So how exactly does a monoflange work?

Monoflanges combine the function as high as three valves in an especially compact body, thanks to an accurate 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 some control applications. One of many variables that affect the response time may be the volume and the length between process and instruments. If the medium to be measured is gas, and the process will fluctuate strongly sometimes or if the control is crucial, mounting the instrument near the process may be the solution.
Vibrations are also critical, for example, if impulse lines are linked 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 reduction in volume, dimensions, weight and potential leakage points.
Emphasize may be the solution
According 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 process and another (with a red cap) regulates the venting of the medium trapped inside 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 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 process 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;
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.
Blunder shut-off valves allow a better isolation from the process: In case the initial shut-off valve will not isolate the medium properly, the second one will act as a safety means against accidental leaks. In some instances, customer specifications don’t allow the medium to be in touch with the instrument when it is 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
Comfortable on our valves can be found on the WIKA website or in the video Exactly what is a monoflange? For those who have any questions, your contact will gladly help you.

Leave a Comment