Due to their special design , single-stage screw pumps are frequently used in the oil and gas, petrochemical, food, pharmaceutical, and water and wastewater treatment industries. The core of these pumps consists of two components: a metal impeller and a rubber stator. The stator forms a hermetic seal between the impeller and the pump body , ensuring consistent pressure and flow of the pumped fluid.
Since the stator is in direct contact with the fluid, the type and quality of the rubber it is made of are crucial. To ensure long-term service and prevent premature wear, swelling, and failure, chemical testing of the monopump’s stator rubber is required. These tests determine the rubber compound’s resistance to chemical environments, temperature, pressure, and fluid type.
Importance of chemical testing of solid rubber materials
Choosing the wrong tires can cause the following problems:
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When rubber absorbs oil or solvents, it swells.
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When it comes into contact with strong acids and bases, it hardens or cracks.
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Loss of elasticity and reduced firmness.
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Loss of efficiency and line downtime due to premature pump failure
Therefore, chemical tests must be carried out before use or when selecting the type of rubber (NBR, EPDM, FKM, NR, etc.).
Types of rubber materials used in single-acting pump parts
Depending on the type of liquid, different types of rubber are used in the pump:
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NBR (nitrile butadiene rubber) : resistant to oils and hydrocarbons
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EPDM (ethylene propylene diene monomer) : resistant to acids, alkalis and hot water.
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FKM (Viton) : resistant to aggressive chemicals and high temperatures.
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NR (natural rubber) : Excellent abrasion resistance, suitable for dirt and mineral liquids.
To select each of them correctly, chemical and physical tests must be carried out according to the working conditions.
Basic chemical tests on solid rubber materials
1. Oil and solvent resistance test
In this test, a rubber sample is immersed in a synthetic oil or a special solvent. The following changes are measured:
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Expansion rate by volume or weight
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Hardness change (Beach A )
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Change in tensile strength
: The purpose of this test is to check the compatibility of rubber with fuels, oils and hydrocarbons.
2. Testing for resistance to acids and alkalis
In the chemical industry, water supply, and water treatment, stationary parts may be exposed to acidic or alkaline environments. For this purpose, the sample must be placed in a solution of H₂SO₄, HCl, or NaOH. The evaluation criteria are as follows:
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Discoloration or cracks
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Deterioration of mechanical properties
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Absorption or swelling rate
3. Testing for heat and oxidation resistance.
Tires harden , crack, and lose elasticity at high temperatures . Heat resistance tests are conducted at temperatures ranging from 70 to 150 °C (depending on the tire type). This test demonstrates the tire’s ability to withstand operating temperatures without loss of quality.
4. Water and moisture absorption test
Solid parts that operate in humid environments or come into contact with aqueous liquids can absorb moisture. In this test, rubber is immersed in distilled or seawater, and changes in weight and volume are measured.
5. Accelerated aging test
In this test, rubber samples are exposed to a combination of chemicals, temperature, and pressure to accelerate the degradation process. Changes in their physical and chemical properties are then observed. This method helps predict the service life of durable components.
6. Compatibility test
Sometimes solid parts must be compatible with certain liquids, such as metals, food, or pharmaceuticals. In this test, the sample is placed directly into the liquid, and after a certain period of time, its appearance and mechanical changes are observed.
Additional test methods
In addition to chemical tests , some analytical tests are used to examine the structure of rubber:
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FTIR (FTIR spectroscopy): Identification of functional groups and polymer types
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TGA (Thermogravimetric Analysis): Checking thermal stability and filling level
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DSC (Differential Scanning Calorimetry): measures the glass transition temperature (Tg)
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SEM (scanning electron microscope): observation of surface changes and microscopic degradation
Relevant international standards
There are several criteria for the chemical testing of monopump stator rubber. The most important of these are:
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ASTM D471: Test for resistance of rubber to liquids
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ASTM D573: Thermal Aging Test for Rubber
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ASTM D1415: Rubber Hardness Test
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ISO 1817: Determination of the effect of liquids on vulcanized rubber
These standards provide an accurate and consistent basis for comparing tire quality.
Advantages of chemical testing over material selection
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Reduced maintenance costs and frequent replacement of the stator part
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Extends pump life and reduces production downtime .
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Ensure the compatibility of the material with process fluids.
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Increased efficiency and reduced energy consumption
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Improving security in sensitive industries such as the pharmaceutical and food industries
Finally
The pump stator is one of the most important and sensitive components in liquid pumping. Its durability and efficiency directly depend on the correct choice of rubber material and standard chemical testing. A thorough investigation of resistance to solvents, acids, alkalis, temperature, and humidity allows for the selection of the optimal solution for each specific application.
By investing in quality control and chemical testing of stator materials, companies and industries can avoid premature failures, high repair costs, and production downtime. Ultimately, chemical testing of stator rubber materials is not just a technical requirement, but an economic and strategic investment for every industry.