If there is one decision that determines how long a progressive cavity pump lasts, it is the stator elastomer. The stator is the rubber lining that forms the pump’s seal, and it is also the first part to fail. Choose the right rubber for your fluid and the stator can run for years. Choose wrong and it swells, tears, or hardens in months, taking the rotor and your schedule down with it.
Here is what we tell customers about the four stator compounds we build with, and how to pick between them without guessing.
NBR (nitrile rubber)
NBR is the everyday workhorse. It handles oils, fuels, and water-based fluids well, resists abrasion reasonably, and costs the least of the four. Its working range is roughly -20 °C to 80 °C.
Use it for diesel, lubricants, oily water, and light slurries. Its weakness is chemical: strong acids and aggressive solvents attack it, and ozone degrades it over time. If your fluid is oily, start here. If it is acidic, look further down this list.
EPDM (ethylene propylene diene)
EPDM is almost the opposite of NBR. It loves water, steam, and many chemicals, and it shrugs off ozone and weathering, which makes it the standard choice for outdoor and hot-water duty. Working range roughly -30 °C to 120 °C.
It is also the food-service favourite, because food-grade EPDM meets FDA requirements and survives CIP cleaning. The catch: EPDM and oils do not get along. Pumping diesel or mineral oil through an EPDM stator will swell the rubber fast. Water, chemicals, food, steam. That is EPDM’s territory.
FKM (fluorocarbon, commonly known as Viton)
When the fluid is nasty or the temperature is high, FKM is the answer. It resists strong acids, solvents, and aggressive chemicals, and it keeps working up to about 200 °C. That capability costs money, and FKM stators are the most expensive of the four.
Use it for hot aggressive chemical service where NBR and EPDM both fail. Just make sure the temperature really is high, because paying FKM prices for a moderate application is a waste of budget.
HNBR (hydrogenated nitrile)
HNBR is what you get when you take nitrile’s oil resistance and add serious mechanical toughness. It handles extreme wear, high pressure, and higher oil temperatures than NBR, with a working range around -25 °C to 150 °C. It is the preferred compound for oil-and-gas and abrasive high-pressure service, and it outlasts NBR noticeably in tough duty.
It costs more than NBR but less than FKM, which makes it the sensible middle ground for abrasive or high-pressure jobs where the fluid is oily.
How to choose without a chemistry degree
You do not need to memorise compatibility tables, because the choice usually collapses to a few questions:
- Is the fluid oily or fuel-based? Start with NBR.
- Is it water, steam, chemical, or food? Start with EPDM.
- Is it hot and aggressive, over 120 °C or strongly acidic? FKM.
- Is it abrasive, high-pressure, or both, with an oily base? HNBR.
- Does it carry hard solids? Upgrade the rotor to chrome-plated or tungsten-carbide coated, and match the stator compound to the fluid’s chemistry first, abrasion second.
The same logic applies across all ten of our pump series. The stator compound is selected for the fluid; the series is selected for flow and pressure; the rotor finish is selected for abrasion. Get the stator right and the rest of the pump gets a fair chance to live a long life.