by Ed Weaver, Tarrant Regional Water District

The reliability of this pumping station had to be improved to keep up with demand and prevent service outage.

Tarrant Regional Water District (TRWD) was established in 1924 as a result of Fort Worth area flooding and the need for a reliable water supply.

Today, supply and flood control activities span a ten-county area in North Texas. Currently, TRWD provides raw water to approximately 1.5 million end users through 32 municipal and industrial wholesale customers, with the service area population projected to increase to 2.66 million by 2050. The supply system consists of four large supply reservoirs and three major raw water transmission pipelines.

The performance of ten new 5000-hp motor/pump units that went into operation in early January this year was carefully monitored right from the beginning as part of an ongoing TRWD program to stay ahead of the growing demand for fresh water in Fort Worth and the surrounding area.

Even with these new units in place, up to 80 percent of system capacity will soon be needed just to meet prime-time demand, reducing the amount of backup available in case mechanical problems occur. A failure at one of the unmanned pumping stations could severely reduce the delivery of water from our four reservoirs. Compounding matters, operations and maintenance staffing has decreased by 30 percent over the past ten years, while power costs continue to go up.

Clearly, a high level of mechanical reliability is necessary to operate at 80 percent capacity with reduced maintenance. The solution was a vibration monitoring and analysis technology that provides a continuous flow of performance and condition data from the remote stations. This becomes the basis for predictive maintenance at all of the pumping stations.

“We don’t just sit and wait for an alarm or for something to go wrong anymore,” according to Boyd Miller, pipeline operations manager at TRWD. “Vibration levels are monitored on a continuous real-time basis to make sure they remain within prescribed limits. In addition, the accumulated data are analyzed monthly, looking for any indication of a developing problem or a potential failure.”

Since online monitoring was initially adopted in 2001, overall system reliability has increased significantly with fewer unplanned outages due to unexpected failure of critical equipment. Specifically, TRWD has experienced:

  • A 20 percent reduction in emergency costs
  • Lower overall maintenance costs
  • 100 percent increase in the accuracy of factory acceptance testing
  • 50 percent reduction in staffing requirements for remote stations

Factoring in all improvement costs, the District’s annual savings are on target, with the original cost-justification estimates that projected a 10-year economic benefit of $306,000.  \

Table 1 – Cost Justification

10-year cost of online system $94,000 higher than periodic vibration service

$400,000 cost avoidance with vibration data based on actual problems:

  • $120,000 – excessive thrust on three units
  • $166,000 – broken rotor bars on two units
  • $114,000 – failed motor bearing

Online monitoring provides 2,920 times more trend data

Added value:

  • Trending and operational parameter determination
  • Enhanced decision-making, planning, scheduling, and forecasting

District savings could actually increase with the new pumping capacity. Many costs are fixed, while the avoidance of repair costs will improve the overall benefit. In effect, the payback period will be shorter.

The Challenge

In the past, maintenance workers conducted daily visual inspections and monthly predictive maintenance evaluations to detect such threats as bearing failures, broken motor rotor bars, or flow problems such as cavitation or re-circulation. This was both time consuming and expensive, as personnel had to travel a 150-mile circuit each day to reach all eight stations in operation at that time.

Vibration analysis using portable equipment was partially successful, but no performance data was available to identify evolving pump and process problems, which could go undetected for long periods. Unexpected failures were all too common, followed by high emergency maintenance costs.

A New Approach

In 2001, 34 pump/motor sets ranging in size from 1000-hp to 5500-hp were equipped with CSI 4500 machinery health monitor systems from Emerson Process Management (Knoxville, TN), which continuously measure vibration levels, perform advanced processing, and calculate specific analysis parameters.

The multiple stations were tied to a central host via a frame relay network, with the host connected to the plant network.

5,500-hp vertical pump lineup at the Richland Chambers Lake Pump Station.

5,500-hp vertical pump for scale.

The condition of all critical pumping equipment can be observed from the host, where pump status and alarms are displayed by the AMS™ Suite: Machinery Health Manager software. In addition, all trend data is stored for advanced predictive diagnostics. This workstation has full diagnostic, analytical, and reporting capabilities, allowing maintenance decisions and plans to be made from one central location.  

Vibration sensor pick-up on a 5,000-hp horizontal pump. Typical set-up for all horizontal pumps – 1,000-hp through 5000-hp.