Monoflanges combine the function of up to three valves in a particularly compact body, thanks to a precise network of internal passages and valve chambers. But what really happens in the monoflange valve, once installed?
In a chemical process a higher response speed is necessary for most control applications. One of the variables that affect the response time is the volume and the distance between process and instruments. If the medium to be measured is gas, and the procedure tends to fluctuate strongly at times or if the control is crucial, mounting the instrument close to the process may be the solution.
Punish may also be critical, for example, in case that impulse lines are connected to a vessel. Timely -up, the wider is the amplitude of the vibration causing possible failures of the nozzle. A monoflange includes one, several needle valves in the compact, flange-shaped body, allowing a significant reduction in volume, dimensions, weight and potential leakage points.
Monoflange is the solution
Depending on requirements of the plant it really 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 where 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, is 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.
The next picture illustrates the process 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;
Once the first shut-off valve [1] is closed, the medium trapped between valve and instrument could 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 process: In case the first shut-off valve does not isolate the medium properly, the second one will act as a safety means against accidental leaks. Sometimes, customer specifications do not allow the medium to be in touch with the instrument when it is not measuring. That is why the medium shall 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 are available on the WIKA website or in the video Exactly what is a monoflange? In case you have any questions, your contact will gladly help you.