With the increasing efforts of environmental protection in various countries around the world, Gas station gasoline nozzles use oil vapor recovery refueling nozzle, which has become a common phenomenon, However, with the popularity of oil and gas recovery refueling nozzle, Refuelers at gas stations report that the refueling nozzle interface (that is, the connection between the refueling nozzle and the hose) is loose from time to time. What exactly is going on? Let’s analyze it together today.
1. Failure analysis
First, let’s take a look at the difference between an oil and gas recovery nozzle and an ordinary fuel nozzle. There is only one channel in the tail of the ordinary fuel nozzle body, This channel is used to drain oil, The oil and gas recovery fuel nozzle is different, In addition to the oil channel inside the gun body, there is also an isolated thin channel in the center. This channel is used to transport oil and gas, How does this oil and gas go? This oil and gas are sucked in from a set of small holes above the barrel, Come out from the central hole at the end of the gun, Then through the pull-off valve connected to the tail of the gun, the center pipe in the hose, the oil and gas separation joint, the air pipe on the tanker, the recovery pump, and the air pipe on the foundation, it was finally pumped into the underground oil tank.
Because of this, the oil and gas recovery fuel nozzle has a much more complicated structure than our ordinary fuel nozzles. It not only requires refueling but also sucks oil and gas inside. This complex structure also determines that the oil and gas recovery gun does not make us worry so much when using it. If there is a problem with the oil line, it must be dismantled. If there is a problem with the airline, it must be dismantled. If it is disassembled frequently, it cannot be disassembled like an ordinary fuel nozzle. Apply sealant to the end of the gun and twist the joint at the back. In that case, it will be too inconvenient to disassemble. Therefore, the design of the oil and gas recovery fuel nozzle adopts a relatively simple straight thread and O-ring sealed connection method. This connection method is more convenient for disassembly, maintenance, and replacement of the fuel nozzle in case of failure. In addition, the straight thread can also ensure the accurate and reliable sealing position of the internal center tube.
Secondly, let’s take a look at the specific differences between the connecting threads of oil and gas recovery fuel nozzles and ordinary fuel nozzles. Most of the connecting threads of ordinary fuel nozzles are American-made NPT threads (3/4-diameter fuel nozzles are NPT3/4 threads, and 1-inch diameter fuel nozzles are NPT1 threads). This thread connection has a certain taper. It is necessary to apply sealant on the threads. After tightening, the sealant solidifies due to lack of oxygen in the thread gap and plays a sealing and tightening role. The torque during disassembly is relatively large and a wrench must be used to disassemble. Most of the threads used in oil and gas recovery fuel nozzles are metric M34×1.5 threads. This thread is a non-sealing thread, that is, the thread itself only serves as a connection, and the seal is sealed by the O-ring at the root of the thread, so the disassembly torque is very small. Small and can be disassembled by hand (even if you tighten it with a wrench, it can also be unscrewed by hand)
Under normal circumstances, although the connection torque of the oil and gas recovery fuel nozzle is not large, the machine has been assembled and tightened to pass the oil test before leaving the factory. Generally, it will not loosen on its own. Why does the fuel nozzle appear to have a loose interface as soon as it arrives at the oil station? Does it often become loose after being opened or used for a period of time? After careful observation, we found a detail issue in use that may cause looseness, and that is the coiling direction of our hose after hanging the gun. There are two coiling directions of the hose: left-hand or right-hand (or clockwise and counterclockwise). If you are not sure what left-hand and right-hand are, you can understand it simply. The cup lid that everyone uses when drinking water As we all know, the direction of tightening is to turn right, and when opening, you need to turn left.
Since the M34×1.5 threads at the end of the fuel nozzle are all right-hand threads, the threads will become tighter and tighter in the right-hand state, so it is difficult to loosen. However, if the hose is a left-hand coiled hose, the moment the hose is pulled open, it will There will be a left-handed force to loosen the thread, especially when the hose is filled with oil and this force will be greater.
Some people may say, no, there are union joints at both ends of the hose that can be flexibly rotated. If such a strong force could loosen the fuel nozzle, wouldn’t the union joints be rotated to offset it long ago? You are right. Under normal circumstances, the unions at both ends of the housework. However, if you pull the hose quickly when refueling, or if the union is not flexible enough, the joints will indeed loosen in an instant.
2. Failure prevention
◆ Before debugging a newly installed machine, check whether there is an obvious gap between the tail of the fuel nozzle and the pull-off valve, and between the pull-off valve and the flexible joint of the hose, because when the machine is unpacking and draining the fuel nozzle, the hose may be pulled and the joints may become loose. possible;
◆ Before each time you lift the gun for refueling, first check whether there is an obvious gap between the tail of the fuel nozzle and the pull-off valve, and between the pull-off valve and the flexible joint of the hose. If there is a gap, it means that the fuel nozzle or the pull-off valve has become loose. Retighten (remember to turn right to tighten);
◆ Regularly check the union at the end of the hose. If the union is stuck, it is easy to bring a pine fuel nozzle when pulling the hose;
◆ Develop the habit of turning the hose right after use. This action is very simple, but it can prevent the oil vapor recovery gun from loosening.