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Valve is one kind of devise to control liquid
flow, pressure and direction. Controlled liquid may be liquid, air,
air and liquid mixture, or solid and liquid mixture. IN general, valve
composed of body, bonnet, seat, closure member, actuator, seal and
fasten etc. control function is achieved through closure member rise,
slippage, circle or rotary to change alleyway acreage which drive
by actuator and flow medium. Valve is widely used in daily life. For
example, water faucet and reducing valve are all called valve that
be used in water pipe and LPG kitchen. The same time, valve is one
indispensable part for all kinds of machine equipments such as gas
engine, steamer, compressor, pump, pneumatic actuator, hydraulic gear,
watercraft and aerocraft. In 2000 B.c., Chinese have been used bamb oo
and wooden plug valve in water pipeline, using water gate valve for
irrigate channel, using disc check valve for bellows when smelting,
using bamboo and disc check valve to distill salt water in exploiting
wall salt aspect. With the development of smelting technical and water
mechanical, copper and lead plug valve were created In Europe; in
1681,lever weighted safety valve was created along with boiler’s
using. Plug valve and check valve is the uppermost valve before steam
engine have be invented in 1769. The invention of steam engine put
valve into mechanical industry field. Butterfly valve also be used
to adjust flow in watt’s steam engine expect plug, safety, and
check valve. Increase with steam flow and pressure, Plug valve that
control steam admission and exhaust can’t satisfy with steam
engine 's needs, and then Slide valve was created
It is a great innovate that globe valve having
screw stem and wedge gate valve having trapezoidal thread stem were
created in 1940. Not only satisfy with increasing pressure and temperature,
but also satisfy with flow regulating. High and middle pressure valve
gained rapid development with the developing of Electric power, petroleum,
chemical and shipbuilding industry.
After Second World War, immemorial plug and butterfly get new application
and ball valve and diaphragm valve get rapid development for the
evolution of polymeric material, lubricate material, stainless steel
and Co-stellite. The varieties of globe, gate, and other valve were
increased and quality was improved. Valve manufacturing has become
one important branch of mechanical industry. Valve can be classified
six species that is intercept valve, regulating valve, check valve,
shunt valve, safety valve and multipurpose valve.
Intercept valve is mainly to stop flow gateway
that includes globe valve, gate valve, plug valve, ball valve, butterfly
valve and diaphragm valve etc; regulating valve is mainly to adjust
fluid pressure and flow etc that includes regulating valve, reducing
valve and float ball regulating valve etc; check valve is mainly to
prevent fluid adverse current; shunt valve is mainly to distribute
the direction of fluid or to separate two way fluid that includes
slide valve, multiway valve, trap valve and drain valve etc; safety
valve is mainly to protect and prevent boiler and pressure vessel
or pipeline from damaging when pressure over working pressure.
Industry pipeline valve can be classified as vacuum valve, low
pressure valve, middle pressure valve, high pressure valve, super
high pressure valve according to normal pressure; valve can be classified
as normal temperature valve, middle temperature valve, high temperature
and low temperature valve according to working temperature; valve
can also be classified according to actuator type, pipeline connection
type and body material. Valve can separately or compositely named
according to different classify, and also named according to structure
feature or specific purpose.
The basic parameter of valve is working pressure,
working temperature and normal diameter. For many kinds of valve that
using in industry pipeline, Normal pressure and normal diameter is
basic parameter. Normal pressure is maximum working pressure that
certain material valve can be endured pressure in special temperature.
Normal diameter is name diameter of meet end between body and pipe.
According to different kinds and purpose,
it is produce different require for valve that is seal, intensity,
regulate, flow, open and close etc performance. When design and select
valve, Fluid performance that includes fluid state, causticity, viscidity,
toxicity, flammability, explosion hazard, the degree of valuable and
radioactivity etc should be take into consideration expect Basic parameter
and performance.
Seal and intensity performanc e
are the most important and basic foe each valve. The seal of valve
can be classified as inside seal and outside seal. Inside seal is
the seal between disc and seat, while outside seal is that seal between
stem and bonnet, body and bonnet, body with pipeline connection part.
it is not only need good seal performance but also ensure using safety
for valve in use.
It would bring various degrees of economic
losing if leakage occurred because seal performance failure or parts
damaged because the intensity is not enough. It would result in serious
safety accident if transports toxicity, flammability, explosion hazard
or strong causticity fluid. It is necessary that to select correct
material expect to ensure process quality and to design structure
according to relevant standard In order to ensure valve seal and intensity.
In general, cast iron or copper be used for the valve when the
medium is low pressure non-corrosive fluid; cast steel or forged
steel be used for high or middle pressure valve; alloy steel be
used for high pressure and temperature condition; stainless steel,
plastic, anticorrosion alloy or lining anticorrosion material that
made of cast iron or cast steel be used for the valve when the medium
is corrosion fluid.
Seal face of low-pressure valve usually adopts
copper or bronze, high and middle pressure valve adopts stainless
steel, high pressure and high temperature valve that need special
requirements adopts Co-stellite. Polymer has been widely used in valve
field. For example, seat material of ball valve mainly adopts PTFE;
seal of butterfly and the diaphragm of diaphragm valve usually adopt
some kinds of rubber. The material has superior seal performance than
metal material in the range of its using temperature.
With the development of modern industry, petrochemical industry,
electronic industry, space flight industry, process autocontrol
and distance transportation, modern low temperature, vacuum valve,
nucleus valve and many kinds of regulate valve has achieved great
develop. More and more valve actuator shall be used for distance
control and procedure control.
>It is the direction for future valve to extend product parameter,
develop saving energy and labor valve and autocontrol valve, improve
structure, adopt new material and new process, increase valve using
life and develop special valve series etc aspects. Such as low temperature
valve, vacuum valve, nucleus valve, safety valve, regulate valve,
trap valve and valve actuator etc that be used for liquid oxygen,
liquid hydrogen and LPG etc medium.
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