3three keys to butterfly valve choice

Plastic physique and disc butterfly valves can be used for quite so much of functions. From primary on/off valves for swimming 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 applying, correct operation and upkeep play a crucial role within the life of a valve once put into service.
When it comes to butterfly valve choice, consider these three elements: materials, body type and the way the valve is operated.
Materials
No single thermoplastic materials is the answer for all applications. Two of the most typical materials for plastic butterfly valves are polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC), which are extensively used all through many industries. In looking at the variations between PVC and CPVC, we see that both have a most high working stress of 150 psi, however CPVC has the next working temperature than PVC. In an application like a swimming pool, both material would work for chemical resistance and temperature, however for warm water service above 140ºF, PVC is not an possibility. CPVC, however, has the next temperature limit of roughly 195ºF.
Valve liner materials choice may also be influenced by temperature. Ethylene propylene diene terpolymer (EPDM) and fluorinated elastomer (FKM) are two frequent liner materials. 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 under 23ºF because of the hardening of the rubber compound. This causes the big resilient seat of the valve to turn out to be hard, 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 on the valve’s location within a piping system. Valves in the course of a course of line, sandwiched between two mating flanges with bolts that cross via the valve and usually are not threaded into the valve physique, are generally known as wafer style valves.
For end-of-line functions, lug fashion butterfly valves allow one mating flange to be eliminated. Threaded metal lug inserts are either overmolded into the valve physique, or the valve body 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 utilizing a blind flange.
Operators
Manually operated butterfly valves require either a lever or a gear operator to open and close the valve. A lever handle can be utilized for smaller valves (up to four inches in diameter). An operator manually rotates the lever 90 degrees to drag the valve disc out of the valve seat to open the valve. Rotating the valve in the opposite direction 90 degrees will close it once more. Typical rotation is counterclockwise to open, and clockwise to close. The solely mechanical benefit right here is the length of the lever performing on the fulcrum point turning the valve stem. The longer the deal with, the easier it is to function the deal with, but too long a deal with turns into impractical.
A gear operator is a mechanical operator the place a hand wheel is hooked up to a shaft with a worm gear on one end that engages a central gear connected to the valve stem. This offers a mechanical benefit due to the ratio of the gearing. Gear operators require multiple 360-degree rotations of the hand wheel to realize the ninety levels 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 in the closed position for an prolonged period of time might get caught closed and turn out to be inoperable. Sediment can build up in opposition to the disc, which might be tough to push out of the greatest way as the disc swings open. The rubber liner can take a set around the disc, making it difficult to drag the disc out of the liner to open the valve. In the event of a chemical attack, the liner can swell across the disc effectively limiting its movement.
Since butterfly valves are utilized in many applications, there are completely different necessities for upkeep primarily based on the type of media within the system, and different ways the valve may be affected by the fluids passing through it.
Clean fluid techniques with low chemical concentrations ought to require little maintenance; Periodic biking of the valve should ensure its dependable operation.
Harsh chemical substances could assault 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 replacement. Swelling of the liner can also result in excessive stem torque to operate the valve, which might result in a extra catastrophic sort of failure where the valve disc may crack or split.
Suspended particles in fluid may be abrasive and cause hassle in an installed valve. In functions where particulate travels underneath strain through a valve opening, wear on the valve disc and liner turn into obvious. Affected areas include the outside diameter of the disc, as nicely as the rubber liner. The wear on these surfaces could have a adverse impact on sealing performance because the sealing elements (disc and liner) become out of tolerance with their design dimensions, which may end in leakage previous a closed position valve as a end result of abraded materials. Additionally, the general thickness of the disc could be reduced, compromising the important cross-section dimension, which might lead to a cracked disc failure.
Debris within the form of massive particles or overseas objects can become lodged in the valve opening, causing a damaged disc or liner. Damage to the sealing surface of the disc will end in a leak path. While the flow shall be decreased, constructive shutoff cannot be achieved. This sort of failure would require disassembly and replacement of the broken elements.
Scaling or buildup of overseas materials on the internal valve components can happen in some processes. Landfills use chemicals to treat the leachate or groundwater that has leached by way of a waste pit. The remaining compound can build up and coat a butterfly valve’s inside disc or liner. Operating เกจวัดแรงดันสูง creates a wiping action of the valve disc towards the liner because it opens and closes, which may be sufficient to disturb the foreign layer and reestablish normal disc-to-liner sealing performance.
Even the best butterfly valves is not going to last endlessly, however careful consideration and choice of valve supplies and style, coupled with correct upkeep and an consciousness of potential problems, can greatly improve the lifetime of a valve in even the harshest applications.
Share

Scroll to Top