Dosing systems

Simplifying Your Dosing System

A dosing system is one that consists of one or more positive displacement pump(s) that transport extremely precise flow rates of a chemical or other substance into a flow of water, gas or stream. The dosing system is usually automated to allow industries that handle substantial amounts of fluid to perform certain functions – such as water treatment, agriculture, pharmaceutical, food processing and mining. In wastewater treatment, chlorine dosing pumps inject chlorine into the water to cause a chemical reaction. This either kills pathogens in the water or brings pH to a specified range.

Dosing systems can also treat effluent. Dosing pumps transport flocculants that separate solids from liquids, or inject chemicals into foul water, sewage, or slurries so that industrial effluent can return to the natural water course. Dosing systems are also used to prepare glue or additives for the paper industry or to treat corrosion in high-temperature and pressure boilers and smelter feeds.

Types of dosing systems:

There are several dosing pumps that are commonly used in dosing systems. These positive displacement pumps include metering pumps such as diaphragm, peristaltic and magnetic drive (gear or vane) pumps.

Diaphragm pumps

Compatible with most chemical dosing systems, diaphragm pumps are the most common pump used in the metering industry. A reciprocating diaphragm compresses and decompresses the liquid chamber, while check valves on the suction or discharge force the liquid to flow in the chosen direction. The metered flow rate is proportional to the displacement of the liquid chamber multiplied by the number of strokes per minute: precise flow proportional to the stroke speed of the diaphragm.

While relatively low cost, the diaphragm pump can have some disadvantages:

  • The pulsation of the diaphragm pump can cause damage to pipes or the dosing system, especially with larger pumps
  • The pulsing flow can also be difficult to measure with flow meters
  •  There may be a long time between chemical doses at low flow rates

Peristaltic pumps

Highly accurate and easy to use, peristaltic pumps are commonly used in dosing systems. Here, a hose or tube is contained in a “C” channel and compressed by a two or three roller rotor that traps liquid between rollers and forces it towards the discharge. The metered flow is proportional to the rotational speed of the rotor.

Peristaltic pumps have several advantages – they can run dry and are excellent for chemicals that naturally off-gas. Because they don’t have check valves, they don’t clog, making them well-suited to handling liquids that contain solids (slurries). They also have excellent suction capability.

Some of the disadvantages of peristaltic pumps include:

  • Mechanical wear on the hose results in frequent maintenance
  • If the hose breaks, the leaking chemical can cause damage and is dangerous to personnel
  •  Hoses are limited to elastomeric compounds, which limits chemical compatibility

Magnetic-Drive Gear Pump

A rotary, positive displacement pump, gear pumps create flow using two meshed gears housed in the pump’s body cavity. Liquid is trapped in the gear teeth as they rotate away from each other at the suction and is forced out the discharge when the gear teeth mesh on the discharge side. The metered flow is proportional to the volume of the gear tooth gaps times the number of revolutions per minute.

These pumps are exceptionally precise with very little pulsation and are constructed from a wide range of materials. Their design is also 100% leak free.

The main disadvantage with a magnetic drive pump is that it cannot be used to pump solids, making it unsuitable for many dosing systems.

Magnetic-Drive Vane Pump

Another rotary, positive displacement pump, vane pumps use an eccentric rotor with embedded carbon-graphite vanes. Liquid is trapped between the vanes in the open section of the cavity as they rotate away from suction and is forced out the discharge when the vane cavity is compressed on the discharge side. The metered flow is proportional to the volume between the vanes times the number of revolutions per minute.

Like magnetic drive gear pumps, vane pumps are very precise, with virtually zero pulsation and are constructed in a wide range of materials in a leak-proof design. In addition, they can handle very low NPSHa.

Again, they can’t pump solids, making them unsuitable for dosing systems in wastewater treatment and other similar industries.

What type of pump to use in your dosing system – our recommendations

Unsure what type of pump to use? Here are our recommendations based on your metering requirements:

1. Less than 200 LPH metering:

  • Diaphragm
  • Peristaltic

2. Greater than 200 LPH metering:

  • Mag-Drive gear
  • Mag-drive vane

3. Systems requiring flow measurement:

  •  Mag-Drive gear
    Mag-drive vane

4. System with large turndowns:

  • Peristaltic
  • Mag-drive gear

5. Liquids containing solids:

  • Peristaltic
  • Diaphragm

Simplifying your dosing system with the DICE module

One of the industrial dosing systems in our product range is the DICE module.We believe that the module allows for your dosing system to be more precise than ever before. With its reduced connections and block-type design, it overcomes many piping design problems in the system, which can affect operations. Due to the machined fabrication of the DICE module, we believe the results are better than any other chemical dosing system.

With the DICE module, you can have one dosing module for up to three pumps. The module is so simple to use that any issue can be quickly diagnosed, and replacements made by the operators, which minimizes downtime. The module also allows for the calibration of pumps to correct suction head and discharge pressure.

If you’d like to find out more about the dosing systems we recommend and how they can be retrofitted or installed, call our toll-free number at 1-800- 367-4180 (toll-free) for more information. As your industrial pumps’ supplier in Canada, we’re here to help you choose, install, maintain, and monitor a variety of equipment. And to answer questions about things you’ve previously tried gone wrong.