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Valves

A valve is a flow-control device. Valves are used to regulate the flow of fluids, liquids and gases in piping systems and machinery. There are many different types of valves in operation — each designed to perform a specific function. Valves may be made from a variety of materials, depending upon their particular function and the stress they undergo during operation. Brass and bronze are usual in valves for general service. Cast iron may be used where there arelow steam pressures and temperatures, or hydraulic pressures. However, steel and alloy steels are required for the highest operating pressures such as 5000 psi and 1200°F steam. Where there are chemical and process applications, special metals must be used..

Obviously valves are used for hydraulic turbines and hydroelectric systems. The purpose of the valves and gates in these systems is to control water flow for regulation of power output at sustained efficiency and with minimum wastage of water. In compressors, valves are usually automatic, operating by pressure difference on the two sides of a moveable, spring-loaded member and without any mechanical linkage to the moving parts of the compressor mechanism. Valves here have to tolerate and handle air speeds to the order of 5000 ft/min. Where pressure is greater than 1000 psi, the normal plate valve is replaced by automatic poppet valves to give greater strength and tightness under loading.

Like those for compressors, pump valves are usually of the automatic type operating by pressure differences. However, working conditions are very different because liquids are handled and the valves therefore have to be capable of dealing with entrained solids, corrosive chemicals, and high viscosity.

Flow-control device	пристрій, що регулює потік
Valve	клапан
To perform	виконувати
To undergo	проходити, підлягати
Cast iron	чугун
Steam pressure	тиск пару
Alloy steels	сплави сталі
Hydraulic turbines	гідравлічні турбіни
Gate	вентиль
Moveable	рухливий
Power output	вихідна потужність
Sustained efficiency	підтримувана ефективність
Wastage	витрати
Mechanical linkage	механічний зв’язок
Viscosity	в’язкість

Comprehension check.

1. What is a valve? Where are they used?

2. What materials are they made from?

3. Describe the work of valves in compressors.

4. What is the purpose of using valves in hydraulic systems?

5. What is the difference in working conditions between pump valves and compressor ones?

Дата добавления: 2015-11-16