The screw pump stator is the heart of every progressive cavity and single screw pump.
Understanding how a screw pump stator is constructed, which materials are used, and how
the geometry affects performance is essential for engineers, maintenance specialists, and
technical buyers who need reliable, long?term pumping solutions.
In a screw pump, often called a progressive cavity pump or
single screw pump, the stator is the fixed component that houses
the rotating screw, also known as the rotor. Together, the rotor and the screw pump stator
form sealed cavities that move fluid from the suction side to the discharge side.
Unlike a centrifugal pump that relies on high rotational speed and impeller action, a screw pump
uses the positive displacement principle. The progressive cavities maintain almost
constant volume, making the screw pump stator a critical element for controlled flow, low pulsation,
and high suction lift capabilities.
The typical screw pump stator is an elastomer-lined tubular component with an internal
helical cavity. The rotor, usually a metallic single or multiple-start screw, rotates eccentrically inside
the stator, creating continuously progressing chambers that transport the medium.
The screw pump stator performs several essential functions in progressive cavity pumps and related
screw pump designs:
creating isolated chambers that ensure accurate positive displacement.
mechanical loads while maintaining dimensional stability.
elastic lining, preventing excessive deformation under vacuum or high pressure.
pumped fluids, cleaning agents, and process additives.
influences pump lifetime, efficiency, and maintenance intervals.
Because of these functions, the construction details of the screw pump stator—geometry, rubber formulation,
bonding quality, and steel tube design—are decisive for pump performance.
Although designs vary, most screw pump stators share the same basic construction. A typical
screw pump stator assembly contains:
The outer tube of the screw pump stator is usually made from carbon steel or stainless steel. It provides:
The tube may be cylindrical with constant wall thickness, or it may have
reinforced sections and external ribs where higher pressure capability
is required.
The inner functional surface of the screw pump stator is the elastomer lining that
forms the helical cavity. Its geometry is the negative of the rotor geometry. The lining:
At both ends of the screw pump stator, the metallic tube is adapted to the pump structure using:
Proper end connection design ensures centering, correct compression of sealing elements, and safe pressure
containment.
The choice of material for a screw pump stator is a major design decision. Both the
metallic tube and the elastomer lining must be matched to the
pumped medium, operating temperature, and mechanical loads.
Common materials for the stator tube include carbon steels and stainless steels. The following table
illustrates typical options:
| Material Type | Examples | Main Characteristics | Typical Use Cases |
|---|---|---|---|
| Carbon Steel | ASTM A106, A53 | Good mechanical strength, cost-effective, requires coating for corrosion protection | General water, oil, low-corrosive media, industrial processes |
| Low-Alloy Steel | 16Mn, 42CrMo | Higher strength, improved fatigue resistance, weldable | High-pressure screw pumps, demanding mechanical loads |
| Stainless Steel | 304, 316, 316L | Excellent corrosion resistance, good hygiene, higher cost | Food and beverage, pharmaceuticals, aggressive chemicals |
| Duplex Stainless | 2205, 2507 | High strength, superior corrosion resistance in chlorides | Offshore, seawater, high-chloride chemical processes |
The elastomer stator is usually made from a molded rubber compound. The choice of rubber
type is governed by:
| Elastomer Type | Abbreviation | Key Features | Typical Media | Approx. Temperature Range |
|---|---|---|---|---|
| Natural Rubber | NR | Very good elasticity, excellent abrasion resistance, limited chemical resistance | Water, slurries, mineral ores, low-aromatic oils | -20°C to +80°C |
| Nitrile Rubber | NBR | Good oil and fuel resistance, widely used, good mechanical properties | Crude oil, fuel oil, oily wastewater, drilling fluids | -20°C to +100°C |
| Hydrogenated Nitrile | HNBR | Improved heat and chemical resistance compared with NBR | Hot oils, higher temperature hydrocarbon service | -30°C to +140°C |
| Ethylene-Propylene-Diene | EPDM | Excellent resistance to hot water, steam, many chemicals; poor with oils | Hot water, CIP media, polar chemicals | -40°C to +140°C |
| Fluoroelastomer | FKM | Outstanding chemical and temperature resistance, high cost | Strong solvents, aggressive chemicals, high-temperature oils | -20°C to +200°C |
| Silicone Rubber | VMQ | Very high temperature stability, flexible at low temperatures, moderate mechanical strength | Food-grade applications, pharmaceuticals, high-temperature fluids | -50°C to +200°C |
The hardness of the screw pump stator elastomer, often in the range of
50–80 Shore A, directly affects sealing behavior and wear rate. Softer materials
seal well but wear faster under abrasion, while harder rubbers reduce deformation but require closer
manufacturing tolerances to maintain seal integrity.
The construction of a screw pump stator is defined by several key geometric parameters. These design
variables determine the pump’s displacement, pressure capability, and efficiency.
In a progressive cavity screw pump, the rotor has a single or multiple-start helical profile, and the
stator has a corresponding double or multiple-start cavity. Typical arrangements include:
The pitch and diameter of the rotor and stator determine the
volumetric displacement per revolution.
Screw pump stators are often described by the number of stages. Each stage is
associated with a certain pressure capability. A longer stator with more stages can generate higher
pressure at the same rotor speed.
A simplified rule of thumb used in the industry is that each stage may produce approximately
6 bar of differential pressure, although actual performance depends on the exact
construction and fluid properties.
The screw pump stator typically has a small designed interference between the rotor and stator elastomer.
This interference ensures tight sealing, but it also generates friction. As the stator wears, interference
decreases, reducing sealing capacity and volumetric efficiency.
The wall thickness of the metallic stator tube is chosen based on:
Construction of a screw pump stator must account for the different thermal expansion
coefficients of elastomer and metal tube. The design must prevent excessive internal stress
that could lead to debonding or cracking at high or low temperatures.
The construction of a screw pump stator involves several sequential manufacturing steps. Strict control
of each step is essential for consistent quality and long service life.
and prepared for flanges or threads.
treated to improve bonding with elastomer.
are crucial for rotor-stator fit.
To attach the elastomer securely to the metal, a bonding agent system is applied
to the prepared surface. This may include:
The bonding system must be compatible with the curing cycle and the process temperature of the chosen rubber.
The internal helical shape of the screw pump stator is formed using:
During this stage, the elastomer is forced into intimate contact with the tube and the cavity that defines
the stator geometry.
The molded elastomer is cured under controlled temperature and pressure, a process known as
vulcanization. Key parameters:
Correct vulcanization is essential for achieving the target hardness, chemical resistance, and bonding strength.
Finished screw pump stators undergo several quality checks:
High-quality construction ensures that the screw pump stator will operate reliably within its specified
pressure and temperature range.
The way a screw pump stator is constructed directly impacts the pump’s hydraulic and mechanical performance.
Volumetric efficiency is affected by:
An optimized stator construction minimizes leakage between cavities, maintaining high volumetric efficiency
over a long period.
Mechanical efficiency is influenced by:
Proper material pairings and surface finishes can reduce energy losses due to friction and heat.
The airtight seal between rotor and stator defines how well the pump can generate vacuum at the inlet. A
high-quality screw pump stator with low permeability elastomer and good construction can achieve
strong suction lift even with viscous or multiphase fluids.
Maximum differential pressure depends on:
An accurately machined screw pump stator with uniform elastomer thickness and consistent hardness
contributes to low noise, low pulsation, and smooth operation typical of progressive cavity pumps.
When properly designed and manufactured, the screw pump stator provides several advantages:
protecting sensitive processes.
fibrous materials better than many rigid designs.
self-priming up to significant suction heights.
stator concept can handle diverse fluids.
such as food or biological media.
appropriate drive control.
The construction of the screw pump stator can be tailored for different industries by adjusting elastomer
type, tube material, and geometry. Typical applications include:
Each application imposes specific requirements on screw pump stator construction in terms of
chemical compatibility, wear resistance, and temperature handling.
When selecting a screw pump stator, engineers should consider a combination of hydraulic, mechanical, and
chemical factors. Key selection parameters include:
interference to manage wear.
The screw pump stator is usually the primary wear component. Considering total life-cycle cost means
balancing:
The following example tables provide a typical overview of screw pump stator specifications.
Values are illustrative and do not correspond to any specific manufacturer.
| Stator Size | Nominal Rotor Diameter (mm) | Stator Inner Diameter (mm) | Overall Length (mm) | Number of Stages | Tube Outer Diameter (mm) |
|---|---|---|---|---|---|
| S10 | 20 | 22.5 | 600 | 2 | 60 |
| S25 | 40 | 44 | 1100 | 4 | 90 |
| S50 | 65 | 70 | 1500 | 4 | 130 |
| S80 | 90 | 96 | 1900 | 6 | 180 |
| Stator Size | Displacement per Revolution (L/rev) | Max. Differential Pressure (bar) | Recommended Speed Range (rpm) | Viscosity Range (mPa·s) |
|---|---|---|---|---|
| S10 | 0.025 | 12 | 200–1200 | 1–5,000 |
| S25 | 0.12 | 24 | 150–800 | 1–50,000 |
| S50 | 0.45 | 24 | 100–600 | 1–100,000 |
| S80 | 1.10 | 36 | 80–400 | 1–200,000 |
| Process Fluid | Recommended Elastomer | Comments |
|---|---|---|
| Cold potable water | EPDM or NR | Ensure potable water approvals if required |
| Diesel and light fuels | NBR | Standard nitrile rubber generally sufficient |
| Hot vegetable oils | HNBR or FKM | Higher temperature stability required |
| Concentrated acids | FKM | Check compatibility for specific acid and concentration |
| Highly abrasive mineral slurry | NR (high abrasion grade) | Consider reduced speed to lower wear rate |
Even with optimized construction, the screw pump stator is a consumable component. Understanding typical
wear mechanisms and failure modes helps in planning maintenance and extending service life.
increasing clearance.
of the rubber.
the stator, leading to blistering and softening.
cracks over time.
Correct construction of the screw pump stator, combined with appropriate operational practices,
significantly extends maintenance intervals and reduces total cost of ownership.
As industrial processes become more demanding, screw pump stator technology continues to develop.
Key trends include:
chemical, and abrasion resistance.
ingress and chemical attack at the bond line.
geometry to minimize stress and enhance sealing.
of the elastomer section, reducing waste and cost.
coatings and finishes reduce friction and wear at the rotor–stator interface.
These developments make modern screw pump stators more efficient, durable, and cost-effective
across a wide range of applications.
The lifetime of a screw pump stator varies greatly with operating conditions. In clean, non-abrasive,
chemically compatible applications, lifetimes of several thousand operating hours are common.
Highly abrasive or chemically aggressive fluids can reduce lifetime significantly. Correct elastomer
selection and operating conditions are decisive.
In many cases, it is possible to change only the screw pump stator elastomer while keeping the same rotor,
provided that the rotor material is compatible with the new process fluid. However, any change in elastomer
hardness or swelling behavior may affect rotor–stator interference and pump performance, so engineering
evaluation is recommended.
Elastomer selection for screw pump stators should be based on:
Data from elastomer compatibility charts and experience from similar applications are commonly used.
Running a screw pump dry can cause rapid overheating of the stator elastomer because there is no fluid to
carry away frictional heat. This can lead to softening, blistering, cracking, and permanent damage to the
screw pump stator. Dry-run protection is strongly recommended.
Minor surface wear is usually not repairable. In most industrial scenarios, a worn screw pump stator
is replaced with a new unit to restore performance. Some special designs allow re-lining of the elastomer,
but this is less common and depends on the pump series and construction.
The screw pump stator is a complex and highly engineered component that defines the performance, reliability,
and efficiency of progressive cavity and single screw pumps. From the choice of elastomer and tube material
to the geometric design, bonding system, and manufacturing process, every aspect of stator construction
plays a role in how the pump will behave in real industrial conditions.
By understanding the fundamentals of screw pump stator construction, engineers and technical buyers can
make informed decisions about material selection, design parameters, and maintenance strategies, ensuring
long-term, stable operation of their screw pump systems.
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Copyright ? Jiangsu Longjie Pump Manufacturing Co., Ltd.
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