Functionality Of A Pressure Control Spool - Danfoss PVG 32 Application Manual

Application Guide
Using flow or pressure control spools

Functionality of a pressure control spool

© Danfoss | Feb 2017
A PC spool works as a variable orifice controlling flow P>A/B and A/B>T, like an FC spool, and also
controls LS>T. See the concept in
Basic principle of a PC spool
The Pc has a connection to the tank through a fixed orifice in series with a variable orifice (controlled by
spool displacement). This means that the LS signal is manipulated by the variable orifice. See the
characteristics of a PC spool in
PC spool
Adrain variable connection from Pc to tank (manipulates the LS signal)
A(pc->Pl)
physical opening area of the spool as a function of its position
Pl load pressure
Pc
manipulated LS pressure + spring pressure
Ql
flow out of the valve
The example in PC spool on page 7 shows a Ql curve, which is the flow out of the valve. Flow starts when a
pressure drop across the spool exist. So in this example, the flow will start and increase when Pc gets
higher than Pl. As a result, the spool deadband varies as the size of the load changes.
So for PC spools a certain position of the main spool is proportional to a certain Pc pressure.
Basic principle of a PC spool
PC spool on page 7.
on page 7.
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