Choosing the correct metering pump involves many considerations. Among them are accuracy, repeatability, chemical output, material compatibility, line pressure, control input, off-gassing of the chemical and the environment where the pump will be placed.
Even for pumps that meet the requirements for a particular application, the environment in which the pump operates can pose a significant challenge. Metering pumps often are used in wet conditions and require daily washdowns of the equipment.
To choose the best pump for an application, end users must consider the application’s environment and how water will affect the equipment.
Manufacturing a food or beverage—as well as maintaining a hygienic work area during the process—requires copious amounts of water. Washing down the equipment requires either raw water or water containing chemicals such as oxidants.
The inundation of water during the washdown process frequently causes pump failure because of water intrusion into the electrical drive or control.
Repairing these pumps is time-consuming and requires a replacement pump to keep the line producing. If the pump is replaced, the new equipment also faces the risk of failure because it operates in the same environmental conditions. In some cases, end users replace these pumps with a waterproof version that can handle the washdown procedures.
There are pumps available with a rating of Ingress Protection (IP) 67 (NEMA 6 equivalent), which means they were tested under 3 feet of water for 30 minutes and continued to run properly.
For example, one manufacturer’s line of these types of metering pumps have been used extensively in the produce disinfection market where washdowns, condensation from low temperatures and perpetually
wet surfaces exist.
In this specific example, these pumps also can be used in many environments and processes where water intrusion, flooding or washdowns occur.
IP 67 Pump Benefits
Chemical metering pumps are the workhorse in produce applications because all produce must be disinfected to remove or kill disease-causing pathogens. The process typically requires an oxidizing disinfectant such as chlorine, chlorine dioxide or peracetic acid to be pumped into the water that comes into contact with the produce.
The residual oxidant must be maintained during the process for the required contact time to ensure that the microorganisms are killed and cannot reproduce. This usually requires an accurate, reliable and waterproof chemical metering pump in conjunction with a controller and an appropriate chemical sensor.
The produce disinfection process places pressure on chemical pumps because of the constantly wet environment. Several tools and accessories can protect these pumps, but they often pose their own challenges. Pump covers, for example, can make the pump difficult to access for adjustment or servicing. Pump boxes also make pump adjustments difficult, and they can contain heat, which may cause a heat overload or failure.
The pumps can be moved to a dry location, but this makes it difficult to monitor the performance and make adjustments. The pump also may require lengthy runs of tubing, which can cause loss of prime and chemical feed.
One of the simplest solutions to this challenge is an IP 67-rated chemical metering pump. Manufacturing a pump to this specification is not an easy task, but some technology can meet the challenge. One company’s pump that has been in the produce processing market for more than six years has a complete gasket surrounding the cover, which mates with the faceplate to create a waterproof seal.
With this equipment, the glands used for wiring the pump are waterproof when used as described in the manual. In addition, the cabling used for control must have a tight fit to ensure it stays waterproof. If the cable diameter does not have a snug fit, water can seep into the drive.
The bolts on the cover plates also must be tight and in the correct position. It is advisable to tighten them diagonally to ensure that the seal has equal pressure on all sides.
All pumps must be secured, preferably to a bracket or a shelf. If a pump is placed on top of a chemical tank, it may be dislodged during washdown or when the tank is moved. This is probably the second leading cause of pump failures in food and beverage plants.
Other Pump Considerations
There are other important installation points users must consider to ensure that these pumps work as specified.
When pumping an oxidant that off-gasses, it is important to install an auto-degassing valve. This valve purges gases from the pump head through a low-pressure line so that the pump does not lose prime because of a vapor lock. The purge line returns to the chemical tank. Vapor lock occurs because gas is compressible and liquid is not.
When the pump is unable to purge the gas, the gas in the head is continually compressed and decompressed, so no liquid moves through the lines. It is always advisable to have the shortest suction line possible, so gas cannot accumulate. This will reduce the time required for the pump to purge the gas from the tubing, which will help keep the chemical residual consistent.