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33 keys to butterfly valve selection

Plastic body and disc butterfly valves can be used for a variety of purposes. 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 applying, proper operation and upkeep play a crucial role within the lifetime of a valve once put into service.
When it involves butterfly valve choice, consider these three elements: material, body type and the way the valve is operated.
Materials
No single thermoplastic material is the solution for all purposes. เกจวัดแรงดันน้ำไทวัสดุ of the most common supplies for plastic butterfly valves are polyvinyl chloride (PVC) and chlorinated polyvinyl chloride (CPVC), which are widely used throughout many industries. In looking on the differences between PVC and CPVC, we see that both have a maximum excessive working strain of 150 psi, however CPVC has the next working temperature than PVC. In an utility like a swimming pool, both material would work for chemical resistance and temperature, however for hot water service above 140ºF, PVC is no longer an option. CPVC, however, has the next temperature limit of roughly 195ºF.
Valve liner materials selection may also be influenced by temperature. Ethylene propylene diene terpolymer (EPDM) and fluorinated elastomer (FKM) are two frequent liner supplies. Both have higher temperature limits equal to or greater than PVC and CPVC, but butterfly valves with FKM liners can turn out to be inoperable beneath 23ºF due to the hardening of the rubber compound. This causes the massive resilient seat of the valve to turn into hard, which makes it troublesome to seat the valve to a closed place, or unseat it to open.
Body styles
Butterfly valve body styles largely depend upon the valve’s location within a piping system. Valves in the midst of a process line, sandwiched between two mating flanges with bolts that cross through the valve and are not threaded into the valve physique, are often known as wafer type valves.
For end-of-line purposes, lug style butterfly valves enable one mating flange to be eliminated. Threaded metal lug inserts are either overmolded into the valve physique, or the valve physique is molded or machined to merely accept a lug with an inside thread for mating flange bolts from either facet of the valve.
Once downstream piping is removed, an end-of-line valve must be secured utilizing a blind flange.
Operators
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 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 incorrect way ninety degrees will shut it once more. Typical rotation is counterclockwise to open, and clockwise to close. The only 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 simpler it’s to function the handle, however too lengthy a handle becomes impractical.
A gear operator is a mechanical operator the place a hand wheel is connected 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 a number of 360-degree rotations of the hand wheel to achieve the ninety degrees required for open or close.
Operation, upkeep & failure prevention
Like all valves, butterfly valves need to be operated periodically to ensure reliability. A butterfly that stays within the closed place for an prolonged time frame might get caught closed and turn into inoperable. Sediment can construct up towards the disc, which could be difficult to push out of the way in which because the disc swings open. The rubber liner can take a set across the disc, making it tough to tug the disc out of the liner to open the valve. In the occasion of a chemical assault, the liner can swell across the disc effectively limiting its movement.
Since butterfly valves are used in many applications, there are totally different necessities for upkeep based mostly on the kind of media in the system, and alternative ways the valve may be affected by the fluids passing via it.
Clean fluid techniques with low chemical concentrations should require little upkeep; Periodic cycling of the valve should ensure its reliable operation.
Harsh chemical substances may attack rubber liner seals, resulting in cracking or swelling of the liner. In such cases, it is strongly recommended to keep affected elements in stock for rebuilding or replacement. Swelling of the liner can also lead to excessive stem torque to function the valve, which might result in a more catastrophic sort of failure the place the valve disc could crack or break up.
Suspended particles in fluid can be abrasive and cause trouble in an put in valve. In functions where particulate travels beneath stress via a valve opening, wear on the valve disc and liner become obvious. Affected areas embrace the skin diameter of the disc, as nicely as the rubber liner. The wear on these surfaces will have a unfavorable impact on sealing efficiency as the sealing parts (disc and liner) turn into out of tolerance with their design dimensions, which may result in leakage previous a closed position valve as a outcome of abraded supplies. Additionally, the general thickness of the disc could be reduced, compromising the critical cross-section dimension, which might result in a cracked disc failure.
Debris in the form of large particles or overseas objects can turn into lodged in the valve opening, inflicting a broken disc or liner. Damage to the sealing floor of the disc will end in a leak path. While the circulate might be reduced, optimistic shutoff cannot be achieved. This type of failure would require disassembly and alternative of the damaged parts.
Scaling or buildup of international material on the inner valve parts can occur in some processes. Landfills use chemical compounds to treat the leachate or groundwater that has leached via a waste pit. The remaining compound can construct up and coat a butterfly valve’s internal disc or liner. Operating the valve creates a wiping motion of the valve disc towards the liner as it opens and closes, which may be enough to disturb the foreign layer and reestablish regular disc-to-liner sealing efficiency.
Even the best butterfly valves will not final forever, but cautious consideration and number of valve materials and elegance, coupled with proper maintenance and an awareness of potential problems, can greatly increase the life of a valve in even the harshest applications.
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