Definition
Silo tanker transport is the hermetic carriage of bulk materials in loose form inside the pressurised tank of a silo tanker — with no sacks or big-bags en route. The material (most often polymer regranulate or powder) travels sealed inside the tank, and on arrival it is pneumatically blown straight into the recipient’s silo or installation. From the moment of loading until it drops into the customer’s silo, the entire chain stays closed, so the material has no contact with its surroundings.
From the terminal’s perspective, one thing is certain: for a large producer that consumes raw material by the tonne every day, silo tanker transport is not a luxury but the default mode of delivery. Sacks and big-bags appear where the scale is smaller or where the recipient has no silo. When there is a silo, the silo tanker wins on speed and cleanliness.
How silo tanker transport works
The chain looks as follows. The material enters the silo tanker’s tank through the top manholes — in our case most often during transloading of big-bags into a silo tanker, when the regranulate from a big-bag is stripped of its packaging and fed in bulk into the chambers. The tank is then hermetically sealed. The tanker sets off on its route with a load of around 24-26 tonnes of light regranulate.
On arrival, the driver connects the discharge pipe to the recipient’s silo coupling. A compressor driven from the tractor unit forces compressed air (around 2 bar) through aeration pads at the bottom of the chambers. The air fluidizes the material — the regranulate begins to flow like a liquid — and the overpressure pushes it through the line into the silo. Once the chambers are empty, the tank is blown through and the driver disconnects the hoses. The whole unloading of 25-30 tonnes usually takes 60-90 minutes.
The key point is that at no stage is there any manual transloading on the recipient’s side. There is no need to cut open sacks, lift pallets or tip regranulate into a hopper. The material drops into the production silo ready for use. It is precisely this contactless quality that gives silo tanker transport its logistical and qualitative edge.
It is also worth understanding the economics of volume. Polymer regranulate is light — the bulk density of PE or PP is usually 0.5-0.6 t/m3. This means a 60 m3 tank fills up with material before the combination reaches the permissible 40 tonnes gross weight. In practice, a silo tanker with regranulate carries around 24-26 tonnes of load, because the cubic capacity runs out before the load rating. That is why, when choosing a tanker for plastics, what matters above all is capacity, not mass payload — unlike with heavy mineral powders, where weight is the limit.
Silo tanker design
A silo tanker is a semi-trailer with a pressurised tank mounted on the frame. The most important components are:
- Tank shell — usually made of an aluminium-magnesium alloy of the 5xxx series, primarily EN AW-5083. Aluminium is light (every kilogram of tare weight saved is a kilogram more of load) and corrosion-resistant. Welds are made with ER5183/ER5356 wire. The frame and chassis may be of S355 structural steel or of 6xxx aluminium profiles.
- Chambers — the tank is usually divided into 2-4 chambers separated by bulkheads. Dividing into chambers makes it easier to distribute the load across the axles and allows more than one material or batch to be carried, as well as sequential unloading.
- Cones and aeration pads — the bottom of each chamber has a conical slope towards the discharge outlet, with aeration pads (membranes) through which fluidizing air is injected.
- Couplings — the standard in silo tankers is the Storz quick coupling, alongside the flanged PERROT and the lever-action Camlock. Compatibility between the tanker’s coupling and the recipient’s installation coupling must be confirmed before delivery.
The market capacity range is around 30-90 m3, but in the transport of PE/PP regranulate the dominant tankers are 55-65 m3. Our fleet consists of silo tankers in the ~60 m3 class. Types found on the market include the Spitzer SF/SK series, Feldbinder EUT/KIP and Kässbohrer K.SSK/K.SSL — they differ, among other things, in whether the tank is non-tipping (purely pneumatic unloading) or hydraulically tiltable. I go into the structural details in the article on silo tankers.
Pneumatic unloading — the heart of the technology
The heart of silo tanker transport is pneumatic unloading. A compressor (mounted on the tractor unit or on the trailer) generates overpressure that performs two functions at once: it fluidizes the material at the bottom of the chamber and conveys it through the line to its destination. Without fluidization, the regranulate would sit in the cone — only when the air aerates it does it begin to flow and become pumpable.
Here an important technological caveat arises. Pneumatics work excellently for powders and free-flowing materials, but with PE/PP regranulate they come at a price: the friction of the grains against the pipe walls generates electrostatic charging of regranulate as well as fine dust and so-called angel hair (long strands of melted polymer). That is why some recipients and producers deliberately limit the number of pneumatic transloads along the raw material’s route. You can find more about the unloading process itself in the study pneumatic unloading of a silo tanker.
At our terminal we separate two things: the transport by silo tanker (where pneumatics are essential for unloading at the recipient) and the transloading in Chorula, which we carry out without pneumatics — by gravity, so as not to disturb the grain structure during the big-bag → silo tanker transfer. This distinction has real significance for the quality of the regranulate reaching the customer.
Pneumatic unloading comes down to several parameters that the driver controls at the recipient’s gate. Working pressure is usually set at around 1.8-2 bar — too high generates more dust and angel hair, too low lengthens the unloading and risks blocking the line. Unloading time depends on the material, the length and diameter of the hose and the distance to the silo; for 25-30 tonnes of regranulate it is typically 60-90 minutes. Chamber sequence matters for the combination’s stability — the chambers are emptied in an order that maintains the load distribution across the axles. After emptying, the system must be blown through so that no material remains in the line to contaminate the next load.
Silo tanker transport vs big-bag — when to use which
The most common question from a producer is: silos or big-bags? The answer depends on whether the recipient has a silo and what scale of consumption the process has. Below is a comparison drawn from my practice:
| Criterion | Silo tanker transport | Big-bag (FIBC) |
|---|---|---|
| Packaging en route | none (in bulk) | sack 0.5-2 t + pallet |
| Unloading at recipient | pneumatic, into silo | cutting, manual/crane tipping |
| Material loss | minimal | residue in sack, dusting when cut open |
| Contamination risk | low (closed system) | tearing, moisture ingress, OCS |
| Packaging waste | none | sacks + film for disposal |
| Optimal scale | large, continuous consumption | medium, batches, buffer stock |
| Requirement on recipient’s side | silo + compressed air | forklift/crane, unloading station |
Silo tanker transport wins where cleanliness, no losses and speed matter. A producer with a silo and steady consumption saves on the sack, the pallet, the shrink-wrapping and the unloading labour, while the regranulate enters the process without contact with its surroundings. The big-bag remains sensible for smaller batches, for recipients without silo infrastructure and as buffer stock. We often combine both worlds: regranulate arrives at our facility in big-bags imported from Asia, and sets off to the end customer by silo tanker. I also describe this model in the context of warehousing of bulk materials.
What we carry by silo tanker
In silo tanker transport one feature of the material counts: it must flow well and not be a dangerous good. Our terminal handles primarily:
- polymer regranulate: PE (polyethylene), PP (polypropylene), as well as ABS, PS, PA, PVC, PET;
- powders and mineral materials that flow well;
- regranulate and recyclates, provided they meet the free-flowing requirement.
There is, however, one limit: we do not carry ADR materials (classified as dangerous goods) by this route. Our profile is non-ADR raw materials — primarily plastics for the processing industry.
For each material, three features decide whether it is suitable for silo tanker transport. The first is free-flowing behaviour and flowability — the material must be capable of being fluidized and must not cake in the chamber. The second is susceptibility to electrostatic charging: polymer regranulate accumulates an electrostatic charge with every pneumatic flow, which translates into dusting and grains sticking to the walls — which is why we limit the number of pneumatic transloads in the chain. The third is sensitivity to moisture and contamination: hygroscopic materials (such as PA or PET) require dry unloading air and a sealed silo, so as not to take on moisture before processing. These differences determine whether a given raw material might not be better carried in big-bags after all.
PHS Magnum fleet and terminal
Real silo tanker transport is not just tankers but the entire support base. Our fleet numbers 26 DAF XF 480 Euro 6 tractor units and 31 silo tankers in the ~60 m3 class. The base is the terminal in Chorula near Opole, 4 km from the A4 motorway — the logistical midpoint between the ports and the German-speaking market, about 180 km from the German border.
The terminal has a warehouse for 2000 big-bags and a transloading capacity of 200 tonnes per day. Thanks to this, in one place we combine silo tanker transport with packaging and warehousing — the customer can leave the raw material with us, and we release it by silo tanker in batches in line with their production schedule. The full transport and transloading offer is described by the PHS Magnum hub.
A practical note from the terminal: when planning silo tanker transport, always confirm three things in advance — the compatibility of the discharge coupling, the availability and pressure of compressed air on the recipient’s side, and the free capacity of the target silo. A mismatch in any of these is the most common cause of standstill at the recipient’s gate. Cleanliness between loads is ensured by our EFTCO (ECD) documentation, which safeguards against cross-contamination when the material changes.
Who silo tanker transport is for
From the terminal’s perspective, the typical recipient of silo tanker transport is a plastics processing plant — an injection moulding shop, an extrusion plant, a maker of film, pipes or packaging — that consumes raw material continuously and has a feed silo on site. For such a customer, delivery by silo tanker is the cheapest and cleanest way to replenish the raw material stock: one combination delivers 24-26 tonnes of regranulate, which after 60-90 minutes is already in the production silo.
The second group is plastics distributors and traders who import regranulate and distribute it to smaller processors. Here two models are often combined: the raw material arrives in bulk or in big-bags at our terminal, is warehoused, and is then released either by silo tanker to large recipients or packaged into sacks and big-bags for smaller ones. This flexible model — one point, two release channels — is the essence of the advantage of a terminal with its own transloading.
Silo tanker transport is not always the right choice. If the recipient has no silo, consumes raw material irregularly or needs many different materials in small quantities, a big-bag or a 25 kg sack is often more sensible. That is why the first conversation with a customer begins for us with three questions: what is the scale of consumption, is there a silo, and what does the production schedule look like. The answers to these decide the choice of packaging and delivery mode more than anything else.
Related topics
- Silo tanker ~60 m3 — design, types, couplings, TDT inspections.
- Pneumatic unloading of a silo tanker — details of the technology.
- Big-bag (FIBC) — the packaging from which we load the silo tankers.
- Transloading without pneumatics — why in Chorula we transfer by gravity.
- DACH - Poland routes — silo tanker transport corridors.
Sources
- Operational practice of the SMIALA / PHS Magnum terminal in Chorula — Aleksy Pasternak, over 30 years of experience in the transloading and transport of bulk materials. Expert portal: pasternak.me.
- Tank cleanliness documentation: the EFTCO ECD system (European Cleaning Document).
- Tank construction materials: 5xxx series alloys, in particular EN AW-5083 (aluminium material standard).
