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Hydraulic and Pneumatic Systems 42005/2006 I.
Hydraulic cylinders
Cylinder types: piston, double acting
Hydraulic and Pneumatic Systems 292005/2006 I.
Valves
Pressure relief valve
xA k C
Fspring
m
N
psys
Qp
Symbol
Hydraulic and Pneumatic Systems 302005/2006 I.
Pressure relief valve
Theoretical basics
xcFFAp SSsys 0
f
sys
fcrv
pxk
pxkvAQ
22
AcxF
xkQ S
frv
02
Force equilibrium:
(1)
Curtain surface:
Circumference height = k ∙ x∙ = Ac
Bernoulli equation:
(2)
(3)
(4)
7,0...6,0
Qrv depends nonlinearly on x or if we express x from (1)
then:c
FApx Ssys 0
sysf
Ssysrv p
c
FApkQ
20
Hydraulic and Pneumatic Systems 312005/2006 I.
Pressure relief valveTheoretical basics:
0Ssys FAp
syssyssys
const
fsys
f
syssysrv ppp
cAk
pc
AppkQ
22
(5)
Let be the pressure when the valve just opens (x = 0)
subst. to (4)
*sysp
(5) is valid from x = 0 to x = xmax, xmax being the displacement when the spring is completely compressed
max0 xx
syssyssysrv pconstpppconstQ max
If p > pmax :
Hydraulic and Pneumatic Systems 322005/2006 I.
Pressure relief valveTheoretical basics:
Qrv
negative part: physically impossible
pmax
psys
belongs to xmax
*sysp