MORE TOPICS | Positive Displacement Pumps
CPP Design Then & Now
How seal engineering transformed the circumferential piston pump.
Layne Meyers | Ampco Pumps Company
| IMAGE 1: A circumferential piston pump manufactured in 1957 (left) and one manufactured in 2026 (right) (Images courtesy of Ampco Pumps Company)
At first glance, a circumferential piston pump (CPP) manufactured today looks remarkably similar to one produced 50 years ago. Walk into a dairy plant or meat-packaging facility, and you will find a heavy, precision-machined stainless-steel fluid head with two rotors that looks virtually unchanged. The operating principle of nongalling rotors rotating through annular-shaped cylinders to create pulse-free, high-viscosity fluid displacement has stood the test of time. It can preserve shear-sensitive products, maintain efficiency under high differential pressures and deliver durability in demanding processing environments.
Viewing these pumps as mechanical relics frozen in time ignores one of the most dynamic evolutions in fluid handling. While rotor geometries and casing profiles have remained largely unchanged, the true performance of the circumferential piston pump has undergone a quiet revolution at the pump shaft seal.
The Era of Simple, Cheap & Functional
Decades ago, processing standards were straightforward, product run-times were shorter and sanitation regulations were less rigorous. Sealing systems were built around three principles: simplicity, low cost and functionality.
- Braided packing and gland seals: Early pumps relied on compression packing wrapped around the rotating shaft within a stuffing box. These seals depended on controlled leakage to lubricate and cool the packing material. They were inexpensive and easy to tighten with a wrench, but they still required constant adjustment, which could introduce particulate contamination into the product and potentially waste a substantial amount of product.
- Single O-ring shaft seals: Then, in many cases, single O-ring seals replaced packing. O-rings were inexpensive to manufacture and easy to replace, but they often lacked flexibility under varying dynamic loads, could wear out rapidly under shaft deflection and offered minimal tolerance against abrasive fluids.
- Simple elastomer face seals: Early mechanical face seals relied on elastomer compounds and organic face materials. Adequate for low-pressure fluid transfer at ambient temperatures, these materials were vulnerable to increased temperatures, viscous or abrasive slurries and aggressive caustic cleaning cycles. This vulnerability led to swelling, hardening, wear and loss of performance.
Downtime was built into early schedules, maintenance teams dismantled pumps between shifts and clean-in-place (CIP) technology was in its infancy. As manufacturing moved toward continuous processing alongside stricter hygiene standards and higher uptime requirements, these early sealing systems became a potential limitation on pump performance and reliability.
| IMAGE 2: Seal technology 75 years ago was only offered in O-ring configuration (left). 25 years later, pumps were made “field-convertible,” and a new O-ring and mechanical seal configuration were available for the same basic pump (right).
Modern Operational Demands
In modern food, beverage, personal care and pharmaceutical production, a pump is only as reliable as its seal. Modern facilities operate under demanding conditions:
- Continuous CIP and steam-in-place (SIP): Equipment must withstand thermal shocks up to 356 F and resist aggressive washdown chemicals without requiring manual disassembly.
- Extended mean time between failures (MTBF): Plants no longer accept weekly or monthly seal replacements, mandating seals that run for thousands of continuous hours without dripping or degrading.
- Strict chemical compatibility and product integrity: From high-fat dairy creams and abrasive sugar syrups to active pharmaceutical ingredients (APIs) and solvent-heavy syrups, seal faces and elastomers must remain inert to prevent leaching, swelling or blistering.
The Engineering Pillars of Next-Generation CPP Seals
Pump engineers updated seal design into a multidisciplinary focus to meet modern industrial requirements. Modern circumferential piston pumps rely on several advancements in sealing design and material science.
Advanced Mechanical Seal Design
Single O-ring seals have evolved into front-loading single and double mechanical seal systems. Modern cartridge-style mechanical seals isolate the mechanical springs from the product zone, minimizing potential dead zones where bacteria, product residue or particulate could accumulate.
Front-loading designs allow technicians to access and replace the seal without disconnecting the pump from piping. Pumps remain piped and in line during service, reducing maintenance time from hours to minutes and minimizing downtime.
Material Science & Synthetic Face Materials
The materials used on seal contact faces have evolved. Silicon carbide (SiC) and tungsten carbide (TC) are now standard for abrasive or high-pressure applications. Silicon carbide provides extraordinary hardness and thermal conductivity, dissipating heat away from the seal faces even when pumping nonlubricating or high-viscosity fluids. Carbon-faced mating rings provide self-lubricating properties during dry-start conditions, preventing immediate catastrophic failure.
Specialized Elastomers
Where basic nitrile (NBR) and neoprene once were common, modern seal assemblies use engineered elastomers precisely matched to the target process fluid:
- Ethylene propylene diene monomer (EPDM) offers hot water, steam and caustic wash resistance. Ideal for dairy, brewing and standard CIP processing lines.
- Fluoroelastomer (FKM) provides oil, fat and solvent resistance at high temperatures. Ideal for edible oils, chocolate, high-fat sauces and cosmetics.
- Perfluoroelastomer (FFKM) delivers near-universal chemical inertness up to 572 F+. Ideal for aggressive pharmaceutical solvents and harsh chemicals.
- Polytetrafluoroethylene (PTFE)/encapsulated compounds feature zero leaching and an ultra-low friction coefficient. Ideal for aseptic fluid handling and sterile injection products.
Flushing & Barrier Systems for Aseptic & High-Solids Applications
For fluids that tend to crystallize (like high-fructose corn syrup) or burn onto hot surfaces (like chocolate), double mechanical seals with external flush media have expanded CPP capabilities. A low-pressure steam, water or compatible barrier fluid runs between the inner and outer seal faces. This barrier cools the faces, washes away microcrystallized particulates before they abrade the seal and creates a sterile barrier that prevents ambient air or microbes from entering aseptic processes.
Expanded Pump Capabilities
Because of seal advancements, circumferential piston pumps have expanded into processing applications that were previously impossible or cost-prohibitive:
- Automotive paints: Driven by environmental regulations, automotive paints shifted from solvent-based to waterborne formulations, making CPPs a common solution for paint kitchens. These pumps provide reliable performance despite viscosity changes while offering improved mechanical seal integrity. To handle abrasive mica and fine particulates that accelerate seal wear, pumps were equipped with improved ceramic seal faces and specialized suction-vent ports. This design aids paint circulation around the seal area to use the product itself as a flush medium, improving seal life and reliability.
- Pharmaceutical applications: Hygienic, front-loading mechanical seals incorporating specialized European Hygienic Engineering and Design Group (EHDGE) technology and 3-A Sanitary Standards enable CPPs to handle delicate biological serums with minimal mechanical stress. Gentle pumping action prevents excessive shear and compressive forces that could damage sensitive bacteria and microorganisms, preserving therapeutic properties.
- High-pressure viscous dosing: Enhanced mechanical seal face balancing prevents hydraulic pressure from forcing seal faces open. As a result, modern CPP pumps generate differential pressures upwards of 250-450 pounds per square inch (psi) on highly viscous doughs, peanut butters and polymers.
- Reduced total cost of ownership (TCO): Although modern ceramic and carbide seals carry a higher initial purchase price than primitive O-rings, they pay for themselves quickly through reduced batch loss, fewer emergency shutdowns and water and chemical savings during CIP cycles.
Looking Ahead
The fundamental design of the circumferential piston pump—a pair of nontouching, interlocking rotors sweeping smoothly through an engineered casing—proved so effective nearly three-quarters of a century ago that its core geometry remains largely untouched today. Yet, running a modern CPP side by side with its historical counterpart reveals two entirely different machines.
As processing plants shift toward digital monitoring, smart sensors embedded directly within seal flush lines will detect microchanges before failure occurs. Ongoing material science advancements in sealing technology will continue to unlock new performance levels, ensuring this classic fluid-handling design remains a trusted solution for the future.
Layne Meyers is PD pump product manager and remanufacturing operations lead for Ampco Pumps Company in Glendale, Wisconsin. For more information, visit ampcopumps.com.
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