So how exactly does a monoflange work?

Monoflanges combine the function 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 higher response speed is necessary for some control applications. One of many variables that affect the response time is the volume and the distance between process and instruments. If เกจ์วัดแรงดันน้ำมันเครื่อง to be measured is gas, and the procedure tends to fluctuate strongly sometimes or if the control is crucial, mounting the instrument close to the process is the solution.
Vibrations are also 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 in the compact, flange-shaped body, allowing a significant reduction in volume, dimensions, weight and potential leakage points.
Monoflange is the solution
With regards to 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 procedure and the other (with a red cap) regulates the venting of the medium trapped inside the instrument. That is mostly found in applications which are relatively uncritical (e.g. low pressure) or where 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 something 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] ; when 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] are in an angled position, which allows the flow to feed them.
Both shut-off valves allow a better isolation from the process: In case the initial shut-off valve does not isolate the medium properly, the second one will become a safety means against accidental leaks. Occasionally, customer specifications don’t allow the medium to be in touch with the instrument when it’s not measuring. That is why the medium will be discharged using the vent line. In other cases ? due to the 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 What is a monoflange? If you have any questions, your contact will gladly help you.

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