Is hydraulic fluid flammable?: In a hydraulic system, fluids play an important role. The truth is that no operation is possible for a hydraulic system without the presence of hydraulic fluid. Environmental changes, such as temperature variations, will affect hydraulic fluids and system operation. When the temperature increases, the fluid will evaporate and when the temperature decreases, the fluid will freeze. This is one of the main problems related to hydraulic fluid.
Hydraulic system applications range from small toys to larger applications such as aircraft and robotics. In such cases, there will be applications that involve contact with ignition sources and hot surfaces. Furnace loaders and unloaders, hot metal shears, coke oven door openers, die casting machines, etc. are some applications that involve a higher temperature and contact with an ignition source. What will happen when the hydraulic fluid is exposed to these situations? The effects will depend on the type of hydraulic fluid used.
Mineral oils, fire resistant fluids, water/oil emulsions, water glycol, and phosphate esters are the different categories of hydraulic fluids. Petroleum-based hydraulic fluids, like mineral oils, have a flash point (the lowest temperature at which vapors ignite) that ranges from 300 to 600 degrees Fahrenheit. Water-based hydraulic fluids are flammable. But, there is a corrosion problem when using water based hydraulic fluids. The flammability test of hydraulic fluids is carried out according to the ISO 12922 specification.
Fire resistant hydraulic fluids are mainly classified as oil-water emulsion, water-polymer solution, anhydrous synthetics. Fire resistant hydraulic fluids that contain water will have more than 35% water content. ISO 12922:2012 again classifies them into HFAE, HFAS, HFB, HFC, HFDR and HFDU.
- HFAE: This is an oil-in-water emulsion that has a milky to translucent appearance.
emulsion appearance. It contains more than 80% water and is resistant to ageing. HFAE has applications in the field of mine support, hydrostatic drives, extension of hydraulic struts underground.
- HFAS: This is a synthetic aqueous fluid that has a transparent appearance. It is free of mineral oils and contains more than 80% water content. Mine support, foundry technology, press hydraulics, etc. are the HFAS applications.
- HFB: This is a water-in-oil emulsion containing more than 40% water. Underground coal mining is an application of HFB. 650 °C is the minimum ignition temperature required according to ISO standards.
- HFC: HFC is known as glycol solutions, polyalkylene glycol solutions, or water glycols. 600 °C is the minimum ignition temperature required. This is a water polymer solution containing more than 35% water. HFC has application in all fields where water-free hydraulic fluids are not used such as steel industry, coking plants, foundries, hardening plants, forming presses, injection molding, etc.
- HFDR: HFDR uses phosphoric acid ester and has poor viscosity and temperature characteristics. This is classified as a hazardous work material because it will generate toxic gases in the event of a fire. The turbine control system is an HFDR application.
- HFDU: HFDU can again be classified into glycol base and ester base. Glycol-based HFDU has good viscosity, temperature characteristics, shear stability, and aging resistance. This is a water soluble fluid that has good wear protection. Mobile systems with high thermal load properties use glycol-based HFDU. Ester based HFDU has a high soil dissolving capacity.
To ensure job site safety, you can convert existing mineral/petroleum-based hydraulic oil into fire-resistant hydraulic oils. While performing operations, always follow the four checklists mentioned below.
- Check the compatibility of all other components used in the circuit with fire resistant fluid.
- Drain existing fluid and clean lines, pumps, hoses, valves, etc.
- Fill with fire resistant liquid and check the system.
Is hydraulic fluid flammable?
Fluids play a key role in hydraulic systems. In fact, any operation requires hydraulic fluid within the hydraulic system.
These fluids can be affected by environmental changes such as temperature variations. Therefore, the entire hydraulic system can be affected.
As temperatures rise, hydraulic fluid can begin to evaporate. As temperatures drop, the fluid can freeze. This is one of the main concerns when we consider hydraulic fluids and climate changes.
Hydraulic systems can operate from small objects like toys to large applications like airplanes or mechanical robotics.
In many of these cases, there will be times when the applications come in contact with sources of ignition and very hot surfaces.
Some examples of applications that come into contact with higher temperatures and ignition sources include hot metal shears, coke oven door openers, and oven loaders and unloaders.
Such applications leave the question: what will happen if the hydraulic fluid is exposed to high temperature situations and is it flammable? Well this usually depends on the type of hydraulic fluid being used.
Hydraulic fluids are considered serious fire hazards due to their high ignition temperatures. If hydraulic oil is sprayed around an area, it can burn just as fiercely as other hydrocarbons.
Today, we will be discussing the flammability of hydraulic fluid and how safe it is in certain applications. Read on for more information on the use of such liquids.
What is a hydraulic system?
A hydraulic drive system consists of hydraulic fluid as well as three major mechanical components. These are considered pressure generators or hydraulic pumps and can be powered by an electric motor or a hand pump/motor.
The system consists of valves, pipes, filters with the motor can be hydraulic, a hydraulic cylinder or a hydraulic actuator.
Almost all aircraft use some type of hydraulic system. The hydraulic components of a general aviation aircraft are usually limited to the brakes on its wheels.
In larger aircraft, the hydraulic system can provide the motive power for other systems such as landing gear retract/extend, nose wheel steer, flight control actuation, emergency power generation and much more.
As you can guess, the risk of fires from hydraulic fluids is a serious problem. A hydraulic fluid fire can result in the loss of an aircraft or piece of machinery and, in the worst case, loss of life.
Hydraulic fluid categories
As we mentioned earlier, there are different categories of hydraulic fluids. These are:
- mineral oils
- fire resistant fluids
- water/oil emulsions
- glycol water
- phosphate esters
Petroleum-based hydraulic fluids, like mineral oils, have a flash point that ranges from 300 to 600 degrees Fahrenheit. Flash point is the lowest temperature at which vapors can ignite.
Water-based hydraulic fluids are flammable. However, a problem with corrosion can arise when using these types of fluids. To test how flammable hydraulic fluids are, an investigation is carried out according to the ISO 12922 specification.
Fire-resistant hydraulic fluids tend to be classified as oil-water emulsion, anhydrous synthetics, and water-polymer solutions.
Fire resistant hydraulic fluids containing water will have more than 35% water content. ISO 12922:2012 classifies them into:
HFAE– Hydraulic fluids in this category are considered an oil-in-water emulsion. They have a milky to translucent emulsion appearance. These fluids contain more than 80% water and are resistant to aging. HFAE has applications in the field of mine support, underground hydraulic strut extensions, and hydrostatic transmissions.
HFAS – They are synthetic aqueous fluids that have a transparent appearance. These fluids are free of mineral oils and contain more than 80% water content. The main applications of HFAS are mine support, press hydraulics, foundry technology and much more.
HFB – HFB fluid is a water-in-oil emulsion containing more than 40% water. One application of this is coal mining. The minimum ignition temperature (flash point) of HFB is 1202 degrees Fahrenheit or 650 degrees Celsius according to ISO standards.
HFC – These are known as glycol solutions, polyalkylene glycol solutions, or water glycols. The flash point of this fluid is 1112 degrees Fahrenheit or 600 degrees Celsius. It is a water-polymer solution containing more than 35% water.
It has fields of application where waterless hydraulic systems are not used. These include the steel industry, foundries, coking plants, hardening plants, injection molding, forming presses, and more.
HFDR– This one uses phosphoric acid ester. It tends to have poor viscosity as well as poor temperature characteristics. HFDR is considered a dangerous work material, as it can generate toxic gases in the event of a fire. One application that uses HFDR is the turbine control system.
HFDU – HFDUs can be classified as ester-based and glycol-based. Glycol-based HFDU generally has good viscosity, good temperature characteristics, shear stability, and is resistant to aging. It is a water soluble fluid with excellent wear protection.
Mobile systems that have high thermal load properties use glycol-based HFDUs, while ester-based HFDUs have a higher soil dissolving capacity.
So is hydraulic fluid flammable?
Hydraulic fluid is extremely flammable. It has been a factor in many fires over the years and when ignited can significantly increase the extent of fire damage.
Hydraulic systems are highly pressurized. This means that the flames from a hydraulic oil fire can spread a great distance.
In factory settings these flames can easily reach cables and other combustible materials which will quickly catch fire and be quickly destroyed.
Therefore, it is essential that you assess the risks associated with hydraulic oils so that you and others are protected at all times.
The risk of a hydraulic oil fire can actually be eliminated by switching to non-combustible hydraulic fluids or by using electrical or pneumatic equipment instead.
Types of Fire Resistant Hydraulic Fluid
In many industrial systems, hydraulic fluids may come into contact with sparks, flames, or may be subject to extreme environmental conditions caused by nearby equipment. When these conditions are present, hydraulic system designers are tasked with selecting fluids that will safely withstand the presence of high temperatures or other sources of ignition. Hydrocarbon hydraulic oil is generally not suitable for use near open flames or sparks, or in environments where the oil may come into contact with machine parts that are above the specific flash point of the oil.
However, there are a range of fire resistant hydraulic fluid options available to us in a wide variety of applications. Please note that not all of these solutions will be ideal for all applications. Contact a member of the Cross team to discuss your equipment and application to determine which may be best for you. Below are some of the more common types of fluids used when fire resistance is needed.
Phosphate ester fluids
Although phosphate ester fluids offer very good lubricity for hydraulic components, great care must be taken when handling or disposing of this type of fluid. Special seals and hoses must also be used on all hydraulic components within the hydraulic system. Typically “Viton” seals are used with phosphate ester fluid.
Phosphate ester fluids also offer very good fire resistant properties. This fluid was originally formulated in the mid 1940’s and is still very popular in the aviation industry for use in aircraft hydraulic systems. Phosphate esters have fallen out of favor in recent years, due to the need for special seals and coatings, as well as the care required when handling or disposing of this fluid.
water glycol liquids
Water Glycol fluids offer excellent fire resistance properties due to their high water content. However, when this fluid is subjected to high pressure, the protective lubricating film required by the hydraulic components will be affected by the low lubricity of the water contained in the fluid. Many times, the pressure and velocity ratings of hydraulic components are reduced when used with water glycol, due to the reduced film strength of this fluid. Water does not work well as a lubricant.
Emulsion oil fluids
Water emulsion fluids are made by mixing typical hydrocarbon hydraulic oil with water. This type of fluid requires between 35% and 45% water added to the specially formulated hydraulic oil to maintain its fire resistance. Again, due to the poor lubricity of the water, the pressure ratings of the hydraulic components are often reduced. In addition, water emulsion fluids require careful control of the water content, to ensure that evaporation of the water does not cause the fluid to become flammable once again.
Polyol ester fluids
In recent years, many fluid manufacturers have developed new synthetic fluids known as polyol esters. These fluids offer very good fire resistant properties, excellent lubricity (even under high pressure conditions) and good viscosity levels over a wide range of temperatures. Also, these fluids can normally be used with standard NBR (Buna) seals.
When selecting a hydraulic fluid for high-temperature applications, be sure to follow the manufacturer’s recommendations for viscosity, shear rates, and lubricity requirements for the specific hydraulic components you intend to use. The longevity of hydraulic components can be affected by specific application problems that can arise when using special hydraulic fluids.
Additionally, care must be taken to select the proper cooling system when using water-based systems. When fluid temperatures exceed 122 degrees F, the evaporation of water can affect the chemical balance of the fluid, resulting in a possible loss of fire resistance.
In summary, significant improvements have been made in recent years for fire-resistant fluids, giving hydraulic designers many options for hydraulic systems that require fluids that operate in high-temperature environments. However, when selecting high temperature fluids, care must be taken to avoid damaging hydraulic system components. Designers must also be aware of the potential environmental hazards associated with some fire resistant fluids.
It is always better to be “safe than sorry”, so if you need clarification, help or a second opinion, it is best to consult a trusted fluid energy specialist.
Hydraulic fluid can be extremely flammable due to its high flash point. Some of these fluids are more likely to catch fire than others due to their properties and water content.
However, sufficient and proper care must be exercised whenever hydraulic fluids are used on or near them. With preventative measures, catastrophic fires can be avoided.
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