One of the reasons engineers specify AODD pumps for slurry and suspension duties is the ability to pass solid particles that would immediately block a centrifugal pump or damage a gear pump. But that capability has hard limits that vary by model size — and using a pump outside those limits doesn’t just reduce performance, it causes premature ball seat wear, diaphragm fatigue, and manifold damage.
The Actual Numbers from the Phoenix Technical Table
The Fluimac Phoenix specifications table gives maximum solid passing diameter for each model. These figures are determined by the internal geometry of the ball check valves and manifold passages — a particle larger than the rated size will wedge against a ball seat and prevent the valve from closing cleanly.
The specifications by model group are as follows:
P3–P7: 2mm maximum solid passing diameter
P18: 2.5mm
P30: 3mm
P50, P55, P60, P65: 3.5mm
P90, P100, P101, P120: 4mm
P160, P170, P171, P250, P252: 7.5mm
P400: 8mm
P700: 8.5mm
P1000: 12mm
The jump between the P120 and P160 is significant — 4mm to 7.5mm — because the larger models use physically bigger ball check valves with correspondingly larger clearances through the manifold.
What Happens When Particles Exceed the Rated Size
A particle that exceeds the maximum solid passing diameter doesn’t simply fail to pass through — it gets carried into the manifold by fluid momentum, then lodges between a ball and its seat at the end of a suction or delivery stroke. The ball can’t seal. Fluid flows back through the open check valve on the delivery side, or air enters the suction side, and pump output drops sharply.
This presents in exactly the same way as a worn or fouled ball seat — the pump runs but delivers less than its rated flow, or runs but doesn’t pump at all. If the root cause is particle size rather than seat condition, cleaning the seats won’t fix it. The problem returns immediately on the next cycle if the oversized solid is still in the fluid.
Particles at or just below the rated limit cause accelerated ball and seat wear. Every time a solid particle passes through the check valve, it contacts the sealing surfaces of both the ball and the seat. Abrasive media — sand, ceramic powders, mineral slurries — grind away those surfaces progressively. In abrasive service, ball and seat inspection intervals should be tightened relative to the standard maintenance schedule.
Specific Gravity and the Hidden Limit
Solid particle size is only part of the equation. The Phoenix manual specifies that operation with suspended products whose specific weight is higher than the liquid’s is forbidden as improper use. The given example is water with sand — a slurry where the solid phase is denser than the carrier fluid.
This isn’t a blanket prohibition on slurry pumping — AODD pumps are widely used for slurries in practice. It’s a warning that the specific gravity of the slurry as a whole must be within the pump’s rated parameters. Very dense suspended solids can overload the diaphragm during the suction stroke, causing premature fatigue at the diaphragm flex zone.
Selecting the Right Model for Particle-Laden Duty
The practical approach is to start with the known particle size distribution in your fluid, then select the smallest Phoenix model whose solid passing rating clears that maximum particle size with some margin. You don’t want to be operating at the absolute limit of the rating.
For a fluid with particles up to 6mm, the P160 (rated 7.5mm) is the smallest model that works with margin. The P120 (rated 4mm) is not suitable. Running the P120 on that fluid will cause ball seat fouling on every cycle.
For abrasive slurries — mineral processing, ceramic suspensions, sand-laden wastewater — consider specifying SS316 balls and seats rather than PP or Acetal. The harder material wears more slowly against abrasive particles. PTFE seats are chemical-resistant but relatively soft; they’re not the best choice for high-abrasion solids service.
After specifying based on solids, verify the model also meets your flow rate, delivery head, and viscosity requirements from the same technical table. The solid particle rating alone doesn’t complete the selection — it just establishes the floor.
To discuss pump selection for slurry or particle-laden applications, or to get a recommendation on the right Fluimac Phoenix model for your duty, contact us at info@autoflotechnology.com.