PC spools are beneficial when they are used with oscillating applications. The spool design applies
dampening to the port because flow from the valve varies with load change. See Natural oscillation
example on page 9.
Natural oscillation example
A Pressure
B Time
C Flow
Yellow line Pl
Red line Pc
Dotted line Ql
A certain position of the spool is given leading to a constant pressure, Pc. The load pressure, Pl is
oscillating. Over time, the pressure drop across the main spool (Pc minus Pl) varies, which leads to a
variable flow. The flow out, Ql, is also shown on the graph as a dotted line. The amount of dampening
applied is dependent on the relative difference in pressure between spool set point pressure and load
varying pressure. The relative difference is shown on the graph as ΔP1 and ΔP2.
Application Guide
Using flow or pressure control spools
Pressure control spools in oscillating systems
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Danfoss | Feb 2017 AB00000079en-US0101 | 9
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