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Major Factors to Consider in Designing and Installing a Chemical Injection Skid System

5. List of major components and procurement planning

While the chemical pump is the central unit of this system, it cannot work effectively without correct accessories and components that make a wholesome functioning system. The basic requirement for a metering pump hook up is to have a calibration column and strainer before the pump and pressure gauge with isolator, pulsation dampener, back pressure valve, pressure relief valve and flow meter on the discharge as shown in the graphic below. Most people think they do not need some or many of these accessories. However they are important in their own rights. Calibration column is more than just a flow measuring device, it also shows the effectiveness or lack thereof of the check valves on the pump. If the meniscus on the calibration column drops steadily it shows good valves, if it bounces around it indicates the check valves are leaking. A strainer prevents debris from getting caught into the check valves which causes leakage when it is closed. The pressure gauge is the stethoscope for the system which shows the pressure and how it fluctuates with each stroke. The back pressure valve ensures that there is enough back pressure on the check valve to close regardless of the discharge conditions. Pulsation dampener will reduce the pressure fluctuations giving a more steady read out from the flowmeter.

Picture 1 - AquFlow Metering Pumps

Depending upon the size and scope the chemical tank should be taken into account. If the tank is just a day tank and hence small it is often mounted on the skid itself. If not t hen it is located close by and the pump located below the level of the chemical at the lowest level to allow for flooded suction for the pump which is ideal. Then we need to account for electrical controls. Very often there are flowmeters that give a signal to the controller which uses that to increase or decrease the pump capacity. This can be achieved by either increasing or decreasing the speed of the pump with a VFD or by using an Electronic Capacity Adjuster for the stroke of the pump. Sometimes all this controlled in done at a centralized controller such as SCADA located remotely. In that case all these signals and feedback need to be transmitted to that controller. See below example of a control system from AquFlow.

Picture 2 - AquFlow Metering Pumps

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