2005/2006 I. Hydraulic and Pneumatic Systems1 Directional valves Classification schemes: 1.Spool valves or poppet valves 2.Switching or continuously adjustable valves 3.Number of ports and positions 4.The kind of governing and positioning unit

2005/2006 I. Hydraulic and Pneumatic Systems2 Directional valves 1. Spool valves or poppet valves: Spool valvesPoppet valves have always leakagescan be totally sealed need relatively large displacements because a positive overlap is needed for sealing need smaller displacements to let fluid through preferred in all other cases because of their flexibility and lower price preferred for large flow rates need radial and axial pressure relief,

2005/2006 I. Hydraulic and Pneumatic Systems3 Directional valves 2. Switching or continuously adjustable valves: Directional valves work either in certain switching positions or they are continuously adjustable. Latter by electrohydraulic or electric governing units.

2005/2006 I. Hydraulic and Pneumatic Systems4 Directional valves 3. Number of ports and positions: Two positions Three positions Basic symbols 4/3 valve with ports, operation positions and governing elements

2005/2006 I. Hydraulic and Pneumatic Systems5 Directional valves 4. Kind of governing and positioning unit: By hand, electrically or electrohydraulically Cross- section: Symbol:

2005/2006 I. Hydraulic and Pneumatic Systems6 Electrically governed continuously adjustable valves Servo valves:  Servo valves  Proportional valves They are able to govern a very large output power with a very small input power. Large masses have to be moved in a short time against varying forces to precise positions. These valves are very expensive because they have to be manufactured with very high accuracy. Because of this, their operation is also expensive, because the fluid has to be very well filtered. They have usually two (for very large flow rates three) amplifying stages.

2005/2006 I. Hydraulic and Pneumatic Systems7 Servo valves Double nozzle – impinging plate (bridge circuit): User s0-ss0-s s0+ss0+s s Q2Q2 Q1Q1 QUQU QUQU Q 01 p1p1 p0p0 p2p2 1 0,8 -0,8 Linear part in the middle

2005/2006 I. Hydraulic and Pneumatic Systems8 Servo valves Operation: If there is no current, there is no displacement, the valve body is kept in the middle. If there is current, the iron core is displaced and the impinging plate that is rigidly coupled with it is also displaced and a pressure drop is created. Note that there is a small negative overlap, the manufacturing must be very good. There must always be a flow. Disadvantage: it is difficult to hold the zero position, because of dry friction or contamination. Solution: There are also three-stage servo valves. They are used for very large powers.

2005/2006 I. Hydraulic and Pneumatic Systems9 Continuously adjustable valves Proportional valves: Continuously adjustable proportional magnets are able to adjust continuously and precisely the position of a directional valve. The magnetic force is proportional to the current and nearly independent of the position. The core reaches out far from the coil. They might be connected with a position control, where hysteresis effects are smaller. They are often used for flow rate control but all pressure valves can work with a proportional magnet instead of a spring. They are more precise.

2005/2006 I. Hydraulic and Pneumatic Systems10 Accessories Liquid reservoir: Tasks:  Storing of necessary liquid volume  Conducting heat away from the system  De-airing of the liquid (large surface, long stay of the liquid)  Separation of condensed water  Carrying element of other system components (pumps, valves, pipes, etc.) Pipes: Steel of flexible hoses. Key point: sealing

2005/2006 I. Hydraulic and Pneumatic Systems11 Accessories Filter: Surface filter Volume filter – an order of magnitude better but not cleanable It can be before the pump, after the pump, before every sensitive elements or in the back flow line.

2005/2006 I. Hydraulic and Pneumatic Systems12 System concepts Delivering of liquid by:  Flow sources  Pressure sources In case of flow sources normally for each actuator a separate source. One pressure source can deliver several actuators parallel. Pressure source should not be controlled by restriction valves because the losses will be then too high. * Better is to control by adjusting the displacement volume of the actuator. It can happen with a hydromotor easily but for a hydraulic cylinder one needs a hydraulic transformer. This is called secondary control. * → exp. on next slide

2005/2006 I. Hydraulic and Pneumatic Systems13 System concepts Cont. * Basically there are two main subgroups: 1. The pressure is always constant In this case the main task is to find a control system to change the flow rate for the oscillating flow rate needs of the actuators. Various control mechanisms can be used here 2. The pressure is not constant -Secondary control (see previous page) -Load sensing control (much more complicated)

2005/2006 I. Hydraulic and Pneumatic Systems14 System concepts Constant pressure sources: -Pump with pressure relief valve: not very effective – lot of lost energy. -The displacement volume or the rotational speed of a pump can be controlled by measuring the pressure. In fact flow rate control but indirectly pressure control. The constant valve is for safety: it limits the maximum possible flow rate through the system and prevents a breakdown of the pressure. These valves are all between the actuator and the reservoir. This has the advantage that the actuator is between two liquid columns that are both under pressure. VDr = Restriction valve VW = direction valve -All three versions have a 4/3 valve -All three versions have two restriction valves, one constant and one adjustable Position drives:

2005/2006 I. Hydraulic and Pneumatic Systems15 System concepts Drives

2005/2006 I. Hydraulic and Pneumatic Systems16 Constant pressure sources Position drives: With the adjustable resistance the velocity can be controlled: a)Is a simple circuit. Problem is drifting in the holding position since the spool valve has a leakage. b)Solves this problem by putting a 2/2 directional valve before the 4/3 valve. This seals perfectly. In addition, a double check valve prevents the cylinder from moving. c)Is even better. It allows a very accurate positioning. The directional valve 1 has the job to switch between a creeping mode and a normal speed mode. From the creeping mode it is easy to stop accurately. Hold: 1 Normal speed: 2 Creeping speed: 0

2005/2006 I. Hydraulic and Pneumatic Systems17 Constant pressure sources Velocity drives: VW = directional valve EV = fast forward ER = fast backward AV = working forward AR = working backward VSZ = flow control valve VDr = restriction valve Simpler circuits can be derived. If for example no working backward mode is needed then VW4 and VSZ1 can be omitted. If the working velocity is so small that the flow rate is around the leakage flow rate, large errors occur. In this case spool valves may not be applied, instead pilot operated check valves. Directional valve positions

2005/2006 I. Hydraulic and Pneumatic Systems18 Constant pressure sources Force drives: Holding of work pieces, lifting of weights, forming of materials a)Simple circuit without adjustment of force. Why is it a constant force drive? Because the pressure pushes the cylinder as long to the right as there is no equilibrium with the spring force. b)Force adjustable with a pressure relief valve. c)Large force. Force is adjustable in two stages. d)Weight balancing, not adjustable. e)Weight balancing with two-stage adjustability. a)b)c) d) e)

2005/2006 I. Hydraulic and Pneumatic Systems19 Big pictures End of normal presentation Beginning of big pictures

2005/2006 I. Hydraulic and Pneumatic Systems20 Directional valves Spool valves – pressure relieves 1 – axial, 2 – axial

2005/2006 I. Hydraulic and Pneumatic Systems21 Directional valves Spool valves - overlaps O > 0O = 0O < 0

2005/2006 I. Hydraulic and Pneumatic Systems22 Directional valves Spool valves Centred by springs Pneumatically operated Hydraulically operated Spool typesWith two switching positions and latch

2005/2006 I. Hydraulic and Pneumatic Systems23 Directional valves Spool valves Electro-hydraulicaly governed, centred by spring Electro-hydraulicaly governed, centred by pressure Back

2005/2006 I. Hydraulic and Pneumatic Systems24 Directional valves Spool valves

2005/2006 I. Hydraulic and Pneumatic Systems25 Directional valves Spool valves

2005/2006 I. Hydraulic and Pneumatic Systems26 Directional valves Spool valves

2005/2006 I. Hydraulic and Pneumatic Systems27 Directional valves Spool valves - spool types

2005/2006 I. Hydraulic and Pneumatic Systems28 Directional valves Spool valves

2005/2006 I. Hydraulic and Pneumatic Systems29 Directional valves Spool valves

2005/2006 I. Hydraulic and Pneumatic Systems30 Directional valves Spool valves

2005/2006 I. Hydraulic and Pneumatic Systems31 Directional valves Spool valves

2005/2006 I. Hydraulic and Pneumatic Systems32 Directional valves Poppet valves With one ball 1 - ball2 - spring 3 - poppet 4 - housing5 – lever ? 6 – operating pin ? 7 - ball8 - poppet Electrically governed 3/2 poppet valves With two ball Ball Taper Plate Back

2005/2006 I. Hydraulic and Pneumatic Systems33 Directional valves Poppet valves

2005/2006 I. Hydraulic and Pneumatic Systems34 Directional valves Poppet valves

2005/2006 I. Hydraulic and Pneumatic Systems35 Directional valves Poppet valves

2005/2006 I. Hydraulic and Pneumatic Systems36 Directional valves Number of ports and positions: a)2/2 b)3/2 c)4/3 d)5/3 e)5/3 f)4/3 g)6/3

2005/2006 I. Hydraulic and Pneumatic Systems37 Directional valves 5/3 valves:

2005/2006 I. Hydraulic and Pneumatic Systems38 Directional valves Number of ports and positions:

2005/2006 I. Hydraulic and Pneumatic Systems39 Directional valves Number of ports and positions:

2005/2006 I. Hydraulic and Pneumatic Systems40 Directional valves Kind of governing and positioning unit:

2005/2006 I. Hydraulic and Pneumatic Systems41 Directional valves Kind of governing and positioning unit:

2005/2006 I. Hydraulic and Pneumatic Systems42 Directional valves Kind of governing and positioning unit:

2005/2006 I. Hydraulic and Pneumatic Systems43 Directional valves Kind of governing and positioning unit:

2005/2006 I. Hydraulic and Pneumatic Systems44 Directional valves Kind of governing and positioning unit:

2005/2006 I. Hydraulic and Pneumatic Systems45 Directional valves Kind of governing and positioning unit:

2005/2006 I. Hydraulic and Pneumatic Systems46 Directional valves Kind of governing and positioning unit:

2005/2006 I. Hydraulic and Pneumatic Systems47 Directional valves Kind of governing and positioning unit:

2005/2006 I. Hydraulic and Pneumatic Systems48 Servo valves Construction Torque motor Permanent magnets Iron core with coils tube Bending tube Double nozzle – impinging plate Return springs Spool valve Constant restrictions User

2005/2006 I. Hydraulic and Pneumatic Systems49 Servo valves Positioning with spring

2005/2006 I. Hydraulic and Pneumatic Systems50 Servo valves Positioning with spring

2005/2006 I. Hydraulic and Pneumatic Systems51 Servo valves Positioning with spring

2005/2006 I. Hydraulic and Pneumatic Systems52 Servo valves Positioning with inductive device

2005/2006 I. Hydraulic and Pneumatic Systems53 Servo valves Three stage servo valve

2005/2006 I. Hydraulic and Pneumatic Systems54 Servo valves Three stage servo valve

2005/2006 I. Hydraulic and Pneumatic Systems55 Proportional valves Proportional directional valve

2005/2006 I. Hydraulic and Pneumatic Systems56 Proportional valves Proportional directional valve

2005/2006 I. Hydraulic and Pneumatic Systems57 Proportional valves Proportional directional valve

2005/2006 I. Hydraulic and Pneumatic Systems58 Proportional valves Proportional flow rate valve

2005/2006 I. Hydraulic and Pneumatic Systems59 Proportional valves Proportional flow rate valve

2005/2006 I. Hydraulic and Pneumatic Systems60 Proportional valves Proportional pressure valve

2005/2006 I. Hydraulic and Pneumatic Systems61 Proportional valves Proportional pressure valve

2005/2006 I. Hydraulic and Pneumatic Systems62 Accessories Filters

2005/2006 I. Hydraulic and Pneumatic Systems63 Accessories Filters

2005/2006 I. Hydraulic and Pneumatic Systems64 Accessories Filters

2005/2006 I. Hydraulic and Pneumatic Systems65 Accessories Filters

2005/2006 I. Hydraulic and Pneumatic Systems66 Accessories Filters

2005/2006 I. Hydraulic and Pneumatic Systems67 Accessories Filters

2005/2006 I. Hydraulic and Pneumatic Systems68 Accessories Filters

2005/2006 I. Hydraulic and Pneumatic Systems69 System concepts Positioning drives Against bumpers Drift-free holding of the cylinder Positioning out of creeping motion

2005/2006 I. Hydraulic and Pneumatic Systems70 System concepts Positioning drives Against bumpers Drift-free holding of the cylinder Positioning out of creeping motion

2005/2006 I. Hydraulic and Pneumatic Systems71 Velocity drives Circuit plan

2005/2006 I. Hydraulic and Pneumatic Systems72 Velocity drives Directional valve positions

2005/2006 I. Hydraulic and Pneumatic Systems73 Velocity drives Modification for very low working speeds

2005/2006 I. Hydraulic and Pneumatic Systems74 Force drives Without adjustment of force

2005/2006 I. Hydraulic and Pneumatic Systems75 Force drives Force adjustable with pressure relief valve

2005/2006 I. Hydraulic and Pneumatic Systems76 Force drives Force is adjustable in two stages

2005/2006 I. Hydraulic and Pneumatic Systems77 Force drives Weight balancing, not adjustable

2005/2006 I. Hydraulic and Pneumatic Systems78 Force drives Weight balancing with two-stage adjustability