33 keys to butterfly valve selection

Plastic body and disc butterfly valves can be used for a big selection of applications. From primary on/off valves for swimming pools to throttle management valves for chemical processing, the butterfly valve is the workhorse valve of many industries. Regardless of the severity of the application, correct operation and maintenance play a important position within the lifetime of a valve once put into service.
When it comes to butterfly valve choice, contemplate these three components: materials, body fashion and how the valve is operated.

No single thermoplastic materials is the solution for all purposes. Two of the commonest materials for plastic butterfly valves are polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC), that are extensively used throughout many industries. In trying on the variations between PVC and CPVC, we see that each have a maximum excessive working strain of 150 psi, but CPVC has a better working temperature than PVC. In an software like a swimming pool, either material would work for chemical resistance and temperature, but for hot water service above 140ºF, PVC is no longer an possibility. CPVC, however, has the next temperature limit of roughly 195ºF.
Valve liner material selection can be influenced by temperature. Ethylene propylene diene terpolymer (EPDM) and fluorinated elastomer (FKM) are two common liner supplies. Both have upper temperature limits equal to or higher than PVC and CPVC, however butterfly valves with FKM liners can become inoperable under 23ºF due to the hardening of the rubber compound. เกจวัดแรงดัน causes the massive resilient seat of the valve to turn out to be onerous, which makes it troublesome to seat the valve to a closed place, or unseat it to open.
Body styles

Butterfly valve body kinds largely rely upon 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 by way of the valve and aren’t threaded into the valve physique, are often recognized as wafer fashion valves.
For end-of-line purposes, lug fashion butterfly valves allow one mating flange to be eliminated. Threaded metallic lug inserts are both overmolded into the valve physique, or the valve physique is molded or machined to just accept a lug with an internal thread for mating flange bolts from both side of the valve.
Once downstream piping is removed, an end-of-line valve ought to be secured using a blind flange.

Manually operated butterfly valves require either a lever or a gear operator to open and shut the valve. A lever handle can be utilized for smaller valves (up to four inches in diameter). An operator manually rotates the lever ninety degrees to tug the valve disc out of the valve seat to open the valve. Rotating the valve in the different way 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 acting on the fulcrum point turning the valve stem. The longer the handle, the easier it is to operate the handle, but too lengthy a handle turns into 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 connected to the valve stem. This provides a mechanical benefit as a end result of ratio of the gearing. Gear operators require multiple 360-degree rotations of the hand wheel to attain the ninety degrees required for open or close.
Operation, upkeep & failure prevention

Like all valves, butterfly valves have to be operated periodically to make sure reliability. A butterfly that stays in the closed position for an prolonged time frame might get stuck closed and turn into inoperable. Sediment can construct up in opposition to the disc, which could possibly be troublesome to push out of the method in which because the disc swings open. The rubber liner can take a set across the disc, making it tough to drag the disc out of the liner to open the valve. In the event of a chemical assault, the liner can swell around the disc successfully limiting its movement.
Since butterfly valves are used in many functions, there are different requirements for maintenance primarily based on the type of media in the system, and other ways the valve may be affected by the fluids passing via it.
Clean fluid systems with low chemical concentrations ought to require little upkeep; Periodic cycling of the valve ought to guarantee its reliable operation.
Harsh chemical compounds could attack rubber liner seals, leading to cracking or swelling of the liner. In such situations, it is recommended to maintain affected components in stock for rebuilding or substitute. Swelling of the liner may lead to excessive stem torque to function the valve, which might lead to a more catastrophic sort of failure where the valve disc might crack or split.
Suspended particles in fluid can be abrasive and cause hassle in an installed valve. In purposes the place particulate travels under stress via a valve opening, wear on the valve disc and liner become apparent. Affected areas embrace the skin diameter of the disc, in addition to the rubber liner. The wear on these surfaces could have a unfavorable impact on sealing efficiency as the sealing components (disc and liner) turn out to be out of tolerance with their design dimensions, which can end in leakage previous a closed position valve due to the abraded supplies. Additionally, the general thickness of the disc could be lowered, compromising the crucial cross-section dimension, which might result in a cracked disc failure.
Debris in the type of giant particles or foreign objects can become lodged in the valve opening, inflicting a damaged disc or liner. Damage to the sealing surface of the disc will result in a leak path. While the flow will be reduced, positive shutoff cannot be achieved. This type of failure would require disassembly and substitute of the damaged components.
Scaling or buildup of overseas materials on the inner valve parts can occur in some processes. Landfills use chemical substances to deal with the leachate or groundwater that has leached via a waste pit. The remaining compound can construct up and coat a butterfly valve’s inside disc or liner. Operating the valve creates a wiping motion of the valve disc towards the liner because it opens and closes, which may be sufficient to disturb the overseas layer and reestablish normal disc-to-liner sealing performance.
Even the most effective butterfly valves will not final eternally, but cautious consideration and choice of valve materials and style, coupled with correct maintenance and an awareness of potential complications, can significantly improve the lifetime of a valve in even the harshest purposes.

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