hydraulic

What is the 'diesel effect'

The diesel effect occurs in a hydraulic cylinder when air is
drawn past the rod seals, mixes with the hydraulic fluid and
explodes when pressurized.

How does this happen?

When a double acting cylinder retracts under the weight of its
load, the volume of fluid being demanded by the rod side of the
cylinder can exceed the volume of fluid being supplied by the
pump.

When this happens, a negative pressure develops in the rod
side of the cylinder, which usually results in air being drawn
into the cylinder past the rod seals. This occurs because most
rod seals are designed keep high-pressure fluid in the cylinder
and are not designed to keep air out. The result of this is
aeration - the mixing of air with the hydraulic fluid.

Aeration causes damage through loss of lubrication and
overheating, and when a mixture of air and oil is compressed in
a cylinder it can explode, damaging the cylinder and burning its
seals. As you have probably gathered, the term 'diesel effect'
is a reference to the combustion process in a diesel engine.