The worn paint on this Warman® expeller demonstrates ideal operating conditions, as the pump’s hydraulic design has prevented any abrasive particles from encountering the centre of the component at the point where it meets the shaft seal.

A more recent innovation is the Warman^® Hi-Seal^®, our next-generation centrifugal seal. It features an increased diameter, which results in a larger differential pressure being created when in operation. This higher differential pressure results in a better sealing experience and allows even larger pump sizes to seal effectively. Warman® Hi-Seal® is now the standard centrifugal seal offering for most pumps.

Comparison of shaft seal types

	Gland seal	Centrifugal seal	Mechanical seal
Capital cost	Low	Medium	High
Maintainability	Easy	Medium	Hard
Water consumption	High	Low	Low
Likelihood of application suitability	High	Low	Medium

When not to use centrifugal seals

While centrifugal seals are suitable for the vast majority of pumps operating in most mines and quarries, there are a few circumstances which make gland or mechanical sealing a better option.

Centrifugal seals rely on shaft speed and only work when they are generating a higher pressure than the impeller. Therefore, they are unsuitable for applications with varying speed of operation, total head and suction pressure. Filter press pumps, dewatering pumps managing variable sumps, and pumps that are frequently switched on and off are all unsuited to this dynamic sealing method.

Similarly, because of the leakage risk while the shaft is not rotating, centrifugal seals have specific packing and lubrication requirements and are unsuitable for pumps handling dangerous chemicals.

Centrifugal seals do consume a small amount of additional energy compared to glands. While this is much lower than the cost of water for small pumps, the cost of power for larger pumps makes centrifugal seals a poor choice. For this reason, Weir Minerals does not offer centrifugal seals on Warman® pumps with a discharge diameter greater than 250mm.

Calculating your gland water costs

The costs associated with the use of water to flush the gland of a slurry pump can be split into two components, the supply cost and the removal cost. The former depends on the type of pump, its size and gland type, the latter depends on the particular process and commodity being handled.

Using the following formulas included in Warman® Technical Bulletin #32: Total Ownership Cost model for slurry pumps, an approximate cost of gland water consumption can be determined.

Firstly, gland water has to be supplied at a supply pressure which is generally 70kPa above the discharge pressure of the pump. The power required to deliver the water to the gland (P_g) can be approximated by:

P_g = 0.02 x (H + 7 / SG_m) x Q_g

where

SG_m = specific gravity of slurry mixture

H = total head developed by pump (m slurry)

Q_g = gland water flowrate (l/s)

The energy cost (c_ge) is then:

c_ge = P_g x c_e x h_o

where

c_e = unit power charge ($ / kWh)

h_o = total operating time (h/y)

The actual consumption cost for the water then needs to be added to the energy cost. The total water consumption cost (c_c) is:

c_c = 3600 x Q_g x c_gw x h_o

where

c_gw = cost of water supply ($/L)

With tightening environmental standards in some cases requiring complete liquid containment on site, any slurry dilution can incur substantial cost penalties. In the alumina industry in particular, the costs associated with drying hydrate may be up to $2.20/kl. The total cost of unwanted dilution water (c_d) is:

c_d = 3600 x Q_g x c_rw x h_o

where

c_rw = cost of removing the water ($/l)

From this the total service water cost (C_w) can be calculated by summing the three terms:

C_w = c_ge + c_c + c_d

For a fuller assessment of the money and water your mine or quarry could save by switching your Warman® pumps to be centrifugally sealed, contact us today. Our engineers have extensive expertise in providing full solutions, giving them the skills to advise on how any modification would affect the overall operation, not just an individual piece of equipment.