Monoflanges combine the event as high as three valves in an especially 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 required 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 process will fluctuate strongly at times or if the control is critical, mounting the instrument close to the process may be the solution.
pressure gauge น้ำมัน may also be critical, for example, if 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 inside a compact, flange-shaped body, allowing a substantial decrease in volume, dimensions, weight and potential leakage points.
Monoflange may be the solution
Depending on the requirements of the plant it 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 procedure and another (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 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 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 next 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 can be discharged via the vent valve [3] through the vent outlet. Both shut-off valves [1, 2] are in an angled position, which allows the flow to pass through them.
The two 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 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 ? due to the vent line ? instruments can 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 Exactly what is a monoflange? When you have any questions, your contact will gladly help you.