Dosing Pumps/ Positvie Displacement Pump for industrial use

 Dosing pumps are positive displacement pumps. They generate constant flow rates irrespective of the head of the system. They are mainly used for chemical dosing in different process industries like food industries, water treatment industries, chemical industries etc. we can even change the flow rate using the potentiometer knob provided on it and set it to certain flow rate of the fluid to be dosed.

Dosing pumps are made using different configurations of internal mechanism and each has its pros and cons. These are the following configurations of the dosing pumps.

1. Reciprocating dosing pump/metering pump 

This pump uses a piston or plunger that moves back and forth (reciprocates) within a cylinder. It is a classic example of a positive displacement pump where the movement of the piston creates a vacuum to draw liquid in through the suction valve and then pushes it out through the discharge valve at high pressure.

Features:

• High Pressure Capability: Reciprocating pumps are the best choice when the system head or discharge pressure is very high. They can maintain a constant flow even against significant backpressure.
• Extreme Accuracy: These pumps offer high volumetric efficiency. Because the piston displacement is constant, they provide very precise metering, making them ideal for high-precision chemical injection.
• Durability with Non-Corrosive Fluids: When used with lubricating and clean liquids, the piston and cylinder arrangement has a very long service life.
• Adjustable Stroke: The flow rate is typically adjusted by changing the stroke length of the piston using a micrometre dial or a control knob, allowing for fine-tuning of the dose.
• Pulsating Flow: A characteristic of this pump is its pulsating discharge. In many industrial setups, a pulsation dampener is installed at the outlet to smooth the flow and protect the downstream piping.
• Seal Maintenance: Since the piston slides against a seal or packing, these parts require periodic inspection and replacement to prevent leakage of the chemical being dosed.

2. Diaphragm pump 

A diaphragm pump uses air for suction and pushes the liquid through it. It uses a combination of the reciprocating action of a rubber, thermoplastic or Teflon diaphragm and suitable valves on either side of the diaphragm. 

                                                                images from Wikipedia

Features:

• Leak-Proof Operation: Since the diaphragm acts as a static seal between the internal drive and the fluid, there are no packing or mechanical seals to leak. This makes them the primary choice for handling hazardous, toxic, or corrosive chemicals.

• Superior Chemical Resistance: By choosing the right diaphragm material (like PTFE/Teflon), these pumps can handle highly aggressive acids and bases that would otherwise damage a piston-style pump.

• Ability to Handle Solids: Unlike reciprocating pumps with tight piston clearances, diaphragm pumps can often handle liquids with small particles or suspended solids without clogging the internal mechanism.

• Self-Priming: These pumps have excellent suction lift capabilities, meaning they can pull fluid from a tank located below the pump level without needing to be manually primed.

• Dry-Running Capability: If the chemical tank runs empty, the pump can continue to operate "dry" for a period without suffering immediate damage to the internal components.

• Variable Control: In motor-driven versions, the flow is adjusted by changing the stroke length or the motor speed, while in air-driven versions, the flow is controlled by adjusting the air inlet pressure.

. Peristaltic pump

This pump uses a flexible tube to push the liquid through it by the help of compression from rotary motion of the motor shaft. The motor shaft comes with a pressing roller at a certain radius, and they apply the compressive forces on the tube that make the liquid flow ahead. This pump has gots it's name from the biological mimic of the intestine of the human stomach, in which food movement is happens in a peristaltic fashion. 

                                                       Ref. Image from mmc webshop

Features:

• Liquid doesn't get contaminated with anything; it only flows through the tube and not through the pump body. This makes them suitable for applications where sterility is crucial, such as in the pharmaceutical, food and beverage, and medical industries (e.g., infusion systems, dialysis machines, and media preparation).

• It's less noisy compared to other pumps.

•  Precise Dosing and Flow Control: Peristaltic pumps deliver a fixed volume of fluid per rotation, allowing for high accuracy and repeatable results, which is essential for chemical dosing in water treatment, aquariums, and laboratory experiments.

• Versatility with Fluids: They can handle a wide range of fluids, including viscous liquids, abrasive slurries, and shear-sensitive materials, by selecting appropriate tubing materials (e.g., silicone, PharMed, Norprene).

• Self-Priming and Dry-Running Capability: These pumps are self-priming and can run dry without damage, simplifying operation and maintenance.

• Low Maintenance: With no valves, seals, or glands in the fluid path, the only maintenance typically required is the periodic replacement of the tubing

4. Solenoid pump 

   A solenoid pump (often called an electronic metering pump) uses an electromagnetic coil to move a diaphragm. When the solenoid is energised by an electric current, it pulls a plunger forward, which in turn pushes the diaphragm to discharge the fluid. A spring then returns the plunger to its original position for the next suction stroke.

solenoid dosing pump 

Features:

• Electronic Control: Unlike mechanical pumps, the stroke frequency is controlled electronically via a circuit board. This allows for extremely precise integration with external sensors (like pH or ORP controllers).

• Compact Design: These are generally smaller and have fewer moving parts than motor-driven pumps, making them ideal for space-constrained installations.

• Maintenance: Since the drive is electromagnetic rather than mechanical (no oil-filled gearbox), maintenance is primarily limited to the "liquid end" (diaphragm and valves).

• Suitability: Best suited for low-flow, high-pressure applications where high-frequency pulsing is acceptable.