33 keys to butterfly valve selection

Plastic body and disc butterfly valves can be used for quite so much of functions. From fundamental on/off valves for swimming pools to throttle control valves for chemical processing, the butterfly valve is the workhorse valve of many industries. Regardless of the severity of the appliance, proper operation and maintenance play a critical position in the lifetime of a valve as soon as put into service.
When it involves butterfly valve choice, consider these three elements: material, physique type and how the valve is operated.
Materials
No single thermoplastic materials is the answer for all functions. Two of the most typical materials for plastic butterfly valves are polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC), that are widely used throughout many industries. In looking at the variations between PVC and CPVC, we see that both have a maximum excessive working pressure of one hundred fifty psi, but CPVC has the next working temperature than PVC. In an utility like a swimming pool, both material would work for chemical resistance and temperature, but for hot water service above 140ºF, PVC is now not an possibility. CPVC, nonetheless, has a higher temperature restrict of approximately 195ºF.
Valve liner materials choice can be influenced by temperature. Ethylene propylene diene terpolymer (EPDM) and fluorinated elastomer (FKM) are two widespread liner supplies. Both have upper temperature limits equal to or greater than PVC and CPVC, but butterfly valves with FKM liners can turn out to be inoperable below 23ºF as a end result of hardening of the rubber compound. This causes the large resilient seat of the valve to become exhausting, which makes it troublesome to seat the valve to a closed position, or unseat it to open.
Body types
Butterfly valve physique styles largely depend on the valve’s location inside a piping system. Valves in the midst of a course of line, sandwiched between two mating flanges with bolts that move via the valve and aren’t threaded into the valve body, are generally identified as wafer type valves.
For end-of-line purposes, lug style butterfly valves permit one mating flange to be eliminated. Threaded steel lug inserts are both overmolded into the valve physique, or the valve body is molded or machined to simply accept a lug with an internal thread for mating flange bolts from both aspect of the valve.
Once downstream piping is eliminated, an end-of-line valve must be secured using a blind flange.
Operators
Manually operated butterfly valves require both a lever or a gear operator to open and close the valve. A lever handle can be used for smaller valves (up to 4 inches in diameter). An operator manually rotates the lever 90 levels to pull the valve disc out of the valve seat to open the valve. Rotating the valve in the reverse direction ninety degrees will close it again. Typical rotation is counterclockwise to open, and clockwise to close. The solely mechanical benefit here is the length of the lever appearing on the fulcrum point turning the valve stem. The longer the deal with, the easier it’s to operate the handle, but too long a handle becomes impractical.
A gear operator is a mechanical operator where a hand wheel is attached to a shaft with a worm gear on one finish that engages a central gear hooked up to the valve stem. หลักการทำงานของเกจ์วัดแก๊ส provides a mechanical advantage because of the ratio of the gearing. Gear operators require multiple 360-degree rotations of the hand wheel to achieve the 90 levels required for open or shut.
Operation, upkeep & failure prevention
Like all valves, butterfly valves must be operated periodically to ensure reliability. A butterfly that stays within the closed position for an extended time frame may get caught closed and become inoperable. Sediment can construct up in opposition to the disc, which could probably be troublesome to push out of the finest way because the disc swings open. The rubber liner can take a set across the disc, making it troublesome to pull the disc out of the liner to open the valve. In the event of a chemical assault, the liner can swell across the disc effectively restricting its motion.
Since butterfly valves are used in many applications, there are completely different requirements for upkeep based on the kind of media within the system, and other ways the valve could be affected by the fluids passing via it.
Clean fluid techniques with low chemical concentrations ought to require little upkeep; Periodic cycling of the valve ought to ensure its reliable operation.
Harsh chemical substances could attack rubber liner seals, leading to cracking or swelling of the liner. In such instances, it is strongly recommended to maintain affected parts in inventory for rebuilding or substitute. Swelling of the liner may result in excessive stem torque to function the valve, which could lead to a more catastrophic kind of failure the place the valve disc could crack or break up.
Suspended particles in fluid can be abrasive and cause trouble in an installed valve. In purposes where particulate travels under stress through a valve opening, put on on the valve disc and liner become apparent. Affected areas embrace the surface diameter of the disc, as properly as the rubber liner. The put on on these surfaces could have a unfavorable influence on sealing efficiency because the sealing elements (disc and liner) turn into out of tolerance with their design dimensions, which can lead to leakage previous a closed position valve because of the abraded supplies. Additionally, the overall thickness of the disc could be decreased, compromising the crucial cross-section dimension, which could result in a cracked disc failure.
Debris within the form of massive particles or international objects can turn into lodged within the valve opening, causing a broken disc or liner. Damage to the sealing surface of the disc will end in a leak path. While the flow shall be reduced, positive shutoff cannot be achieved. This type of failure will require disassembly and replacement of the damaged elements.
Scaling or buildup of foreign material on the internal valve elements can occur in some processes. Landfills use chemicals to deal with the leachate or groundwater that has leached via a waste pit. The remaining compound can build up and coat a butterfly valve’s inner disc or liner. Operating the valve creates a wiping motion of the valve disc in opposition to the liner as it opens and closes, which may be sufficient to disturb the international layer and reestablish regular disc-to-liner sealing performance.
Even the best butterfly valves is not going to final eternally, but cautious consideration and selection of valve supplies and elegance, coupled with correct maintenance and an awareness of potential issues, can greatly enhance the lifetime of a valve in even the harshest applications.
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