharge valve, hose fittings, or manifold don't match your down hole drilling equipment, you're stuck. I learned this after ordering a unit with a 3-inch outlet when our hoses were 2-inch. The adapter kit cost $650 and arrived three weeks late.

Checkpoint: Take photos of your current connections. Send them to the dealer. Ask for a written confirmation of compatibility.

Step 4: Size the silent diesel generator for starting current, not running current

If you're pairing a compressor with a silent diesel generator, the generator must handle the compressor's starting surge. A 200 kW compressor might need 400 kW for a few seconds. I ignored this in 2022 because the quote looked fine. The generator breaker tripped every time the compressor kicked in. We ended up renting a second generator for $2,400 while waiting for a larger one.

Checkpoint: Ask the compressor dealer for the locked rotor amps (LRA) or starting kVA. Then size the generator 1.5–2x that number. Also confirm noise level—if you're near residential areas, 'silent' means under 75 dB(A) at 7 meters. As of January 2025, most major brands publish this in their spec sheets.

Step 5: Verify the dealer is authorized and parts are genuine OEM

Everyone says they sell genuine parts. Not everyone does. I saved $800 once by buying a 'compatible' aftermarket valve for a screw air compressor. It failed after 400 hours. The downstream damage—oil contamination, seized rotor—cost $3,200. To be fair, the aftermarket part worked fine for the first month. But for DTH drilling, downtime is brutal. Now I only order from authorized Atlas Copco distributors or equally vetted OEM channels. Check the dealer's authorization letter and ask for the part's traceability number.

Checkpoint: Request a photo of the OEM packaging with part number before shipping. If they hesitate, walk away.

Step 6: Calculate total cost of ownership, not just the quote

The lowest quote is rarely the lowest total cost. I built a simple TCO sheet after my third mistake. It includes: base price, freight, startup/commissioning, first-year filters and oil, extended warranty, and estimated fuel consumption. On one order, the 'cheap' compressor was $4,000 less than the premium option. But it burned 12% more fuel and needed service every 250 hours instead of 500. Over two years, the cheap one cost $9,000 more. (Surprise, surprise.)

Checkpoint: Ask for fuel consumption at 75% load and service intervals in writing. Multiply by your expected annual hours.

Step 7: Do a pre-delivery inspection—even if it costs extra

I used to skip factory pre-delivery inspections to save $500. Then a unit arrived with a cracked cooler. The warranty covered the part, but not the $1,200 crane rental or the 6-day project delay. Now I pay for the inspection. It's the cheapest insurance you can buy. If the dealer won't allow it, that's a red flag.

Checkpoint: Request a video walkaround before shipping. Confirm serial numbers match the order.

Step 8: Run the final 5-minute checklist before you hit 'confirm'

This is the step that saves me most often. Even after choosing the right equipment, I kept second-guessing. What if the voltage is wrong? What if the lead time slips? The two weeks until delivery were stressful. So I made a final checklist:

• Voltage and phase match site power (e.g., 480V/3ph/60Hz).
• Lead time confirmed in writing with a penalty clause for delays.
• Shipping address includes gate width and unloading equipment.
• Emergency contact for the dealer's service manager.
• Spare parts kit quoted alongside the main unit.

Run this before every order. It takes 5 minutes. It has caught 14 potential errors in the past 18 months (I keep a log).

Common mistakes (and what they cost)

Mistake 1: Buying the cheapest screw air compressor. Saved $800, spent $3,200 on repairs. Net loss: $2,400 plus downtime.

Mistake 2: Forgetting the generator's starting load. The generator tripped repeatedly. Rented a backup for $2,400. Project delayed 4 days.

Mistake 3: Skipping the compatibility check. Adapter kit cost $650 and 3 weeks. Could have been avoided with a 5-minute email.

Mistake 4: Ignoring altitude. A compressor rated at 1,000 CFM at sea level delivers about 850 CFM at 5,000 feet. We had to derate the drilling speed by 30%.

Final word: prevention beats cure

It took me 7 years and about 60 equipment orders to understand that the 5 minutes you spend verifying a spec is worth 5 days of rework. I'm not 100% sure every checklist item will apply to your specific DTH rotary drilling project. But I am sure that skipping them is how you end up writing a $3,000 email apology.

If you're ordering a rotary screw air compressor or a silent diesel generator for down hole drilling, start with the manufacturer's spec sheet. Then call an authorized dealer. Then run this list. Your future self will thank you.