Metaramics Corporation in Sunnyvale, California, was having problems controlling wastewater pH due to leakage and corrosion of chemical metering pumps. The plant, which manufactures metal ceramic packages for the electronics industry, has electroless nickel, gold and silver plating lines. Wastewater from the processes must be sent through a treatment system before it is discharged to the sewers. The wastewater from the plating lines, which contains acids and cyanides, is pumped to holding tanks for neutralization. Metal particulates are removed by pumping wastewater through a sludge press.

Troubles developed with three chemical metering pumps mounted on top of a three-partition, 14’ long, 10’ wide, 8’ high holding tank. One section in the tank was used for storage of sodium hydroxide and the other two sections for neutralization. The pumps failed because they were exposed to weather conditions. The seal between the baseplate and the electrical control housing would allow chemicals, fumes and rainwater to damage the electrical controls. Three pumps were installed to provide the desired flow rate, and the operator had to constantly readjust the strokelength and speed of the pumps because of ruptured pumping diaphragms. As a result, flow rates were low and irregular. The pumps had to be repaired every seven or eight months at a cost of $550 each.

Metaramics Corp. replaced the three existing pumps with an air operated , all-plastic metering pump from Plast-O-Matic Valves, Inc. The body, shaft and piston of the self-priming pump is constructed of Type 1, grade 1 polyvinylchloride (PVC) that can withstand a variety of highly corrosive liquids including sulphuric acid, hydrochloric acid, chlorine, caustics and demineralized water. The compact 3 ½" diameter x 13" long unit can deliver seven ounces per cycle. An adjusting bolt on the bottom plate can be turned farther into the air chamber to shorten the piston stroke and lower the output per cycle. The location of the inlet and outlet check valves, on the upper plate facing the liquid chamber, allows the liquid chamber to self-prime. Patented vent ports in the pump midsection facilitate escaping liquid to exit to a safe location instead of contaminating the air chambers. If a primary seal fails, immediate shut-down would not be necessary and the operator would be alerted of a primary seal failure by checking for liquid flow out of the vent ports. The air operated chemical metering pumps are also available with discharge capacities of 10, 32 and 128 ounces per cycle. Discharge accuracy and repeatability is ½ of 1%.

Sensors located in each of the neutralization tanks determine the pH and actuate the sodium hydroxide pump. The pump is controlled by a four-way solenoid valve that admits and exhausts air in two separated pumping chambers. Depending on the pH of the wastewater, the positive displacement pump may cycle from two minutes to 60 minutes per hour. For maximum protection, relays and wiring are enclosed in weatherproof conduit and fixtures.

The air operated, all-plastic metering pump has been maintenance-free since it was installed. It does the work of the three previous pumps and has eliminated the need for constant changing of the piston stroke. At one-third the price of the electric pump, the PVC plastic pump paid for itself within 60 days. Metaramics Corp. considered the trial run successful and installed eight more of the air operated plastic pumps in similar critical metering applications.

For more information, contact Plast-O-Matic Valves at 973-256-3000 or e-mail: info@plastomatic.com and request Metering Pump Catalog.