Monoflanges combine the event of up to three valves in an especially compact body, because of 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 necessary for most control applications. One of 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 procedure 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, in case that 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 another (with a red cap) regulates the venting of the medium trapped in the instrument. This is mostly used in applications that 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, 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 following picture illustrates the procedure inside a DBB monoflange:
The flow enters the monoflange from the pipeline and stops below the initial 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 connected to the process line;
When the first shut-off valve [1] is closed, the medium trapped between valve and instrument can 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.
Gleeful shut-off valves allow a better isolation from the procedure: In case the first shut-off valve will not isolate the medium properly, the second one will act as a safety means against accidental leaks. Occasionally, customer specifications do not allow the medium to be in touch with the instrument when it is not measuring. That is why the medium will be discharged utilizing the vent line. In other cases ? because of 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 Exactly what is a monoflange? When you have any questions, your contact will gladly assist you to.