Monoflanges combine the event of up to three valves in an especially compact body, thanks to an accurate network of internal passages and valve chambers. But what really happens in the monoflange valve, once installed?
In a chemical process a high response speed is required for some control applications. Among Superb 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 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, in case that 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 in the compact, flange-shaped body, allowing a significant decrease in volume, dimensions, weight and potential leakage points.
Monoflange is the solution
According to the requirements of the plant it really is installed in, the monoflange can incorporate one, two or three 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 in the instrument. This is mostly used 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, 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 process 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 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. Mischievous shut-off valves [1, 2] come in an angled position, that allows the flow to feed them.
Both shut-off valves allow an improved isolation from the process: In case the first shut-off valve will not isolate the medium properly, the next one will become a safety means against accidental leaks. In some cases, customer specifications don’t allow the medium to stay touch with the instrument when it’s not measuring. Because of this the medium shall be discharged using the vent line. In other cases ? because of the 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? In case you have any questions, your contact will gladly assist you to.