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# Hydraulic Cylinder Dangers

### Dangers Associated with Hydraulic Cylinders

Although hydraulic cylinders are a necessary and integral part of industry, there some very real dangers
associated with them that could become fatal. Not least of
which is pressure multiplication.
Pressure multiplication in hydraulic cylinders
The force applied in a hydraulic cylinder is calculated with
the equation (F = P * A). In
a double acting cylinder(one that is powered both in and
out) the area of the
piston on the bottom or cap end side is much larger than
the area of the
piston on the rod side. This causes an unequal pressure
difference on
either side because, on the rod side, the smaller area has
to have more
pressure pushing on it to keep the piston from being
moved by the
pressure pushing on the larger area of the piston on the
other side.
If the effective surface area of the piston on the rod side of the cylinder has half the area of that on
the piston side, it will produce half the force on the piston side for the same amount of pressure.
Getting back to our equation, Force = Pressure multiplied by effective piston surface Area using a 3”
piston on a 2” rod and a pressure of 2000psi we get a force of 14000lb on the piston side and only
8000lb on the rod side.
If, for any reason, the piston side of a double-acting cylinder is pressurized and at the same time fluid
is blocked on the rod side, pressure will increase (multiply) in the rod side of the cylinder until the
forces become balanced or the cylinder fails catastrophically. When we transpose the equation above to
calculate the pressure produced, we get P = F/A, Pressure = Force divided by piston surface Area.
Applying this to our 3” piston 2” rod and 2000psi pressure, on the piston side we get:- P = 14000 / 4
which equals 3500 psi. Considerably more than the pressure on the other side. If we take the main
relief pressure of most systems of 2800psi, then our pressure goes to a staggering 4900psi which is
definitely not good for your system. Depending on where the hydraulic fluid is blocked, this could result
in anything from a blown hose to blowing the gland seals out or even catastrophic damage to the
cylinder.
Remember, at Central Qld Hydraulics, we take any old cylinders that are preserved well, replace their
damaged parts to make them go on doing their outstanding work as new cylinders.
Call us today for more information
07 4952 5621

Surface area 7 inch²

Surface area 4 inch²

Cross sectional
surface area 3 inch²

2000psi

# CENTRAL QUEENSLAND HYDRAULICS

As well as selling new parts and
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