How does a monoflange work?

Monoflanges combine the event of up to 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 required for most control applications. One of many variables that affect the response time is the volume and the length between process and instruments. If Alluring to be measured is gas, and the process tends to fluctuate strongly at times or if the control is critical, mounting the instrument close to the process may be the solution.
Vibrations may also be critical, for example, in case that impulse lines are connected to a vessel. The longer the hook-up, the wider may be the amplitude of the vibration causing possible failures of the nozzle. A monoflange includes one, two or three needle valves inside a compact, flange-shaped body, allowing a significant decrease in volume, dimensions, weight and potential leakage points.
Monoflange is the solution
According to the requirements of the plant it is installed in, the monoflange can incorporate one, two or three valves. In a monoflange with two valves (block & bleed), one valve (with a blue cap) isolates the procedure and the other (with a red cap) regulates the venting of the medium trapped in the instrument. That is mostly found in applications which are relatively uncritical (e.g. low pressure) or in which a first shut-off valve is provided right before the monoflange.
The safest configuration, and the main 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 following picture illustrates the procedure within a DBB monoflange:
The flow enters the monoflange from the pipeline and stops below the first shut-off valve [1];
Once the first shut-off valve [1] opens, the flow proceeds towards the next shut-off valve [2] ; once the valve [2] is open, the instrument is thus linked 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] come in an angled position, which allows the flow to feed them.
The two shut-off valves allow an improved isolation from the procedure: In case the first shut-off valve will not isolate the medium properly, the next one will become 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. For this reason the medium will be discharged using the vent line. In other cases ? as a result of vent line ? Unique can be easily calibrated without dismounting them from the line.
Note
More info 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.

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