In Brief
Silo trailer faults fall into three groups: (1) pneumatic and aeration system — worn pads, valve failures, pressure leaks (~50% of all call-outs); (2) tank and welds — cracks at hatches, supports and nozzles (~20%); (3) running gear — bearings, brakes, EBS (~30%). Most pneumatic failures show warning signs 2–4 weeks before becoming critical. Diagnosis at our workshop: 1–4 hours. PHS Magnum has 30+ years of silo trailer service experience and stocks parts for Spitzer, Feldbinder and Kassbohrer trailers.
Silo trailers don’t fail without reason — and rarely fail without warning. Most faults have recognisable symptoms that appear days or weeks before a critical breakdown. The following is a field guide to the most common faults, based on 30+ years of silo trailer service at PHS Magnum.
If you’re specifically diagnosing a discharge problem, see the dedicated guide: silo trailer not discharging.
Aeration system — discharge problems
Slow or incomplete discharge
Symptoms: discharge takes longer than usual, kilograms of residue remain at the chamber floor, the customer reports under-weight deliveries.
Most common causes:
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Worn aeration pads — the fluidisation membrane loses permeability through abrasion, alkaline attack from cement or lime, or oil contamination from the compressor. Spitzer BT 65 pads in intensive cement service are typically replaced every 3–5 years.
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Blocked aeration lines — cement or lime sets hard in the pipework if not cleared regularly. A partial blockage can go unnoticed for weeks until aeration fails completely.
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Check valve fouling — check valves on the air inlet to each chamber can clog with hygroscopic materials, preventing airflow to that chamber.
Diagnosis: pressure test of individual chambers with the outlet closed, acoustic pad test at low pressure (a healthy pad hisses uniformly across its full surface), visual inspection inside the chamber through the inspection hatch.
Repair: pad replacement, compressed-air or water flush of aeration lines, check valve replacement. Typical time: 4–8 hours. Full Spitzer BT 65 pad set: 6–8 hours including disassembly.
Noise and pulsation during discharge
Symptoms: irregular knocking or “chuffing” from the pneumatic system during discharge, visible vibration in flexible hoses.
Most common causes: a safety or relief valve opening cyclically (marginal seal condition), loose connections on flexible hose joints, malfunctioning pressure regulator on the compressor.
Repair: identify and replace the faulty valve or hose section. Safety valves in stock →
Compressor — common failures
Compressor not reaching working pressure
Symptoms: pressure in the vessel rises slowly, drops below minimum during discharge, pneumatic loading takes significantly longer than normal.
Causes:
- Worn piston rings — piston compressors lose seal after hundreds of thousands of cycles. Symptom: oil in the air line downstream of the compressor (grease on hoses after the moisture separator).
- Blown cylinder head gasket — characteristic whistling during compressor operation.
- Broken drive belt — complete compressor seizure.
- Clogged inlet air filter — output reduction of 20–40%.
Diagnosis: pressure measurement downstream of compressor under constant load, visual inspection of the belt, inlet filter check.
Repair: piston ring/head replacement (overhaul or unit exchange), belt replacement, filter cleaning or replacement.
Oil in the air line
Symptoms: grease or oil traces on hoses downstream of the compressor, discolouration of discharged material (especially with white granules or flour).
Cause: worn piston rings allow oil to enter the compressed air stream. For food-grade or oil-sensitive materials — stop discharge immediately and repair before next use.
Repair: compressor overhaul or replacement, oil change, purge of all air lines.
Valves and fittings — common failures
Leaking safety valve
Symptoms: constant hissing from beneath the trailer bodywork, vehicle loses pressure during discharge, TDT inspector refuses certification.
Important: a safety valve that opens below its rated set pressure is defective even if it holds static seal. Verification requires a pressure test — not a visual check.
Repair: valve replacement. Safety valves are never repaired — only replaced. Specify the set pressure (bar) from the vessel nameplate when ordering a replacement. Safety valves and spare parts →
Leaking discharge valve
Symptoms: bulk material trickles through a closed valve, the discharge hose remains slightly dusty.
Cause: worn ball seat or butterfly seal. Cement and lime cause abrasive wear on the ball seat over time.
Repair: seal replacement or full valve replacement. Ball valve DN150 for Spitzer — replacement typically 2–3 hours. Valve regeneration service →
Seized ball or butterfly valve
Symptoms: lever cannot be moved or requires excessive force, valve jams in intermediate position.
Cause: bulk material residue packed around the ball or disc, corrosion of the stem, PTFE seal swollen or hardened.
Repair: disassembly, cleaning, seal replacement. If ball or disc seat is scratched — full valve replacement.
Tank — cracks and corrosion
Weld cracks
Symptoms: visible cracks or rust-stained water traces at welds, leak during pressure test.
High-risk locations: cracks most commonly initiate at welded ladder brackets, handles and hatch frames — points of stress concentration under road vibration. Feldbinder EUT tanks with stainless steel (304L/316L) are less susceptible; aluminium Spitzer tanks at the lower weld seams of chambers are more vulnerable.
Repair: TIG welding (aluminium) or MIG/MAG (steel) with TDT documentation. Requires TDT-certified welder qualification (PN-EN ISO 9606). After any tank weld, a special TDT inspection is mandatory before returning the vehicle to pressurised service. Tank crack repair service →
Subcutaneous corrosion on steel tanks
Symptoms: paint blistering or peeling on the tank surface, particularly at lower edges and weld seams.
Cause: moisture penetrates through micro-cracks or through areas where surface preparation before painting was inadequate. Sub-surface corrosion is invisible until it has advanced significantly.
Repair: local or full paint renovation with sandblasting to Sa 2.5. At advanced stages — section plate replacement before painting. Renovation that skips sandblasting to Sa 2.5 will fail in 2–3 years.
Running gear — axles and brakes
Bearing noise at the wheel
Symptoms: hum or knocking at a specific wheel, intensifying under load, audible when turning.
Cause: worn hub bearing (BPW, SAF, ROR). Silo trailers typically run at GVW 44 tonnes — bearing loads are proportionally high. Axle and bearing service →
Diagnosis: jack the axle, check for lateral play at the wheel, touch-test the hub temperature after a run (should not be painfully hot).
EBS warning light
Symptoms: ABS or EBS warning lamp active on the tractor dashboard (trailer circuit), vehicle can be stopped by ITD road inspectors.
Causes: ABS sensor fault (cable break, contamination on the tone wheel), modulator valve fault, ECU power supply issue, configuration parameter out of range. EBS diagnosis service →
Repair: diagnostic scan (Wabco TEBS G2/G3/G4, Haldex EB+), sensor or modulator replacement, ECU re-programming if needed. Mobile service available on the A4 corridor within 100 km of Chorula.
When to bring the trailer in
Immediately (stop operating): no discharge possible, material leaking through a closed valve, visible tank crack, ITD stop order, TDT certificate expired.
Within one week: slower-than-normal discharge, minor air leaks from fittings, compressor running longer than usual to reach pressure, EBS warning light active.
At next scheduled service: aeration pads approaching expected service life, valves over 5 years old showing early wear signs, paint blistering on tank surface, TDT due within 3 months.
Contact
Tel: +48 602 716 551 (Mo–Fr 06:00–20:00, Sa 07:00–15:00)
biuro@magnumchorula.pl
Emergency breakdown on the A4: +48 602 716 551 (24/7)
Related: Silo trailer service overview · TDT inspection · Spare parts · Mobile breakdown service A4