How to install a metering pump correctly

The correct installation of a metering pump is essential to ensure optimal operation and to avoid potential problems or accidents. Below are some steps and tips for the proper installation of a metering pump.

Step 1:

Choosing the right type and model of metering pump

There are different types and models of dosing pumps, which are classified according to the operating principle, flow rate, pressure, type of liquid to be dosed, material of construction and control system. It is important to choose the type and model of dosing pump that best suits the needs and characteristics of the application. See our article How to choose a metering pump.

Some factors to consider when choosing a metering pump are:

The flow rate and pressure required for dosing.
Properties of the liquid to be dosed.
Pipe type, length, diameter, valves and fittings.
The type and level of control you wish to have over dosing (manual, automatic, proportional or programmable).

Step 2:

Preparing the site and materials for installation

Before installing the metering pump, it is necessary to prepare the site and the materials required for the installation.

Some recommendations are:

Choose a place that is safe, accessible and protected from adverse environmental conditions such as direct sun, rain, dust and vibrations.
Fix the metering pump on a solid and level base, which can support its weight and prevent it from moving or shifting.
Have a suitable power supply for the metering pump, which meets the voltage, frequency and power requirements. A switch or circuit breaker should also be provided to protect the dosing pump from possible overloads or short circuits.
Have the necessary pipes, hoses, valves and fittings available to connect the dosing pump to the system. These must be compatible with the type and model of dosing pump chosen and with the liquid to be dosed. They must also be clean and free of obstructions or leaks.
Have the necessary equipment and instruments to measure and regulate the dosing flow and pressure, such as pulse counters/emitters, rotameters, regulating valves and sensors.
Have the necessary equipment and instruments to verify the correct operation of the dosing pump and the system, such as multimeters, flow sensors, pH and conductivity meters.

Step 3:

Installation of the dosing pump

Once the site and installation materials have been prepared, the metering pump is connected to the system.

Metering pumps are generally self-priming, and there are a number of different types of pumps. two types of installation: in suction or on load. In general, it is advisable to install them under load (see illustration 1)The pump is positioned below the maximum height of the product to be dosed. In this way, greater dosing accuracy is achieved and vacuum operation is avoided. However, suction dosing is very common. (see illustration 2)For example, when the pump is installed directly above the canister or storage tank of the product to be dosed.

Illustration 1. Example of an installation under load

Illustration 2. Example of suction installation

Some tips are:

Suction pipe diameter (Illustration 3): It is of vital importance to choose the right suction line diameter in order to obtain a proper functioning of the dosing pump:

- An undersized diameter will prevent complete filling of the pump delivery chamber, as it will reduce the amount of liquid that the pump can draw in per unit of time. This may lead to phenomena such as cavitation, which could damage the pump.
- A larger than adequate diameter (in the case of a pump installed "on suction") may result in the pump not being able to lift the liquid column to the discharge chamber.

It is therefore recommended that the diameter of the suction pipe is the same as that of the suction valve of the dosing pump.

Suction pipe length: The suction line should be as short as possible. For "suction" installation, dosing pumps generally allow a maximum height of 1 m above the liquid level in the accumulation tank. This height could be extended up to 1.5 m for certain types of pumps, such as electromechanical diaphragm pumps with mechanical return (see Seko Kosmo dosing pump).

Illustration 3. Examples of correct installations

Suction filter (Illustration 3): In the event that the liquid to be dosed may contain particles in suspension, it is important to prevent these from reaching the pump, as they would end up accumulating in the suction and delivery valves (between the ball and the seat). This could lead to clogging of these valves, accelerated wear of their components and defective closing of the valves and, therefore, loss of efficiency of the metering pump. In these cases it is highly recommended to install a filter (foot or Y-strainer) in the suction line of the pump, always upstream of the suction valve.

As explained above, in this case it is also essential to choose a suitable filter size. Its diameter must be the same as that of the suction pipe. On the other hand, the filter mesh must be suitable for the flow rate of the dosing machine and the viscosity of the product to be dosed.

Dosing of viscous liquids: Some precautions must be taken when dosing viscous products:

If there is chemical compatibility, it is advisable to use a stainless steel dosing pump.
For products with a viscosity of more than 5,000 cp, suction and discharge valves with spring return must be installed. This ensures correct sealing of the balls against the seats.
For high viscosity products (above 2.000 cp) it is recommended that the suction pipe has the diameter immediately above the pump suction valve.

In the Illustration 4 some examples of correct installation for viscous liquids can be found.

Illustration 4. Example of correct installations for viscous products

Back pressure valve (Illustrations 1, 2 and 5)It often happens that the height of the product to be dosed in its respective accumulation tank is higher than that of the dosing point, which could cause the entire product to be displaced through the dosing pump by communicating vessels or siphons, even if the pump is not active, with potentially catastrophic consequences in the case of corrosive or toxic products. To avoid this, it is necessary to install a back pressure valve. As a minimum pressure is required to open the back pressure valve, the outflow of liquid through the siphon is prevented.

On the other hand, a back pressure valve allows for greater precision in the dosing of the product since, by dosing at a constant pressure, a constant flow rate is obtained in the pump (the flow rate varies with the working pressure: the higher the pressure, the lower the flow rate).

Illustration 5. Installation of back pressure valve when dosing below product level

Pulsation damping (Illustrations 1 and 2): metering pumps cause vibrations in the delivery line due to their pulsed operation, which shortens the service life of the piping due to material fatigue and can lead to pipe rupture. Likewise, pressure peaks can occur in the delivery line, which can shorten the life of the pump. Therefore, it is advisable to install a pulsation dampener in the delivery line. In this way, a much more linear flow would be achieved, greatly reducing both pulsations and pressure peaks.

Safety valve (Illustrations 1 and 2): In the event of a blockage in the delivery line of the dosing pump (a frequent case would be, for example, sodium hypochlorite, which has a tendency to crystallise and clog the injection fitting) it could happen that, as pressure builds up in the delivery pipe, it could break at its weakest point (or even break some element of the pump), causing splashes of product that could affect personnel or surrounding equipment. To avoid this, it is recommended that a safety valve be installed, which would open if the pressure in the delivery circuit rises above a certain value. If there is also a back pressure valve, the safety relief valve should be set at a higher pressure than the back pressure valve.

Thus, the steps to follow would be:

Follow the manufacturer's or supplier's instructions for making electrical and mechanical connections to the metering pump. Ensure that the connections are tight and watertight.
Connect the dosing pump to the tank or reservoir containing the liquid to be dosed. Place a foot valve (in suction installations) and the filter at the inlet of the dosing pump to prevent the entry of impurities.
Connect the dosing pump to the injection point of the system. Fit a non-return valve and an injector at the injection point to prevent the liquid from escaping.
Connect the dosing pump to the control system, if available. Fit the necessary sensors and actuators to control the dosing flow rate and pressure, as well as other parameters such as pH, conductivity and redox potential.
Check that all connections are correct and that there are no leaks or blockages.

Step 4:

Commissioning and adjustment of the metering pump

After connecting the metering pump to the system, it is started and adjusted. Some steps and tips are as follows:

Fill the tank or reservoir containing the liquid to be dosed with sufficient quantity to perform the test. Make sure that the liquid is suitable for the application and that it is clean and homogeneous.
Open the inlet and outlet valves of the dosing pump and the dosing circuit.
Switch on the dosing pump and check that it is working properly. Observe if there is any noise, vibration or abnormal heating. Check if there are any error or alarm lights or beeps.
Measure flow rate and dosing pressure with appropriate equipment and instruments. Adjust the flow rate and pressure to the required specifications for the application. Use regulating valves, injectors and control system to make necessary adjustments.
Measure other parameters of the dosed liquid, such as pH, conductivity or redox potential, with the appropriate equipment and instruments. Adjust these parameters according to the specifications required for the application. Use sensors, actuators and control system to make the necessary adjustments.
Check that the dosage is uniform, accurate and stable. Observe for any variations or fluctuations in flow rate, pressure or other parameters.

Step 5:

Regular maintenance of the metering pump

To ensure the proper functioning and durability of the metering pump, regular maintenance is necessary. See our article How to maintain a metering pump.