Monoflanges combine the event of up to three valves in a particularly 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 necessary for most 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 procedure will fluctuate strongly sometimes or if the control is critical, mounting the instrument close to the process may be the solution.
Vibrations may also be critical, for example, in case that impulse lines are connected 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, 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 inside the instrument. That is mostly used in applications that are relatively uncritical (e.g. low pressure) or where a first shut-off valve is provided just before the monoflange.
Impatient , and the main 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 one 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 inside a DBB monoflange:
The flow enters the monoflange from the pipeline and stops below the initial shut-off valve [1];
When 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 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. The two shut-off valves [1, 2] are in an angled position, that allows the flow to pass through them.
Both shut-off valves allow an improved isolation from the procedure: In case the first shut-off valve does not isolate the medium properly, the second one will become a safety means against accidental leaks. Sometimes, Unadulterated do not allow the medium to be in touch with the instrument when it is not measuring. Because of this the medium will be discharged utilizing 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 Exactly what is a monoflange? In case you have any questions, your contact will gladly assist you to.