Vesconite bearings in cooling water feed pumps at the largest New Zealand gas fired thermal power station have significantly overcome problems caused by the interruption of process water causing serious bearing failure.

Originally the pumps, used for pumping sea water were fitted with cutlass rubber bearings.

Designer	Drysdale
Pump size	Variable – 5" discharge pipe
Pressure head	5 Bar
Pump power	60 HP
Pump speed	1450 RPM
Pumped medium	Sea water
Shaft size :	2" (50 mm)
Housing size :	2 5/8" (66 mm)
Bearing length :	8" (200 mm)

The water supply to the pumps is interrupted by sea weed blocking the inlets. The "no cooling water" alarm sounds when this happened but the pumps could run dry for up to 45 seconds before they are stopped.

The rubber bearings would often overheat and be severely damaged within 30 seconds, often before the alarm was sounded.

Cutlass rubber is an acceptable pump bearing material provided a stable supply of cooling water is available – this is however not always the case in practice as this case study demonstrates. The bearings may be dry at startup before the pumped water reaches them or they may run dry if the water flow is stopped due to blockages.

In their search for a solution, the power station first tried replacing the rubber bearings with an elastomeric material widely used for pump bearings. However, this material wore the expensive 316L stainless steel shafts. This proved more costly than the bearings, and was more difficult to repair and entailed additional downtime.

The bearings were then replaced with Vesconite. The pumps fitted with Vesconite bearings have shown no bearing or shaft wear, much to the amazement of the engineers concerned.

Date first installed : November 1996

The Chief Engineer is now committed to using Vesconite bearings for these pumps.

The internal lubricants in Vesconite (and an even more advanced lubricant in Vesconite Hilube) make this an ideal material for pump bearings where there is the possibility of a dry start or an interrupted flow during operation.

The following dry running tests were conducted on Vesconite Hilube.

Operating conditions are typical to pump bearings.

• Pressure P = 0.4 kg/cm² (5.7 psi)
• Surface velocity v = 360 m/min (1152 fpm)
• PV = 136 kg.m/min.cm² (6566 psi.fpm)

Vesconite Hilube survived these conditions for well over 1 minute without damaging the bearing!

This is far better than alternative water lubricated pump bearing materials, many of which melt down or burn within seconds. 90% of dry start up specifications require only a 1 minute running time.

At this power station, a further advantage noted is that the installed running clearance was much closer for the Vesconite bearings than was possible with the original cutlass rubber bearings. The benefit is that the impeller does not run on the casing and therefore the pump is more efficient, both in respect of pumping ability and a saving in power consumption.