Hydraulic fluids

Flame retardant hydraulic fluids are classified in VDMA 24317. They are available as HFAE, HFAS, HFB, HFC and HFD oils:

• HFAEs are oil-in-water emulsions with a water content of greater than 80% and a mineral-oil or soluble polyglycol-based concentrate. In the mineral-oil based option it is necessary to watch out for decomposition and microbe growth. The fluid can be used at temperatures from +5 °C to +60 °C (+41 °F to +140 °F).
   
• For HFASs with synthetic concentrates there is no danger of decomposition. However, attention should be paid to the significantly increased tendency for corrosion.
   
• HFBs are water-in-mineral oil emulsions with a water content greater than 40%. These hydraulic oils can also be used from +5 °C to +60 °C (+41 °F to +140 °F), but are not approved for use in Germany due to their inadequate fire safety characteristics.
   
• HFCs are so-called aqueous glycols, quasi aqueous monomer or polymer solutions (frequently polyglycols). Their water content is generally between 35% and 65%. These flame resistant hydraulic fluids can be used at pressures of up to 250 bar (3625 PSI) and temperatures between -20 °C and +60 °C (between -4 °F and +140 °F.
  When using HFC fluids, it must be clarified whether the seal materials being used are suitable. While fluororubber (FKM) is not suitable in every case, seals made of acrylnitrile-butadiene rubber (NBR) are unproblematic. 

• HFDs are water-free fluids that can be used in the temperature range from +20 °C to +150 °C (+68 °F to +302 °F). Their compositions differ greatly, which means that a further distinction is made among HFD-R, HFD-S, HFD-T, HFD-U. These fluids are flame retardant, but can cause problems in the suction performance of pumps, and they are corrosive to many seal materials.
   

Caution: If HFC fluids are used, it must be clarified whether the sealing materials used are suitable. Fluorocarbon rubber (FKM) is not suitable in every case. Seals made of acrylonitrile-butadiene rubber (NBR) are unproblematic..