PUMPS
PUMPS, VAL
ALVES & AC
ACTUATORS
FEA
FEATURE
To accomplish this, a bypass loop uses a three-way valve as the firs t valve in the configuration, allow ing the diversion of flow a round the sect ion requiringmaintenance. The systemfilter, or other component, c an now be repair ed or replac ed without the entire system
experiencing downtime. The bypass loop c an al so he lp av oid hydraulic shock – al so kno wn as “water hammer” – that c an result from sudden systemflow shutoff.
KNOW YOUR TYPES OF BLOCK VALV LVES
Ball valves and needle valves are the twomost com mon choices for use as block valves in instrumentat ion lines. In practice, the choice i s oft en determin ed by existing systemspecifications. In addit ion to block valve selection, it is good practice to install a pressure indicator downstreamfromthe second block valve in the isolati on configuration. This will enable a visual check on pressure at the time of maintenance. Engineers desig ning the systemc an consider either opt ion depending on their needs. Each has its pros a nd cons:
Ball Valves. Ideal for quick shutoffs in high flow applications, ball valves are al so helpful in indicating directional flow or shutoff via their handle orientation. However, due to their quick shutoff, ball valves can create hydraulic shock (water hammer) in liq uid applications. Depe ndi ng on the severity, this c an result in damage to pressure indicators, flowmeters, and other components upstreamof t shutoff. Including a bypass loop in the des ign is one way to e eliminate hydraulic shock. Otherwise, ball valves sh ould not be consider ed in liqu id applications in which hydraulic shock is a significant concern.
ffectively he
Needle Valves. Needle valves provide gradual shutoff and therefore will eliminate potential for hydraulic shock. They are primarily desig ned for flow or metering control, but they are generally effective at positive shutoff. Wh en consider ing a needle valve for use as a block valve, it sh ould be designed for that specific purpose, us ing a rotating or soft stemtip. In relat ion to ball valves, needle valves c an be somewhat temperamental wh en it comes to leak prevention, and this must be consider ed during the desi gn stage. For example, the metal V- t ip can potentially gr ind i nto themetal seat during shutoff, lea ding to scoring and small leaks.
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The complete valve package from Bürkert
Figure 3: An integral DBB valve helps reduce the potential for leaks, and is more compact and lightweight than other configurations
All images©Swagelok
Integral DBB Valve. A third opt ion is available in the form of an integral DBB configurat ion (Figu re 3), provi ding additional reliability to the application. This configurat ion c an remove some of the complexity fromthe applicat ion by eliminating the ne ed for multiple individual block valves. An integral DBB c an also reduce the number of potentia l leak points, contribut ing to a safer system. ,
Overall block valve select ion for fl uid systemline insulat ion is just as important as any component choice wit hin a fl uid system. Block valves he lp contribute to safer maintenance activities, as well as inc systemuptime and plant profitability, and sh ould be a priorit plant technicians and engineers.
y for all reased
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Joe.Bush@swagelok.c Swage lok
om
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