So how exactly does a monoflange work?

Monoflanges combine the function of up to three valves in a particularly compact body, because of a precise network of internal passages and valve chambers. But what really happens inside Badass , once installed?
In a chemical process a high response speed is required for most control applications. Among 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 tends to fluctuate strongly sometimes or if the control is crucial, mounting the instrument near 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, several needle valves inside a compact, flange-shaped body, allowing a significant reduction 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, 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, may be the three-valve monoflange or the so-called double block & bleed (DBB), which features two shut-off valves in series and something valve for venting.
Monoflange functionality
The monoflange bodies are drilled internally with holes which connect the annular valve chambers.
The next picture illustrates the procedure inside a DBB monoflange:
The flow enters the monoflange from the pipeline and stops below the first shut-off valve [1];
When the first shut-off valve [1] opens, the flow proceeds towards the second shut-off valve [2] ; when 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, that allows the flow to feed them.
Both shut-off valves allow a better isolation from the procedure: In case the initial shut-off valve does not isolate the medium properly, the second one will become a safety means against accidental leaks. In some cases, customer specifications do not allow the medium to be in touch with the instrument when it’s not measuring. For this reason the medium shall be discharged utilizing the vent line. In other cases ? as a result of vent line ? instruments could 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 What is a monoflange? For those who have any questions, your contact will gladly help you.

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