Which Sanitary Pumps are Most Common in High-Purity Applications?
Sanitary pumps used in high-purity applications such as pharmaceutical processing and biotechnology typically require a level of design that is higher than in most other processing industries. The pumps not only need to transfer product efficiently, but they must also meet strict design and cleanability requirements mandated by the many organizations that establish standards for ultra-clean processing!
The first big question when selecting a pump is: ‘What type of pump do I need?’ To answer that, it helps to understand a little about pump design and consider the various pump styles that are available to fit your application.
In general, there are two main categories of pumps – kinetic and positive displacement.
Each of these categories is distinguished by the mechanics of how they transfer fluids. Pumps in both categories have advantages and disadvantages depending on your high-purity requirements, and both have the necessary hygienic features suitable for high-purity processing. This article will outline the following sanitary pumps for commonly used high-purity applications.
- Centrifugal
- Liquid Ring
- Rotary Lobe
- Diaphragm
- Peristaltic
- Eccentric Disc
Kinetic Pumps
Pumps of this type (also known as “dynamic” or “rotodynamic”) are designed to impart kinetic energy into the fluid to transfer it. They are characterized by the use of an impeller that spins at high speed to accelerate the fluid inside the pump casing. The energy imparted into the fluid by the impeller generates centrifugal force that creates pressure as the fluid pushes against the outer area of the casing.
This pressure is the force that discharges the product out of the pump’s discharge port and through the process lines.
Two types of kinetic pumps are common in high-purity processing:
Centrifugal Pumps
This style is by far the most common example of the kinetic pump design. In fact, the majority of all pumps currently being used in the processing industries are centrifugal.
Their dependability, hygienic design, and relatively low cost make them a popular choice for many high-purity applications.
Centrifugal pumps are typically the go-to choice for transferring lower viscosity fluids.
Since less viscous liquids are much easier to accelerate with kinetic energy, centrifugal pumps can transfer them more efficiently than other designs. They are capable of very high flow rates with consistent, non-pulsing flow and are available in multi-stage versions for applications that require extremely high output pressures.
However, not all products are a good fit for centrifugal pumps. The high-speed impeller creates a dynamic environment inside the pump casing, which may be harmful to some shear-sensitive fluids. And while some centrifugal pumps are capable of pumping fluids with viscosities as high as 1000 cPs, the efficiency of a centrifugal pump drops considerably once the fluid viscosity exceeds about 100 cPs.
Advantages
- Excellent for transfer of low-viscosity fluids
- Available with hygienic design and traceability options for high-purity applications
- Flow rate can be easily adjusted with a valve at the pump outlet
- Low purchase cost compared with many other pumps
- Simple, reliable design is easy and inexpensive to maintain
- Small dimensional footprint
- Steady, pulsation-free output
- Available in single-stage through multi-stage designs capable of a wide range of flow and pressure outputs
- Compatible with fluids containing some suspended particulates or small solids
Disadvantages
- Not recommended for viscous liquids
- Not recommended for fluids with large suspended solids
- Not recommended for shear-sensitive fluids
- Limited inlet suction (or “lift”). The inlet must be adequately flooded to meet the pump’s net positive suction head (NPSH) requirements to avoid cavitation
- Turbulence in the casing can cause surface corrosion (rouging) on the casing’s internal surface with some fluids
- Flow rate is impacted by changes in head pressure
- Dynamic action of the impeller tends to entrain air into product
Liquid Ring Pumps
A liquid ring kinetic pump usually plays a very specific role in processing applications. It is designed to pump fluids with entrained air or gases without losing its prime – something that a standard centrifugal pump has difficulty doing.
This design feature makes the liquid ring pump an excellent choice as a clean-in-place (CIP) return pump in high-purity processing applications.
While liquid ring pumps made by most top-quality manufacturers are 3A compliant with hygienic options, they may not be sufficiently hygienic for product contact in high-purity applications.
Advantages
- Highly effective as a CIP return pump
- Excellent for pumping fluids containing air or gases
- Capable of superior suction lift
- Self-priming once the casing is half-filled
- Minimal maintenance required
Disadvantages
- Not recommended for high viscosity fluids
- Typically not available with high-purity options for product handling applications
- Low capacity output compared to other standard centrifugal pumps
Positive Displacement (PD) Pumps
Members of this pump category transfer fluid by capturing and moving specific volumes of fluid from the pump inlet to the pump outlet through the use of rotational mechanical force. Unlike kinetic pumps that accelerate fluid to generate flow and pressure, PD pumps transfer product by physically forcing fluid through the pump outlet.
Several different designs of PD pumps are suitable for high-purity applications. Diaphragm or piston pumps use a reciprocating motion to transfer fluids and others; lobe or peristaltic pumps use a rotary motion to do the job.
Regardless of the design, positive displacement pumps all share some common characteristics. They all are very effective at pumping high viscosity fluids, some as high as 1 million cPs.
They are also known for their energy efficiency, gentle product handling, and the ability to maintain consistent flow rates in spite of fluctuating head pressures.
Rotary Lobe Pump
Rotary lobe pumps have two parallel shafts that drive lobed rotors. As the shafts rotate in opposite directions, the lobes on the rotors alternately mesh and un-mesh with each other, repeatedly creating then collapsing cavities to capture the fluid. Near the pump inlet the lobes un-mesh, creating a low-pressure cavity that helps to pull fluid into the pump casing. The fluid becomes trapped between lobes and is carried around the pump casing to the discharge port. As the lobes mesh back together near the outlet, the fluid cavity is compressed, creating high pressure and forcing the fluid through the outlet.
A common choice for pharmaceutical and biotech applications, rotary lobe pumps are readily available with hygienic options that make them a good fit for high-purity processing.
Although predominantly used for transferring high viscosity fluids, rotary lobe pumps are also very effective for transferring less viscous fluids in low-pressure applications. Because of their design, rotary lobe pumps are generally unaffected by system pressures, so they generate a constant flow regardless of changes in the process head pressure. And since they discharge a specific amount of fluid per revolution, their output is easily controlled by varying the pump speed, typically with a variable frequency drive (VFD).
Advantages
- Ideal for high viscosity fluids
- Can be used as a metering pump due to its accurate, consistent output
- Gently handles shear-sensitive fluids and fluids containing soft or fragile solids
- Available with hygienic design and traceability options for high-purity applications
- Flow output is unaffected by changes in head pressure
- Reversible direction of flow
- Output can be controlled by varying drive speed
- Good suction lift capacity and can be self-priming if wetted
Disadvantages
- Low viscosity fluids can “slip” at high output pressures, reducing efficiency
- Typically driven with motor/gear reducer unit creating a large footprint
- Cannot be shut off without recirculation
- Moderate flow and pressure pulsation
- Requires maintenance of two mechanical seals
- Some rotor styles may contact the casing causing particulate shedding
- Initial cost is typically higher than centrifugals
Diaphragm Pump
Air operated diaphragm (AOD) or double-diaphragm (AODD) pumps (sometimes referred to as “membrane” pumps) are powered by compressed air rather than electric motors or drives. They repeatedly compress and decompress flexible diaphragms to pull fluid into the pump chamber then push it out. Check valves control the flow of fluid in and out of the pump chambers during each stroke. Diaphragms separate the pump drive components from the wetted area, so they don’t have a mechanical seal, which makes maintenance more straightforward and provides superior cleanability. It can also run dry for extended periods without damaging the pump.
Diaphragm pumps are 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.
One characteristic common to diaphragm pumps is significant pulsation. While pulsation-dampening devices are available for reducing or eliminating unwanted pulsation, consider the use of an AODD carefully to be sure they meet the cleanability requirements of your high-purity application.
Air-operated diaphragm pumps, also known as “multiple-use” pumps, can be cleaned-in-place (CIP) or steamed-in-place (SIP) and reused many times. Single-use versions have pump chambers designed for just one process or batch. With single-use pumps, the pump chamber is removed and discarded after each process and replaced with a new chamber.
Chamber replacement can save time and money by avoiding some cleaning and validation procedures, and it eliminates the risk of cross-contamination between batches or products. If products are changed frequently and require quick changeovers, single-use AODDs may be a wise choice.
Advantages
- Excellent for high viscosity fluids, large suspended solids or high suspended solids content
- Well suited for hazardous environments due to the air-powered, intrinsically safe design
- Common choice for areas where electricity is unavailable or not allowed
- Available in a wide variety of metal and non-metal materials
- Pumps can run dry for extended periods without damaging the pump
- Self-priming
Disadvantages
- Significant flow and pressure pulsation
- Not recommended for high-pressure applications; Fluid output pressure is limited to the air pressure available to drive the pump, typically around 120 psi maximum
- Low maximum flow capabilities compared to other pumps
- Vibration and air venting can create a significant amount of noise
Peristaltic Pump
In a peristaltic pump (sometimes referred to as a roller pump, hose pump or tube pump), the fluid is contained inside a flexible tube or hose that is curled around the inside circumference of a circular casing. The ends of the tube are connected to the inlet and outlet of the pump. A single rotor with two or more lobes is mounted in the center of the casing and rotates within the casing.
Rollers mounted on the tips of the lobes compress the tube at pinch points, capturing a very accurately controlled volume of fluid in the tube between the pinch points. As the rotor turns, the rollers alternately squeeze the tube to force the fluid out then release the tube to allow it to expand, drawing in fluid through the inlet.
Peristaltic pumps are a good choice for transferring sterile fluids in low-flow, low-pressure applications.
They easily transfer viscous liquids and thick slurries, and they are well-known for gentle handling of shear-sensitive fluids such as cell suspensions. They are extremely accurate and can be run continuously or indexed with partial rotations to deliver smaller volumes of product.
Their design is well-suited to the ultra-clean demands of pharmaceutical and biotechnology processing. Depending on your needs, the tube inside the casing can be “multi-use” or “single-use.” In multi-use applications, the tube can be thoroughly cleaned and sterilized between runs and re-used many times. In single-use strategies, the tube is disposed of after each process, and a new tube assembly is used for each batch. This prevents any possibility of cross-contamination and simplifies cleaning, maintenance, and validation procedures.
Advantages
- Gentle handling of shear-sensitive fluids
- Excellent for viscous and aggressive fluids
- Tubes can be easily cleaned and sanitized for multi-use
- Single-use of tubing eliminates contamination concerns
- Requires limited maintenance
- Design prevents backflow and siphoning without using valves
- Accurately controllable flow. Ideal for metering applications
Disadvantages
- Limited maximum flow rate compared with many other pumps
- Tubing will degrade or wear over time requiring periodic replacement
- Moderate pulsation, particularly with high viscosity fluids at low rotational speeds
- Effectiveness is limited by fluid viscosity
Eccentric Disc Pump
The eccentric disc pump uses a unique pumping design that can be very effective for low and high viscosity applications. Its pumping action is created by a disc which is mounted on an eccentric shaft inside a cylinder. As the shaft rotates, the offset disc creates chambers that alternately increase and decrease in size. As the chamber enlarges on the inlet side, product is drawn into the pump. As the chamber decreases in size on the outlet side, product is forced out of the pump.
This design has been used in Europe for many years and is gaining popularity in the U.S. because of its gentle product handling, leak-free design, and low maintenance. Eccentric disc pumps also feature a seal-free design, which eliminates leakage and reduces maintenance time.
Advantages
- Gentle product handling
- Low pulsation
- Seal-less, leak-free design, and less maintenance required
- Self-priming
- Excellent suction lift
- Cleanable by CIP or SIP
Disadvantages
- Low maximum flow rate compared to other PD pumps
- Low maximum output pressure compared to other PD pumps
- Cannot be used to pump water
Next Steps
Transfer your products safely from point A to point B with a pump solution from Central States Industrial (CSI).
CSI is known in the sanitary stainless steel business as a market leader in the specification, sizing, and supply of pumping technology for hygienic industry processes. As a master distributor and pump supercenter, we have many pumps in stock and ready to ship today!
ABOUT CSI
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 www.csidesigns.com.
A Guide to Choosing the Right Pump for Hygienic Applications
This guide is intended for engineers, production managers, or anyone concerned with proper pump selection for pharmaceutical, biotechnology, and other ultra-clean applications.