Trim design will affect how the valve capacity changes as the valve moves through its complete travel. Because of the variation in trim design, many valves are not linear in nature. The relationship between valve capacity and valve travel is known as the flow characteristic of the valve. Valve trims are specially designed, or characterized, in order to meet the large variety of control application needs. This is necessary because most control loops have some inherent nonlinearities, which you can compensate for when selecting control valve trim.
The percent of full flow through the valve is plotted against valve stem position. The curves shown are typical of those available from valve manufacturers. These curves are based on constant pressure drop across the valve and are called inherent flow characteristics
The quick-opening characteristic provides large changes in flow for very small changes in lift. It usually has too high a valve gain for use in modulating control. So it is limited to on-off service, such as sequential operation in either batch or semi-continuous processes.
The majority of control applications are valves with linear, equal-percentage, or modified-flow characteristics.
Linear – flow capacity increases linearly with valve travel.
Equal percentage – flow capacity increases exponentially with valve trim travel; equal increments of valve travel produce equal percentage changes in the existing Cv.
A modified parabolic characteristic is approximately midway between linear and equal-percentage characteristics. It provides fine throttling at low flow capacity and approximately linear characteristics at higher flow capacity.
When valves are installed with a pump, pipes, fittings, and other process equipment, the pressure drop across the valve will vary as the plug moves through its travel. When the actual flow in a system is plotted against valve opening, the curve is called the installed flow characteriscic.
Control Valve Flow Characteristics
January 29th, 2010Introduction of Ball valve
January 13th, 2010A ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it. The sphere has a hole, or port, through the middle so that when the port is in line with both ends of the valve, flow will occur. When the valve is closed, the hole is perpendicular to the ends of the valve, and flow is blocked. The handle or lever will be inline with the port position letting you “see” the valve’s position. The ball valve, along with the butterfly valves and plug valve, are part of the family of quarter turn valves.
Ball valve are durable and usually work to achieve perfect shutoff even after years of disuse. They are therefore an excellent choice for shutoff applications (and are often preferred to globe valves and gate valves for this purpose). They do not offer the fine control that may be necessary in throttling applications but are sometimes used for this purpose.
The body of ball valves may be made of metal, plastic or metal with a ceramic center. The ball is often chrome plated to make it more durable.
Ball valves are used extensively in industry because they are very versatile, supporting pressures up to 700 bars and temperatures up to 200°C. Sizes typically range from 0.5 cm to 30 cm. They are easy to repair and operate.
The Butterfly Valve In The Industrial World
January 6th, 2010In its simplest terms, a valve is a tool that establishes the flow of any particular substance, from gases, fluidized solids, any kind of liquids, to slurries. Normally, this device regulates the flow of such substances by opening, closing, or fractionally obstructing different passageways. This kind of tools is used in a number of applications, including residential, transportation, commercial, military,and of course, industrial applications. These valves are used in two ways; either driven by pressure, such as for safety reasons in steam engines, or used in a controlled manner, like when driven by a camshaft, where valves play a major role in engine cycle control.
When it comes to valves, there are a lot of types that can be used in different ways. One particular type of valve would be the butterfly valve .butterfly valve have three different types. The high performance butterfly valve , which is generally double eccentric in design, is working the pressure for up to 725 PSI. The second type would be the resilient butterfly valve, which has a flexible rubber seat. This type would work the pressure for up to 232 PSI. And finally, the last type would be the tricentric butterfly valve, which is normally designed with metal seating. This valve works the pressure for up to 1450 PSI.
This valve is specifically used in large pipes, and is described as a disk rotating on a diametrical axis inside a pipe, also used as a throttle valve or a damper. The butterfly valve is a sort of device that controls the flow, normally used to administer a certain fluid that would flow through a certain section of a pipe. This valve is similar (with regards to operation) to a ball valve . The butterfly valve, having a flat circular plate, is positioned in the center of the pipe, and the plate has a rod through it that is attached to a handle on the outside of the valve. This valve works by rotating the handle, and turning the plate over either in a parallel position, or perpendicular to the flow. Not like the ball valve, the plate in the butterfly valve is always there within the flow; therefore a kind of pressure drop is always induced in the flow, despite the position of the valve.
There are also several kinds of butterfly valves available in the market. Wafer style valves would be the most common, since people who get to order such would not even say the word wafer, but still get the butterfly valve that they want. This kind is under plastic butterfly valves, which is available in two styles, the wafer and the lug. On the other hand, lug style valves have metal inserts that are established in the bolt holes of the valve. These inserts are threaded on both ends, and this alone allows them to be positioned into a specific system with the use of two bolts and no nuts. Also called a butterfly damper, this valve simply controls the flow by use of a disk through a specific port.
Hope the above recommendations can give you some help.
Check Valve sealing principle
January 6th, 2010Check Valve sealing principle
check valve sealing principle and design principles are generally divided into lift, Swing, butterfly, and diaphragm and other several types .now,we take vertical lift type check valve and Swing Check Valve for examples.
1) vertical lift type check valve
vertical lift type check valve and gate valve have similar structure that the valve flap moves along the channel centerline. The sealing principle is:
For the vertical lift check valve, is closed by self-weight, once the valve flap closed, relying on counter-current when the media pressure on the valve flap in the formation of seal pressure, the higher the pressure, the higher the specific pressure on the the seal surface of valve flap and valve seat and sealing will be easier. On the contrary, the lower the medium pressure, the lower the seal specific pressureof the valve flap and the valve seat’s sealing surface , and result in more difficult to seal. In order to ensure the sealing, it is necessary to ensure the actual sealing pressure is greater than the specific pressure , but still less than the material allows . In this way, a higher working pressure for the vertical lift check valve, sealing surface pressure should be designed to be more wide accordering to the material allowable pressure.on the contrary, the lower working pressure for the vertical lift check valve , because the work pressure is low, sealing force inevitably small, to ensure adequate sealing pressure ,it is need to design seal surface to be narrower.
For the straight-through valve, because most can only be installed on a horizontal tube, valve flap can not close the valve by self-weight, so can only add a compression spring, relying on the elastic force of compression spring, once the pump stops,pull the valve flap to the valve seat, and then rely on the working media pressure to ensure sealing. Thus, in calculating the sealing force should add the spring force, it is not only include medium pressure to calculate the specific pressure seal. Lift check valve fluid resistance is greater, it is because in the medium flow process, turning around an S-shaped bend, but reliable work. As the structural relationship, only suitable for small-caliber occasions.
Swing Check Valve valve flap valve body rotates around the shaft, the axis of shaft and the sealing surface of valve body must be on a plane, in order to guarantee seal when closed. Swing check valve generally only installed in a horizontal tube . when Useing, depend on the medium working pressure and the valve flap weight to put the flap valve rotating around the axes inside valve body , and put valve and valve seat close together to close the valve on purposes. Once Swing check valve closed,then the sealing force is formed which is the reverse-media pressure forces on the aortic valve, then sealing pressure is formed, and will also be able to ensure the seal of Swing Check Valve . Higher pressure the medium pipe work, the greater the sealing force, and will the higher the seal specific pressure, and will be more likely to ensure seal; On the contrary, the lower the pressure medium pipe, and will the smaller seal force, and so is specific pressure.that is not easy to ensure seal. At this time, in order to ensure the seal specific pressure, only the sealing surface be designed to be narrower in order to guarantee the achievement of sealing. It should be noted, when the medium work pressure is high, its seal power must be very great , and also the specific pressure. To ensure that the actual seal specific pressure than the actual seal specific pressure , the same time must be less than the material allows , this is the only way not only to guarantee the seal, but also the safe and reliable.
Globe valve
December 22nd, 2009
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Detailed Products Description:Globe valve
Feature and Function：
1.with a simple structure and reliable seal,it is used to shut off the fluids in conduits
2.with the short stoke,it features an easy operation,short opening/closing stroke and low in height.
3.easy to repair and maintain.
4.bevel gear,pneumatic actuator,hydrulic actuator or electric actuator can be equipped if customers need.
For more information,just feel free to contact us.
Swing check valve
December 22nd, 2009
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Detailed Products Description:Swing check valve
Feature and Function：
1.Simple and reliable,it is used to prevent fluids from flowing back.
2.Convenient to repair and maintain.
For more information,just feel free to contact us.
Duo-Disc spring check valve
December 22nd, 2009
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Detailed Products Description:Duo-Disc spring check valve
Feature and Function：
1. short in face to face dimension;
2. small in size and light in weight;
3. fast open and close,small water hammer pressure;
4.such valve can best used in horizontal or vertical pipelines,and be very easy to be mounted;
5.expedite in flowing system,small in fluid resistance;
6.quick action and good seal;
7.short in disc travel distance,small in valve shut impaction pressure.
8.simple and compaction configuration with nice shape;
9.prolong the usage life,high reliable.
For more information,just feel free to contact us.
JLH Fireproof Multi-Functional Valve
December 22nd, 2009
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Detailed Products Description:JLH Fireproof Multi-Functional Valve
Feature and Function：
1.as a combination of shutting-off,throttle&checking functions,it can be installed at the pump outlet to replace the three valves,i.e.,Globe valve,throttle valve and check valve ,realizing the three functions in a singe valve.
2.it can be used as the conduit automatic balance distribution valve.once the initial flow rate is setup,there is no need to adjust the valve later for keeping the pre-set flow rate because of pump stop or re-start.
3.the disc automatically shuts off upon the pump stop for quickly stopping flow with smooth closing and with no water hammer.
4.long time no use or for repair,for the sake of safety,it is recommended to tighten the stem to the maximum extent to support the disc for use as one stop valve.
For more information,just feel free to contact us.
Floating ball valve
December 22nd, 2009
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Detailed Products Description:Floating ball valve
Feature and Function：
With a structure simple and opening closing fast,it is used to link or shut off fluids in conduits.
Fluid resistance small and sealing ability excellent.
Worm gear actuator,pneumatic actuator,hydraulic actuator or electric actuator can be equipped according to customers’requirements.
For more information,just feel free to contact us.
Fixed ball valve
December 22nd, 2009
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Detailed Products Description:Fixed ball valve
Feature and Function：
1.Simple and reliable.
2.Convenient to repair and maintain.
For more information,just feel free to contact us.