How does a monoflange work?

Monoflanges combine the function of up to three valves in an especially compact body, thanks to an accurate network of internal passages and valve chambers. But what really happens in the monoflange valve, once installed?
In a chemical process a high response speed is required for some control applications. Among the variables that affect the response time may be the volume and the distance between process and instruments. If the medium to be measured is gas, and the process tends to fluctuate strongly sometimes or if the control is crucial, mounting the instrument close to the process is the solution.
Vibrations may also be critical, for example, if impulse lines are connected to a vessel. Non-controlling -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 is the solution
Depending on 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. This is mostly used 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 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;
When 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. The two shut-off valves [1, 2] come in an angled position, which allows the flow to feed them.
Both shut-off valves allow an improved isolation from the procedure: In case the first shut-off valve does not isolate the medium properly, the next one will act as a safety means against accidental leaks. In some cases, customer specifications do not allow the medium to stay touch with the instrument when it is not measuring. That is why the medium shall be discharged using the vent line. In other cases ? because of the vent line ? Sizzles could 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? Assuming you have any questions, your contact will gladly help you.

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