Fluid quality: water and oil
The thermal fluid is a consumable: its quality determines limescale, scaling and corrosion in water, and degradation and oxidation in oil. Keeping it within specification protects resistors, pump and circuit.
The quality of the fluid defines the life of the circuit. In water, for reference: pH 7,5–8,5, total hardness <15 °dH and conductivity <150 mS/m. In high quality synthetic oil for a range of −20 a +320 °C. In SMART equipment, everything that is in contact with the fluid is brass or stainless steel.
Cooling water is not water circuit
While potable water was used in the circuit, corrosion problems were rare, in part because of the previously lower operating temperatures. With high-quality engineering plastics came higher mold temperatures—and with them, more problems.
Today, due to cost and environment, practically no installation uses potable water: tower water systems are installed that dissipate heat through cooling towers. That water is treated, and it is usually taken for granted that it more than meets the requirements. It's true up to about 40 °C, which is what he is preparing for.
The problem is the dual use: this same water is also used as a circulation fluid at 90, 180 °C or more, temperatures for which, as a general rule, it is not prepared. This is where most lime and corrosion problems arise.
The water that a team asks for high temperature
| Parameter | Reference value | Why it matters |
|---|---|---|
| pH | 7,5 – 8,5 | Defines the behavior against corrosion |
| Conductivity | < 150 mS/m (≈ 1500 µS/cm) | Indicates the dissolved salts |
| Total hardness | < 15°dH | Too hard → lime |
| Carbonate hardness | < 4 °dH (< 20 stabilized) | Forms scale when heated |
| Chlorides (Cl) | < 100 mg/l | Aggressive to metals (pitting) |
| Sulfates (SO₄) | < 150 mg/l | They promote corrosion |
| Ammonium (NH₄) | < 1 mg/l | Attacks brass and copper |
| Iron (Fe) | < 0.2 mg/l | Deposits and turbidity |
| Manganese (Mn) | < 0.1 mg/l | Deposits |
| Suspended solids | Missing | They clog channels and erode |
Marse recommends treating the water with a anticorrosive, and non-ferrous metal protector and a hardness stabilizer. The best indicator of quality is calcium-carbon balance (determined by pH): water in equilibrium serves well as a thermal fluid, whether soft or medium hard.
Thickening: When pure water evaporates – especially above 90 °C – the salts remain and concentrate. If the filling water enters at 500 µS/cm and the circuit water reaches 1000 µS/cm, the thickening factor is 2. Rule of thumb: if the conductivity exceeds 1500 µS/cm, the water must be renewed. Measuring conductivity is the simplest way to follow its evolution.
Additional conditions
Lime and corrosion: what do they cause
The oil that the closed circuit
On oil units, Marse requires high quality synthetic oils to avoid premature degradation, with a working range of −20 a +320 °C. These are the reference specifications.
| Property | Reference value |
|---|---|
| Density at 15 °C | 0,870 / 0,890 g/cm³ |
| Color | 3 max |
| Kinematic viscosity at 40 °C | 15 / 26 cSt |
| Flashpoint | 170°C min. |
| Freezing point | −30 °C max |
| Viscosity at 50 °C | 2,0 / 2,5 °E |
| Temperature range | −20 °C to +320 °C |
| Approximate dilation | ±8% volume per 100°C |
Why a quality synthetic oil
Materials and sensors that resist
Due to cost, many manufacturers limit stainless steel to the tank and use brass, bronze or copper in pumps, tubes and coolers. On SMART devices, however, all components in contact with the fluid are made of brass or stainless steel —no aluminum, galvanized iron, or low-quality hoses—preventing galvanic corrosion, stress cracks, and fluid contamination.
In high-end pressurized water, there are even stainless steel pumps with ceramic shafts, PEEK impellers and SiC bearings. The level is controlled with a electrode sensor (or stainless steel float for non-conductive fluids, such as glycol), which also protects against dry running.
How to ensure the water quality
Connecting the equipment to the existing cooling circuit and letting it run rarely works. If the water is treated, the specialist must know that this water not only cools: it also circulates through the equipment at temperatures above 40 °C, which requires a different treatment.
Materials that last and a well-treated fluid
We help you define the water or oil in the circuit for your working temperature. Talk to our technical service.
Fluid quality determines the life of the unit and the mould: see the magnetic filters for cooling circuits and the range of industrial water and oil temperature control units.
Construction in brass and stainless
All components in contact with the fluid are made of brass or stainless steel, and the level is controlled by electrodes with dry running protection. Keeping water or oil within specification is the condition to avoid damage due to corrosion or degradation of components.
Common questions
How often should you renew or purge the water?
When the conductivity approaches the reference maximum (150 mS/m, ≈ 1500 µS/cm). The frequency depends on evaporation and make-up water; Measuring conductivity is the best guide.
Can antifreeze be used?
Below 5 °C it is advisable to add an antifreeze with a corrosion inhibitor. For non-conductive fluids, such as glycol, the level is controlled with stainless steel float instead of electrodes.
What oil should you use?
A high quality synthetic oil, with a working range of −20 to +320 °C, to avoid premature degradation. The quality sheet includes density, viscosity, flash and freezing points and reference expansion.
What materials are the parts in contact with the fluid made of?
Made of brass or stainless steel throughout the range, avoiding aluminum, galvanized iron and low quality hoses.
Why are resistors embedded?
Due to high hardness/lime: lime deposits on the hot surface of the resistance, insulating it and causing overheating.