Valve is a kind of control element with function of shut off ,control ,diversion ,anti-back flow etc . There are lots of valve types from simple to complex equipment . The valves can used to control the fluid such as air ,water ,steam ,corrosive medium ,slurry ,oil etc . The valves can also be classified according to the material ,such as cast iron valve ,casting steel valve ,stainless steel valve ,hascrome valve ,plastic valve，duplex stainless steel and so on .Pneumatic conveyor is driven by the compressed air, transporting the powder material from on end of the sealing vessel to another end .The applied industry is widely, take the following as an example:Power industry: Coal powder, coal ash and blaster furnace slag Building industry: Cement and lime powder .Others: Any powder and particle material in food and medicine industry
It is very important for selecting the correct valves in pneumatic conveyor system. The requirement of the valve is anti high temperature, anti-corrosive and anti-abrasive performance.
The typical of positive pressure pneumatic conveying system is described as the following picture. We can group the valve into several types according to their position and function in the system: feed valve, vent valve, inlet valve, bleeder valve ,switching valve and so on .
Positive pressure pneumatic conveying system
 
Vent valve (Air release valve ):Vent valve is used to release the air in the system to feed bin or flue when the medium is conveying by pneumatic .The benefits of this valve is to short the feeding time and make discharging more frequently . The medium is air with a little of powder. The valve type worked as vent valve include ceramic gate valve, butterfly valve, ceramic ball valve and Pneumatic Rotating Type Ceramic Gate Valve etc .
Inlet Valve :The following valves work as inlet valve ,including butterfly valve ,ball valve.The medium for inlet valve is compressed air ,so they have little requirement on anti-abrasive performance .
Bleeder Valve :To make the medium flow in the pipes under the compressed air ,the inlet valve and bleeder valve will be opened when the transporting device full of material .So the medium is the powder with compressed air . The valve type works as bleeder valve ,including ceramic gate valve ,ceramic ball valve , Pneumatic Rotating Type Ceramic Gate Valve etc .
Switching Valve:The function of switching valve is converge or distributes the medium .The valve type work as switching valve include ceramic ball valve or other combined valve ,different valve manufacture selecting different valve type as switching valve . Switching valve can be installed at pipes and the top of tank . when they are installed on the top of tank ,a ceramic elbow is necessary at the inlet of valve inlet . A small discharge tank need to be installed on the top of tank ,the purpose of that is to enlarge the transporting passageway ,and reduce the fly dust of ash storage .