How Metering and Dosing Pumps Work During Clean-in-place

In addition to maintaining hygienic standards essential to processing, CIP is key to operational safety. Metering and dosing pumps automatically add chemicals to a CIP system to ensure accuracy and prevent employee exposure to potentially dangerous chemicals. In this post, we explain a variety of pump designs for chemical addition during CIP and how they transfer caustics, acids, sanitizer/disinfectants, and sterilizers to meet requirements for effective, repeatable clean-in-place cycles.

Air-operated double-diaphragm (AODD) pumps

Diaphragm pumps are relatively simple devices that use elastic chambers and rods to produce a pumping action. A valve located between two elastic chambers alternately pressurizes and vents the chambers to transfer chemicals.

Saniflo™ Hygienic HS and FDA double-diaphragm pump
Saniflo™ Hygienic HS and FDA double-diaphragm pump.
Almatec Biocor air-operated double-diaphragm pump
Almatec Biocor air-operated double-diaphragm pump

AODD pumps handle a variety of feeds including abrasive and shear sensitive fluids. They are limited to low pressure applications. If the processing environment does not permit electrical equipment, as in explosive-chemical applications, air operated double diaphragm pumps may be the best solution.

Diaphragm pumps are also excellent for metering applications where highly accurate volume control is critical. For this reason, they are commonly used in high-purity processing for dosing, coating and filling operations, chromatography, fluid injection, and aseptic transfer of proteins, cells and other materials.

Some air-operated double-diaphragm pumps for sterile applications within the pharmaceutical, biotech, and food industries are sterile by design and have no horizontal areas. The aseptic pumps are EHEDG certified and in compliance with FDA, USP Class VI, and ATEX standards.

Operators drain such diaphragm pumps by magnetically lifting valve balls from the outside. The pump has no drives, no rotating parts, and no shaft seals within the fluid. This specialized design—with the integrated cleaning system—have clean-in-place (CIP) and sterilization-in-place (SIP) capabilities.

Double diaphragm pumps have two side housings with a center housing between them. Side housings contain product chambers separated by a diaphragm that moves back and forth. Compressed air moves the diaphragm, displacing liquid from one chamber through a discharge port while drawing fluid into the second chamber.

AODD pumps are reliable because they have few moving parts and their chamber volume is large enough to sustain flow-through and prevent clogging.

Peristaltic pumps

Used for dosing and metering of CIP chemicals, peristaltic pumps use a flexible tube and pinching rollers to draw chemicals into an inlet and push chemicals out of an outlet to add or dose accurate volumes of CIP chemicals.

By design, nothing but the pump tube comes in contact with the fluid, eliminating the risk of cross-contamination. Also, the complete closure of the tube between the track and roller when it is squeezed gives the pump a positive displacement action, which prevents backflow and eliminates the need for check valves when the pump is not running.

Without seals, valves, or moving parts in the path of the fluid, peristaltic pumps are ideal for use in hygienic environments. To ensure product quality is never compromised, the fluid is pumped very gently and with extremely low shear forces. Additional benefits include low maintenance requirements and rapid product changeovers.

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Chemical Basics

Below are some common CIP chemicals and general guidelines for their use. Given the many variables that go into selecting the right chemicals and pumps for each CIP application, contacting your CIP engineering partner is a good practice.

The right chemical cleaning agents in the right concentrations make a significant difference in the efficiency of your CIP system. When used properly, CIP cleaning agents

  • Reduce surface tension of water, making it easier for the cleaning solution to penetrate soil
  • Break down bonding forces between soil and surface
  • Soften fats so they can be rinsed away
  • Dissolve soils for easier cleaning
  • Emulsify water-soluble soil in the cleaning solution for easier transport

Without chemical additives, most CIP systems still achieve a reasonable level of cleanliness and safety, but time, action, and temperatures required to do it increase.


Also known as caustic soda, sodium hydroxide or NaOH. This is an alkali with a very high pH that is typically used in a concentration range of 0.5-2.0%. Concentrations as high as 4% may be used for highly soiled surfaces.

  • Typically used as the main detergent in most CIP wash cycles
  • Softens fats, making them easier to remove
  • Non-foaming formulation can help reduce pump cavitation and increase efficiency



Nitric acid is the most commonly used wash for scale removal and pH stabilization after a caustic wash. At a typical concentration of 0.5%, it can be used effectively at lower temperatures than caustic solutions, requiring less heating.

Phosphoric acid is sometimes used but is somewhat less common.

  • Used by dairies regularly to remove milk scale or “milk stone”
  • Excellent for brightening up discolored stainless steel by removing calcified mineral stains
  • Must be used with caution because they can attack some elastomers in the system like gaskets or valve seats causing premature degradation or failure
Tip: Acid wash should not precede a caustic wash when removing milk deposits as acid could cause protein precipitation thus making the deposits more difficult to remove


The job of a sanitizer, also referred to as a disinfectant, is to reduce microorganisms to a level where they don’t pose a risk to food safety or public health.

For many years various hypochlorite solutions (potassium, sodium or calcium), also known as “hypo,” have been used as sanitizers in many CIP cycles.

Their active ingredient is chlorine (bleach) so they

  • Are relatively inexpensive to use
  • Are very effective as a sanitizing rinse for soils that are prone to bacterial growth such as dairy products
  • Can be very harmful to stainless steel, causing staining, corrosion and pitting
  • Can cause some significant environmental problems when dissolved in wastewater streams by killing vital microorganisms in streams and waterways

Chlorine dioxide has been used as an alternative to hypochlorite solutions in cleaning applications with high organic loads such as poultry or fruit processing. It has much more oxidizing power than bleach but is less corrosive to equipment and is less harmful to the environment.

In recent years more sanitation managers have turned away from bleach-based sanitizers in favor of peracetic acid (PAA). A combination of hydrogen peroxide and acetic acid, it is a strong disinfectant even at low temperatures and rinses away well leaving little or no chlorine residue to corrode stainless steel. It is effective against spoilage organisms, pathogens and bacterial spores. It has also proven to be more eco-friendly in the wastewater stream. Peracetic acid has a strong, pungent odor so it should only be used in well-ventilated areas.

Care should always be taken to rinse all sanitizers thoroughly from the system to reduce the risk of corroding stainless steel and potentially forming poisonous chlorine gas if mixed with acid. It should also be noted that it is possible to sanitize a system without using any chemicals at all by applying either hot water (approx. 195 - 205° F for 15-20 minutes) or low pressure steam. Both of these non-chemical options, typically seen in biopharm applications, would require a significant increase in energy costs.


Sterilizing a system means completely eliminating all living microorganisms. Sterilization can be done using chemicals but it is usually done with high pressure steam (approx. 250° F for 30 minutes).

While food, dairy and beverage processing plants seldom require sterilization in their CIP process, it is a common cleaning operation for pharmaceutical or extended shelf life (ESL) products.


Bonus Tips When Using Chemicals

1. Elevating the temperature of a cleaning solution increases its soil removal efficiency. The additional energy required to heat the solution adds cost to the process, but hot molecules with high kinetic energy dislodge soil faster than the slow-moving molecules in a cold solution.
2. A concentrated cleaning solution cleans a dirty surface better than a dilute solution. More chemicals mean more money, but the increased surface-binding capacity of a higher concentration cleans better and faster.
3. Longer periods of detergent contact exposure clean better than shorter periods of exposure. More time spent cleaning means less time making profitable product, but over time the chemicals dissolve hard soils from the surface.
4. Chemical solutions can lose their strength over time. Check the concentration of your wash solutions daily and adjust or replace them as needed.

Recovery and re-use

Environmental impact issues and chemical costs in the 1960s and 1970s drove the move to CIP systems that could re-use caustic and acid solutions. In situations where there is light to moderate soiling, the wash solutions can be returned to their appropriate CIP tank and be re-used for subsequent cycles. The number of cleaning cycles that wash solutions can be re-used for will vary depending on the amount of soiling and the chemical concentration, but re-using some solutions for dozens of washes is not uncommon.

For heavy soiling applications it isn’t practical to re-use the wash solution so it is typically sent to drain after a single use. A single-use system should always be used if your cleaning protocols demand that absolutely no cross-contamination occurs between batches.

In many systems, it is common for the final rinse water to be recovered and reused as the pre-rinse solution for the next cleaning cycle. The residual heat and chemicals it retains from the final rinse will help make the following pre-rinse more effective and economical. However, the solution from the sanitizing rinse cycle should never be re-circulated under any circumstances. Sanitizers reduce bacterial growth but don’t completely kill all pathogens in the system so, since it is the last step in the cleaning process, re-circulating the sanitizing solution could run the risk of spreading any leftover contamination that might be present. Sanitizers can also be sensitive to high temperatures and can lose their effectiveness fairly rapidly once they are in solution.

Clean-in-place Buying Guide

This Buying Guide for Clean-in-Place Solutions is a comprehensive resource for anyone who designs, owns, or operates processing systems and wants information about all aspects of CIP Systems.

Clean-in-place Buying Guide

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Central States Industrial Equipment (CSI) is a leader in distribution of hygienic pipe, valves, fittings, pumps, heat exchangers, and MRO supplies for hygienic industrial processors, with four distribution facilities across the U.S. CSI also provides detail design and execution for hygienic process systems in the food, dairy, beverage, pharmaceutical, biotechnology, and personal care industries. Specializing in process piping, system start-ups, and cleaning systems, CSI leverages technology, intellectual property, and industry expertise to deliver solutions to processing problems. More information can be found at