The valve is a control component in the pipeline fluid conveying system. It
is used to change the passage section and the flow direction of the medium. It
has the functions of diversion, cut-off, adjustment, throttling, check, shunt or
overflow and pressure relief. Valves used for fluid control, from the simplest
shut-off valve to various valves used in extremely complex automatic control
systems, have a wide range of varieties and specifications. Valves for
industrial pipelines.
The valve can be used to control the flow of various types of fluids such as
water, steam, oil, gas, mud, various corrosive media, liquid metals and
radioactive fluids. From the ultra-low temperature of -269℃ to the high
temperature of 1430℃. The valve control can adopt a variety of transmission
methods, such as manual, electric, hydraulic, pneumatic, worm gear,
electromagnetic, electromagnetic-hydraulic, electric-hydraulic,
pneumatic-hydraulic, spur gear, bevel gear drive, etc. ; Under the action of
pressure, temperature or other forms of sensing signals, it can act according to
predetermined requirements, or simply open or close without relying on the
sensing signal. The valve is driven by * or automatic mechanism to make the
opening and closing parts lift, Sliding, pendulum or rotary motion, thereby
changing the size of its flow channel area to achieve its control function.
1. Strength performance The strength performance of the valve refers to the
ability of the valve to withstand the pressure of the medium. The valve is a
mechanical product that is subjected to internal pressure, so it must have
sufficient strength and rigidity to ensure long-term use without rupture or
deformation.
2. Sealing performance The sealing performance of the valve refers to the
ability of each sealing part of the valve to prevent the leakage of the medium,
which is the most important technical performance index of the valve. There are
three sealing parts of the valve: the contact between the opening and closing
parts and the two sealing surfaces of the valve seat; the matching between the
packing and the valve stem and the stuffing box; the connection between the
valve body and the bonnet. The leakage in the former part is called internal
leakage, which is commonly referred to as lax closure, which will affect the
ability of the valve to cut off the medium. For shut-off valves, internal
leakage is not allowed. The leakage in the latter two places is called external
leakage, that is, the medium leaks from the inside of the valve to the outside
of the valve. External leakage will cause material loss, pollute the
environment, and even cause accidents in severe cases. For flammable, explosive,
toxic or radioactive media, leakage is not allowed, so the valve must have
reliable sealing performance.
3. Flow performance After the medium flows through the valve, there will be a
pressure loss (that is, the pressure difference before and after the valve),
that is, the valve has a certain resistance to the flow of the medium, and the
medium will consume a certain amount of energy to overcome the resistance of the
valve. Considering energy saving, when designing and manufacturing the valve,
the resistance of the valve to the flowing medium should be reduced as much as
possible.
4. Action performance
1). Action sensitivity and reliability
This refers to the sensitivity of the valve to respond to changes in medium
parameters. For throttle valves, pressure reducing valves, regulating valves and
other valves used to adjust medium parameters, as well as safety valves, steam
traps and other valves with specific functions, their functional sensitivity and
reliability are very important technical performance indicators.
2). Opening and closing force and opening and closing torque
Opening and closing force and opening and closing torque refer to the force
or torque that must be exerted by the valve to open or close. When closing the
valve, it is necessary to form a certain sealing specific pressure between the
opening and closing parts and the two sealing surfaces of the hair seat, and at
the same time, it is necessary to overcome the gap between the valve stem and
the packing, between the valve stem and the thread of the nut, the support at
the end of the valve stem and the The friction force of other friction parts, so
a certain closing force and closing torque must be applied. During the opening
and closing process of the valve, the required opening and closing force and
opening and closing torque vary, and the maximum value is at the final moment of
closing or opening. the initial moment. The valve should be designed and
manufactured to reduce its closing force and closing moment.
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