Mechanical Seal vs Gland Packing

Every centrifugal pump has to seal a rotating shaft against a pressurised casing. There are only two common ways to do it on a water pump, and they fail in opposite directions.

The Flowsteer FA series offers both: a single mechanical seal as standard with gland packing optional. The other metal series use a single mechanical seal.

How a Mechanical Seal Works

Two flat faces — one rotating with the shaft, one static in the seal chamber — are pressed together by a spring. A microscopic film of pumped liquid between them provides lubrication and cooling.

When it works, leakage is effectively zero and the seal needs no attention at all between services. That is why it is the standard on unattended plant.

When it fails, it usually fails quickly rather than gradually, and it is replaced rather than adjusted.

How Gland Packing Works

Rings of braided packing are compressed into a stuffing box around a shaft sleeve. The compression is adjusted by a gland follower.

The packing must be allowed to leak a controlled drip. That leakage carries away the frictional heat generated between packing and sleeve.

Tightening the gland until the drip stops is the single most common way to destroy a shaft sleeve. It is also the most common mistake made with packed pumps.

Which To Choose

Clean water, unattended plant, no fitter on site — mechanical seal. It needs nothing until it needs replacing.

Poorer water, a fitter on site, remote installation — gland packing. It can be repacked in place with basic tools rather than waiting for a replacement cartridge.

Water carrying abrasives — packing wears the sleeve, a seal wears the faces. Neither is comfortable; a flushed arrangement helps both.

Potable or environmentally sensitive duty where any leakage is unacceptable — mechanical seal.

What Each Costs You Over Time

A mechanical seal costs more at purchase and nothing until replacement. The failure is abrupt and the pump usually has to come apart.

Gland packing costs less at purchase and requires routine attention: periodic adjustment, occasional repacking and eventual sleeve replacement.

On a remote irrigation pump, packing often wins. On a plant room circulation pump running continuously, the seal usually does.

Sealing On Submerged Pumps

Neither option suits a pump that sits below the liquid level. A mechanical seal there cannot be flushed, inspected or adjusted; packing cannot be tended to at all.

That is why the Flowsteer VNP vertical sump pump uses a labyrinth seal or a lip ring seal instead. The labyrinth has no rubbing faces to wear; the lip ring gives a positive barrier and is renewed when the pump is lifted.