What may be the safest solution to separate an activity and the attached pressure measurement technology? The HSG 253 standard must be put on this question, and it answers unequivocally: by means of an instrumentation valve with double block & bleed (DBB). This configuration for risk minimisation applies especially, but not only, to processes with critical media.
An instrumentation valve with double block & bleed is typically a monoblock. It features two shut-off valves (block) and one vent valve (bleed). If the shut-off valve on the procedure side no longer closes in the event of a fault, the next shut-off valve prevents uncontrolled media leakage or contamination of the procedure from outside.
For applications with liquid or viscous media, shut-off valves with a ball valve design are employed. For optimised damage prevention, ball valves from WIKA have a combination of plastic and metal sealing: If the PEEK or PTFE seal fail, the pressure pushes the ball seamlessly towards the metal ring. The redundant system is leak-tested relative to BS6755 / ISO 5208 leakage rate A.
Measuring assembly with ball valve in DBB design: Ball valves from WIKA feature a redundant plastic-metal sealing system. In Ingredients of failure of the ?soft? seal (marked in yellow), the pressure pushes the ball seamlessly towards its metal seat.
Each double block & bleed configuration offers a triple protection:
For personnel
Fitters and technicians can work at a measuring location with critical media without concern with coming into connection with them. Maintenance or replacement of the measuring instrument is thus possible without danger with a double-blocked valve.
For the environment
Instrumentation valves with double block & bleed prevent the process medium from escaping in to the environment. WIKA ball valves and needle valves even prevent fugitive emissions in the appropriate design. These variants are manufactured in accordance with the ISO 15848-1 and VDI 2440 (TA Luft) standards.
For the instruments
Double block & bleed supplies the connected measuring instrument optimum protection against potential damage from the process, for example throughout a cleaning process with aggressive substances. Simultaneously, this configuration ensures long-lasting and reliable valve operation.
Compact solution instead of self-build
Shut-off solutions as described here could, in principle, be made of individual components. However, they might have a correspondingly large dimension, which would affect the stability of the measuring assembly. Due to numerous parts and connections, there would also be considered a higher risk of leakage.
Valve solutions in a concise body get rid of the disadvantages mentioned previously. For risk-free applications, however, it is advisable to use standard valves (e.g. WIKA models IV10, IV20 and BV). Regarding critical media, monoblocks with double block & bleed configuration are clearly the initial choice.
WIKA offers a comprehensive DBB portfolio for an array of applications (from left to right): model IBM, model IBF (with flange connection), model IBS (for sampling) and model IBJ (for injection processes) in addition to the monoflange model IVM. The high-quality workmanship of most valve parts enables smooth and precise operation, even at high pressures and after prolonged lack of use.
Note
To find out more on monoblock instrumentation valves with double block & bleed, please go to the WIKA website. Should you have any questions, your contact will gladly help you.
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