Summary
Spitzer silo trailer not discharging – the most common causes: worn or blocked aeration pads (60% of cases), insufficient compressor pressure, jammed DN100/DN125 discharge valves, material caking after moisture exposure. Step-by-step diagnostics: (1) check the pressure gauge, (2) identify which side of the tank has the problem, (3) visual inspection of pads through the top hatch, (4) check the valves. If pressure is fine but discharge fails – the problem lies in the aeration system. Service: +48 602 716 551.
The Spitzer trailer is sitting at the loading dock, pressure is up, and nothing comes out. Or material exits but 10–15% remains in the tank. Or one side empties normally while the other does not respond at all.
Each of these symptoms has a specific cause — and a diagnostic procedure you can carry out before calling a recovery truck. For a broader overview of pneumatic discharge faults in silo trailers, see the article by Aleksy Pasternak.
Discharge Diagnostic Procedure
Step 1: Check the pressure gauge
Before getting into the details: what is the air pressure during discharge?
Pressure below 1 bar — the problem is on the compressor or supply valve side, not the trailer tank itself. Check the compressor drive belt (Spitzer silo trailers are typically fitted with a PTO-driven or independent compressor), the air filter condition, and the integrity of the supply hoses. This is a tractor or trailer mechanical issue, not a tank issue.
Pressure reaches 2–2.2 bar but material does not discharge — the fault lies in the aeration system or the discharge valves. Continue below.
Pressure drops sharply when the discharge valve is opened — air leak present; check hatch seals or a pad allowing material into the manifold.
Step 2: Identify whether the problem is one-sided
Spitzer SF-series tanks have aeration pads distributed across the entire length of the floor. With a two-row pad arrangement (standard for larger capacities): is material exiting from one side of the tank while the other side remains full?
Yes – one-sided discharge: damaged pad or blocked manifold on one side. Enter through the top hatch and visually inspect the pads on both sides.
No – little or nothing discharging from the entire tank: a general fault – insufficient pressure, blocked main manifold, material caking, or all pads worn simultaneously (rare, but it happens with cement after two seasons without replacement).
Step 3: Visual inspection of aeration pads
Through the top hatch with a torch:
- Normal pad — polyester or polyamide fabric, uniform, undamaged, lying flat in its channel
- Worn pad — frayed, with visible holes, swollen from the top (material has entered the pad interior), discoloured by product
- Blocked pad — no visible damage, but the tank does not aerate in that zone
A blocked pad is difficult to identify visually. Pressure test: underneath the trailer, each pad has its own air inlet from the manifold — connect a pressure gauge to each inlet and check which pad fails to pass air at 0.5 bar.
Step 4: Check the discharge valves
A DN100 or DN125 valve at the manifold outlet is stuck or not opening fully:
- Mechanical seizure — residue from dried cement or binder. Test: try opening the valve by hand without pressure. If it will not move — cement is in the valve. Do not force it; you may damage the seal.
- Worn valve seal — the valve opens but does not close fully, causing pressure loss. Symptom: a constant hiss of air with the valve closed.
Step 5: Check hatch seals
With working pressure applied (2 bar), run your hand around each hatch seal — can you feel a draught? Any leak equals pressure loss equals slower, incomplete discharge.
EPDM hatch seals harden and lose elasticity after 4–5 years of service (or sooner with alkaline bulk materials). A hardened seal will not hold pressure.
Most Common Causes of Discharge Problems
| Symptom | Most Likely Cause | Action |
|---|---|---|
| Nothing discharges, pressure normal | Jammed discharge valves | Mechanical clearing or replacement |
| 10–20% remains in tank | Worn aeration pads | Pad replacement |
| One-sided discharge | Damaged pad on one side | Localised pad replacement |
| Slow discharge | Insufficient pressure | Check compressor and hoses |
| Powder in air system | Pad allowing material through | Immediate pad replacement |
| Pressure builds without discharge | Material caking | Mechanical breaking-up + service before next load |
When to Visit a Service Centre
Some faults can be resolved by the driver on site. Others require a workshop:
Driver-repairable on the road:
- Clearing valve residues (provided there is no underlying damage)
- Temporarily sealing a hatch with emergency sealing paste (temporary fix only)
- Checking and replacing the compressor air filter
Requires a service centre (PHS Magnum or another authorised facility):
- Aeration pad replacement — requires tank entry and specialist tools
- Replacing valve and hatch seals
- Pressure test after repair
- Full aeration manifold leak test
If after working through Steps 1–5 the cause is still unclear, call us: +48 602 716 551. Based on your description of the symptoms, we can in most cases diagnose the fault before the trailer arrives and have the correct parts ready.
Related: Spitzer Service · Spare Parts · TDT Inspection · Repair and Overhaul
