Monoflanges combine the event as high as three valves in an especially compact body, thanks to a precise network of internal passages and valve chambers. But what really happens inside a monoflange valve, once installed?
In a chemical process a high response speed is necessary for some control applications. One of the variables that affect the response time is the volume and the length between process and instruments. If the medium to be measured is gas, and the process will fluctuate strongly at times or if the control is critical, mounting the instrument close to the process is the solution.
Argumentative may also be critical, for example, if impulse lines are linked to a vessel. The longer the hook-up, the wider is the amplitude of the vibration causing possible failures of the nozzle. A monoflange includes one, several needle valves inside a compact, flange-shaped body, allowing a substantial decrease in volume, dimensions, weight and potential leakage points.
Monoflange may be the solution
Based on the requirements of the plant it is installed in, the monoflange can incorporate one, several valves. In a monoflange with two valves (block & bleed), one valve (with a blue cap) isolates the process and the other (with a red cap) regulates the venting of the medium trapped inside the instrument. That is mostly used in applications which are relatively uncritical (e.g. low pressure) or in which a first shut-off valve is provided just before the monoflange.
The safest configuration, and the one we advise for aggressive media or critical operating conditions, may be the three-valve monoflange or the so-called double block & bleed (DBB), which features two shut-off valves in series and one valve for venting.
Monoflange functionality
The monoflange bodies are drilled internally with holes which connect the annular valve chambers.
Know It All following picture illustrates the procedure within a DBB monoflange:
The flow enters the monoflange from the pipeline and stops below the initial shut-off valve [1];
Once the first shut-off valve [1] opens, the flow proceeds towards the second shut-off valve [2] ; once the valve [2] is open, the instrument is thus connected to the process line;
When the first shut-off valve [1] is closed, the medium trapped between valve and instrument can be discharged via the vent valve [3] through the vent outlet. Both shut-off valves [1, 2] are in an angled position, which allows the flow to pass through them.
Both shut-off valves allow a better isolation from the procedure: In case the first shut-off valve will not isolate the medium properly, the next one will act as a safety means against accidental leaks. In some instances, customer specifications don’t allow the medium to stay touch with the instrument when it’s not measuring. For this reason the medium will be discharged utilizing the vent line. In other cases ? as a result of vent line ? instruments can be easily calibrated without dismounting them from the line.
Note
Further information on our valves can be found on the WIKA website or in the video Exactly what is a monoflange? Should you have any questions, your contact will gladly assist you to.