AustraliaFLOMECThe relationship between the elliptical gear flowmeter and the measuring medium is based on chemical compatibility. The higher the compatibility, the longer the measurement time, and it will not cause unnecessary damage to the flowmeter and measurement data. Poor compatibility can cause serious damage to the flowmeter and affect its service life. Therefore, it is necessary to verify whether the measuring medium and flowmeter material are compatible.FLOMEC elliptical gear flowmeterIt is composed of the body, rotor, bearing, sealing ring and other parts, and each component needs to be compatible with the measuring medium.

The body and measuring medium are compatible, but if the O-ring measuring medium is not compatible, problems may also occur at some point. For example, most fuels and oils are compatible with PPS rotors made of aluminum, but if the O-ring material is incompatible, the sealing ring may loosen, harden, or expand, causing instrument damage and missing measurement values due to leakage. Some solvents such as alcohol require stainless steel body and stainless steel rotor, while fluororubber is not suitable. Generally, PTFE sealing rings are suitable for chemical applications.

Of course, chemical compatibility is just an issue, just like any success, a long-term partnership, although a small matter, has achieved a smooth and barrier free cooperation. This is also an important reason for the selection of bearings. The rotor has a very thin (approximately 0.1 mm) drive shaft that allows it to rotate without rubbing against the instrument cover or body. Stainless steel rotors use carbon ceramic shafts, which can self lubricate but are more prone to wear. Aluminum rotors use quenched steel roller shafts - not suitable for the water treatment industry or media with low viscosity and no lubricity like water. PPS rotors can self lubricate and do not require bearings, and are used for measuring non lubricating media. The selection of bearings, like other small components such as seals, is crucial for the normal operation of instruments.

There are two manufacturing methods for stainless steel rotors: first, hot compression: metal powder is cast, compacted, and heated to a temperature below its melting point, and then subjected to complex solid-state bonding to form a shape similar to that of a cast product. 2、 Wire cutting: The rotor is directly cut from non embroidered steel bar material. The sintering process has low efficiency but is more material efficient and does not require excessive processing techniques. However, in acidic media, 316 stainless steel can be used normally, but there are limitations to sintering rotors. Because sintered stainless steel is more porous than cast metal in the chemical process of solid-state bonding. Due to the poorer adhesion produced by sintering process compared to casting process, the extensive erosion of acidic substances can break the adhesion between particles, causing them to layer and potentially revert back to the metal powder state before casting.

We have the following types of sintered and wire cut rotors according to production needs:

烧结型316SS 转子: OM004，OM006，OM008,，OM015，OM025，OM050

Wire cutting SS rotor: OM040, OM080

Alcohol is generally believed to be compatible with aluminum materials, provided that the purity reaches 99.8%. However, most tanks storing alcohol will absorb water vapor from the air and form oxide coatings on the aluminum surface. Alcohol is weakly acidic, especially methanol, which will dissolve the oxide layer and further corrode it. For this reason, GPI recommends using a stainless steel elliptical gear flowmeter to measure alcohol

PPS material can resist many organic chemicals and is declared suitable for pump manufacturers. Aromatic chemicals such as benzene, toluene, and xylene can cause PPS to expand. When measuring with an elliptical gear flowmeter, the internal cavity space is very small, and if the rotor expands, it can cause the instrument to become blocked.

Polyethylene (p-phenylenediamine sulfide) (PPS) is a polymer composed of alternating sulfur atoms and phenylene rings in para substitution mode. Its molecular structure has highly stable chemical bonds, which enable its molecules to achieve a considerable degree of stability in thermal degradation and chemical reactivity. The molecular structure is also easily encapsulated in a heat-resistant crystal lattice, so PPS is a semi crystalline polymer with a high crystallization melting point of 285 ° C (545 ° F). PPS has not been found to dissolve below a temperature of 200 ° C (392 ° F), although there may be expansion.

When mixed with glass fiber or other fibers, PPS is a remarkable engineering composite material with the following characteristics:

Significant long-term and short-term thermal stability

● Extremely high elastic modulus and creep resistance performance

● Widely applicable to environments with chemical corrosiveness

High repeatability precision injection molding

PPS has been used as a material for instrument production for more than 30 years, especially in positive displacement flow meters. However, so far, PPS has been widely used in the production of automation parts, and its mechanical and chemical properties have made it popular. The performance under high temperature, oil resistance, high stability, and mechanical strength make PPS a material for production automation parts, which also explains why PPS is the material of flow meters. In addition to the excellent mechanical properties of PPS, its ability to form complex component tolerances makes flow meters containing PPS components precise devices, and the purchase and maintenance costs are also very cost-effective.

PPS (polyphenylene sulfide) is a glass fiber polymer with strong thermoplasticity, capable of working at temperatures up to 200 ℃. PPS can resist various chemical corrosion, such as non aromatic (containing benzene), non halogenated (containing halogens such as chlorine, fluorine, bromine), any concentration of organic solvents, even at high temperatures. PPS is suitable for service with some aromatic, halogenated, or amine based solvents at temperatures close to ambient, but its lifespan will be reduced, and it is necessary to confirm its suitability for these types of solvents before use.

PPS itself can also resist most water-based solvents such as acids, bases, or neutral salts, as well as strong oxidizing acids such as nitric acid, hydrofluoric acid, and hydrochloric acid. Due to the sensitivity of reinforcing PPS filling material, it is not suitable for any type of strong acid (pH<2). Strong alkali cannot degrade PPS, but at high temperatures, strong alkali will reduce the mechanical strength of the rotor.

PPS is not suitable for high concentration chemicals with oxidizing properties or at high temperatures, but these chemicals can be measured under mild conditions in special working conditions. For example, hydrogen peroxide, chlorine, and sodium hypochlorite can cause swelling when the concentration exceeds 5% or when the concentration is low but at high temperatures. But PPS can be used for ordinary cleaning with moderate solvents or disinfection products with temperatures close to the environment.

Hot steam is a very dangerous environment for PPS, considering its chemical resistance may not be reasonable. However, it is not affected by polymer degradation, but it will separate the polymer from its surface glass reinforcement. Affected by hot water, the material expands and weakens the structural strength of the polymer. PPS is suitable for hot water environments with temperatures below 80 ℃, even hot seawater or water containing low concentrations of chlorine. When the temperature is above 80 ℃, the issue of reducing the service life of the flowmeter needs to be considered. For all environments containing hot water, the flow rate should not exceed 80% of the flow range, as water has poor lubrication performance. If it is inevitable to operate beyond 80% of the flow range, it will reduce the service life of the flowmeter.

The following figure is a reference for an aluminum instrument working in a water environment. It is not uncommon to use a diesel gauge to measure water. This is a very incorrect application because stainless steel shafts can rust. Aluminum rotors should not be selected for water treatment applications. Elliptical gear flow meters are not the preferred choice for most water treatment applications. That's why it's not a typical example of compatibility matching

The following picture shows a case of an aluminum instrument being corroded by methanol. As mentioned in the previous "common misconception", aluminum instruments can measure alcohol with a purity of 99.8%. However, most tank stored alcohol absorbs water vapor from the atmosphere and flows towards the oxide coating on the aluminum surface. Alcohol is weakly acidic, especially methanol, which can dissolve the oxide layer and further corrode it.

If you read some guidelines on chemical compatibility, you may find that the instrument you are using is not for the application. Don't wait until the entire system crashes, check as soon as possible for potential major issues.

Before checking the instrument maintenance, ensure the following:

Isolate relevant alarms or control outputs so as not to affect the process

● Turn off the instrument power supply

● Stop liquid supply

● Instrument pressure reduction and liquid discharge from instruments/pipelines

Seals can be ordered to accommodate any size of instrument