Seal-less pumps raise mining machine reliability

Dosco Roadheading machines feature a newly designed raised-pressure water spray system to suppress dust and cool the picks on the cutting head.

"No news is good news", says Dosco mining equipment designer Alan Owens, commenting on the absence of feedback from Roadheader machine operators as far apart as Nevada (gold mining), Wyoming (oil mines) and China, Iran and Russia (coal mines).

All these customers have something in common.

Their Dosco Roadheading machines have all been supplied or retrofitted within the last two years with a newly designed raised-pressure water spray system to suppress dust and cool the picks on the cutting head.

And not a single problem has been reported.

The new system, optionally available on all Dosco Roadheaders, is based on Wanner Hydra-Cell seal-less pumps - a type of pump well suited to conditions underground and uniquely able to deliver mine water at high pressure, without needing fine filtration.

Dosco is based in the UK at Tuxford, Nottinghamshire, and operates world wide as a major designer and manufacturer of mineral mining machinery, tunnelling machines for the civil engineering sector, and pipe conveyors.

Its Roadheaders have been used in more than 50 countries, excavating tunnels for underground mine access, sewers, railways and roads, and also for mining production in the case of minerals such as coal, bauxite, salt, iron ore, potash, phosphates, gold, gypsum and copper.

To reduce airborne dust, prevent sparking at the rock face and prolong the life of the tungsten carbide cutting tools, Dosco offers an integral raised-pressure water spray system in two versions - working at 38 or 140bar.

Typically water is fed by gravity from a lagoon/reservoir at the surface to the machine inlet, where it is filtered before being pumped to 0.8mm diameter spray nozzles mounted in the machine's rotating head close to the cutting picks.

The system is very reliable, field proven and requires little maintenance.

In developing and improving it, Dosco have successfully overcome an initial problem.

An earlier version incorporated gear-type pumps, chosen for their pressure capability and rugged construction.

But in practice service life was below expectation.

And as the Dosco system has inbuilt safety switches that shut down the machine if water flow or pressure drops below preset values, there was potential for costly production downtime if a pump were to fail at an inconvenient moment.

Conditions underground can be hot (up to 48C), dusty and damp.

Mine water is not naturally clean.

Pumping it (even when filtered, as here, to 100um) can cause problems for any pump which incorporates dynamic seals, or relies on close tolerances to achieve its pumping action.

Both features are fundamental in the design of most pumps capable of pumping at the required pressures.

And ultra-fine filtration is not a viable option.

The Hydra-Cell pumps now fitted as standard on Dosco's raised-pressure water systems have none of these limitations.

They have no dynamic seals.

Pumping action is achieved by means of hydraulically balanced cells which are totally isolated from the mine water by diaphragms.

The pumps can easily handle abrasives and particles as large as 500um, and the diaphragms operate without stress right up to their maximum pressures.

On this application both models - G25 for the 38bar version and model G15 for the 140bar system - are working well within their rated pressure capabilities, respectively, 70 and 170bar.

Even if discharge pressures should fluctuate, the hydraulic principles employed in the pumping action ensure that Hydra-Cell pumps produce a constant, reliable flow.

Among other features commending them to Dosco were their simple construction, making them robust and easy to service, and their exceptionally compact build in relation to performance.

Notwithstanding a reputation for reliability claimed for the Hydra-Cell pump on demanding applications elsewhere and in other industries, Dosco engineers had to satisfy themselves on its field performance in roadheaders, which often have to operate in exceptionally hostile conditions.

"Two years without a problem", suggests Alan Owens, "proves how well it can cope".

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