In the past it was common practice to supply a high speed, high powered Boiler Feed Pump used in a power station with gear type mechanical couplings between the driven equipment. Most of these couplings are injected with oil between the two coupling hubs and coupling boss.
Below are excerpts from a paper titled “So what did we learn about pumps during the past 20 years” presented by Anton Edward Cattaert, Willem van der Westhuizen and Gugulethu N C Ngcobo of Eskom at the 30th Pump Users Symposia in Houston.
Typical gear type coupling
The newer installed Eskom Boiler Feed Pumps such as those installed at Matimba Power Station have been equipped with Flexible Membrane Couplings. The average operating hours of the couplings installed on the 18 off 12 069 hp (9 MW) Boiler Feed Pumps at Matimba Power Station are >50,000 running hours. One of the Matimba Power Station boiler feed pump sets has run for more than 120 000 running hours.
Typical flexible membrane coupling
If one compares our experiences with the gear type couplings compared to flexible membrane couplings installed on our high speed, high powered Boiler Feed Pumps the following is worth noting:
• Gear Type couplings tend to weigh more when compared to the same coupling application equipped with a flexible membrane coupling
• Gear injected couplings always leak at coupling housing or supplied oil pipe work
• Flexible membrane coupling are dry and have no oil injection
• Flexible membrane couplings are more rotordynamic friendly when compared to gear type couplings – better pump vibration behavior
• Oil condition, oil carbonization and blocking of gear teeth could lead to gear teeth hang-up, which results in expansion thrust related problems
• Flexible membrane couplings are expensive compared to gear type couplings.
