Understanding your Dosing Pump

Looking to understand how a Dosing Pump works, what they can be used for and the options available from Tapflo, keep reading below.

What is a Dosing Pump?

A Dosing Pump is a low flow, controllable, positive displacement pump that delivers a precise, repeatable and measured flow of a variety of fluids such as chemicals, additives, flavourings or medicines into mixing/batching or pumping systems. Positive Displacement Pumps are generally used for these types of applications as they provide a constant flow rate which is independent of the system pressure. The flow rate is directly proportional to the stroke length/speed of the reciprocating element in the pump e.g. the diaphragm or the rotational speed of the rotating element (the lobes, rollers or gears).

Most Dosing Pumps are also required to be self-priming so that they can draw the process fluid from bulk, storage or day tanks.

Dosing Pumps capacities are generally controlled either manually, digitally or through analogue signal feedback from fluid accessories on the system such as flow meters or sensors. They are also becoming more controlled by a signal from a central control system such as SCADA where operators can monitor and control their process systems from a central control room.

What Dosing Pumps do Tapflo offer?

Tapflo offer an enormous range of different pump types and variations thereof to satisfy almost any dosing or metering requirement. Below is a very brief summary of the pump types we offer for dosing or metering applications. To find out more about each one visit or product sections on the website or give us a call to chat through the options available to you. We are always here to help!

Peristaltic Pumps: ALH (high pressure up to 15 bar) and ALP (low pressure up to 4 bar) with flow rates from as low as 1 l/hr. Hose & insert materials can be catered to almost any application and even the pump casing can be supplied in numerous materials to ensure that even when the hose leaks the pump can be protected from corrosion by the pumped media. Hose leak detection can be provided upon request also.

Peristaltic Pump for dosing
Low Energy Air Pump

LEAP Air Operated Diaphragm Pumps: Provide consistent, low pulsating flow rates with high volumetric efficiency making them ideal for batching and metering applications. Available in HDPE/PTFE, Metal and Sanitary series of products they can be catered to almost any application.

We can also supply Precision Mag Drive Gear Pumps, Mechanically Sealed Lobe Pumps and Solenoid and Motor Driven Diaphragm or Piston Pumps with traditional electric motors or stepper motors – please enquire for more details.

Typical materials available for Tapflo’s range of Dosing and Metering Pumps are, but not limited to: PP, PVC, PE, PTFE, PVDF, Stainless Steel AISI 316L & Hastelloy C.

Tapflo can also supply bespoke or catalogue dosing skids and systems to allow for drop in solutions with limited on-site integrations and commissioning where time is of the essence.

A variety of accessories such as suction lances, injection nozzles, pulsation dampeners, back pressure & relief valves, tanks, control panels & controllers, probes, flow meters and filters can also be provided on request to make sourcing your dosing equipment easier. Why go to anyone else when Tapflo UK can provide flow solutions all in one place!

How does a Dosing Pump work? H2

Although all Dosing Pumps are Positive Displacement Pumps, they have various operating principles that are explained on the product pages. Below is a brief overview of how each of our main Dosing Pumps work:

LEAP Air Operated Diaphragm Pumps: Compressed Air is supplied to the pump, this drives the diaphragms inside the pump. Simultaneously a 24V DC signal is also supplied to the on-board solenoid system to energise the pump. Compressed air is supplied to the pump to drive the diaphragms inside the pump, the air pressure forces one diaphragm forwards which lifts the discharge ball check valve and seats the suction ball check valve to push the fluid towards the discharge port. Simultaneously, this action forces the other diaphragm back, which creates a vacuum drawing liquid into the pump whilst lifting the suction ball check valve and seating the discharge ball check valve. LEAP Diaphragm Pumps are effective and an excellent choice for Dosing and Metering applications as they provide a slow and consistent flow onto the process. Unlike traditional Diaphragm Pumps where pressure builds up behind the diaphragms to create an immediate and quick shifting of the diaphragms, creating a slug of fluid, LEAP technology slowly builds up the pressure behind the pump’s diaphragms and as the internal losses within this pump are much less than a standard AODD the diaphragms are constantly moving at a very slow rate therefore providing a consistent and measured dose. Accuracy of our LEAP technology in TC Diaphragm Pumps is directly related to the displacement per stroke as well as the speed at which the diaphragms are being moved. The flow range of the pump can be set across the 4-20 mA span of a digital pressure regulator to enable incredibly accurate control of the flow rate and pressure of the pump. Pulsed feedback from every stroke that the pump makes provides the operator with a live indication of pump performance.

Operating Principle of a Diaphragm Pump

How does a Diaphragm Pump work?

Peristaltic Pumps: A positive displacement force and near absolute vacuum is created in a Peristaltic Pump by rollers or shoes that are attached to a rotating wheel in the centre of the pump casing, sequentially compressing the hose fitted into the pump. The hose is the only part of the pump that comes into contact with the liquid which makes these types of pumps very easy and cheap to maintain. As the rollers or shoes place pressure on the hose, it pushes the liquid forwards towards the outlet, whilst also creating a continuous suction to draw liquid in through the inlet.

Accuracy on the ALH and ALP series of Peristaltic Pumps has been tested to be as accurate as +/- 0.5% of the rated flow of the pump. Revolution counters can be fitted to the pumps to also provide pulsed feedback for every revolution the wheel makes to enable operators to monitor pump performance.

Peristaltic Pump Operating Principle

How does a Peristaltic Pump work

Solenoid Driven Diaphragm Pumps:A powerful electromagnet, when energised by the motor attracts the solenoid plunger which is attached to the single working diaphragm within the pump head to create a reciprocating action. As the diaphragm moves forwards and backwards within the pump head the internal ball check valves are lifted and re-seated in the same way as an Air Operated Diaphragm Pump. These pumps are suitable and widely used when a variety of control and fluid accessories are required thanks to their ability to have in-built PLCs and controllers to vary the flow rate of the pump, receive signals from flow meters, probes or sensor or operated on timed batch control. Tapflo offers a wide variety of Solenoid Driven Diaphragm Pumps which can be supplied with varying levels of on-board controls and features to suit almost any application such as data logging, recipe saving, timer operation, error & fault indication. Accuracy can be as low as +/-0.5% and as high as 2% of the rated flow.

Motor Driven Diaphragm & Piston Pumps: Similar to the Solenoid Driven Diaphragm Pump, a single working diaphragm or piston is moved backwards and forwards within a pump head however these are attached to a shaft and crank mechanism within a gearbox attached to an electric motor. These are typically used for higher flow and pressure applications which cannot be satisfied by Solenoid Driven Diaphragm Pumps. However, unlike the aforementioned pump, adjusting the capacity, controlling and integrating Motor Driven Diaphragm & Piston Pumps is inherently more difficult as are not typically delivered with built on electrical controls. Tapflo can however deliver these types of pumps with specialised servo control devices, built-on controllers, interface modules and inverters or electronic or pneumatic actuators to realise effective control and integration of Motor Driven Diaphragm Pumps into a variety of processes.

Stepper Motor Driven Diaphragm Pumps: can also be provided which enable incredible high turn down ratios up to 1:1000, low pulsation and micro-processor control as well as a plethora of on-board features & inputs / outputs. These types of units allow operation at different suction and discharge strokes to provide constant flow rates and gentle, low pulsating dosing requirements. Slow modes can also be activated when pumping viscous media to reduce suction speed and avoid cavitation and inconsistent operation often experienced with traditional Solenoid or Motor Driven Diaphragm Pumps.

Dosing Pump Applications

Dosing Pumps can be used for a plethora of applications in almost every industry, below are some examples of where Tapflo’s range of Dosing Pumps can be used:

  • - Water Treatment Industries: Legionella Control, Disinfection, & pH Correction
  • - Leisure Industries: pH Correction & Dosing, Chlorine Dosing (Redox or Free Chlorine based) & PAC or Flocculant Dosing
  • - Industrial Process Industries: CIP (Clean in Place), Waste Water Treatment, Biocides (Such as Sodium Hypochlorite, Sodium Bromide & Isothiazalone), Corrosion - Inhibitors & Descalers for Cooling Towers, Pipework, Valve and Pump Systems
  • - Food, Beverage & Dairy Industries: CIP, Flavourings & Additives
  • - Poultry & Farming Industries: Transfer of a variety of chemicals, such as hydrogen peroxide, and additives into water supplies to ensure the welfare of livestock.
  • - Agricultural Industries: Irrigation, Chemigation & Fertigation utilising chemicals such as Nitric Acid
  • - Wash Down Applications: Pumping of various detergents & waxes in vehicle wash applications for example.

What can our Dosing Pumps offer you?

  • - High dosing accuracy across a high range of flow rates
  • - Pulsed, low Pulse or Pulseless Flow
  • - High Discharge Pressures
  • - Easy operation
  • - Robust and reliable product
  • - Long service life of wear parts
  • - Low maintenance and operational costs
  • - Low energy consumption
  • - Dry running
  • - High suction lift
  • - Solids passage
  • - Leakage free
  • - Feedback and easy system integration
  • - Customisation to specific applications
  • - Various on-board controls and features to make your life easier

How do I avoid cavitation, overloading or excessive delivery from my Dosing pump?

To avoid cavitation of Dosing Pumps you need to consider the following factors:

  • - Avoid installations with high suction lifts – Pumps have been named accordingly because that is what they do, they are not suckers! Max suction lift capabilities vary according to pump type which needs to be considered when assessing the installation of the pump. As a general rule of thumb for most solenoid and motor driven diaphragm dosing pumps suction heights should be kept to a maximum of 1.5 m. This can be higher when using pumps such as Peristaltic or LEAP Air Operated Diaphragm Pumps for dosing.
  • - Increase the suction pipe ø to reduce the velocity through the suction line. The recommended maximum fluid velocity for fluids up to 100 cPs on solenoid & motor driven Diaphragm Pumps is ~0.7 m/s. For fluids over 100 cPs ensure that the pipe lengths are as short as possible with minimal bends and sized to be the same as the pump connections. Below is a table giving a rough guide to recommended nominal pipe øs vs maximum flow rates:
Maximum Flow Rate (l/hr)Recommended Nominal Pipe ø (mm)
<156
15-3010
30-12516
125-15520
155-26025
260-50032
>50040
  • - Velocity of the fluid through the suction pipework can also be reduced by slowing the stoke or operating speed of the pump.
  • - Improve the suction conditions of the pump system – utilise a configuration whereby the pump is ideally situated below the fluid level wherever possible. If the pump needs to be located above the fluid source then keep the suction pipework within the recommended nominal ø, utilise as few bends (swept rather than straight) and fluid accessories as possible and also ensure total suction lengths do not exceed the maximum for the pumps rated max suction lift.

In order to avoid overloading or excessive delivery pressures you need to consider that all Positive Displacement Pumps, with the exception of the Air Driven Diaphragm Pump will deliver pressure onto the line up to the max available from the installed motor power. This can result in over pressurisation of pipework and accessories on the line which can have extremely adverse effects, especially when dosing aggressive chemicals.

It is highly recommended that a pressure relief valve is used to either relieve fluid back to the feed tank, back to the suction of the pump, in the form of a by-pass loop, or round the pump head, in the form of an integral relief valve.

If the product being pumped is solids laden or sticky which can cause issues with spring loaded pressure relief valves re-seating, then a dual action pressure switch is recommended which can start and stop the pump according to the pre-set values. This ensures that the pump is activated when required and stopped when faced with a “dead head” or over-pressurisation on the system.

When utilising an Air Operated Diaphragm Pump, if the system pressure rises higher than the air supply pressure then the pump will stall on the line and will only come back into action once the system pressure drops below that of the air supply pressure.

Tapflo can supply External Pressure Relief Valves and Sensors to assist in protecting your pumps and system from over-pressure. Talk to us to discuss your requirements as we are always more than happy to assist in recommending the best way to keep your system working healthily!

Cavitation

Cavitation is the formation of cavities in liquid, or bubbles, which is created by low pressure in the liquid. If these cavities collapse, they can send shockwaves through your pump which would cause damage and unnecessary downtime that can be avoided through simple steps.

Case Study

Tapflo were asked by one of our many trusted distributors to supply some Soap & Peroxide Metering Pumps for an industrial application. They were required to provide a suction lift of 4 m and a variable and accurate flow rate ranging from 30-124 l/hr and a discharge pressure of up to 4 bar. This type of application would cause problems for solenoid & motor driven diaphragm pumps however Tapflo were able to provide the following equipment which worked perfectly and provided the user with a number of intrinsic advantages.

Supplied equipment: 2 x ALP13 Low Pressure Peristaltic Pumps + IFM-IFC258 Revolution Counters with sensors and connectors.

Specification:

Rated Capacity: 30 - 124 l/hr

Displacement: 41- 42 ml/rev

Accuracy: +/-0.5%

Rated Speeds: 12 - 50 rpm

Rated Frequencies: 12 - 50 Hz

Max Discharge Pressure: 4 Bar

Max Suction Lift: 9 m

Max Solids Passage: 2.6 - 3.25 mm ø

Duty Class: Rated for Continuous Operation

Connections:DN15 ISO Flanges

Inserts: Stainless Steel AISI 316

Hose: EPDM, w/ Internal Reinforcements

Casing & Cover: Aluminium

Roller: Aluminium

Rollers: Nylatron

Frame: Electroplated Steel

Geared Motor: 0.25 kW / 4 Pole / 230-400V / 3 Ph / 50 Hz / IP55 / Class F / IE1 Efficiency Class / 3 x PTC Thermistors for Inverter Operation

Paint: Anti-Corrosion Coating, Green, Primary and Final Polyurethane. Acry-Epoxy, 150 microns thickness

Peristaltic Pump used as a Dosing Pump

Advantages of using a Peristaltic Pump as a Dosing Pump:

  • - Due to the near absolute vacuum created by the Peristaltic Pump technology they were easily able to overcome the 4 m suction lift requirement which would have starved traditional Dosing Pumps.
  • - The +/- 0.5% volumetric accuracy and low displacement value of 41-42 ml/revolution of the supplied Peristaltic Pumps ensured that the end user was more than happy with the performance and reduced wastage and over-filling.
  • - Thanks to the installed IFM-IFC258 Revolution Counter, the pumps were also easily integrated into the end users central control system for monitoring flow without the need for expensive flow meters. The counter can also be fitted with a 6 digit LED display with optional analogue and switching outputs to enable local readout of performance and control of other accessories on the line such as valves.
  • - As the hose is the only wear part in the pump the customer’s spares holding costs were kept to an absolute minimum and operators were incredibly happy with the ease and speed of maintenance. The hose for both units was also supplied as EPDM which also meant that the customer didn’t need to stock more than 1 material of hose!
  • - The motors were supplied suitable for inverter operation which allows the end user to accurately tweak the capacity of the pumps on the line.

If you require a Dosing Pump, get in contact with the Sales Team today using the chat in the bottom right hand corner of the screen.

Alternatively, you can call us on 023 8025 2325 or email [email protected]

 

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