The original 15 hydraulic diaphragm metering pumps at the Moores Bridges Water Production Facility in Norfolk, Va., had reached the end of their life. Daily leaks alerted operators to failing diaphragms and check valves. Every stroke of the pulsation dampener jarred the pipes, causing structural fatigue and more leaks.

By 2009, 10 pumps were permanently out of service. Of the remaining five, one or two were constantly in the facility's large repair shop. "My operations supervisor and I lost a lot of sleep worrying about the pumps not lasting through the night or dosing sodium hypochlorite correctly," says maintenance supervisor William Branch.

Two mechanics spent a combined 20 to 30 hours per week maintaining the five pumps. Repair kits cost $2,200 to $2,500 each, and they used one every six months. Parts and maintenance cost the facility $3,000 to $5,000 annually.

When an attempt to solve the problem with a hose pump failed, Branch and his mechanical supervisor investigated gear pumps and progressive cavity pumps. Stuart Taylor of Tencarva Machinery offered a seepex MD 05-6LT progressive cavity metering pump rated at 120 gallons per hour for a 90-day trial.

Installed in two days to replace an original pump, the test unit treated the entire flow and kept the plant compliant when the remaining pumps failed simultaneously.

Doomsday

The 108 mgd (design) Moores Bridges plant delivers an average of 65 mgd to a population of 850,000. The City of Norfolk receives its raw water from eight reservoirs, two rivers and four deep wells. Pumps inject sodium hypochlorite into the chlorine contact basin and into a 102-inch pipe returning to the filters.

Before the new pump arrived, operators modified some piping and electrical at the contact basin and installed a variable-frequency drive. "It took a week and a half to get everything ready," says Branch.

After installing the pump, with titanium and ethylene propylene diene monomer wetted parts, operators manually adjusted the feed rate by watching chlorine levels rise and fall. The pump, protected from run-dry and over-pressure, operated in a manual mode for the trial, pumping against high pressures without pulsation or vapor lock.

Branch ordered two identical units at the end of the trial, but before they arrived, the old pumps had a final massive breakdown. Mechanics worked overtime just to keep one running. "I told Stuart our situation and he immediately returned the trial pump," says Branch. "I promptly bought and reinstalled it, and we were pumping in 90 minutes."

Since then, Branch has purchased two additional MD series pumps and will purchase more for redundancy. At present flows, the plant runs two pumps with three on standby and alternates them every 10 days.

On a roll

The facility also had eight diaphragm pumps dosing aqueous ammonia. They occasionally began to lose prime or lost it completely, causing injection points to receive less than a full dose. Branch asked Taylor if seepex made an ammonia pump. "I was confident they would perform as well as the sodium hypochlorite pumps, so I ordered four when Stuart said they had them," says Branch.

Four MD 012-12 stainless steel pumps rated at 30 gallons per hour were soon joined by two more, then two MD 025-6L stainless steel pumps rated at 15 gallons per hour. Besides the pumps delivering an accurate feed rate, a sensor automatically adjusts their speed to rising and falling water levels, and they integrate with SCADA.

Seepex recommended changing the oil in the gearbox annually, but Branch added changing the rubber stator every two years or sooner if the calibration is low. "It took four hours to change diaphragms or check valves on the old pumps," he says. "Changing a stator takes 30 minutes."

Sound night's sleep

Sodium hypochlorite vendors, PVC manufacturers and Internet research helped Branch find the best components for the pumping system. To avoid potential maintenance problems, he buys O-rings, unions and valves rated for sodium hypochlorite, and special glue to join PVC pipes carrying the compound.

In three years, the facility has saved $15,000 in maintenance. "We went from spending more than $2,000 on repair kits to spending $5 on a quart of 220 oil," says Branch. "For the cost of a diaphragm pump and two repair kits, I can buy a new pump and reduce maintenance to almost nothing."

Branch has since ordered more MD series units to replace the sodium hypochlorite pumps on the other side of the plant. "I'll sleep even better after we install them," he says.