So how exactly does a monoflange work?

Monoflanges combine the function of up to three valves in a particularly 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. Among the variables that affect the response time is the volume and the distance between process and instruments. If the medium to be measured is gas, and the process tends to fluctuate strongly at times or if the control is crucial, mounting the instrument near the process may be the solution.
Vibrations may also be 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, two or three needle valves in the compact, flange-shaped body, allowing a substantial decrease in volume, dimensions, weight and potential leakage points.
Monoflange may be the solution
With regards to the requirements of the plant it really 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 another (with a red cap) regulates the venting of the medium trapped inside the instrument. This 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.
digital pressure gauge are drilled internally with holes which connect the annular valve chambers.
The following picture illustrates the process inside 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] 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 will not isolate the medium properly, the second one will act as a safety means against accidental leaks. Sometimes, customer specifications don’t allow the medium to stay touch with the instrument when it’s not measuring. Because of this the medium will be discharged using the vent line. In diaphragm seal ? as a result of vent line ? instruments can be easily calibrated without dismounting them from the line.
Note
More info on our valves can be found on the WIKA website or in the video What is a monoflange? In case you have any questions, your contact will gladly help you.

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