A truck loading system is the loading point that transfers liquid product from storage into a road tanker compartment in a preset quantity, at a controlled flow rate, and only once the safety permissives are in place. On its way to the tanker the product passes through a pump, a strainer or filter, an air/vapor eliminator, a meter and a flow control valve before reaching the loading arm. A batch controller supervises the whole chain: it counts the delivered quantity, opens and closes the valve in stages, and stops the load as soon as a grounding or overfill signal is lost.
This page covers the process flow and components of a single loading point. The choice between top and bottom loading, multi-bay layout, terminal automation and custody transfer measurement each have their own pages.
How product moves through a loading point
1. Pump or shared supply header: Delivers product from the storage tank at the required flow and pressure. A loading point may have a dedicated pump or share a header with other positions.
2. Strainer or filter: Protects the meter and valve from solids; monitoring differential pressure gives early warning of plugging.
3. Air/vapor eliminator: Keeps entrained air or vapor from reaching the meter and being registered as liquid. Metrological requirements for liquid measuring systems treat the gas elimination device as part of the measuring system.
4. Meter and secondary measurements: A positive displacement, turbine or Coriolis meter measures the quantity; temperature, and where needed pressure and density, are used to convert it to base conditions.
5. Flow control valve: Opens on command from the batch controller, limits flow rate and closes when the preset quantity is reached.
6. Loading arm or hose connection: Delivers product into the compartment; its type and connection depend on whether the bay is top or bottom loading.
Metering skid, loading rack or terminal: defining the scope
Quotations often cannot be compared because each party has a different scope in mind. Industry guidance separates these layers too: guidelines for gantry measurement systems state explicitly that they do not cover the design of the complete loading system or its safety aspects.
Scope layer | Typical content | What it means for your decision |
Metering and control skid | Strainer, air eliminator, meter, temperature and pressure measurement, control valve, batch controller, grounding and overfill connections | Narrowest scope; pump, loading arm and civil works usually excluded |
Loading point or rack | The skid plus loading arms, pump, shutoff and relief valves, piping and bay equipment | Arm type and bay layout are decided at this level |
Complete terminal | Storage tanks, tank gauging, product receipt, vapor recovery, terminal automation system and several bays | Outside the scope of this page; see the terminal pages |
Batch controller and the staged loading profile
The batch controller receives the target quantity from the driver or a supervisory system and runs the load step by step. The control valve follows those steps: it starts at low flow, moves to high flow once permissives and flow are stable, drops back to low flow as the target approaches, and then closes completely. This low–high–low profile serves two purposes.
· Low flow at start-up: Helps limit splashing and static charge generation while the fill outlet is not yet submerged.
· Low flow before shutoff: Lets the valve close accurately at the preset and reduces the pressure surge that an abrupt closure would create.
The controller also applies the meter factor, converts the quantity to base conditions using temperature and, where needed, density, may handle additive injection or blending, and keeps a record of every batch. Which functions sit in the controller and which in the terminal automation system should be settled early in the project.
Pressure surge and valve closing speed
When a valve closes quickly, the moving column of liquid in the loading line produces a sudden pressure rise. That surge can damage the meter, seals, hoses and the loading arm, and it can also disturb the final meter reading. Control valves with adjustable opening and closing speeds are used for this reason. Beyond normal shutoff, the valve closing time and pump stop sequence should be reviewed together for emergency shutdown, loss of permissive and power failure. Long supply lines, or a header feeding several positions, may justify a dedicated hydraulic study.
Loading permissives: grounding, overfill and arm position
The loading point runs on interlock logic that prevents flow until defined conditions are met. Typical permissives include:
· Truck ground verification: The tanker's connection to ground is confirmed by a device that monitors continuity, not just by a clamp being attached.
· Compartment overfill prevention: Monitored through sensors on the tanker for bottom loading, or typically through a level probe used with the arm for top loading. This is different from overfill protection on storage tanks.
· Arm position and connection status: Confirms that the arm has left its parked position and is connected.
· Emergency stop: Pushbuttons on the bay close the valve and stop the pump.
If any permissive drops during loading, the control valve closes and the batch is suspended with its record intact. Which permissives are treated as safety functions, and the integrity level they need, is decided by the project risk assessment.
Design inputs
Parameter | Why it matters in design | Effect on selection |
Product and properties | Viscosity, vapor pressure, conductivity and temperature change metering and safety decisions | Meter type, air eliminator, seal materials and static control measures |
Target loading rate | Determines time per truck and pump capacity | Line size, meter size and control valve selection |
Number and size of compartments | Each compartment can be loaded as a separate batch | Controller configuration and minimum batch quantity |
Purpose of measurement | Inventory tracking and sales measurement have different requirements | Proving connections, sealing and record keeping |
Supply arrangement | A dedicated pump or shared header sets the hydraulic behavior | Pressure control, valve characteristic and surge measures |
Loading method | Top and bottom loading use different interfaces | Arm type, overfill prevention and vapor connection |
Hazardous area classification | Sets the protection method for electrical equipment | Controller, transmitters, panels and cabling |
Where TLY Enerji fits in a loading point project
TLY Enerji supports truck loading projects with engineering input on meter, control valve and instrument selection based on your product and operating data. Depending on the project, scope can include supply of flow meters, valves and pumps, integration between the batch controller and the PLC, site installation, testing and commissioning, and maintenance and spare parts support. Who provides the skid, the loading arm and the site infrastructure is agreed with you through the technical specification.
Information needed to quote a loading point
· Products to be loaded, with viscosity, density and temperature range for each
· Tanker type, number of compartments and typical batch sizes
· Target loading rate and expected trucks per day
· Existing or planned pump and supply line data
· Top or bottom loading
· Whether measurement is for inventory control or for sales
· Additive injection or blending requirements
· Hazardous area classification and the control system to interface with
Related solutions
· Top loading systems: Arm, fill pipe and platform design when loading through the dome.
· Bottom loading systems: Adapters, vapor return and the tanker sensor interface.
· Automated truck loading terminals: Process automation from order verification to delivery documents.
· Custody transfer truck loading skids: Verification and sealing of measurement when loading for sale.
· Truck unloading systems: Suction-side design and quantity checks when receiving product from tankers.
Truck loading FAQ
Does a batch controller do the same job as a PLC?
Their roles overlap but are not identical. The batch controller counts meter pulses, applies the meter factor and temperature conversion, drives the control valve through the loading profile and records each batch. The PLC usually handles pump logic, permissives, emergency shutdown and bay equipment. Small systems can combine some functions, but where the measurement record is held should be decided up front.
Why doesn't loading start at full flow?
At the very start the fill outlet is not yet covered by liquid, and high flow can cause splashing and increase static charge generation. A short low-flow stage also confirms that permissives and flow are stable before ramping up. The actual start-up rate is set in the project according to the product, arm type and the safety guidance being applied.
Is an air eliminator needed at every loading point?
Where air or vapor can be entrained it matters for measurement accuracy, and for sales measurement it is treated as a required part of the measuring system. Systems fed continuously with liquid from a tank under good pump suction conditions carry less risk. The decision depends on the product's vapor pressure, the supply arrangement and the purpose of measurement.
Can one loading point deliver more than one product?
Yes. Each product can have its own meter and valve run, or products can be delivered one after another through the same arm. In that case the product left in the line, the risk of contamination and any flushing needs must be assessed. Planning several bays and products together is covered under multi-bay terminals.
What happens if the ground connection is lost during loading?
The ground verification device detects the loss and removes the loading permissive. The batch controller closes the control valve, the pump is stopped according to the interlock logic, and the batch is recorded with the quantity delivered up to that point. Whether loading may resume once the connection is restored and verified is set by the operating procedure.