Shaft Sealing Options: Expeller, Packing or Mechanical Seal
Expeller, packing or mechanical seal: the choice decides whether the plant needs a gland water circuit at all, so it belongs at layout stage.
The shaft seal decides whether your site needs a gland water supply at all. That is a plant-layout decision, not a spare-parts decision — settle it before the pipework is fixed, not after.
Overview
A slurry pump can be sealed three ways: an expeller (dynamic seal), packing with gland water, or a mechanical seal.
Most people meet this as a spare-parts choice. In practice it decides a water circuit: choose an expeller and the plant needs no gland water pipework at all; choose packing and every pump needs a clean, pressurised supply and a permanent consumption to go with it.
That is why the decision belongs at layout stage.
The expeller has one hard limit
An expeller is a dynamic seal — a small auxiliary impeller behind the main impeller generates enough pressure to hold the pumped medium away from the shaft while the pump runs.
Its value is that it needs no gland water, which removes both the consumption and the pipework from the installation.
Two limits come with it:
It seals only while running. When the pump stops, a static packing set holds instead.
Inlet pressure must not exceed 10 % of discharge pressure. Beyond that the expeller cannot hold the slurry back and the gland will pass.
This is why the decision belongs at plant-layout stage. If the pump will sit under a flooded suction, or the inlet carries appreciable positive pressure, the expeller option is already ruled out the moment the pipework is drawn.
Applies to single-stage pumps, or the first stage of a series set.
Packing — the option that costs you water
Packing needs clean gland water, supplied above the discharge pressure at the gland.
The rate is set by frame type — from 0.15 L/s on frame A through to 2.1 L/s on frame U.
That is a continuous consumption per pump. On a concentrator running a dozen pumps, both the water and the pipework are a real cost.
What you get in return: no inlet-pressure limit, and sealing that holds when the pump is stopped.
Mechanical seal — where leakage cannot be tolerated
Used where leakage is not acceptable, or where the medium must not be diluted.
Gland water enters the medium, and for some processes that alone rules packing out. A mechanical seal avoids it, at the cost of a more complex arrangement that is more sensitive to the medium and the pressures.
Reading a leak — when it leaks tells you what is worn
| What you see | What it points to |
|---|---|
| Leaks while running | The clearance between expeller and expeller ring |
| Leaks only when stopped | The packing, not the expeller |
The expeller and its ring wear as a mating pair and must be renewed together. Fitting one new part against a worn partner restores only part of the sealing.
If it leaks only when stopped, repack and confirm the packing grade against the working pressure.
Combination arrangements
Combination arrangements are available for special duties. Send us the medium, the inlet and discharge pressures, and whether clean water is already available on site, and we will confirm the arrangement.
Can we run without a gland water supply?
Yes, with an expeller seal — provided inlet pressure does not exceed 10 % of discharge pressure. Beyond that limit the expeller cannot hold the slurry back.
How much gland water does packing need?
It is set by frame type, from 0.15 L/s on frame A to 2.1 L/s on frame U. Water must be clean and supplied above the discharge pressure at the gland.
The gland leaks while running — what is worn?
The clearance between expeller and expeller ring. Renew both as a mating pair; fitting one new part against a worn partner restores only part of the sealing.
When is a mechanical seal the right choice?
Where leakage cannot be tolerated or the medium must not be diluted. Send the medium and the pressures and we will confirm.
Manufacturer-direct supply · Technical pump-selection support · Export documentation on request.