Quality requirements for hydraulic fluids:
The quality of the hydraulic fluid is an indication of its durability. A major influence on quality have the properties of the oil- antioxidation, anticorrosion, antiwear, antifoaming, pour point depressive, demulsifying and others, that are achieved and improved mostly on the base of multifunctional additive packages.
Influence of certain processes and conditions:
(1) Oxidation: Oxidation is one of the main reasons for reducing the stability of the hydraulic fluids. When the process begins a catalytic effect is obtained. The products of the oxidation can increase the viscosity of the liquid and cause corrosion. The condensation and the polymerization lead to the formation of insoluble residues that impair the functioning of the devices, increase wear, reduce the clearances, pollute lines and valves. The main factors, leading to oxidation are the high temperatures, pressure, contaminants, water, the catalytic influence of metal surfaces and intensive circulation.
(2) Temperature: The rate of oxidation is doubled for every 10 °C. The reaction may begin locally, in a place where the temperature is higher. Once started, the oxidation reaction is catalytic.
(3) Pressure: With increasing of pressure, the viscosity of the liquid also increases, which leads to an increasing of friction and heat generation. This leads to an increasing of the oxidation.
(4) Pollutants: 1% sludge mixed with hydraulic fluid is sufficient to shorten its life two times.
(5) Water and metal: Some metals, such as copper, are catalysts of the oxidation, especially in the presence of water.
(6) The negative influence of water: The water that enters into the hydraulic system can emulgate and accelerate the collection of dust and other contaminants, which is unfavorable for valves and pumps, the wear increases. Furthermore, the water leads to hydrolysis of the additives.
Anti-wear properties of the fluid
The conventional hydraulic fluids are satisfactory at low pressures and speeds. Hydraulic fluids for high pressures (over 6900 KPa) and high speed (1200 rpm) must contain antiwear additives. Such applications do not allow the formation of an uninterrupted film of hydraulic fluid. This condition is known as boundary lubrication. It occurs when the viscosity of the liquid is insufficient to avoid contact between the surfaces. The antiwear additives, however, provide a film, which minimizes the wear.
Types of hydraulic fluids
а. Mineral oil based.
б. Fire safe: Water/glycol, water/oil and synthetic.
Supplier: Rust LLC.