3three keys to butterfly valve selection

Plastic physique and disc butterfly valves can be used for a variety of purposes. 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 appliance, proper operation and maintenance play a crucial role within the lifetime of a valve as soon as put into service.
When it involves butterfly valve choice, contemplate these three elements: material, physique fashion and how the valve is operated.
No single thermoplastic materials is the answer for all purposes. Two of the most common materials for plastic butterfly valves are polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC), that are broadly used all through many industries. In looking at the variations between PVC and CPVC, we see that both have a most high working pressure of one hundred fifty psi, however CPVC has a higher working temperature than PVC. In an utility like a swimming pool, either material would work for chemical resistance and temperature, but for warm water service above 140ºF, PVC is not an option. CPVC, nonetheless, has a better temperature limit of approximately 195ºF.
Valve liner materials choice can also be influenced by temperature. Ethylene propylene diene terpolymer (EPDM) and fluorinated elastomer (FKM) are two widespread liner materials. Both have upper temperature limits equal to or higher than PVC and CPVC, but butterfly valves with FKM liners can turn into inoperable below 23ºF because of the hardening of the rubber compound. This causes the massive resilient seat of the valve to turn into exhausting, which makes it tough to seat the valve to a closed position, or unseat it to open.
Body styles
Butterfly valve body kinds largely depend upon the valve’s location inside a piping system. Valves in the center of a process line, sandwiched between two mating flanges with bolts that pass by way of the valve and aren’t threaded into the valve body, are often known as wafer fashion valves.
For end-of-line purposes, lug fashion butterfly valves permit one mating flange to be removed. Threaded metallic lug inserts are either overmolded into the valve body, or the valve physique is molded or machined to accept a lug with an internal thread for mating flange bolts from both facet of the valve.
Once downstream piping is removed, an end-of-line valve must be secured utilizing a blind flange.
Manually operated butterfly valves require either a lever or a gear operator to open and shut the valve. A lever deal with can be used for smaller valves (up to 4 inches in diameter). An operator manually rotates the lever ninety levels to tug the valve disc out of the valve seat to open the valve. Rotating the valve in the other way ninety levels will close it again. Typical rotation is counterclockwise to open, and clockwise to close. The only mechanical advantage right here is the size of the lever acting on the fulcrum point turning the valve stem. The longer the handle, the better it’s to function the deal with, 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. This supplies a mechanical benefit because of the ratio of the gearing. Gear operators require multiple 360-degree rotations of the hand wheel to realize the ninety degrees required for open or shut.
Operation, maintenance & failure prevention
Like all valves, butterfly valves have to be operated periodically to ensure reliability. A butterfly that stays within the closed place for an prolonged period of time might get stuck closed and turn into inoperable. Sediment can construct up towards the disc, which could be troublesome to push out of the method in which as the disc swings open. เครื่องมือวัดpressure can take a set around the disc, making it difficult to tug the disc out of the liner to open the valve. In the occasion of a chemical attack, the liner can swell across the disc successfully limiting its motion.
Since butterfly valves are used in many purposes, there are different necessities for maintenance based on the kind of media within the system, and alternative ways the valve can be affected by the fluids passing through it.
Clean fluid techniques with low chemical concentrations should require little maintenance; Periodic biking of the valve ought to guarantee its dependable operation.
Harsh chemical compounds might attack rubber liner seals, resulting in cracking or swelling of the liner. In such situations, it is suggested to maintain affected elements in inventory for rebuilding or substitute. Swelling of the liner may also result in excessive stem torque to operate the valve, which might lead to a extra catastrophic type of failure the place the valve disc could crack or cut up.
Suspended particles in fluid may be abrasive and cause trouble in an put in valve. In functions the place particulate travels underneath strain through a valve opening, wear on the valve disc and liner turn into apparent. Affected areas embrace the skin diameter of the disc, as well as the rubber liner. The wear on these surfaces could have a negative impact on sealing efficiency because the sealing parts (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, เกจวัดแรงดัน of the disc could be lowered, compromising the important cross-section dimension, which might lead to a cracked disc failure.
Debris within the form of giant particles or international objects can turn out to be lodged within the valve opening, inflicting a damaged disc or liner. Damage to the sealing surface of the disc will lead to a leak path. While the move shall be lowered, constructive shutoff can’t be achieved. This type of failure will require disassembly and replacement of the broken parts.
Scaling or buildup of foreign materials on the internal valve components can occur in some processes. Landfills use chemical compounds to deal with the leachate or groundwater that has leached through 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 action of the valve disc towards the liner as it opens and closes, which may be enough to disturb the foreign layer and reestablish normal disc-to-liner sealing performance.
Even the most effective butterfly valves won’t last endlessly, but cautious consideration and selection of valve materials and elegance, coupled with proper maintenance and an awareness of potential problems, can significantly increase the life of a valve in even the harshest functions.

Scroll to Top