In Brief
Spitzer BT – horizontal-chamber gravity-aerated silo trailer (0.8–2.0 bar). Best for: plastic granules (PE, PP), flour, starch, granulated salt, sugar. Gravity + aeration fluidises free-flowing cargo. Spitzer SL / SLS / SLSH – conical hopper with full pressure discharge (1.5–3.0 bar). Best for: fly ash, aluminium oxide, soda ash, kaolin, technical carbon black — materials with poor flowability or high bulk density. Choosing the wrong model causes incomplete discharge, accelerated wear and excessive downtime. PHS Magnum advises on model selection, services all Spitzer series.
Two Design Philosophies, One Product Family
Spitzer Silo, the Austrian manufacturer, has built two fundamentally different trailer designs since the 1970s — not to confuse operators, but because bulk cargo handling has no universal solution. Plastic granules and fly ash look similar from a distance. In practice, their flow characteristics, bulk density and required discharge pressures differ dramatically.
Both trailer types are common on European roads. Both are white, cylindrical, and move dry bulk. But their internal engineering — and the maintenance requirements that follow — are entirely different.
Spitzer BT: Gravity-Aerated Discharge System
How the BT Works
The Spitzer BT trailer consists of multiple horizontal cylindrical chambers (typically 3–5) arranged end-to-end along the trailer chassis. The floor of each chamber is lined with microporous aeration pads — permeable textile membranes.
During discharge:
- Compressed air at 0.8–2.0 bar is introduced through the aeration pads from below
- The bulk material becomes fluidised — behaving like a liquid
- The fluidised material flows by gravity through bottom outlet valves into the discharge manifold
- A pneumatic conveying line carries the material to the destination silo
This is a low-energy discharge process. The compressor works at relatively low pressure, the material moves gently, and the discharge rate is consistent and controllable.
FIBC-Compatible Loading
The BT’s top-loading design via roof hatches makes it directly compatible with FIBC (big bag) and pneumatic blow-in loading systems. The horizontal chamber layout also allows partial loading — individual chambers can be filled and discharged independently.
What the BT Handles Well
Ideal cargo for Spitzer BT:
- Plastic granules: PE (LDPE, HDPE), PP, PVC, ABS, PET — the dominant use case in Central Europe
- Wheat, rye and corn flour
- Granulated and powdered sugar
- Potato and corn starch
- Industrial and food-grade salt (fine)
- Dry milk powder (food-grade pads required)
- Semolina, dry yeast
Bulk density range: 0.3–1.0 kg/l
Typical tank volume: 45–65 m³
Working pressure: 0.8–2.0 bar
Spitzer SL / SLS / SLSH: Pressure Discharge System
How the SL Works
The Spitzer SL series uses a conical hopper (Kegelauslauf) — a cylindrical tank with a funnel-shaped bottom. Material collects at the cone apex and is discharged by direct compressed-air pressure through a bottom valve into the conveying line.
No aeration pads serve as the primary discharge mechanism. Instead, full system pressure (1.5–2.5 bar, up to 3.0 bar for SLSH) pushes the material out. Optional floor vibrators or supplementary aeration can be added for particularly difficult materials.
SL Variant Comparison
| Variant | Working Pressure | Key Feature | Best For |
|---|---|---|---|
| SL | up to 2.2 bar | Standard construction | Fly ash, kaolin, ground limestone |
| SLS | up to 2.2 bar | Lightweight steel, lower tare weight | Higher payload where volume allows |
| SLSH | up to 3.0 bar | Reinforced shell, higher MOP | Soda ash, aluminium oxide, carbon black |
What the SL Handles Well
Ideal cargo for Spitzer SL/SLS/SLSH:
- Fly ash (from power plants and co-firing plants)
- Aluminium oxide (alumina)
- Technical carbon black (Ruß / sadza)
- Soda ash (Na₂CO₃, calcined soda)
- Precipitated chalk
- Ground feldspar, talc, kaolin
- Microsilica (silica fume)
Bulk density range: 0.4–1.8 kg/l
Typical tank volume: 35–55 m³
Working pressure: 1.5–3.0 bar (SLSH)
BT vs SL: Comparison Table
| Feature | Spitzer BT | Spitzer SL / SLS / SLSH |
|---|---|---|
| Tank design | Horizontal chambers | Conical hopper |
| Discharge system | Gravity + aeration (pads) | Full pressure discharge |
| Working pressure | 0.8–2.0 bar | 1.5–3.0 bar (SLSH) |
| Aeration pads | Yes — primary element | Optional / supplementary |
| Cargo bulk density | 0.3–1.0 kg/l | 0.4–1.8 kg/l |
| Typical cargo | Granules, flour, sugar | Fly ash, soda, alumina |
| Bridging risk | Low | Higher — addressed by design |
| Typical volume | 45–65 m³ | 35–55 m³ |
| Tare weight | 6.8–7.5 t | 6.5–8.0 t |
| Primary maintenance | Aeration pads, bottom valves | Conical valves, seals |
Choosing the Right Spitzer Model: A Practical Framework
Step 1: Identify the cargo
Start with the actual material being transported. Plastic granules (PE/PP)? BT. Fly ash? SL. Flour? BT. Soda ash? SLSH. This single step eliminates most doubt.
Step 2: Check bulk density
Materials with bulk density below 0.5 kg/l (fly ash, carbon black, precipitated chalk) often cannot be effectively discharged by the BT’s gravity-aeration system — the material column is too light to generate sufficient flow pressure. These need the SL’s direct pressure system.
Step 3: Assess bridging tendency
Hygroscopic materials (soda ash, sulphur) or materials prone to arching in the discharge zone require higher pressure and, in the SLSH case, anti-bridging vibrators. A standard BT or SL will block repeatedly.
Step 4: Payload vs volume trade-off
The SLS variant has a lower tare weight than standard SL — at the same gross vehicle weight (40 tonnes), you can carry more cargo. For light materials (fly ash at 0.6 kg/l), volumetric capacity is the limiting factor anyway, so weight saving in the tank structure translates directly to usable payload.
Real-World Errors When Selecting Spitzer Models
Error 1: Running BT on fly ash
Operators buy a used BT because it’s cheaper, then run fly ash. Result: alkaline fly ash attacks polyester aeration pads, causing pad failure within 3–6 months. Incomplete discharge. Valve blockages. Costly pad replacement every season instead of every 3–5 years.
Error 2: Running SL on plastic granules
SL pressure levels (above 1.5 bar) break down granule surface finish, increase dust generation and can cause static build-up. The conical geometry is not optimised for granule flow — partial loads tend to bridge at the cone. Higher compressor fuel consumption.
Error 3: SL instead of SLSH for soda ash
Soda ash requires 2.5–3.0 bar for reliable discharge. Using SL (2.2 bar max) leads to frequent blockages, manual intervention and driver downtime at every delivery.
Service, Parts and Technical Support – PHS Magnum
PHS Magnum in Chorula, near Opole, Poland has been servicing Spitzer silo trailers for over 30 years. Our workshop is located 4 km from the A4 motorway (Opole West junction), making it accessible for operators from Poland, Germany and the Czech Republic.
We service BT, SL, SLS and SLSH models: TDT (UDT) pressure vessel inspections, aeration pad replacement, valve overhaul, pneumatic system diagnostics, spare parts supply.
Call for service or technical advice: +48 602 716 551
Related: Spitzer trailer service · Spare parts · TDT inspection · Repair & renovation