Why Gland Packing Leaks: Diagnosing the Common Causes

New packing that leaks almost never leaks because the packing was faulty. It leaks because something about the shaft, the fitting or the specification was wrong, and fitting another set without finding out which simply repeats the failure. Work through these in order.

First: is it leaking, or is it supposed to?

Compression packing is designed to drip. The leakage lubricates and cools the packing, and a gland tightened until it runs bone dry will burn out quickly. A slow, steady drip on a running pump is correct. Before diagnosing a fault, confirm you are not chasing normal behaviour.

1. The gland was over-tightened

The most common cause by far. Over-tightening crushes the rings, stops the lubricating film, and the packing glazes and hardens. You will see a hot gland, a scored shaft and packing that comes out shiny and brittle. Tighten the follower finger-tight, run the pump, then take up a flat at a time until the drip reduces to a slow steady rate — not until it stops.

2. The shaft is worn or scored

A grooved shaft gives the packing a leak path that no amount of tightening closes, and tightening harder only cuts the groove deeper. Run a fingernail along the shaft in the packing zone — if it catches, the shaft or sleeve needs attention before new packing goes in. This is the cause most often ignored, because dealing with it means more work than fitting another set.

3. The rings were fitted wrong

Three fitting faults produce immediate leaks:

• Joints not staggered. Ring joints lined up create a straight leak path. Stagger each ring by 90 degrees.
• Rings not seated individually. Each ring must be pushed home before the next goes in; stacking them loose leaves the bottom rings uncompressed.
• Spiral-wound instead of cut rings. Wrapping a continuous length in rather than fitting individual cut rings leaves a helical path straight through the box.

The step-by-step installation guide covers the method.

4. The section size is wrong

Packing cut too small never fills the annulus and leaks from the start; too large and it will not seat, or it is forced in and binds the shaft. This comes from ordering by the old packing rather than measuring the shaft and box — the measurement guide covers how to get it right.

5. The grade does not suit the duty

Packing that leaks after a short, healthy service life is usually a specification problem rather than a fitting one. Abrasive duty chews soft packings — aramid resists it far better, though it is hard on a soft shaft. Hot or steam duty needs graphite packing. Aggressive chemistry needs pure PTFE. See choosing the right gland packing.

Also check the lantern ring

If the box has a lantern ring, it must sit level with the flush connection. Fitted at the wrong depth — easily done when the ring count changes — the flush cannot reach the packing, and the set runs dry and fails early regardless of everything else being correct.

If it still leaks

Send us the shaft and box dimensions, the medium, temperature, pressure and shaft speed, plus a photograph of the old packing as it came out. The condition of the removed set usually identifies the cause on sight.