There are generally the following safety facilities on oil tank trucks: mechanical breathing valves, hydraulic safety valves, flame arresters, measuring holes, manholes, daylighting holes, oil inlet and outlet pipes, foam generators, electrostatic grounding wires, lightning rods, ladders, and railings. During the use of oil tanks, these safety facilities are required to be kept in good condition.
(1) Mechanical breathing valve
The mechanical breathing valve is an important accessory to protect the oil storage safety of the oil tank. It is installed on the top plate of the oil tank and consists of a pressure valve and a vacuum valve. Its function is to maintain the tightness of the oil tank under normal circumstances and reduce the evaporation loss of oil to a certain extent. When necessary, it can automatically ventilate, adjust and balance the pressure inside and outside the oil tank, and protect the oil tank.
The working principle of the mechanical breathing valve is: when the oil and gas pressure in the tank is greater than the allowable pressure of the oil tank, the oil vapor escapes through the pressure valve, and the vacuum valve is closed; when the oil and gas pressure in the tank is less than the allowable vacuum of the oil tank, fresh Air enters the tank through the vacuum valve while the pressure valve is closed. The allowable pressure (or vacuum pressure) is controlled by the weight of the adjusting disc.
It must be noted in use that if the breathing valve seat plate is too light or damaged, it is easy to cause a large amount of light oil vapor in the tank to escape to the outside of the tank, increasing the risk of fire. If the vent of the breathing valve is incorrectly selected, the pressure valve is too heavy, or the valve disc fails to lift, it may cause the oil tank to burst or collapse. Mechanical breathing valves sometimes rust and become blocked. In winter, the valve disc and valve seat will freeze due to water in the oil vapor.
(2) Hydraulic safety valve
The hydraulic safety valve is another important accessory installed on the top of the oil tank to protect the safety of the oil tank. When the mechanical breathing valve fails, the hydraulic safety valve can replace the mechanical breathing valve to exhaust or inhale. The oil tank is equipped with both a mechanical breathing valve and a hydraulic safety valve, which improves the safety.
The pressure or vacuum value controlled by the hydraulic safety valve is 10% higher than that of the mechanical breathing valve, so it will not operate under normal conditions. In the valve, oil with high boiling point (not easy to volatile in summer), slow evaporation, and low freezing point (not solidified in winter) (such as light diesel, solar oil or transformer oil) is used as the sealing liquid (referred to as the sealing liquid). When the gas space in the tank is at a positive pressure, the gas squeezes the sealing liquid into the outer ring space from the inner ring space, the pressure continues to rise, and the sealing liquid level changes constantly. When the sealing liquid level in the inner ring space is When the lower edge is flat, the gas in the tank enters the atmosphere through the lower edge of the partition. On the contrary, when there is negative pressure in the tank, the sealing liquid in the outer ring space enters the inner ring space, and the atmosphere enters the tank. When the pressure in the tank is balanced with the surrounding air pressure, the sealing liquid level in the inner and outer ring spaces is maintained at the same liquid level.
During use, care must be taken to maintain the fluidity of the sealing liquid and a certain amount of sealing liquid. When the amount is small, it must be refilled in time. Otherwise, the tank will directly communicate with the atmosphere and the oil and gas will escape, which will increase the danger of the tank area.
(3) Flame arrestor
The flame arrester is a fire safety device on the oil tank. It is located at the lower part of the mechanical breathing valve on the top of the tank. It looks like a box and contains a certain aperture of copper, aluminum (or other heat-resistant metal) multi-layer wire mesh or Corrugated board. Once a flame enters the breathing valve, the metal wire mesh or corrugated plate in the flame arrestor quickly absorbs the heat of the burning gas, so that the flame is extinguished and the flame is prevented from entering the tank.
(4) Measuring hole
The measuring hole is also called the oil hole, which is a special accessory used to measure the oil level in the tank and to take oil samples. One is set on the top of each oil tank, most of which are located near the tank ladder platform. The diameter of the measuring hole is 150 ram, and it is equipped with a sealed hole cover and elastic bolts. In order to prevent sparks from collision between the hole cover and the iron when it is closed, an oil-resistant rubber pad or soft metal (copper or aluminum) is embedded in the sealing groove under the hole cover. Because the steel tape for measurement is easy to rub against the outlet to generate sparks, a copper (or aluminum alloy) sleeve is set on the inner side of the bore tube, or a non-ferrous metal guide groove (throwing groove) that does not generate sparks is installed outside the fixed measuring point. .
Oil tank fires often occur at the measurement hole. The main reason is that when the hole cover is opened during the measurement operation, the oil and gas in the tank rush out. If it encounters static sparks, impact, or friction sparks, it will cause the fuel gas to catch fire.
(5) Manhole
The manhole of the non-metal oil tank is set on the tank top. The manholes of the metal oil tanks are located on the bottom plate of the tank wall. Most of them are round holes with a diameter of 600 mm. They are used for tank cleaning or maintenance personnel to enter and exit the tank. They are also called gates. Manholes can be used for lighting and ventilation when inspecting and cleaning oil tanks.
(6) Daylighting hole
The light hole is also called the light hole. The daylighting hole of the oil tank is set on the top of the tank, generally a circular hole with a diameter of 500mm. Usually the perforated cover ring is tightly sealed with bolts. When cleaning and repairing the oil tank, it is used for lighting, ventilation and exhaust.
(7) Oil inlet and outlet pipes
The oil inlet and outlet pipes are the only way for oil products to enter and output from the oil tank. The inlet and outlet pipes of the oil tank are connected from the lower part of the oil tank wall. If the oil inlet pipe is connected from the upper part, the oil pipe will extend to the lower part of the oil tank. Why? This is mainly from the perspective of safety and reducing oil loss. Because the oil enters the oil tank from the upper part, if effective measures are not taken, the oil will be splashed. This will not only increase the large breathing loss of the oil, but also increase the friction between the oil flow and the air and generate a lot of static electricity. , When the electrostatic voltage increases to a certain value, it will discharge sparks and cause explosions and fires.
(8) Foam generator
The air foam generator, also known as the air foam chamber, is a fire-fighting device installed on the tank wall of the uppermost ring plate of the oil tank for spraying foam when the oil tank is extinguished. The spout is sealed with a thin glass sheet (or diaphragm) from the air in the tank to prevent the oil or gas in the tank from entering the foam chamber or fire-fighting pipeline. Fragile cracks are engraved on one surface of the glass sheet, and the cracked surface is installed along the direction of the ejection port. When it is 1~0.29Pa, it can be crushed. The type and number of foam generators installed in the oil tank are determined by calculation based on the capacity of the oil tank, the type of oil stored, the size of the oil surface, and the type of foam, but at least two, and There is also a separate fire line to supply the foam mixture.
(9) Electrostatic grounding wire
The electrostatic grounding wire is a protective device that introduces the electrostatic charge accumulated in various parts of the oil tank and the electric charge generated by the lightning induction effect into the earth, avoids the discharge of sparks, prevents the oil tank from exploding and catching fire, and protects the safety of the oil tank.
(10) Lightning rod
Lightning rods are lightning protection devices used to prevent oil tanks from being struck by direct lightning. The tip of the lightning rod directly installed on the oil tank must be at least 5m higher than the breathing valve, and the highest point of the oil tank must be within the protection range of the lightning rod. If it is the oil tank area of one or more groups of oil tanks, it can be calculated according to the specific location of the oil tank to set up single or multiple single lightning rods, so that all oil tanks in the oil tank area are protected by lightning protection devices Within range.