4 Features to Consider When Selecting Your Chemical Metering Pump
Your selection of a chemical metering pump is critical because these pumps must function properly under harsh conditions, such as in municipal water treatment plants. Before sizing the pump, one must understand the application and its requirements, and then consider accessories that will be needed to make the system work. This article highlights some things to think about.
1. The liquid
The first consideration must be the nature of the liquid that will be passing through the meter. Here are some properties to consider:
Temperature – exceedingly hot or cold liquids may spoil pump components; you may need to install heating or cooling jackets to keep within acceptable ranges
Viscosity/specific gravity – viscous/heavy liquids must move slowly to prevent flow from stalling or cavitation. The supplier should recommend specialized 'liquid ends' which accommodate these properties
Off-gassing – chemicals like bleach may react with other components to cause bubbling, resulting in airlocks
Chemical composition – important to ensure pump components are not corroded
When deciding on size, capacity is described using discharge pressure and flow rate. Sizing is important because an over-sized metering pump will interfere with system pressure. The pump should be slightly higher than the maximum desired flow rate. This will give additional capacity in case the estimate was wrong. Similarly, minimum capacity should be slightly lower than minimum flow rate for system accuracy.
The location is considered in relation to the injection point/discharge line and the supply tank. Many positive displacement pumps function properly with positive or flooded suction heads. Insufficient suction line pressure is the leading cause of malfunction in such pumps. The supply tank shouldn't be very far from the pump, as distance causes pressure loss that will affect performance as well as meter accuracy. In addition, the pump should be close enough to the delivery line. Ambient climatic conditions of the location should also be considered in order to plan for proper protection of the pump.
The metering pump does not work on its own, but rather as part of a bigger system that injects controlled chemical amounts into a process to achieve a specific concentration. The pump can only function properly if other components have been selected to ensure efficiency of the entire system.
You can talk to your supplier to get the right accessories based on your application and pump size, but below are common accessories used in most systems:
Suction side – calibration column and strainer
Discharge side – pressure gauge (often overlooked, but very important. Should have an isolator), safety relief valve, back pressure valve, flow meters and pulsation dampener
It helps to get your pump and accessories from the same supplier, as they can also help you to install the system, choose matching accessories and even build custom systems perfectly suited for your application.