Quick answer: size a compressor for a mixed YT rock-drill fleet from the credible maximum number of each model that can run together, using each drill’s air consumption at the planned operating pressure. Then add other simultaneous air users, measured leakage, explicit future demand and any stated planning allowance before applying the compressor supplier’s site-performance correction. Finally, verify dynamic pressure at the drill inlets under the real combined load. Do not approve the system from compressor kW, receiver size or a headline cfm figure alone.
This guide covers mixed fleets such as YT28 plus YT29A, or a combination that also includes YT24-family and YT27 drills. It does not repeat the existing YT28 single-model compressor sizing guide. If every drill is YT28, use that page. Use this page when different models, different data quality or different operating points must be brought into one auditable calculation.
Inputs required before the calculation
| Input | Symbol | What to record | Why it matters |
|---|---|---|---|
| Installed drill count | ni | Quantity of each exact model or suffix | Defines the possible load, not the actual simultaneous peak by itself |
| Simultaneous factor | di | Maximum simultaneous count divided by installed count; use 1 when the peak is uncertain | Prevents average shift use from hiding a real production peak |
| Per-drill demand | qi | Air consumption at the selected pressure from the exact controlled data sheet | Different pressure points and model families cannot be mixed casually |
| Other air users | Qother | Concurrent breakers, pumps, blow-off or other tools with their duty pattern | They consume the same source capacity |
| Measured leakage | Qmeasured leak | Leak rate from an existing system audit, if available | A measured load is better than hiding leakage in a generic percentage |
| Future demand | Qfuture | Only loads the project actually intends to add | Keeps expansion capacity explicit and reviewable |
| Temporary unknown allowance | Aunmeasured | A separately stated project assumption when leakage or growth cannot yet be measured | Shows uncertainty instead of presenting it as product demand |
| Site performance factor | Ksite | Compressor-supplier correction for actual altitude, temperature, pressure and condition | Catalog delivery can differ from delivery at the mine or quarry |
| Distribution loss | ΔPtotal | Calculated or measured loss through piping, hose, couplings, treatment and valves | The drill must still receive its required dynamic inlet pressure |
Current controlled starting values
The table is deliberately incomplete. The live PerfoMax product record currently provides pressure-specific values for YT28 and YT29A. YT24 remains a family identification entry, and YT27 does not yet publish a fixed controlled air-consumption value. Obtain those two values from the final suffix/model data sheet before completing a fleet calculation.
| Drill | 0.50 MPa reference | 0.63 MPa reference | Use in this calculation |
|---|---|---|---|
| YT24 family | q24: confirm | q24: confirm | Identify YT24C, TY24 or an unknown state, then obtain the controlled value for that suffix |
| YT27 | q27: confirm | q27: confirm | Working range is published as 0.4–0.63 MPa, but fixed consumption remains quotation-controlled |
| YT28 | ≤55 L/s | ≤81 L/s | Use only at the same selected pressure and compatible air-rating basis |
| YT29A | ≤65 L/s | ≤88 L/s | Use only at the same selected pressure and compatible air-rating basis |
Display conversions: 1 L/s = 0.06 m³/min and approximately 2.11888 cfm. A cfm conversion does not prove that the tool-demand and compressor-FAD reference conditions are identical.
A transparent mixed-fleet formula
1. Tool demand: Qtools = Σ(ni × di × qi).
For each model, ni is the installed quantity, di is the justified simultaneous factor from 0 to 1, and qi is the per-drill demand at the selected pressure. The product ni × di should equal a credible maximum simultaneous count. If the work pattern is uncertain, use di = 1 rather than an optimistic average.
2. Site demand: Qsite = Qtools + Qother + Qmeasured leak + Qfuture + Aunmeasured.
Keep every addition visible. Other tools, measured leakage, planned future loads and a temporary allowance for an unmeasured condition are not the same thing. A single unexplained “20% safety factor” prevents the buyer from seeing what capacity is actually buying.
3. Catalog-FAD screening: FADcatalog required = Qsite ÷ Ksite.
Use this division only when the compressor supplier provides Ksite for the actual elevation, temperature, discharge pressure and machine condition. If the supplier already states FAD at the real site condition, compare directly and do not apply the correction twice.
4. Pressure requirement: Psource required ≥ Ptool required + ΔPtotal.
Pressure and flow are separate checks. The source setting must overcome engineered distribution loss while every drill inlet and component remains within its approved pressure range.
Worked example 1: installed fleet versus simultaneous fleet
A site owns three YT28 drills and two YT29A drills, but its documented production plan allows at most two YT28 units and one YT29A unit to drill together at the 0.50 MPa reference point.
- YT28: n = 3; d = 2/3; q = 55 L/s; demand = 3 × 2/3 × 55 = 110 L/s.
- YT29A: n = 2; d = 1/2; q = 65 L/s; demand = 2 × 1/2 × 65 = 65 L/s.
- Base tool demand: 110 + 65 = 175 L/s = 10.50 m³/min ≈ 371 cfm.
This is not the compressor selection. Add the actual other loads, leakage, future demand and any explicit unknown allowance, then check compressor FAD at the site. If the operating rule cannot prevent all five drills from running together, calculate all five with d = 1.
Worked example 2: pressure point and site correction
One YT28 and two YT29A drills are planned to run together using their 0.63 MPa reference values.
- Tool demand: 1 × 81 + 2 × 88 = 257 L/s = 15.42 m³/min ≈ 545 cfm.
- Worked arithmetic only: assume the site audit separately records 20 L/s of other concurrent demand and 10 L/s of measured leakage.
- Worked arithmetic only: assume the compressor supplier provides Ksite = 0.90 for the stated site and duty point.
- Catalog-FAD screen: (257 + 20 + 10) ÷ 0.90 = 318.89 L/s = 19.13 m³/min ≈ 676 cfm.
The 20 L/s, 10 L/s and 0.90 values demonstrate the formula; they are not PerfoMax default allowances. Replace them with measured loads and the compressor supplier’s real performance data. Do not mix the YT28 0.50 MPa value with the YT29A 0.63 MPa value merely to reduce the total.
Worked example 3: a calculation that must stop
One YT24-family drill, one YT27, one YT28 and one YT29A are proposed to run together. At a preliminary 0.50 MPa screen:
Qtools = q24 + q27 + 55 + 65 = q24 + q27 + 120 L/s.
This cannot be converted into a final compressor size. First identify YT24C or TY24, obtain its controlled demand, and obtain the selected YT27 supplier’s consumption at the same operating point and rating basis. A responsible result here is a data request, not an invented cfm number.
FAD, displacement, receiver volume and tool demand are different
| Term | What it tells you | What it does not prove |
|---|---|---|
| Tool air demand | Consumption stated for the exact drill at a defined operating point | That a named compressor can deliver the same basis at the site |
| Compressor FAD/delivered capacity | Usable delivered flow under the manufacturer’s stated reference conditions | Pressure remaining at a distant drill after distribution losses |
| Displacement or theoretical capacity | A machine-design or headline value | Actual delivered air at the required pressure and environment |
| Receiver volume | Short-duration buffering and system stabilization | Sustained replacement of air consumed by continuous drilling |
| Source pressure | Pressure at the compressor, receiver or header | Dynamic pressure at each tool while the mixed fleet is drilling |
Distribution can defeat a correct flow calculation
A total-flow calculation does not size the main pipe, hose, manifold or couplings. Pressure loss changes with total flow, internal diameter, effective length, bends, valves, filters, separators, lubricators, local restrictions and leaks. A 25 mm YT28 tool-hose reference does not mean a shared upstream header for several drills should also be 25 mm.
Use the pneumatic rock-drill air-hose sizing guide for the branch-selection inputs and the long-hose pressure-drop guide for source/header/branch/tool-inlet diagnosis. The mixed-fleet page calculates demand; those pages diagnose how the distribution path delivers it.
High altitude, temperature, storage and operating reality
- Altitude and temperature: request delivered-capacity data or a correction from the compressor supplier for the actual site. Do not invent Ksite.
- Compressor condition: filters, cooling, regulation and maintenance can change actual delivery; a nameplate does not certify current output.
- Receiver or header: it can buffer starts and support distribution, but continuous drills require continuous production capacity.
- Branches: a shared header can work only when it and every branch are sized for the credible simultaneous load and acceptable loss.
- Moisture and lubrication: air treatment and line oilers add pressure loss and must have the correct flow rating, service condition and installation direction.
Commission the fleet under real combined load
- Confirm every exact drill model or suffix, selected operating point, demand value and air-rating basis.
- Record the installed and credible maximum simultaneous count for each model.
- Add other tools, measured leakage, explicit future loads and any temporary unknown allowance as separate lines.
- Check the compressor supplier’s FAD curve at the required discharge pressure and actual site conditions.
- Map the complete path: compressor, receiver/header, treatment, main line, manifold, valves, lubricators, couplings, branch hoses and tool inlets.
- Install suitable rated measurement points under the approved site procedure.
- Run the planned mixed fleet at production load and record source, header and each tool-inlet dynamic pressure at the same time.
- If one branch falls, inspect its diameter, length, fittings, kinks, treatment and leaks. If every branch falls, review source capacity and the common header.
- Record the accepted configuration and readings as the baseline for later maintenance and troubleshooting.
What to send for a mixed-fleet air-system review
- Exact drill model, suffix, supplier and controlled data-sheet revision for every fleet member.
- Installed quantity and maximum simultaneous quantity for each model.
- Selected operating pressure and per-drill consumption at that same point.
- Other pneumatic tools, their demand and whether they overlap with drilling.
- Measured leakage or the clearly labelled temporary allowance used in planning.
- Current or proposed compressor make/model, FAD curve and rated discharge pressure.
- Elevation, ambient-temperature range, duty schedule and compressor condition.
- Receiver/header volume and layout, main and branch lengths/IDs, couplings, valves, treatment and lubricators.
- Existing loaded measurements at the source, header and tool inlets.
- Required drill, air-leg, hose, coupling, oiler, drill-steel, bit, spare-parts and inspection supply scope.
Start with the current Air-Leg Rock Drills Collection and the exact YT28 or YT29A reference where applicable. Then send the fleet schedule and air-system inputs for a configuration review. The written quotation and attached supplier data sheets control the final equipment and operating values.
Frequently asked questions
Can I use one diversity factor for the whole fleet?
Only when the operating plan supports it. A better calculation records the maximum simultaneous count for each model. If the production sequence is uncertain, use all installed drills as potentially simultaneous.
Can I average the 0.50 and 0.63 MPa consumption values?
No. Each value belongs to a stated operating point. Select the approved pressure for the exact drill and keep pressure and demand paired.
How do I size a fleet that includes YT24 or YT27?
Keep q24 or q27 as an unknown until the exact suffix/model and controlled data sheet provide a comparable value. Do not borrow a figure from a similar model.
Does a large receiver let me choose a smaller compressor?
Not for sustained drilling demand. A receiver can buffer short transients, but continuous operation still requires the compressor to replace the air the fleet consumes.
What measurement proves the system works?
Record dynamic pressure near every drill inlet while the planned mixed fleet and other concurrent users are operating, together with source/header readings and the exact configuration. Pressure alone is not a flow measurement, but the combined commissioning record can show whether the designed source and distribution system maintain the approved operating condition.