Home appliances can not be separated from the wires, especially the old houses, although the wire is small, “responsibility†is significant. A lot of fires are caused by the aging of the power lines, their unreasonable configuration, or the poor quality of the wires used. Therefore, consumers must polish their eyes when buying electric wires, carefully identify them and prevent them from occurring.
The state has explicitly stated that copper conductors should be used in new houses. However, copper conductors are also used, and inferior copper conductors are also used. The copper core uses recycled copper and contains many impurities. Some poor-quality copper conductors are even less conductive than iron wires, which can easily cause electrical accidents. At present, there are many kinds of wires on the market, many specifications, and prices are chaotic. It is very difficult for consumers to choose. With regard to the prices of 2.5 square millimetres and 4 square millimetres of two kinds of copper wires that are commonly used in home decoration, the price of one line of the same specification may differ by 20%, 12316; 30% because of different manufacturers. As for the quality, whether the length is up to standard, consumers are even more difficult to determine.
According to industry sources, the reason why the prices of wires are so different is that they are caused by different raw materials used in the production process. The main raw materials for producing wires are electrolytic copper, insulating materials and sheathing materials. At present, the raw material market has about two million yuan per ton of electrolytic copper, and only about 15,000 yuan per ton of recycled copper; the price of high-quality products for insulating materials and sheathing materials is 8,000 yuan per ton, 12316, and 8500 yuan. The price of the product is only 4,000 yuan per ton &12316; 5,000 yuan, and the spread is even more disparity. In addition, the lack of length and inadequate insulation of the insulators are also important reasons for price differences. The length of each line, superior products is 100 meters, while the defective product is only about 90 meters; excellent quality of insulators containing glue accounted for 35% & 12316; 40%, and defective products only 15%. By contrast, it is not difficult for consumers to see that the difference in the sales price of finished wire is due to the presence of tricky materials.
So, how to identify the advantages and disadvantages when buying a wire?
(1) First of all, see the volume of wire packaging cards, whether there is the "Great Wall Mark" and the production license number of the China Electrotechnical Products Certification Committee; see if there is a quality system certification; see whether the certificate is standardized; see if there is a name , site, inspection seal, production date; see if there are trademarks, specifications, voltage, etc. printed on the wire. It also depends on the cross-section of the copper core of the wire. The superior product has a bright, soft color and a reddish yellow color in the copper core, indicating that the quality of the copper used is better, and the yellow white is a reflection of the low quality copper.
(2) It is desirable to use a wire head repeatedly bent by hand, which is a superior product with soft touch, good anti-fatigue strength, high elasticity of plastic or rubber, and no crack on the wire insulation. The outer plastic skin of the wire should be bright in color and fine in texture. There should be no open flame when lit with a lighter.
(3) Take a section of insulation to see if the core is in the middle of the insulation. Non-centered is due to the fact that the process is not high and the eccentricity phenomenon is caused. If the power is small, it can be safe when used. Once the power is used, the thinner side may be broken down by the current.
(4) It must be seen whether the length and the core thickness have any hands or feet. The relevant standards stipulate that the error of the length of the wire cannot exceed 5%, and the diameter of the cross section cannot exceed 0.02%. However, there are a large number of short and short lengths on the market, and frauds are made on the cross section (if the cross section is 2.5 mm 2 ). Lines, in fact, only 2 square millimeters thick) phenomenon.
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A ball check valve is a check valve in which the closing member, the movable part to block the flow, is a spherical ball. In some ball check Valves, the ball is spring-loaded to help keep it shut. For those designs without a spring, reverse flow is required to move the ball toward the seat and create a seal. The interior surface of the main seats of ball check valves are more or less conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow.
Ball check valves are often very small, simple, and cheap. They are commonly used in liquid or gel minipump dispenser spigots, spray devices, some rubber bulbs for pumping air, etc., manual air pumps and some other pumps, and refillable dispensing syringes. Although the balls are most often made of metal, they can be made of other materials, or in some specialized cases out of artificial ruby. High pressure HPLC pumps and similar applications commonly use small inlet and outlet ball check valves with both balls and seats made of artificial ruby, for both hardness and chemical resistance. After prolonged use, such check valves can eventually wear out or the seat can develop a crack, requiring replacement. Therefore, such valves are made to be replaceable, sometimes placed in a small plastic body tightly-fitted inside a metal fitting which can withstand high pressure and which is screwed into the pump head.
There are similar check valves where the disc is not a ball, but some other shape, such as a poppet energized by a spring. Ball check valves should not be confused with Ball Valves, which is a different type of valve in which a ball acts as a controllable rotor to stop or direct flow.
A diaphragm check valve uses a flexing rubber diaphragm positioned to create a normally-closed valve. Pressure on the upstream side must be greater than the pressure on the downstream side by a certain amount, known as the pressure differential, for the check valve to open allowing flow. Once positive pressure stops, the diaphragm automatically flexes back to its original closed position.
A swing check valve or tilting disc check valve is check valve in which the disc, the movable part to block the flow, swings on a hinge or trunnion, either onto the seat to block reverse flow or off the seat to allow forward flow. The seat opening cross-section may be perpendicular to the centerline between the two ports or at an angle. Although swing check valves can come in various sizes, large check valves are often swing check valves. The flapper valve in a flush-toilet mechanism is an example of this type of valve. Tank pressure holding it closed is overcome by manual lift of the flapper. It then remains open until the tank Drains and the flapper falls due to gravity. Another variation of this mechanism is the clapper valve, used in applications such firefighting and fire life safety systems. A hinged gate only remains open in the inflowing direction. The clapper valve often also has a spring that keeps the gate shut when there is no forward pressure. Another example is the backwater valve (for sanitary drainage system) that protects against flooding caused by return flow of sewage waters. Such risk occurs most often in sanitary drainage systems connected to combined sewerage systems and in rainwater drainage systems. It may be caused by intense rainfall, thaw or flood.
A stop-check valve is a check valve with override control to stop flow regardless of flow direction or pressure. In addition to closing in response to backflow or insufficient forward pressure (normal check-valve behavior), it can also be deliberately shut by an external mechanism, thereby preventing any flow regardless of forward pressure.
A lift-check valve is a check valve in which the disc, sometimes called a lift, can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. A guide keeps motion of the disc on a vertical line, so the valve can later reseat properly. When the pressure is no longer higher, gravity or higher downstream pressure will cause the disc to lower onto its seat, shutting the valve to stop reverse flow.
An in-line check valve is a check valve similar to the lift check valve. However, this valve generally has a spring that will 'lift' when there is pressure on the upstream side of the valve. The pressure needed on the upstream side of the valve to overcome the spring tension is called the 'cracking pressure'. When the pressure going through the valve goes below the cracking pressure, the spring will close the valve to prevent back-flow in the process.
A duckbill valve is a check valve in which flow proceeds through a soft tube that protrudes into the downstream side. Back-pressure collapses this tube, cutting off flow.
A pneumatic non-return valve.
Multiple check valves can be connected in series. For example, a double check valve is often used as a backflow prevention device to keep potentially contaminated water from siphoning back into municipal water supply lines. There are also double ball check valves in which there are two ball/seat combinations sequentially in the same body to ensure positive leak-tight shutoff when blocking reverse flow; and piston check valves, wafer check valves, and ball-and-cone check valves.
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