"Verification Regulation of Fuel Dispenser" stipulates that the maximum allowable error of fuel dispenser is ± 0.3%. However, in the sampling inspection, we found that some fuel dispensers have the phenomenon of indication error out of tolerance, when the flow measurement converter, encoder and the lead seal of meter control motherboard are in good condition during the verification period. It is understood that similar situations are common. After further analysis and research, the author thinks that the main reasons are as follows:
Causes of equipment failure
- Due to the damage of the solenoid valve, the overshoot of some fuel dispensers changes greatly. After a certain period of use, there will be a big difference between the quantitative and non quantitative measurement results. The non quantitative measurement often meets the requirements, while the quantitative measurement will exceed the allowable error range. Especially for a small amount of refueling (less than 5L), the impact of solenoid valve on the tanker will be greater. The solenoid valve plays a very important role in the measurement accuracy of the fuel dispenser. The relevant technical specifications of the state also stipulate that the tax controlled fuel dispenser must be installed with the solenoid valve. During the operation of gas stations, the solenoid valves should be checked frequently to ensure the normal operation of gas dispensers. In our daily verification, if we find that there is a big difference between quantitative and non quantitative measurement results, it is very likely that there is a problem with the solenoid valve of the tanker.
- In addition, the oil leakage of the bottom valve of the tanker is also the cause of the large change of the metering indication. The function of the bottom valve of the tanker is to prevent the oil in the pipeline of the tanker from flowing back to the storage tank. If the bottom valve does not work, the oil in the pipeline will return when there is no pump pressure. In this case, the refueling will be mixed with some gas, resulting in large error.
- Besides, the outlet pressure of some fuel dispensers is too high. Many people think that the pump pressure is too high and the oil is fast. However, if the outlet pressure of the oil pump is too high, a large amount of gas will be generated in the oil circuit, making the oil-gas separator unable to work normally. Some gas will be sent to the flowmeter, resulting in insufficient oil filling. According to the national measurement standard, the outlet pressure of the oil pump should not be greater than 0.3MPa, so we must pay attention to whether there are bubbles in the oil sight glass during the daily measurement verification or refueling.
The influence of temperature
- The fuel dispenser takes the volume "L" as the settlement unit, which leads to the problem of heat expansion and cold contraction, especially the gasoline with smaller density is more affected by the temperature. When the gasoline temperature changes by 1 ℃, the volume will change by 0.12%, and the fuel dispenser does not consider the temperature compensation when selling the oil, so the seasonal change and even the temperature change at noon and night will affect the metering accuracy of the fuel dispenser Impact. This requires the quality supervision department to carefully measure the oil temperature and tank temperature in each periodic verification, add temperature compensation, strictly calculate, and treat the interests of gas stations and consumers with a fair attitude.
Human factors
- At present, many new types of fuel dispensers have different degrees of adjustment rods, and some of them even have different adjustment directions from other models. It is very easy to make mistakes in the process of adjustment and repair. This requires the metrological verification personnel to pay attention to the indexing and adjustment direction of the flow measurement converter of the tanker before the adjustment and repair of the tanker. If the adjustment is reversed, the error will be further expanded, resulting in a large change in the measurement indication during the re inspection. Therefore, after the adjustment and repair of the tanker must be qualified again before it can be allowed to use, so as to avoid the adverse consequences caused by mistakes.