An Alabama power plant employs turbine pumps to move spent fuel pumpage into several holding ponds for particulate settling and clarifying. The pump on the last pond began to fail because of age and fine particle caking of the pump. At the time of year, frequent rainstorms swell the pond by several feet, and the freeboard available before a spill would occur was at a premium. Compounding the issue of moving a new pump temporarily was the need to protect the pond liner from tears. The particulates could not leak into the surrounding area, as it was an environmentally sensitive location. There was limited space to place a temporary pump on the levee wall.
The discharge run was just over two miles, made of 8-inch fiber line with a 150 coefficient. The age of the line prevented it being pressurized above 125 pounds per square inch (psi).
To tackle the freeboard with limited space to place a pump coupled with the environmentally sensitive area and tear susceptible pond liner, the power company turned to a rental solutions provider with a national presence. Guidelines for the rental original equipment manufacturer (OEM) include achieving maximum flow while limiting pressure in the fiberglass line to lower the pond quickly in case rain caused an overspill. The rental OEM looked at the head, flow and psi constraints and determined that a single frame mounted centrifugal pump with a two-port 17.5-inch enclosed impeller, 6-inch suction and an 8-inch discharge was the best option.
The rental OEM completed the setup using dual 8-inch suction lines that were manually installed to ensure the integrity of the pond liner. On the discharge side of the pump, 200 feet of 8-inch crimped tank truck hose was connected to the fiberglass line. Initial suction lift was approximately 17 feet on a 3-to-1 slope. However, the pond water level was subject to change with any additional rainfall near the plant. The pump was packaged with an electronically controlled engine, enabling the use of a pressure transducer to maintain a steady flow of water without approaching the maximum psi specified by the power plant.
The panel on the pump was set to maintain at 115 psi, ensuring that the pump would not approach the 125 psi threshold. The system was designed so that in the event of an unexpected pressure spike in the discharge line, the pump would idle down and shut off to prevent damage to the power plant’s permanent piping system.
The pump’s design was seen as forgiving in the various run conditions that the pump could experience, with a broad working range and high efficiency. The pump’s reliability was also a strong consideration in selecting it for the critical job.
The pump was in place for five months and worked without issues. No damage to the liner occurred, the pond did not overtop, the pump worked well and was easily accessible in the confined levee space, and the time allowed the permanent pump to be rehabilitated and brought back online. The pump package has been repurposed by the OEM for use in the applications such water transfer in the oil and gas industry.
Troubleshooting a Rental Pump
This installation went off without a hitch, but from time to time there can be issues with rental pumps in the field. These troubleshooting tips can help with rental pump operations. There are three main problems with a portable priming pump:
1. Pump will not prime, or takes an excessively long time to prime
Here are some common issues and possible fixes.
Part to Inspect/Examine: Possible Fix
- Air compressor hose: Check for damage, nicks or leaks that will prevent priming. Replace if necessary.
- Check valve: Examine to make sure it is free of debris/obstructions.
- Discharge: Make sure discharge is clean, and also check that priming valve is working properly.
- Drain valves: Ensure drain valves are closed. Open valves will affect priming.
- Float adjustment: Inspect for proper tightness, and determine that rubber components seat properly. Also check that float is intact (not filled with fluid) and that linkages and pins are properly connected.
- Hoses: Inspect suction hose for leaks or improper connection.
- Pop off valve: If heard releasing air, priming system could be leaking air. Ensure proper fit.
- Priming system: Refer if vacuum assist dry prime or venturi and follow manufacturer maintenance and cleaning standards.
- Vacuum shutoff valves: Make sure it is open. Inspect hose for kinks, discoloration or blockage.
2. Unit will not pump
Field experience shows that close to 90 percent of problems when a unit will not pump are suction-side related. Most of the other problems are on the discharge side, with very few mechanical seal problems. Start with the most probable and easiest to remedy issues on the suction side. This chart offers some ideas of what to check:
Part to Inspect/Examine
- Suction Lines
- Inspect that they remain leak and damage free. Replace if necessary.
- Check position and readjust. Avoid vortexing. Ensure hose is not on bottom of fluid source, where it is likely to clog.
- Check for airlock. Symptoms include very low vacuum pressure on suction, with high pressure or low flow on discharge.
- Check for vapor lock (stem may be present).
- Determine valves are open and line is not blocked/obstructed.
- Check that seal is not damaged or contaminated.
3. Pump exhibits high vacuum with little or no flow
High vacuum with low or no flow conditions generally indicate a suction side restriction.
Part to Inspect/Examine: Possible Fix
- Suction strainer: Check for clogs and that it is not buried in the mud.
- Suction hose: Check for kinks, leaks, inner liner collapse and improper fitting.
- Suction lift: If NPSHr is too high, lower the pump towards the water source.
- Discharge piping valve: Determine that it is open and operating properly.
- Pump speed: Verify that pump is operating at expected speed for sized conditions.
- Discharge head: Analyze conditions and see if improper NPSHa could contribute.
- Impeller: Check for blocks and restrictions.