ball valve and butterfly valve info
By isolating the valve body and stem with rubber or PTFE, it isn't essential for the valve body to be created of costly corrosion-resistant supplies such as stainless steel, Alloy 20 and C-276.
When the valve body and journals are exposed to the line media such as in gate valves, globe valves and lubricated plug valves, the valve is regarded as to have "wetted" parts.
Characteristics and method requirements
The following are some general control valve terms and characteristics for ball valves when utilized for modulating service. A valve having a stated inherent characteristic might offer a various installed characteristic due to interaction with the method.
Linear. The flowrate is directly proportional to the quantity of disk travel. For example, at 50% open, the flowrate is 50% of maximum flow.
Equal percentage. Equal percentage characteristic means that equal increments of valve travel create equal percentage changes in flowrate as related to the flowrate that existed at the previous travel position.
For instance, if a valve travel change from 20% open to 30% open produced a 70% alter in flowrate, then a valve travel change from 30% open to 40% open would create an additional 70% alter in flowrate. If the flowrate at 20% open was 100 gpm, then flowrate at 30% open could be 170 gpm and also the flowrate at 40% open could be 70% greater than at 30% travel or 289 gpm. The exact same would be accurate for each additional incremental travel position.
Quick opening. A quick-opening valve means precisely that. Flowrate via the valve increases very rapidly for incremental changes in valve travel when valve position is near closed. As valve position becomes more open, flowrate modifications diminish with incremental changes in valve travel approaching zero change as the valve position nears full open.
Traditionally, most ball valves have exhibited equal percentage inherent characteristics at angles of opening from 20 Degrees to 70 Degrees . Advances in disk design have allowed the extension of the equal percent characteristic via to the 90 Degrees , full-open position.
Designs employed for the extension of the equal percentage characteristic have varied from special contouring with planned flow disturbance to wafer-thin types with nearly no flow disturbance. The former causes flow restriction at intermediate travel characteristics.
There are other types of valve disks provided that exhibit inherent flow characteristics approaching linear. This deviation from the conventional characteristic will be the result of very heavy disk cross sections. As these valves are utilized in control applications, the user should make sure suitability of the linear characteristic.
Still another kind of disk exhibits a characteristic midway between linear and equal percentage. Usually, this could be a disk style for high-pressure service but with minimal accessible capacity.
The selection of the suitable control valve characteristic is dependent on the needs of the method. Because there are several elements to be considered, a complete system analysis is needed to figure out precisely which is the optimum characteristic. Often, it is not practical to perform a method analysis; therefore, particular rules of thumb are offered:
If in doubt about the preferred characteristic, choose equal percentage. Such a option may result in a perfect match. If the match is not ideal, it will not be as detrimental as the selection of a linear characteristic when it is not a perfect match.
When the valve body and journals are exposed to the line media such as in gate valves, globe valves and lubricated plug valves, the valve is regarded as to have "wetted" parts.
Characteristics and method requirements
The following are some general control valve terms and characteristics for ball valves when utilized for modulating service. A valve having a stated inherent characteristic might offer a various installed characteristic due to interaction with the method.
Linear. The flowrate is directly proportional to the quantity of disk travel. For example, at 50% open, the flowrate is 50% of maximum flow.
Equal percentage. Equal percentage characteristic means that equal increments of valve travel create equal percentage changes in flowrate as related to the flowrate that existed at the previous travel position.
For instance, if a valve travel change from 20% open to 30% open produced a 70% alter in flowrate, then a valve travel change from 30% open to 40% open would create an additional 70% alter in flowrate. If the flowrate at 20% open was 100 gpm, then flowrate at 30% open could be 170 gpm and also the flowrate at 40% open could be 70% greater than at 30% travel or 289 gpm. The exact same would be accurate for each additional incremental travel position.
Quick opening. A quick-opening valve means precisely that. Flowrate via the valve increases very rapidly for incremental changes in valve travel when valve position is near closed. As valve position becomes more open, flowrate modifications diminish with incremental changes in valve travel approaching zero change as the valve position nears full open.
Traditionally, most ball valves have exhibited equal percentage inherent characteristics at angles of opening from 20 Degrees to 70 Degrees . Advances in disk design have allowed the extension of the equal percent characteristic via to the 90 Degrees , full-open position.
Designs employed for the extension of the equal percentage characteristic have varied from special contouring with planned flow disturbance to wafer-thin types with nearly no flow disturbance. The former causes flow restriction at intermediate travel characteristics.
There are other types of valve disks provided that exhibit inherent flow characteristics approaching linear. This deviation from the conventional characteristic will be the result of very heavy disk cross sections. As these valves are utilized in control applications, the user should make sure suitability of the linear characteristic.
Still another kind of disk exhibits a characteristic midway between linear and equal percentage. Usually, this could be a disk style for high-pressure service but with minimal accessible capacity.
The selection of the suitable control valve characteristic is dependent on the needs of the method. Because there are several elements to be considered, a complete system analysis is needed to figure out precisely which is the optimum characteristic. Often, it is not practical to perform a method analysis; therefore, particular rules of thumb are offered:
If in doubt about the preferred characteristic, choose equal percentage. Such a option may result in a perfect match. If the match is not ideal, it will not be as detrimental as the selection of a linear characteristic when it is not a perfect match.
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