In highly-corrosive chemical and refining applications where in-line and atmospheric sealing is critical, sleeved plug valves provide essential defense against leaks and fugitive emissions. Because they typically face harsh conditions, repair or replacement is an important consideration. However, before those steps have to be taken, there’s a simple step to make them last longer: tightening the bolts.
Sleeved plug valves are non-lubricated quarter-turn valves characterized by a compressible sleeve that provides a large, circumferential sealing surface from port to port. Whether a valve is open, closed or in rotation, the inert PTFE sleeve ensures a superior level of sealing.
While sleeved plug valves in many applications can operate for decades virtually maintenance free, these valves are constantly exposed to demanding processes with temperatures ranging from -20°F (-29°C) to 600°F (316°C). Over time, this harsh environment exerts great stress and may eventually cause a valve to leak.
Body and plug materials, which are manufactured using a variety of materials (from ductile iron and stainless steel to the most exotic alloys) are highly susceptible to erosion and corrosion, two primary causes of sleeved plug valve wear. Add to that the impact of high cycling, and the performance of any valve can quickly deteriorate. That’s why maintenance, repair or replacement is so important.
When a valve begins to show the effects of excessive wear through seepage at the plug stem or downstream, end users may be tempted to replace valve components or even the entire valve. However, in many cases, a few simple adjustments can eliminate the leak, resulting in many additional years of service.
If a brief inspection shows no significant damage or defects, the valve likely can be restored to leak-free functionality easily by merely tightening the bolts while the valve remains inline.
To complete this repair, tighten each adjustment bolt or screw by a quarter turn (depending on the model). After the bolts are tightened, operate and check the valve again for leakage. Repeat this process as necessary to stop seepage.
Consult a product’s specific maintenance and repair manual before any type of valve maintenance is performed. Take care not to over-torque adjustment bolts. While different valve manufacturers require different adjustment techniques, consider this simple tightening/checking solution before opting to replace more costly valve parts.
Also, because excessive tightening of a valve’s adjustment bolts will cause valve stem torque to increase, torque adjustments may need to be made after taking steps to eliminate seat leakage. Since the initial breakaway torque normally reduces with usage and temperature, operate the valve under service conditions for at least 12 hours before adjustments are made.
When Adjustments Aren’t Enough
Although leaking sleeved plug valves often can be fixed with these minor adjustments, certain circumstances require the valve be repaired or replaced. For example, the need for frequent adjustment of the bolts or multiple adjustment turns indicate that seals are worn beyond repair and must be replaced.
A valve that continues to leak despite adjustments to the bolts must be removed from service, disassembled and thoroughly inspected. Before inspection occurs, however, the valve and pipeline must be depressurized and cleaned, and any remaining media must be neutralized.
During inspection, make sure the valve’s critical sealing elements receive careful attention, including the seal surface of the plug stem, the plug surface, the seal surface on the cover, the body seal surface that mates with the cover and the sleeve. Keep these surfaces free from defects typically caused by corrosion, erosion, improper handling and incorrect storage of a disassembled valve. Replace valves with any of this damage rather than repair them.
In general, weigh the benefits of field repair against the advantages of removing the valve from service and returning it to the manufacturer for repair or to purchase a new valve altogether. Also, valves repaired in an authorized facility are tested to the same specifications as new valves, and they may carry the same standard warranty as that new valve.
Chemical and other processors rely on the exceptional sealing performance and fugitive emissions protection delivered by sleeved plug valves. When properly installed, adjusted and operated, these valves require minimal attention from users and have a long and problem-free service life. Sometimes, a simple turn of the top adjustment bolts keeps the sleeve sealing tight and the valve in service even longer while avoiding the need for costly repair and replacement.