HFC hydraulic fluid:A Deep Dive into Composition and Cost

HFC hydraulic fluid, also called Fire-resistant hydraulic fluid, is a hydraulic and lubricating medium specifically engineered for use in high-temperature and flammable conditions, such as those in metallurgical processes and underground coal mining, where high temperatures, high pressures, and flammability or explosion risks are present.

 

Normally, an HFC hydraulic fluid is composed of water, monoethylene glycol (MEG), polyalkylene glycol (PAG), and additives. Because it uses water and glycol as the base fluid and PAG as a thickener, it is also known as a water-glycol fire-resistant hydraulic fluid.

In this formulation, water provides non-flammability, MEG ensures freeze protection, PAG delivers high lubricity, and the additives contribute anti-foam, anti-rust, anti-wear, and extreme pressure (EP) and other functional performance.

 

The typical composition of an HFC hydraulic fluid generally includes the following components:

 

Water: approximately 35%-40% (usually 40%) deionized water or softened water, as the key component providing fire resistance;

Glycol: approximately 25%-45% polyols such as ethylene glycol or propylene glycol, used as antifreeze (lowers freezing point), co-solvent, rust prevention;

PAG thickeners: approximately 10%-20% water-soluble PAG thickeners, used to regulate and maintain hydraulic fluid viscosity for proper system lubrication and sealing.

Additive Package: approximately 3%-5% additive package: rust inhibitors, antifoaming agents, antioxidants, etc., are used to provide lubrication and corrosion protection.

 

 

The performance of an HFC fluid(viscosity, viscosity index, and lubricity) mainly depends on the choice of polyalkylene glycol (PAG) thickener, and PAG thickeners are also the main cost of this type of hydraulic fluid.

 

The PAG thickener is a high-molecular-weight EO/PO (Ethylene Oxide/Propylene Oxide) copolymer. Its high viscosity and water solubility make it an effective thickener for water-glycol hydraulic fluids.

 

The viscosity index of HFC hydraulic fluid is much higher than that of ordinary mineral fluid (170~245), entirely dependent on the performance of the PAG thickener.

 

The viscosity index reflects the performance of hydraulic fluid viscosity as a function of temperature. The effect of water-glycol hydraulic fluid on the volumetric efficiency of pumps [1] extends pump life.

 

The fluid possesses a low viscosity-pressure coefficient, and its polarity contributes to a stable lubricating film. Furthermore, it demonstrates excellent lubricity and strong shear stability.

 

The primary benefit of high-molecular-weight PAG lies in its high thickening efficiency, which allows a substantial viscosity increase in HFC fluid at lower concentrations. However, its longer molecular chains typically result in relatively lower shear resistance. In contrast, lower-molecular-weight PAGs offer superior shear stability, albeit with a weaker thickening effect.

 

Comparison of PAG 75W Products in HFC Hydraulic Fluid Applications

 

Item	PAG 75W-18000 (Lower MW)	PAG 75W-55000 (Higher MW)
Molecular Weight​	16,000	40,000
Thickening Efficiency​	Lower. Requires higher dosage to achieve the target viscosity.	High.​ Achieves a significant viscosity boost at a lower dosage.
Shear Stability​	Excellent.​ Shorter chains resist breakdown, ensuring long-term viscosity retention.	Lower. Longer chains are more susceptible to shear, which can lead to viscosity loss.
Key Application​	Systems demanding long-term shear stability​ and precise lower viscosity control.	Systems requiring high initial viscosity/oil film strength​ in moderate-shear conditions.
Cost Consideration​	Higher formulation cost due to greater additive dosage.	Lower dosage cost, but potential for higher maintenance if shear-induced viscosity loss occurs.

 

Chorus offers Polyalkylene Glycol (PAG) thickeners PAG 75W-18000 and PAG 75W-55000. For more detailed quotations or solutions, please contact us.

Additive Package​:
Beyond the PAG thickener, the additive package-typically comprising 3%-5% of the formulation-plays a critical role in defining key fluid properties such as rust prevention, anti-foaming, and oxidation resistance.

 

Why Rust Prevention?

Because HFC hydraulic fluid systems have high water content, selecting appropriate rust inhibitors is paramount. Selecting the right rust inhibitors is critical. An optimal formulation meets the dual mandate of providing durable corrosion inhibition under severe conditions and complying with tightening environmental regulations, successfully marrying effective protection with low toxicity and eco-safety.

To cut costs, some cheap formulas and low-quality raw materials may appear acceptable on the surface and seem marginally functional. They not only pollute the environment but can also cause severe corrosion or blockages inside equipment, resulting in irreversible damage to the hydraulic system.

 

Chorus offers a variety of compound additive packages​, including antioxidants, rust inhibitors, and defoamers. We also provide various fire-resistant hydraulic oil solutions and the latest pricing. Please inquire for more information.

 

Supplementary Note:​

What is equipment volumetric efficiency?​

 

Equipment volumetric efficiency in a hydraulic system typically refers to the volumetric efficiency of a hydraulic pump or motor, which is the ratio of actual output flow to theoretical output flow. A high viscosity index means that the viscosity of the hydraulic fluid changes less with temperature, helping to reduce internal leakage and thereby maintain high volumetric efficiency of the equipment, ensuring stable system performance.