THAILANDGAUGE LOGO.png

Monoflanges combine the event of up to three valves in a particularly compact body, because of a precise network of internal passages and valve chambers. But what really happens in the monoflange valve, once installed?
In a chemical process a higher response speed is required for some control applications. One of many variables that affect the response time is the volume and the length between process and instruments. If เพรสเชอร์เกจ to be measured is gas, and the process tends to fluctuate strongly sometimes or if the control is critical, mounting the instrument close to the process is the solution.
Vibrations are also 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 significant decrease 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 process and the other (with a red cap) regulates the venting of the medium trapped inside the instrument. pressure gauge octa is mostly used in applications that are relatively uncritical (e.g. low pressure) or in which a first shut-off valve is provided just 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.
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];
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 can be discharged via the vent valve [3] through the vent outlet. The two shut-off valves [1, 2] come in an angled position, which allows the flow to pass through them.
Both shut-off valves allow an improved isolation from the process: In case the initial shut-off valve does not isolate the medium properly, the next 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’s not measuring. That is why the medium will be discharged using the vent line. In other cases ? due to the vent line ? instruments could be easily calibrated without dismounting them from the line.
Note
Further information on our valves are available on the WIKA website or in the video What is a monoflange? Assuming you have any questions, your contact will gladly assist you to.