Slurry pump shaft seal types come down to three on our horizontal pumps: an expeller with packing, packing, and a mechanical seal. Grease-lubricated packing is a way of running packing, not a fourth type.
If you want no shaft seal at all, that is a vertical pump question, and we cover it in our guide to a vertical slurry pump without seal water. On a horizontal pump, you have to choose one of the three.
Three questions decide it
- Is clean seal water available on site, at a pressure above the pump’s discharge pressure?
- What is the pressure at the pump inlet, compared with the discharge pressure?
- Can the process accept a small amount of water entering the slurry?
Answer those three and the list usually shortens to one or two options.
Expeller with packing: when inlet pressure is low
An expeller is a small auxiliary impeller behind the main impeller. While the pump runs, it builds enough pressure to hold the slurry away from the shaft. When the pump stops, the packing behind it does the sealing.
On our SH, SM and SHH series, the expeller is used only on a single-stage pump, or the first stage of pumps in series, and only where the positive pressure at the pump inlet is not greater than 10% of the outlet pressure. Pumps fitted with a mechanical seal carry a spacer sleeve in place of the expeller.
The arrangement also includes a lantern ring, and on a first-stage SZP pump the lantern ring runs with seal water at a specified flow. Send us the duty and we will confirm the seal water it needs.
The expeller ring comes in metal with packing, or in rubber with a lip seal. Where the ring has an oil cup, it is greased through the cup.
Packing: simple, but it uses seal water
Packing is simple in structure and easy to maintain. The price is a steady supply of clean seal water at every pump, fed at a pressure above the discharge pressure.
For our SH, SM and SHH series, the recommended flow depends on the frame size of the pump:
| Frame (SH, SM, SHH series) | Seal water (L/s) |
|---|---|
| A | 0.15 |
| B | 0.25 |
| C | 0.35 |
| D | 0.55 |
| E, F | 0.70 |
| G | 1.2 |
| R, RS | 0.70 |
| S, ST | 1.2 |
| T, TU | 1.6 |
| U | 2.1 |
In service the gland should leak drop by drop. Too tight and the shaft sleeve heats up and draws extra power. Too loose and too much liquid escapes.
Packing can also be run with grease instead of seal water. When the packing is grease lubricated, no seal water is added. The trade is daily attention: the grease has to be topped up once or twice a day to keep the packing properly lubricated.
We have no set pressure or duty limit for grease-lubricated packing, so we do not give one. Send us the duty and we will tell you whether it suits.
Mechanical seal: where leakage is not acceptable
Compared with packing and the expeller, a mechanical seal holds a steadier sealing state over a longer running cycle, and leakage is small.
The seals we fit are usually balanced double-face seals, supplied with a cooling water pipe and a pressure gauge. They leave our works already installed and adjusted, so no further adjustment is needed on site. Spare seals are usually supplied fitted in a stuffing box, as a complete set.
A mechanical seal still needs seal water. Turn it on before the pump starts, and keep it on for a while after the pump stops; we confirm the timing with the pump. Never run the seal dry, or it will burn out.
If the pump or a spare seal will stand idle for a long time, fill the seal section with N46 machine oil to stop the parts rusting and the rubber parts failing.
A quick way to narrow it down
Laid side by side, the slurry pump shaft seal types sort like this:
| Your site | Start with |
|---|---|
| Single-stage pump or first stage in series, inlet positive pressure not above 10% of outlet | Expeller with packing is an option |
| Inlet positive pressure above 10% of outlet | Send us the duty: the expeller is ruled out |
| Clean seal water available, some dilution acceptable | Packing with seal water |
| Leakage or dilution not acceptable | Mechanical seal |
| Pumps in series | Expeller on the first stage only |
If none of these fits cleanly, combination arrangements are available for special duties.
What to send us
Send the medium, the inlet and discharge pressures, and whether clean water is already available on site. If you are still choosing the pump itself, our tailings pump guide shows the duty data we work from. We then confirm the seal and the parts that go with it, down to the expeller and expeller ring.
FAQ
How many slurry pump shaft seal types are there?
Three on our horizontal pumps: expeller with packing, packing, and mechanical seal. Grease-lubricated packing is a way of running packing, not a fourth type.
Can I fit an expeller on every pump in a series?
No. An expeller can be used on a single-stage pump, or the first stage of pumps in series, when the positive pressure at the inlet is not greater than 10% of the outlet pressure.
What should I do if a pump with a mechanical seal will stand idle?
Fill the seal section with N46 machine oil. It stops the seal parts rusting and the rubber parts failing. The same applies to spare mechanical seals kept in store.