Gate valve stem leak: adjusting and replacing the gland packing

Why the gland leaks

Packing consolidates and loses volume and resilience over time, especially after thermal cycles. Scratched or corroded stems, a cocked gland follower and packing unsuitable for the medium or temperature also cause leaks.

Adjusting the gland

Tighten the gland nuts alternately in small steps, about one sixth of a turn at a time, keeping the follower square. Then stroke the valve: operation should stay smooth. A stiff handwheel means the gland is overtightened, which accelerates stem wear. If the leak continues and the follower is already deep in the box, replace the packing.

Replacing packing

Isolate and depressurise the line and let hot systems cool. Remove the follower and extract the old rings with a packing hook without scoring the stem or box. Inspect the stem; deep scoring or pitting needs repair or replacement. Fit rings of the right size and material, for example flexible graphite for steam and hot water, one at a time with joints staggered 90–120 degrees, seating each ring before the next, then tighten the follower evenly.

Repacking under pressure

Many rising-stem steel gate valves have a backseat: when fully open, the stem seats against the bonnet and isolates the packing chamber, which allows gland adjustment in service. Full repacking under pressure is hazardous and should only be done where the manufacturer explicitly permits it and under the site’s safety rules.

Extending service life

Do not leave the valve partly open, exercise rarely used valves periodically and lubricate the stem thread and stem nut. TAZ supplies packing kits for its gate valves; quote the model and DN.

Checklist

• depressurise and cool
• even gland adjustment
• stroke check after adjustment
• stem inspection
• ring size and material
• staggered joints
• seat each ring
• backseat use
• thread lubrication

Primary references

• ISO 5208:2015, Industrial valves pressure testing
• API standards plan and published standards