Even the simplest chemical dosing system consists of many components. When specifying, you need to be certain that each one is fully fit for purpose – with no weak links.
From the storage tank and metering pump to the pipework, valves and other accessories, every item has an important part to play. Along with the capabilities required to fulfil its role, it must have tolerance for the conditions it will face.
The following questions offer a starting point for specification.
What chemicals and what concentration?
All components in contact with the chemical should be made from compatible materials. In some cases, a material will be fine for dilute solutions of the chemical but not high concentrations.
A detailed assessment of each component’s compatibilities is vital. Even something as small as a valve’s internal parts, or the diaphragm in a pressure gauge, may become a point of failure if badly chosen.
If the system handles chemicals which release heat or vapours, its design and specification should be adapted accordingly. Physical challenges may include dealing with lumpy or viscous fluids, for which some pumps and fittings are better suited than others. Hot and cold ambient temperatures also require consideration.
What output volumes and system pressures?
The system and all its components – not least the pumps – will have to function efficiently across the output volume and system pressure range, and up to the maximum levels. This is a matter of choosing items of the right size, capacity and turn down ratio.
Where will components be operating?
If a metering pump is to be located above the storage tank, you will need a pump with higher suction capability – and the propensity of the chemical to form gas bubbles under suction needs checking. Materials in components exposed to sun, wind, rain or extreme temperatures should be specified for resistance to degradation.
Another factor related to location is whether skilled operators and engineers are close at hand. If not, simplicity and low maintenance are important considerations.
For many chemicals, safety is paramount – requiring appropriate spill protection, leak containment and sensing/alarm hardware.
Can your process tolerate interruption?
If the answer is no, you may have to build in back-up measures such as parallel chemical metering streams. Your process criticality is also a factor in selecting whether alarms or automatic pump changeover may be necessary.
