LPG DISPENSER

LPG Dispenser

Many Liquefied Petroleum Gas (LPG) and fuel dispensers are sold on the market. In most cases (LPG stations, LPG filling plants, LPG skid stations) the models sold are LPG dispensers defined as double sided and twin nozzle. Hoses must comply with EN 1762. Small LPG stations, portable skid LPG stations or companies with a dedicated supply area in their own fleets prefer single nozzle dispensers. Although different LPG dispensers show certain differences between manufacturers, the main elements that make up an LPG dispenser are the same in all of them. The housing of an LPG dispenser may be galvanised painted steel (DKP), 430 steel or 316 stainless steel. It must also carry the ATEX2014/34/EU certification required by LPG regulations together with MID B-SK 18 044 MI-005 MID D SK 19-061 D certificates.

How an LPG Dispenser Works

The working principle of LPG dispensers is as follows. LPG arriving from the transfer pump enters a vapour separator beneath the dispenser. The liquid gas leaving this separator passes through a check valve and reaches the mechanical meter of the dispenser, that is the prima meter. From the prima meter the LPG passes through the differential pressure valve at a pressure of approximately 10 bar depending on the dispenser type. The task of this differential pressure valve is to keep the product in liquid form under pressure. Any vaporisation that may occur during this process is connected to the vapour return line from the vapour collecting section on the valve. The LPG that reaches the dispenser hose in liquid form is filled into the vehicle tank with the filling nozzle. For the system to work without error, the LPG vapour coming from the vapour separator and the differential valve is returned to the LPG tank at the station through the system return line. There must be no closed valve on this return line up to the point where it re-enters the tank.

The Dispenser Meter

The LPG dispenser meter (prima meter) is the device that measures the amount of liquid LPG passing through the LPG dispenser. The LPG dispenser meter must hold OIML R 117 certification. It has four pistons and a measurement accuracy of 0.5 per cent. It works with a 14,000 gauss magnet in an improved magnetic system. It has a self cleaning feature. All parts are built on the lego principle, so parts can be replaced easily and at low cost. The crank mechanism is forged steel and long lasting.

The Electronic Unit

The electronic brain of the 2A LPG dispenser is patented by 2A and has a transformer rated at 120-280 volts, 50-60 Hz, with 72 hour data retention and resistance to high voltage. The LCD screen is self illuminating. Connection to the automation system can be made by RS-232, LAN or USB. Its electronic software can communicate in line with the Gilbarco and Wayne Dart protocols, which makes it compatible with automation and cash register systems.

Filter and Safety Features

The box housing the LPG dispenser filter has an inlet and an outlet valve. The filter has both a 10 micron special filter paper and metal protection.

Other important features of the LPG dispenser are that it sees faults in the system and stops operation in the event of a fault. Excess current draw by the Asco brand solenoid valves is prevented by a separate fuse, relay and varistor arrangement. The solenoid valve is also prevented from drawing current when there is no sale. If it does not see LPG flow, it stops operating. The release of LPG into the atmosphere from possible causes such as a hose rupture during vehicle filling is prevented by a sudden flow increase detection system that cuts the flow automatically. The slow flow period at the end of the programme can be set from the relevant menu in the electronic unit.

The device called the pulser, of the Eltomatic brand, works integrated with the meter inside the LPG dispenser and, through the shaft on it, shows on the dispenser screen the litres of LPG delivered to the vehicle together with the price corresponding to those litres.

What matters in an LPG dispenser hose is that it complies with LPG standards, that it does not dissolve or deteriorate on a liquid or vapour basis, and that it withstands LPG pressure, that is, that it is resistant to high pressure. It must also have a conductive wire or weave. This is very important in order to prevent static electricity that may arise from spraying during refuelling. The use of ex-proof certified metal cable glands in the LPG dispenser is an important detail for dispenser safety.

Automatic Temperature Compensation (ATC)

The ATC (Automatic Temperature Compensation) device in the dispenser allows the expansion in the unit volume of LPG to be calculated according to the temperature difference that may occur between the station tank and the dispenser hose. Thanks to its high technology microchip probe it can measure a change of 0.0001 °C in temperature. It then makes a volume correction according to the current measured temperature. In this way the consumer receives a more accurate quantity of LPG without being affected by changes in the temperature factor.

The ATC system must be coupled to the electronic system of the dispenser. A change of density must be made through a password entry. The ATC system must comply with the legislation of the Ministry of Science, Industry and Technology. Both the ATC probe and the connection between the ATC and the electronic unit must be sealed. No sale should be possible while the ATC is in the closed position.

If water has mixed into the product for any reason, it is important that the dispenser has a safety valve and a drain valve.

Pump Capacity and Nozzles

The centrifugal pump capacity used for a single nozzle LPG dispenser is 45-50 litres per minute; for twin nozzle dispensers 90-100 litres per minute is sufficient. At the end of the dispenser hose an Italian filling type T3 nozzle, an acme type nozzle or an LPG cylinder filling nozzle (for bottling plants) can be used.

Operating Pressure

Dispensers generally operate under a pressure of 7-10 bar. The meter inside the LPG dispenser transfers the LPG in liquid form to the vehicle tank at a fixed volume through the dispenser. On every turn of the meter shaft in the dispenser, the electronic counter of the dispenser is driven through the shaft of the Eltomatic pulser above it. In this way the amount of LPG delivered is shown on the dispenser screen in litres and in the monetary value of those litres, so that the consumer can see it.