Low-tech valves have not changed much over the past 100 years, but gate valves play an important role in the equipment of refineries, chemical plants, power plants and industrial enterprises around the world.
The most commonly used type of the valve in the world is the gate valve — the flow controller.
Being diversified in size from 1 / 4 to 144 inches, the gate valve can be found in every refinery, chemical plant, power station and manufacturing facilities of industrial plants. Its main purpose is to cut off the flow, which gives alternative names to it as the “cut-off” or the “block-off” valve.
Advantages of the Gate Valve
A almost unimpeded media flow can be ensured when it is switched on. Among plenty of general valves only the open pore ball valve can match the gate valve in the flow capacity. The symmetrical design and the coordinate seal enable the gate valve to cut off the flow in either direction. It can be made from a variety of materials and it can be made into a diversified collection, from a common bright 1 / 2 inch brass faucets found on hardware store shelves to a rare high alloy one found in nuclear power plant installations.
The gate valves can not be operated in a partially open position or used for regulating purposes due to the potential damage to the seating surface. Why so? The reason is the scratches caused by the switch-off device( the gate or the wedge) swinging between the two seats in a partially open state.
Similar as their outside appearance is, their inside structure is different from each other. Most gate valves consist of a body, a bonnet and a switch-off device (a gate or a wedge). The switch-off device is connected to the stem, which extends through the bonnet and finally reaches the hand wheel or other stem operators. Around the stem, the pressurized packing material in the stuffing box bears the pressure.
Although gate valves can be made from metals ranging from aluminum to zirconium in the chemical periodic table and varieties of engineering plastics, the most common ones are steel, iron and bronze.
Bronze or brass has an excellent machinability with the lowest cost. For its low strength and hardness, the bonze is machinable but suitable only for low-pressure applications. Bronze valves are used primarily in water pipes and service lines with pressures of 300 PSI or less.
The strength of the iron valve is between that of the bronze and steel ones. Iron is difficult to deal with, but cast iron is relatively easy. Iron valves are usually made of two materials, gray iron and malleable iron. With a high percentage of carbon and an excellent rust resistance, iron valves are more suitable for underground applications than steel valves.
For industrial valves, steel materials range from the lowest grade “WCB” to chromium / molybdenum alloy steel. Unlike brass, bronze or iron, most of the low-alloy steel is weldable, which makes steel valves easy to be repaired, rewelded and, in some cases, manufactured. The gate valve can also be made from rare alloys such as titanium to zirconium in the periodical table.
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