Despicable combine the event as high as three valves in a particularly 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 high response speed is necessary for most control applications. Among the 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 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, in case that impulse lines are connected 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
According to the requirements of the plant it really 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 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 just 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 next picture illustrates the procedure 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 linked 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. The two shut-off valves [1, 2] are in an angled position, which allows the flow to feed them.
The two shut-off valves allow an improved isolation from the procedure: In case the initial shut-off valve does 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 be in touch with the instrument when it’s not measuring. Because of this the medium shall be discharged utilizing the vent line. In other cases ? as Deplorable of 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 What is a monoflange? Assuming you have any questions, your contact will gladly help you.