2005/2006 I.Hydraulic and Pneumatic Systems4 Hydraulic cylinders Cylinder types: piston, double...

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