Three Easily Overlooked Details Of Butterfly Valve Routine Maintenance --painful Lessons

Butterfly valve structure is very simple, many people think, ``installed will do." This misunderstanding hurts many people. Butterfly valves are not devices to be left unattended when installed. They have three fatal details that 90% of maintenance staff ignore and only regret when things go wrong. Today, we reveal the three pitfalls, each of which is a painful lesson.
DETAILS 1: The limits of the Electric Actuator are never calibrated
He's the number one hidden killer.
Butterfly butterfly valve The electric actuator has two limits-the opening limit and the closing limit. These are all set up in factories, but over time they drift. Vibration, thermal expansion and contraction, as well as cumulative errors from repeated opening and closing, all lead to a slow drift of the limit. Closing the limit deviation by 5 degrees will prevent the valve from closing completely, leaving a gap the sealing surface and allowing the medium to seep in. The deviation of the opening limit will prevent the valve from being fully opened, resulting in insufficient flow rate and drift of process parameters.
The scariest part is how slow it was. The first three months may be normal, but after six months, a slight internal leak starts, and after a year, it becomes a noticeable leak. By the time you discover it, the sealing surface is corroded into a groove. Changing the sealing ring won't solve the problem. The entire valve must be replaced.
Steam butterfly valve at a pharmaceutical plant drifted eight degrees above their closing limit, and internal leaks went unnoticed for 11 months. During a routine inspection, the sealing surface of the seat was corroded by hot steam into a deep trench, rendering it unusable and causing a two-day production stoppage. A subsequent review revealed that the reason was that no one had ever calibrated the limit position.
Correct: Calibrate the opening and closing limit position of the electric actuator quarterly. First, use the handwheel to fully open and close the valve, then align the actuator's limit markings. The action takes only five minutes, but almost no one did.
DETAILS 2: Stem packing-Only replace the stem if the leak is too late.
Stem packing is a sealed packing ring between the stem and body to prevent media from leaking from valve stem. The component is consumable, but its fault mode is not "sudden leakage" but "slow seepage."
At first, there may be a slight dampness at the bottom of the stuffing box. A lot of people ignore that and think, "Just don't drip." However, once the packaging shows dampness, this means the medium has squirmed along the valve stem. Just not to the point of dripping. By the time the drip becomes visible, the valve stem surface has been etched into a groove by the medium, and the filling is compacted and inelastic. At this point, the replacement packing will not seal properly; the entire valve stem must be replaced.
Even more dangerous, some corrosive media can seep slowly into the actuator through valve stem packing, corroding limiter switches and positioning modules. When the electric actuator suddenly malfunctions, you might think it's broken, but the root cause is that the packaging is long overdue.
At a chemical plant, an acid-base butterfly valve suffered a packaging leak for three months. Acidic media infiltrates the the electric actuator and burns out the positioning module, rendering the entire actuator unusable. Repairs cost 20 times as much as replacement packaging.
Correct thing to do: Touch the bottom of the stuffing box during weekly inspections. If there is dampness, tighten or replace the packaging immediately. Don't wait for the leak, it will be too late. When tightening the packing cover, make sure that the cover is evenly symmetrical, and avoid tightening and loosening at the same time, otherwise the stem will wear out unevenly.
DETAILS 3: Poor protection after a long shutdown leads to disaster when work resumes.
This is the easiest thing to ignore, but also the most costly.
butterfly valve are more than five times more likely to have problems restarting after a long period of inactivity. The reason is simple: during closing, there is no medium lubrication between the valve plate and seat, and the sealing surfaces is pressed directly together. Over time, rubber seal will stick to the valve seat, valve stem bearings will rust from lack of lubrication, and water and dirt will build up in the valve cavity.
What are the consequences of forcing the valve open? The disc is stuck in place on the sealing surface and cannot be opened, forcing it open can cause the valve stem to twist and the sealing surface to tear. A DN400 butterfly valve at a heating station was left unprotected during the winter heating shutdown and forced open when heating was restored the following year. The stem snapped, causing hot water to spew out and scalding two maintenance workers. Three days of shutdown for emergency repairs.
Correct steps: Open the valve to a fully open position to separate the sealing surface before closing for a long time; apply rust grease to the valve stem; drain any water from the chamber; manually rotate the valve once a month to prevent jamming. The actions take less than 10 minutes, but can save the line.
In short: Uncalibrated limit switches can cause slow leaks; uninspected packaging can cause large leaks; and neglecting protection during closure can cause irreparable damage when reopened. None of these three details require advanced skills, but each one requires you to "remember to do it." The biggest cost of maintaining butterfly valves is not parts, but complacency.