Top loading delivers product into a tanker through the dome hatch or a fixed top connection, using a loading arm that reaches out from the gantry. It remains common for fleets without bottom loading equipment, for viscous products loaded hot, and at existing terminals. Design attention shifts to three issues: letting the operator work safely on top of the tanker, getting product into the compartment without splashing or building up static charge, and controlling the vapor that escapes from the open hatch.
The pump, meter and control valve chain is covered on the truck loading systems page. This page deals only with the interfaces and safety topics that make top loading different.
When is top loading the right choice?
· Tankers without bottom loading equipment: Some chemical, specialty product or older fleets have no bottom loading adapters or on-board overfill sensors.
· Hot, viscous products: Products such as bitumen, which are loaded at high temperature, are mostly handled at top loading facilities; confirming that the tanker is free of water before loading is a separate critical check.
· Existing and low-throughput sites: Where the gantry was built for top loading, it may be kept after weighing conversion cost against fleet compatibility.
· Where regulations allow it: Some regulations require bottom loading with vapor collection for volatile products such as gasoline, so whether top loading is permitted must be settled early for the product and jurisdiction.
Loading arm options
A top loading arm reaches from the gantry edge to the tanker dome, and the operator must be able to position it without strain. The main differences are:
· Balanced arms (spring or counterweight): Offset the arm's weight so the operator can move it with little force; a key ergonomic factor.
· Fixed-reach and telescopic arms: Fixed-reach arms need the truck spotted accurately at the gantry; telescopic or multi-joint arms adapt to different tanker lengths and dome positions.
· Arms with vapor return lines: For volatile products, variants with a separate vapor line work with a hood that seals the dome and routes vapor to the collection system.
· Heated or insulated arms: For hot products, heating and insulation are considered to keep product from cooling and solidifying in the arm.
Fill pipe design and avoiding splash loading
Letting product fall freely through the dome opening, known as splash loading, causes two problems: agitation generates more vapor, and free-falling liquid increases static charging. Top loading arms are therefore fitted with a fill pipe, or drop tube, that reaches close to the bottom of the compartment. The European directive on petrol distribution likewise requires that, where top loading is permitted, the arm outlet be kept near the bottom of the container.
The basic static control measures are loading at low flow until the tip of the fill pipe is submerged, ensuring electrical continuity between the arm and the tanker, and grounding the tanker with continuous monitoring before loading starts. The start-up rate and any additional measures for low-conductivity products are set according to the product and the safety guidance being applied.
Platforms, gangways and operator safety
The most obvious drawback of top loading is that the operator has to work at height on the tanker. Occupational safety guidance tackles this risk in order of preference: first remove the need to climb onto the vehicle, then use fixed equipment that prevents falls, and only as a last resort rely on personal fall arrest systems.
· Fixed gantry platform: Should be enclosed by guardrails of adequate height. Platforms are usually fixed in height, so a gangway is needed to serve different tanker sizes.
· Gangway: Lowered from the platform onto the tanker, it can be combined with a safety cage around the working area on top; the gangway's raised position can be tied into the loading permissives.
· Truck positioning: Stopping the truck close to the platform and in the right place reduces the risk of falling into the gap between vehicle and platform.
· Fall arrest systems: Harness systems anchored to an overhead beam require both structure and harness to be designed to take the load of a falling person.
Overfill probe and vapor hood
In bottom loading, overfill prevention relies on sensors mounted in the tanker compartments. Top-loaded tankers often lack those sensors, so overfill detection is usually provided by a level probe lowered into the compartment together with the loading arm. The probe signal is wired into the batch controller's permissive, and the control valve closes when the probe detects liquid. Whether the probe ends up at the correct height depends on the arm position and fill pipe length, which is why probe and arm are selected together.
Vapor escaping from the open dome matters both for operator exposure and for emissions. For volatile products, a vapor hood that seals over the hatch directs vapor through the arm's vapor line to the terminal's vapor collection or recovery system. How well the hood seals against the hatch, and how it copes with different hatch diameters, determines how effective vapor collection is.
Top loading versus bottom loading
Aspect | Top loading | Bottom loading |
Connection point | Dome hatch or fixed top connection | Standard-size adapters under the tanker |
Where the operator works | On top of the tanker, at height; platform and fall protection needed | At ground level |
Compartment loading | Compartments usually loaded one after another | Several compartments can be loaded at once |
Vapor collection | Via a hatch hood and vapor line on the arm | Integrated through the tanker's vapor collection adapter |
Overfill prevention | Mostly a probe lowered with the arm | Compartment sensors on the tanker and a rack monitor |
Typical use | Specialty products, hot viscous products, existing sites | Fuel distribution and new terminal investments |
How TLY Enerji supports top loading projects
At top loading points, TLY Enerji provides engineering support for selecting measurement and control equipment, integrating the overfill probe and grounding permissives with the batch controller and PLC, and for site installation, testing and commissioning. Upgrading the measurement and control side of an existing top loading gantry can also be assessed as part of the project. The scope of supply for loading arms, platforms and steel structures is defined together through the technical specification.
What to share for a top loading project
· Product to be loaded, loading temperature and volatility
· Number of domes, dome positions and hatch diameters across the fleet
· Range of tanker sizes and the existing platform height
· Vapor collection requirements and the terminal's vapor processing system
· Existing loading arms and the equipment to be replaced
· Preferred approach for the overfill probe and ground monitoring
· Heating or insulation requirements
Related pages
· Bottom loading systems: Ground-level loading with adapters and vapor return.
· Truck loading systems: The pump, meter, control valve and batch controller chain.
· Top loading for fuel terminals: Gasoline vapor and the decision to convert to bottom loading.
· Heated loading systems for bitumen: Heating and water hazards when top loading hot bitumen.
Top loading FAQ
Can a top loading gantry be converted to bottom loading?
Yes, but it takes more than swapping the arms. Bottom loading requires a fleet fitted with suitable adapters and compartment overfill sensors, plus a vapor collection line and a sensor monitoring unit at the gantry. The decision weighs fleet compatibility, the regulatory status of the product and the gantry layout together.
Why should the fill pipe end close to the tank bottom?
With the pipe tip near the bottom, liquid covers the outlet quickly and product enters without free fall. That reduces agitation and vapor generation and limits the static charging caused by free-falling liquid. Pipe length should be chosen to suit tanker height and dome position.
How is overfill prevented in top loading?
If the tanker has no compartment sensors, a level probe lowered with the loading arm is typically used. When the probe detects liquid, the batch controller removes the permissive and the control valve closes. As a second barrier, the operating procedure checks that the quantity entered into the batch controller does not exceed the compartment volume.
Can the need for operators to climb onto tankers be eliminated?
With top loading it usually cannot be removed entirely; safety guidance treats eliminating it as the first choice, typically through bottom loading or controls operated from the ground. If top loading continues, the fixed platform, guarded gangway and correct truck positioning should be designed as one system.