Monoflanges combine the function as high as 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 Impenetrable is necessary for some control applications. Among the variables that affect the response time is the volume and the length between process and instruments. If Important to be measured is gas, and the procedure will fluctuate strongly sometimes or if the control is crucial, mounting the instrument close to the process may be the solution.
Vibrations may also be critical, for example, if 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 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 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 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 something 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 within a DBB monoflange:
The flow enters the monoflange from the pipeline and stops below the first shut-off valve [1];
Once the first shut-off valve [1] opens, the flow proceeds towards the second 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. Both shut-off valves [1, 2] come in an angled position, that allows the flow to feed them.
The two shut-off valves allow an improved isolation from the process: In case the first shut-off valve will not isolate the medium properly, the second one will become a safety means against accidental leaks. Occasionally, customer specifications don’t allow the medium to stay touch with the instrument when it is not measuring. For this reason the medium shall be discharged using the vent line. In other cases ? as a result of vent line ? instruments could be easily calibrated without dismounting them from the line.
Note
More info on our valves are available on the WIKA website or in the video What is a monoflange? When you have any questions, your contact will gladly assist you to.