"We are in the process of converting our hydraulic systems to fire-resistant fluids. Is there anything we should be aware of during the conversion?"

The unique characteristics of fire-resistant fluids make it necessary to carefully consider the modifications required before converting to a fire-resistant fluid or when converting from one type of fire-resistant fluid to another.

All of these fluids have a higher specific gravity than does petroleum hydraulic oil. As a result, the pump inlet may need to be enlarged to avoid cavitation. Long inlet lines must be avoided, and inlet fluid strainers should be no finer than 60 mesh.

It may also be necessary to design and install additional filtration circuits on the discharge and return lines because fire-resistant fluids tend to suspend contamination much more readily than petroleum base oils.

Before installing the fire-resistant fluid, the entire system must be flushed thoroughly to remove any residual contamination. Adding varsol to the system and operating all of the circuits before draining the original hydraulic oil can help to dislodge sediment and sludge, which should be removed prior to the installation of the new fire-resistant fluid.

Portable filter “buggies” equipped with extremely fine, absorbent depth-type filters are available to aid in this cleaning process so that the flushing fluid can be reused if several machines need to be cleaned prior to the installation of the fire-resistant fluid.

Make certain that compatibility tests are performed to ensure that seals, packing material and hoses will not deteriorate prematurely after the conversion is completed.

Synthetic fire-resistant fluids, such as phosphate ester, are not compatible with most standard sealing materials. Also, keep in mind that water glycol fire-resistant fluid will attack components with aluminum, zinc or magnesium materials.

After conversion to a fire-resistant fluid is completed, all full-flow filters should be serviced on a regular basis, preferably once a week.

If fine filters of the absorbent depth type are used on side-stream or bypass circuits, these filters should be fitted with pressure gauges or flow meters on the outlet side to monitor the filter condition. The pressure gauges should be installed on the filter housing to show the filter's pressure drop. As pressure increases, it indicates that the filter is becoming plugged with contamination.

When flow meters are used for this purpose, a reduced flow rate from the filter discharge means that the filter is becoming saturated with contaminants. To obtain maximum benefit from these bypass filter circuits, the filter should be replaced before the flow is reduced to zero.

The most important thing to remember when considering a conversion to a fire-resistant fluid is to become aware of all of the potential problems that can occur. Then carefully investigate all of the available options before rushing into a decision that could prove to be very costly.