1. Technical Overview & Operating Architecture
The Riello RL Series represents a monobloc, forced-draught, two-stage light oil burner family engineered for low- and medium-temperature hot water boilers, steam generators, hot-air furnaces, and diathermic oil (thermal fluid) heaters. Across nine primary frame sizes—from the compact RL 34 MZ through the industrial RL 250 MZ—the series covers a thermal firing envelope extending from 154 kW to 2700 kW (13 kg/h to 228 kg/h fuel consumption).
Core Design Attributes:
- 1Combustion Dynamics: Monobloc architecture featuring a backward-curved centrifugal fan blade assembly (models RL 50, 70, 100, and 130) or high-pressure straight blades (models RL 34 MZ, 44 MZ, 64 MZ, 190, and 250 MZ) engineered to overcome high combustion chamber aerodynamic backpressures.
- 2Housing Cooling System (HCS): Integrated on RL 34 MZ and RL 44 MZ, this patented thermal barrier provides continuous cooling-air refreshing across the internal chassis, isolating the microprocessor and electrical components from radiant front-plate heat transfer.
- 3Sound-Attenuated Intake: The air intake manifold is internally lined with acoustic sound-proofing material, keeping running operational sound levels significantly lower than open-cage forced-draught alternatives.
- 4Maintenance Accessibility: All models feature integrated slide bars. The burner housing slides backward while remaining mounted to the boiler front plate, allowing full access to the nozzle assembly, diffuser disc, and ignition electrodes without disconnecting fuel lines or unbolting the boiler flange.
- 5Emissions Certification: Manufactured in compliance with European Standard EN 267 and Directives 2004/108/EC (EMC), 2006/95/EC (LVD), and 2006/42/EC (Machinery). Standard models conform to EN 267 Class 1; MZ designated models achieve Class 2 (Low NOx).
2. Fuel Specifications & Fluid Dynamics
The Riello RL Series is specifically factory-configured for commercial and industrial Light Oil (Gas Oil / Industrial Diesel).
- •Standard Fuel: Commercial Light Fuel Oil / Industrial Diesel conforming to EN 267.
- •Net Calorific Value (Hi): 11.8 kWh/kg (10,200 kcal/kg ≈ 42.7 MJ/kg).
- •Fuel Density: Approximately 0.84 kg/dm³ at 15°C.
- •Kinematic Viscosity: 4.0 to 6.0 mm²/s (cSt) at 20°C.
- •Liquid Biofuel Capabilities: Riello offers engineered biofuel configurations (biodiesel, FAME, and vegetable oils) upon special technical-commercial application evaluation.
Warning: Do not introduce Heavy Fuel Oil (HFO / Furnace Oil) or untreated residual fuels into standard Riello RL burners. The internal gear pump, internal hydraulic damper rams, and nozzle cut-off seats are engineered for clean light fuel oil. Heavy oil requires the dedicated Riello RN Series equipped with preheaters and high-viscosity hydraulic circuits.
3. Comprehensive Master Technical Data Table
The following technical matrix reflects the official factory technical data from the Riello RL Series documentation. Firing rates are designated in both kilowatt thermal output (kW) and fuel mass throughput (kg/h).
| Burner Model | Standard Code | Head Configuration | Min Firing Rate (Stage 1) [kW] | Max Firing Rate (Stage 2) [kW] | Min Fuel Rate [kg/h] | Max Fuel Rate [kg/h] | Electrical Supply (Main/Motor) | Aux Voltage | Motor Power [kW] | Emissions Class (EN 267) |
|---|---|---|---|---|---|---|---|---|---|---|
| RL 34 MZ | 3470210 | Standard (TC: 216 mm) | 97 / 154 | 395 | 8.3 / 13.0 | 33.6 | 1/220–230V / 50–60Hz | 220–230V | 0.60 | Class 2 (Low NOx) |
| RL 34 MZ | 3470211 | Extended (TL: 351 mm) | 97 / 154 | 395 | 8.3 / 13.0 | 33.6 | 1/220–230V / 50–60Hz | 220–230V | 0.60 | Class 2 (Low NOx) |
| RL 44 MZ | 3470310 | Standard (TC: 216 mm) | 155 / 235 | 485 | 13.0 / 20.0 | 41.0 | 1/220–230V / 50–60Hz | 220–230V | 0.70 | Class 2 (Low NOx) |
| RL 44 MZ | 3470311 | Extended (TL: 351 mm) | 155 / 235 | 485 | 13.0 / 20.0 | 41.0 | 1/220–230V / 50–60Hz | 220–230V | 0.70 | Class 2 (Low NOx) |
| RL 44 MZ | 3470340 | Standard (TC: 216 mm) | 155 / 235 | 485 | 13.0 / 20.0 | 41.0 | 3/220–400V / 50–60Hz | 220–230V | 0.75 | Class 2 (Low NOx) |
| RL 44 MZ | 3470341 | Extended (TL: 351 mm) | 155 / 235 | 485 | 13.0 / 20.0 | 41.0 | 3/220–400V / 50–60Hz | 220–230V | 0.75 | Class 2 (Low NOx) |
| RL 50 | 3474632 | Standard (TC: 216 mm) | 148 / 296 | 593 | 12.5 / 25.0 | 50.0 | 3/230–400V / 50Hz | 230V | 0.75 | Class 1 |
| RL 50 | 3474633 | Extended (TL: 351 mm) | 148 / 296 | 593 | 12.5 / 25.0 | 50.0 | 3/230–400V / 50Hz | 230V | 0.75 | Class 1 |
| RL 64 MZ | 3470410 | Standard (TC: 250 mm) | 206 / 391 | 830 | 17.4 / 33.0 | 70.0 | 3/230–400V / 50Hz | 230V | 1.40 | Class 2 (Low NOx) |
| RL 64 MZ | 3470411 | Extended (TL: 385 mm) | 206 / 391 | 830 | 17.4 / 33.0 | 70.0 | 3/230–400V / 50Hz | 230V | 1.40 | Class 2 (Low NOx) |
| RL 70 | 3475032 | Standard (TC: 250 mm) | 255 / 474 | 830 | 21.5 / 40.0 | 70.0 | 3/230–400V / 50Hz | 230V | 1.40 | Class 1 |
| RL 70 | 3475033 | Extended (TL: 385 mm) | 255 / 474 | 830 | 21.5 / 40.0 | 70.0 | 3/230–400V / 50Hz | 230V | 1.40 | Class 1 |
| RL 100 | 3475232 | Standard (TC: 250 mm) | 356 / 711 | 1186 | 30.0 / 60.0 | 100.0 | 3/230–400V / 50Hz | 230V | 1.80 | Class 1 |
| RL 100 | 3475233 | Extended (TL: 385 mm) | 356 / 711 | 1186 | 30.0 / 60.0 | 100.0 | 3/230–400V / 50Hz | 230V | 1.80 | Class 1 |
| RL 130 | 3475432 | Standard (TC: 250 mm) | 486 / 948 | 1540 | 41.0 / 80.0 | 130.0 | 3/230–400V / 50Hz | 230V | 2.60 | Class 1 |
| RL 130 | 3475433 | Extended (TL: 385 mm) | 486 / 948 | 1540 | 41.0 / 80.0 | 130.0 | 3/230–400V / 50Hz | 230V | 2.60 | Class 1 |
| RL 190 | 3475613 | Standard (TC: 370 mm) | 759 / 1423 | 2443 | 64.0 / 120.0 | 206.0 | 3/400V / 50Hz | 230V | 5.87 | Class 1 |
| RL 190 | 20052627 | Extended (TL: 530 mm) | 759 / 1423 | 2443 | 64.0 / 120.0 | 206.0 | 3/400V / 50Hz | 230V | 5.87 | Class 1 |
| RL 250 MZ | 3470010 | Standard (TC: 378 mm) | 600 / 1250 | 2700 | 51.0 / 106.0 | 228.0 | 3/230–400V / 50Hz | 230V | 7.20 | Class 2 (Low NOx) |
| RL 250 MZ | 20052629 | Extended (TL: 528 mm) | 600 / 1250 | 2700 | 51.0 / 106.0 | 228.0 | 3/400V / 50Hz | 230V | 7.20 | Class 2 (Low NOx) |
Note on Firing Range Notation (X / Y ÷ Z kW): The lower values (X / Y) represent the minimum turndown capability. X represents the absolute minimum firing rate under specific low-fire damper configurations, while Y is the standard minimum Stage 1 operational output. Z represents the maximum Stage 2 firing output under positive combustion chamber pressure.
4. Operational Principles: Two-Stage vs. Continuous Modulation
A critical engineering distinction in burner specification is understanding the exact functional operation of Two-Stage (Hi/Low) systems compared to Modulating (/M) burners.
- 1Hydraulic Damper Modulation: On models RL 34 MZ through RL 190, the transition between Stage 1 and Stage 2 is driven by a pressurized hydraulic oil cylinder (ram) linked directly to the air damper linkage.
- •When Stage 1 operates, oil pressure is applied to the first delivery line while the damper remains restricted to the low-fire mechanical stop.
- •When the Stage 2 control circuit closes, the second solenoid valve opens, pressurized oil enters the hydraulic ram, extending the cylinder rod and rotating the air damper to the pre-set high-fire combustion position.
- •On the RL 250 MZ, damper positioning is governed by an integrated electric servomotor.
- 1Fuel Delivery Architecture: Unlike single-stage burners (on/off) which fire directly at 100% capacity and cycle abruptly, two-stage burners start softly on Nozzle 1. If boiler demand increases, Stage 2 engages Nozzle 2 to reach full load. When the pressure setpoint is approached, Stage 2 drops out, allowing the burner to idle efficiently on Stage 1 without short-cycling the boiler.
- 2Difference from Full Modulation: Two-stage operation provides two discrete, repeatable setpoints (Low Fire and High Fire). It does not modulate continuously across a sliding scale (which is reserved for Riello RL/M models equipped with electronic cam profiling or modulating PID controllers).
5. Nozzle Engineering & Sizing Matrix
Nozzles are NOT supplied inside the burner crate. Riello RL burners require two separate nozzles per burner. These must be engineered and ordered as discrete accessories based on the exact boiler thermal rating, combustion chamber geometry, and pump pressure.
Critical Nozzle Sizing Rules:
- •Stage 1 (Low Fire) Nozzle: Typically sized for 40% to 60% of total boiler capacity to permit clean, soot-free ignition without flame impingement.
- •Stage 2 (High Fire) Nozzle: Sized so that Nozzle 1 + Nozzle 2 combined equals the total required thermal heat input at operating fuel pump pressure (standard test rating: 12 bar).
- •Spray Angles & Patterns:
- •RL 34 MZ: Requires 60° Hollow Cone (Type A) nozzles.
- •RL 44 MZ: Requires 45° Hollow Cone (Type A) nozzles.
- •RL 50, 64 MZ, 70, 100, 130, 190, 250 MZ: Require 60° Semi-Solid / Solid Cone (Type B) nozzles.
Riello Official Nozzle Rating & Part Code Matrix (Extract at 10, 12, and 14 Bar)
| Burner Application | Nozzle Type / Angle | Rated Flow [GPH] | Output at 10 bar [kg/h] | Output at 12 bar [kg/h] | Output at 14 bar [kg/h] | Official Riello Part Code |
|---|---|---|---|---|---|---|
| RL 34 MZ | 60° A | 1.00 | 4.1 | 4.5 | 4.9 | 3042078 |
| RL 34 MZ | 60° A | 1.50 | 5.7 | 6.3 | 6.8 | 3042108 |
| RL 34 MZ | 60° A | 2.00 | 7.7 | 8.5 | 9.2 | 3042124 |
| RL 34 MZ | 60° A | 3.00 | 11.5 | 12.7 | 13.8 | 3042148 |
| RL 34 MZ | 60° A | 4.50 | 17.3 | 19.1 | 20.7 | 3042184 |
| RL 44 MZ | 45° A | 1.50 | 5.7 | 6.3 | 6.8 | 20011655 |
| RL 44 MZ | 45° A | 2.50 | 9.6 | 10.6 | 11.5 | 20011666 |
| RL 44 MZ | 45° A | 3.50 | 13.5 | 14.8 | 16.1 | 20011672 |
| RL 44 MZ | 45° A | 5.00 | 19.2 | 21.2 | 23.0 | 20011677 |
| RL 44 MZ | 45° A | 6.00 | 23.1 | 25.5 | 27.7 | 20011679 |
| RL 50 | 60° B | 3.00 | 11.5 | 12.7 | 13.8 | 3042158 |
| RL 50 / 64 MZ | 60° B | 4.50 | 17.3 | 19.1 | 20.7 | 3042182 |
| RL 50 / 64 / 70 | 60° B | 6.00 | 23.1 | 25.5 | 27.7 | 3042212 |
| RL 64 / 70 / 100 | 60° B | 7.50 | 28.8 | 31.8 | 34.6 | 3042242 |
| RL 64 / 70 / 100 | 60° B | 8.50 | 32.7 | 36.1 | 39.2 | 3042262 |
| RL 70 / 100 / 130 | 60° B | 10.00 | 38.4 | 42.4 | 46.1 | 3042292 |
| RL 100 / 130 / 190 | 60° B | 12.00 | 46.1 | 50.9 | 55.3 | 3042322 |
| RL 130 / 190 / 250 | 60° B | 16.00 | 61.5 | 67.9 | 73.8 | 3042382 |
| RL 190 / 250 MZ | 60° B | 20.00 | 76.9 | 84.8 | 92.2 | 3042442 |
| RL 190 / 250 MZ | 60° B | 26.00 | 99.9 | 110.3 | 119.9 | 3042482 |
| RL 250 MZ | 60° B | 30.00 | 110.4 | 122.0 | 132.4 | 3042502 |
| RL 250 MZ | 60° B | 35.00 | 128.8 | 142.1 | 154.5 | 3042522 |
6. Combustion Head Geometry: Standard (TC) vs. Extended (TL)
Combustion head penetration into the boiler furnace door refractory is vital for proper flame formation and burner longevity.
- 1Standard Head (TC): Sized for conventional reverse-flame and three-pass wet-back boilers with standard front door insulation thicknesses (typically 100 mm to 180 mm).
- 2Extended Head (TL): Mandatory on boilers with deep refractory doors, packaged smoke-tube boilers with extended water-cooled front vestibules, or furnaces requiring deep penetration to avoid flame impingement on door brickwork.
- 3Field Conversion: Standard head burners can be converted to extended head configurations using genuine Riello factory extension kits.
Head Lengths and Factory Conversion Kit Matrix
| Burner Model | Standard Head Length (TC) [mm] | Extended Head Length (TL) [mm] | Extension Kit Code | Spacer Thickness S [mm] | Spacer Kit Code |
|---|---|---|---|---|---|
| RL 34 MZ | 216 | 351 | 3010426 | 110 | 3010095 |
| RL 44 MZ | 216 | 351 | 3010425 | 110 | 3010095 |
| RL 50 | 216 | 351 | 3010075 | 110 | 3010095 |
| RL 64 MZ | 250 | 385 | 3010114 | 135 | 3010129 |
| RL 70 | 250 | 385 | 3010114 | 135 | 3010129 |
| RL 100 | 250 | 385 | 3010115 | 135 | 3010129 |
| RL 130 | 250 | 385 | 3010116 | 135 | 3010129 |
| RL 190 | 370 | 530 | 3010444 (or 3010197)* | 102 | 3000722 |
| RL 250 MZ | 378 | 528 | 3010422 | 102 | 3000722 |
\Note: For RL 190, Kit 3010444 applies to serial numbers >= 02426XXXXXX; Kit 3010197 applies to serial numbers <= 02416XXXXXX.*
7. Electrical Supply & Control Circuit Infrastructure
The electrical supply varies substantially across the RL family:
- •RL 34 MZ: Strictly single-phase (1/220–230V / 50–60Hz). Connected via pre-wired external multipin plugs and sockets.
- •RL 44 MZ: Available in either single-phase (1/220–230V / 50–60Hz) or three-phase (3/220–400V / 50–60Hz).
- •RL 50, 64 MZ, 70, 100, 130: Three-phase (3/230–400V / 50Hz with neutral). Internal terminal boards or multipin connectors.
- •RL 190 & RL 250 MZ: Heavy industrial three-phase configurations (3/400V / 50Hz or 3/230V / 50Hz). High motor start-up current (5.87 kW and 7.2 kW motor draws).
Essential Electrical Accessories:
- •PC Interface Adapter Kit (Code: 3002719): Connects the internal microprocessor control box to a service laptop to extract operating run hours, ignition cycle logs, flame intensity trends, and historic lockout fault codes.
- •Volt-Free Contact Kit (Code: 3010419): Provides dry contact relay outputs for remote BMS (Building Management System) telemetry, reporting burner run status, Stage 2 operation, and safety lockout alarms.
- •Electromagnetic Interference (EMI) Protection Kit (Code: 3010386): Recommended for installations where the thermostat/control line exceeds 20 meters or where large Variable Frequency Drives (VFDs) are operating nearby (signal fields >10 V/m).
8. Sizing Methodology & Calculation Framework
To correctly size a Riello RL burner for an industrial boiler:
- 1Calculate Required Burner Heat Input (Qn):
Qn [kW] = Boiler Output [kW] / Boiler Thermal Efficiency (η)
Example: For a 1000 kg/h steam boiler producing steam at 10 bar (h_fg ≈ 650 kW thermal output) operating at 88% efficiency:
Qn = 650 kW / 0.88 ≈ 738.6 kW
- 1Verify Operating Backpressure Against Firing Curve:
Cross-reference the calculated heat input (739 kW) against the combustion chamber overpressure (typically +2.5 to +4.5 mbar).
- •Referring to the firing curve: An RL 70 maxes out at 830 kW at nominal zero pressure, but at +4.0 mbar backpressure its maximum output drops below 700 kW.
- •Correct Selection: The RL 100 (356 to 1186 kW) must be chosen to comfortably sit in the center of its useful working envelope.
9. Troubleshooting & Fault Diagnostic Sequence
All Riello RL burners feature microprocessor lockout diagnostics. The illuminated lockout button on the control box signals error causes via standardized optical flash pulses.
| Symptom / Fault Code | High-Level Root Cause | Inspection & Verification Focus | Corrective Action |
|---|---|---|---|
| Burner does not start; no pre-purge | Control loop open; no electrical permissive signal | External limit thermostats, water level switches, control box seated incorrectly | Inspect fuse, check boiler safety thermostat chain, verify 230V control power on terminal 1. |
| Pre-purge completes, no ignition spark | High-voltage circuit disruption | Ignition electrode spacing, cracked ceramic insulator, disconnected HT leads | Re-gap electrodes to factory specifications; replace cracked ceramic insulators; inspect ignition transformer. |
| Burner fires, locks out after 3–5 seconds | Flame sensor failed to verify flame | Photocell dirty, misaligned, defective; fuel pressure unstable | Clean photocell glass face; verify optical alignment; verify pump delivery pressure at nozzle line. |
| Burner locks out during transition to Stage 2 | Damper or Stage 2 nozzle failure | Stage 2 solenoid coil open circuit, hydraulic ram jammed, Stage 2 nozzle blocked | Check 2nd stage solenoid valve coil resistance; verify hydraulic damper mechanical travel; clean/replace Nozzle 2. |
| Dense black smoke from boiler stack | Fuel-rich combustion / inadequate combustion air | Blocked air suction circuit, incorrect nozzle size, low fan pressure | Check air damper settings with a flue gas analyzer; inspect blower fan blades for lint/dust build-up; verify nozzle GPH rating. |
| Pulsating combustion / flame detachment | Air/fuel velocity mismatch or cold oil viscosity | Excess combustion air, worn nozzle orifice, fuel viscosity >6 cSt | Re-calibrate diffuser disc position; check fuel delivery temperature; replace worn spray nozzles. |
10. Site Procurement Checklist for East African Engineers
When requesting a quotation or sourcing a replacement Riello RL burner through STARNEX Industrial Spares Ltd, have the following parameters ready:
- 1Full Burner Designation: E.g.,
RL 100 TC FS1 3/230-400/50 230/50-60(found on the metal nameplate riveted to the side of the burner body). - 2Boiler Manufacturer & Operating Capacity: E.g., John Thompson, Cochran, Thermax, or Marshall Fowler; steam capacity in kg/h or thermal output in kW/kCal.
- 3Furnace Door Depth (Refractory Thickness): Ensures correct selection between Standard Head (TC) and Extended Head (TL).
- 4Site Electrical Supply: Confirm available site voltage (Single-phase 230V vs. Three-phase 415V/50Hz).
- 5Nozzle Flow Specification: Existing nozzle sizes in GPH, spray angle (45° vs. 60°), and manufacturer code.
- 6Operating Environment: High altitude locations (e.g., Eldoret at 2100m or Nairobi at 1700m) require derating combustion air volume by approximately 15–20% compared to sea-level ratings conforming to EN 267.
