>>>Related Links: Introduce several simple solutions for home wiring LAN Optimized Transmission Media - Home LAN Wire Routing Considerations 1, the choice of network cable In configuring network devices, network cables (only twisted-pair cables used in Ethernet as an example) are usually the easiest for people to ignore. People often think that there is nothing to consider for “network cablesâ€, as long as they are twisted-pair cables, or as long as they are Five types of twisted pairs can be. In actual fact, I once tested several types of Cat. 5 and Cat. 5 twisted pairs and found that some Cat. 5 cords could not be tested with a network tester at all (only 25 meters). However, the indicator on the tester was connected. Either not at all, or it is always red. It can be seen from the indicating state of the indicator light that these five types or ultra-five twisted pairs are either of too high impedance, so that the tester's test signal is not attenuated by the network cable and the level indicator is not strong enough to make the indicator lamp glow, or The network cable has an internal short-circuit phenomenon due to string winding (which can absolutely be eliminated when the crystal head is manufactured). Therefore, when selecting a network cable, it cannot be so casual, especially for some networks that need to be connected at a relatively long distance. In order to reduce signal interference, each pair of twisted pair cables is formed by twisting two insulated copper conductors, and the number of twisting turns of different pairs in the same cable is also different. The pairs in the standard twisted pair cable in the winding direction are twisted counterclockwise. However, in order to simplify the manufacturing process, some cable wires produced by non-regular manufacturers have the same twisting density of all pairs in the cable; the twisted density of the two insulated conductors in the wire pair does not meet the technical requirements, and the twisting direction of the pair does not match. Claim. These undesirable phenomena will cause near-end crosstalk of the twisted pair (referring to the degree of signal interference between the two pairs in the UTP), so that the transmission distance does not meet the requirements. The twisted degree of twisted pair has stricter standards in production. When the actual purchase is made, some professional equipments can be used to measure under conditional conditions, but the average user can only observe with the naked eye. It should be noted that the twisting degree of the five UTP midline pairs is better than that of the three categories. The five categories are more dense than the five categories. This density is generally difficult to see with the naked eye. Unless there is comparison, when selecting the twisted pair, Also choose brand names, because these brand-name products will be taken into account in the production of the above issues, there are quality assurance, such as AMP, LUCENT (formerly AT & T), IBDN (Canada Northern Telecom) and so on. In addition, we must fully pay attention to the category of cable, and some bad companies often use three or four types of wire to impersonate five or even more than five types of lines, or a brand of choice, as long as you remember not to be cheap, not This is generally ensured by the network cable of the selected makers. When we buy wire for the LAN, we usually choose to purchase Category 5 or Category 5 cable because Category 3 and 4 twisted-pair cables are generally used in 10M/bps Ethernet, and Category 5 twisted-pair cables can meet the requirements. Nowadays the 100M/bps Ethernet, which is increasingly popular, is mainly used for the future Gigabit Ethernet. However, it is also commonly used in local area networks because the price is not much more expensive than the Category 5 cable. Now it has 6 Class line, generally used in ATM networks, the company's LAN is not recommended for the moment. These line types are marked on the packaging cover if they are manufactured by regular manufacturers. For example, "3 cable" is used for category 3 lines, "5 cable" is used for category 5 lines, and "5 e" is generally used for category 5 lines. (or 5E) cable, pay attention to see clearly, do not buy Category 3 or 4 cable at the price of Category 5 cable! In addition, the good twisted pair is thicker and softer, and the printed characters are very clear; counterfeit products are usually thin and generally hard to save costs. The characters printed on the wrapped plastic skin are also rough, and the connoisseur sees it right and wrong. Famous brand manufacturers. 2, the production of network cable The above mentioned the choice of network cable. In fact, in the production of network cable, there are also many skills that play an important role in the optimization of LAN performance. In general, twisted wire production methods are as follows, pay attention to one-to-one correspondence, can not be wrong. (1) One by one correspondence. That is, the two ends of the twisted pair must be in one-to-one correspondence. The foot of this head must be connected to the other foot. This network cable is generally used between the switch and the computer. (2), 1-3, 2-6 cross connection method. That is, the first leg of the network cable is connected to the third leg of the other end, and the second leg of the network cable is connected to the sixth leg of the other head, and the other legs correspond one by one. This kind of network cable is generally used in the cascade of switches. (3) 100M connection method. The so-called 100M connection means that it can meet the communication speed of 100M bandwidth. Although it's connection method is also a one-to-one correspondence, but the color of each foot is fixed, specifically: the first foot - yellow white, second foot - yellow, third foot - green white, fourth foot - Blue, fifth foot - blue and white, sixth foot - green, seventh foot - brown, eighth foot - brown. Now I have found that many of my friends are greedy for simplicity. One of my favorite methods is the one-by-one correspondence. In fact, although this method is feasible, I have done experiments (more than 60 meters long on different floors). The workstations that connect the wiring method will often appear to crash when opening the file on the server. Later, the quality of the third type of connection network has changed greatly. The above situations rarely occur. Therefore, it is best to use the third type of network cable production method when connecting to the network cable (that is, from the HUB or switch to the workstation), so that you can maximize the speed advantage of Category 5 or Super Category 5 network cable and make your network Keep it open at all times. In addition, the crystal head used to make the cable interface is also easier to ignore, select the crystal head is also a good choice of brands, such as AMP, good crystal head pins used by the material impedance is relatively small, not easy to oxidation, rust, At the same time, some of the Mickey's crystal head contacts with the RJ-45 jack are relatively small, which may cause poor contact. When selecting the crystal head, be careful not to save a few cents. Pay attention to the production process of the crystal head. The insert must not be oxidized and discolored, and the contact surface should be larger and brighter. The elasticity of the head on the other head is better, otherwise it is easy to cause poor contact due to the buckle is not tight. Wiring hydropower reform 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. Check Valves, Water Check Valves, Brass Check Valves, Sanitary Check Valves ZHEJIANG KINGSIR VALVE CO., LTD. , https://www.cn-kingsir.com
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.