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

2005/2006 I.Hydraulic and Pneumatic Systems29 Valves Pressure relief valve x A k C F spring p sys QpQp Symbol

2005/2006 I.Hydraulic and Pneumatic Systems30 Pressure relief valve Theoretical basics Force equilibrium: (1) Curtain surface: Circumference ∙ height = k ∙ x = A c Bernoulli equation: (2) (3) (4) Q rv depends nonlinearly on x or if we express x from (1) then:

2005/2006 I.Hydraulic and Pneumatic Systems31 Pressure relief valve Theoretical basics: (5) Let be the pressure when the valve just opens (x = 0)  subst. to (4) (5) is valid from x = 0 to x = x max, x max being the displacement when the spring is completely compressed If p > p max :

2005/2006 I.Hydraulic and Pneumatic Systems32 Pressure relief valve Theoretical basics: Q rv negative part: physically impossible p max p sys belongs to x max