Why a routine matters
Valves are often installed and forgotten. They may sit open for years, then be asked to close under pressure. A short, repeatable routine finds leaking packing, seized stems and loose actuators before they cause a shutdown or a spill. The goal is not to disassemble valves regularly, which is usually unnecessary, but to look, listen and record, and to act on what the records show. This fits within wider preventive maintenance planning for the plant.
Always follow the manufacturer’s manual for the specific valve, since intervals and procedures vary with design, fluid and conditions. The tips below are general.
Build the inspection routine
1. Make a list
Start with a valve register: tag number, location, type, size, service, and whether the valve is critical. Rank the valves so inspection effort goes first to those whose failure matters most. A valve that isolates a hazardous chemical deserves more attention than one on a rarely used drain.
2. Walk the line with a purpose
On each round, check the following:
- External leaks. Look for drips, stains, crystals, rust streaks or wet insulation near the stem, bonnet, body joints and end connections.
- Stem and handwheel. Look for rust, damaged threads, a bent stem, or a handwheel that is loose or hard to turn.
- Position. Confirm the valve is where it should be, and that position indicators agree with reality.
- Supports and vibration. Heavy valves and actuators stress the pipe if unsupported. Excessive vibration can loosen fittings and fatigue connections.
- Insulation, labels and access. Damaged insulation, missing tags or blocked access make later work harder.
- Noise. Hissing, whistling, rattling or knocking can indicate leakage, cavitation, or loose internals.
3. Record what you find
A note such as “slight weep at stem, packing gland adjusted” with a date is more useful than memory. Over months, the log shows which valves are drifting toward failure. A computerized maintenance system or even a simple spreadsheet can hold these notes, and this discipline is part of writing good maintenance work orders.
Packing and stem leaks
The stem packing seals the moving stem. As it ages or the stem moves, small leaks appear. A common first response is to tighten the gland nuts slightly and evenly, but over-tightening causes friction, wears the stem and makes the valve harder to operate. Once the packing has no room for further adjustment, it needs replacing with the right material for the fluid and temperature. Valves carrying hazardous or toxic fluids may have strict leak limits, and in those cases only trained staff should adjust anything. Like shaft seals on rotating machines, packing is a wear item, and a small controlled leak is not always a defect while a growing one is a warning.
Lubrication
Gate and globe valves have threaded stems that benefit from the lubricant the manufacturer specifies. Gear operators and some actuator mechanisms have their own lubrication points and intervals. Use the recommended lubricant: the wrong product can wash out, harden, or react with the process fluid or seals. Do not over-lubricate, because excess grease can attract dirt and clog small passages. The principle is the same as in bearing lubrication, where the right amount of the right product matters more than frequency alone.
Exercise valves that rarely move
A valve that stays in one position for a long time can seize with scale, corrosion or hardened deposits. Where the process allows it, operate such valves through part or all of their travel on a schedule and note how they feel. A rise in effort required is a warning sign. Never exercise a valve if doing so could upset the process or create a hazard, and coordinate with operations first. Valves in safety service often have formal test procedures and intervals that should be followed.
Actuator and accessory checks
For automated valves, add these steps:
- Air supply. Pneumatic actuators need clean, dry air at the right pressure. Water or oil in the air line damages positioners, solenoids and diaphragms. Draining filters and checking air lines is often one of the most effective simple tasks.
- Fittings and tubing. Look for loose, cracked or kinked tubes and leaking connections.
- Diaphragm and seals. On spring-and-diaphragm actuators, a hissing at the casing can indicate a ruptured diaphragm.
- Electric actuators. Check cable glands, enclosures, limit switches and any indicator lights, and keep enclosures sealed against moisture.
- Stroke test. Command the valve and watch the full travel. It should move smoothly, without hesitation, and reach both ends. Compare actual position with the position the controller reports.
- Mounting and linkages. Bolts and couplings between actuator and valve can loosen and cause lost motion.
Solenoid valves that pilot an actuator are small but critical, and their coils and vents deserve a look. Position feedback devices such as limit switches should also be confirmed to match the real valve position.
Seat and shutoff checks
If a valve is supposed to isolate but you suspect it passes, the method of confirming depends on the process: pressure holding, a downstream gauge, or leak detection. Do not rely on a single indicator. In critical isolation, a second barrier such as a blind or double block and bleed arrangement is used according to the plant’s own procedures.
Safe working
Before any work beyond observation, follow the plant’s isolation and lockout tagout procedures, verify zero energy, and treat lines as potentially holding pressure or hazardous contents until proven otherwise. Wear the protective equipment the site requires. Tasks like repacking under pressure should be done only by people trained for them and permitted by the plant’s procedures. This is general information, not engineering advice, and the manufacturer’s manual and local regulations take precedence.
Know when to escalate
If a valve shows repeated leaks, worsening stiffness or erratic motion, stop treating each symptom and decide how to deal with the underlying cause. Whether to repair, rebuild or replace is a separate question with its own considerations.