General Features:
The elektrohydraulic control valve SVEW consists of the following elements:
| - | electric control motor, e.g. low-power stepper motor (1) |
| - | hydraulic
control valve consisting of four single, mechanically adjustable hydraulic |
| The following auxiliary components can be supplied optionally: | |
| - | mechanical
electrical monitoring of the extreme control positions (overload component E1/E2) (3) |
| - | zero point switch for stepper motor (rotating disc and sensor) (4) |
| - | magnetic brake for stepper motor (5) |
| - | monitoring of set-value input (6) |
The electronic control unit controls the stepper motor according to the programmed parameters (travel, speed, acceleration).
The high-precision mechanism converts the rotation of the stepper motor to a linear motion, opening the valves and connecting the cylinder or the hydraulic motor with P and T. The resulting pressure difference causes the motion of the cylinder or the motor, the speed of wich is proportional to the number of revolutions of the stepper motor. When the driven component has reached the set value, the mechanical feedback causes the valves to be closed (hydromechanical closed loop).
The diagram shows the signal flow and the symbols for the different drives.
The movement of the valve actuation mechanism is monitored in order to protect the drive against mechanical damage. In order to prevent an overload condition, the overload switch senses excessive degrees of contouring variation and the direction of the overload.
The following factors
may lead to overload:
mechanical collision of the drive (obstruction, limit stop etc.)
insufficient power of the drive (e.g. due to increased friction etc.)
insufficient hydraulic supply capacity (collaps of pressure)
selected speed is to high (causing collapse of pressure)
Every drive is designed for a defined application situation and can be replaced by a drive with the same article number (on site) at any time. Electrical or mechanical adjustment are not required.
The oil supply lines of the electrohydraulic amplifier must have sufficient capacity. The maximum velocity of flow is 5-7 m/s for pressure lines (port P) and 3-5 m/s for tank lines (port T).
Caution!
Take care NEVER to confuse the ports P (pump line) and T(tank line), as this
will destroy the control valve immediately. The same applies to the ports A
and B if external actuator lines are used.
Caution!
The drain port (L) must never be exposed to pressure in excess of 0.5 bar. Even
short exposure to higher pressure will turn the sealing lips of the control
valve over and cause leakage. The drain line must be a separate pipe, and its
outlet opening must be approx. 20 mm above oil level. The drain line must not
be connected with the tank line. If possible, the drain line should be slope
down towards the tank. If you are in doubt about whether the devices have been
connected correctly, please consult H+L.
If pilot-controlled check valves are used in the actuator lines (anti-drop protection), please ensure that prior to operation, the control lines of these valves have been connected correctly.
When installing
drives or changing control valves, special care should be taken to keep all
materials and components as clean as possible.
Keep sealing surfaces (O-ring flanges) free of dirt etc.
Always burr new pipes, and remove dirt and chips.
Always use pressure filters without bypass in the supply duct.
The fineness of the filter (max. 10 ΅m) is specified in the hydraulic plan.
Prior to starting the equipment, check the oil filter cartridge for being
mechanically intact and for having the required fineness (compare with cartridge
marking).
Never refill new oil directly from a barrel, always use the filtering device.
Use the oil grades specified by H+L. Our recommendations are based on many
years of experience.
If the equipment is used for the first time, the hydraulic oil should be changed
after approx. 20 hours of operation. After that, the oil must be changed after
every 3000 hours of operation. We recommend oil changing intervals of 12 months.
Remove the cover
of the stepper motor.
Compare the data specified on the driver board with the stepper motor data,
e.g. Imax.
Check voltage and polarity, including the monitor switches.
Check whether the control software reacts to the signal of overload contacts,
which is indicated by light-emitting diodes (LEDs) 1 and 2 near the type plate.The
function should be tested for each contact separatly.
Check the direction of rotation of the stepper motor
Check the power supply lead. If leads with a lenght exceeding 5 metres are
used, they must be shielded, and the phases must be twisted in pairs to avoid
interference of electric signals. Check leads for fatigue fractures.
After the control valve has been connected with the hydraulic and electric
systems, the electric stepper motor must be alive, which can be checked by turning
the pulley manually. Check the brake if applicable (permanent-magnet brake,
which is open when alive).
The two LEDs near the type plate must be on. (This is a requirement for operating
of the unit.) In case of overload (cf. page 4), one of the two diodes goes out.
LED 2 goes out if and overload condition is reached with a right-hand rotation
(full operating pressure in chamber A and zero pressure in chamber B). LED 1
goes out if an overload occurs with a left-hand rotation (reversed pressure
conditions in the chambers A and B)
Caution!
Disconnected leads only when the electric control is dead, otherwise contact
consumption may result.
Prior starting the equipment, the entire hydraulic system should be bled throughly. To bleed the system automatically, move the drive at low pressure (20-30 bar) without load over the whole travelling distance or angle of rotation. This can be done easily by manually turning the stepper motor side of the shaft while the electronic control is swichted off, but the hydraulic system is on. (Remove the cover of the stepper motor.)
Caution!
Never use air as operating medium. While the equipment is not under pressure,
the piston or hydraulic motor must not be moved by an external force, as this
will destroy the mechanical feedback.
After an emergency shutdown, move the control to middle (neutral) position (manually, if necessary). Switching on the hydraulic system with open valve inserts may cause abrupt movements involving high forces (equivalent to the contour variation). If the control cannot be moved to a middle position, the supply pressure should be increased only gradually after a shutdown until operating pressure is reached.
The basic setting of the control valve (pressures in the chambers A and B while the control is not moving) must not be changed, as this may seriously affect the function of the drive.
The production and identification numbers on the type plate are required for support and repair of components, therefore the type plate must never be painted over.
Prior to moving the equipment (e.g. shipping), secure the driven parts oft the unit (e.g. tool side) against twisting or moving to prevent destruction of the mechanical feedback.
If the equipment is not functioning properly, try to establish whether the malfunction is due to a problem on the set-valve side (electronic control) or on the mechanical/hydraulic side.
Switch off the
control.
Remove the cover of the stepper motor.
Disconnect the steppermotor cable by unplugging the 10-pin Stoko connector
from the board.
Switch on the control and the hydraulic equipment.
Turn the control shaft and see whether the mechanical/hydraulic equipment
reacts to the change in the input value.
The following table specifies possible causes and remedial measures in case
of problems.
| Possible Causes |
||||
| mechanical / hydraulic equipment | What to do | Control / Electrical Equipment | What to do | |
| Overload | - excessive acceleration/speed | - reduce | - defective overload switch | - replace switch |
| - collapse of pressure; P to low | - check pressure supply | |||
| - fixed stop | - allow free movement | |||
| - tool slide requires too much power to move | - repair tool slide | |||
| - hanging valve inserts | - move to both extreme positions manually and rinse | |||
| Positioning Error / Offset | - loose pulley | - fasten clamped joint | - controlsignal errors | - correct errors |
| - defective belt | - replace | - stepper motor - missing phase | - check driver/ stepper motor | |
| - loose feedback mechanism | - fasten loose part(s) | - excessive acceleration / speed | - reduce | |
| Positioning Inaccuracy | - dirt particles in the valve | - change oil, rinse valve | - control signal errors | - correct errors |
| - oil too old | - change oil | |||
| High-Frequency Vibration | - excessive pressure | - reduce pressure | ||
| - wear of mechanism | - repair mechanism / replace parts | |||
Please note that the use of suitable hydraulic oil is indispensable for the safe and reliable function of our equipment. The products listed in the following alphabetical table are lubricants which meet our requirements according to the mineral oil companies. We cannot assume liability for the qualitiy of the products. In the Federal Republic of Germany, mineral oil qualified as motor oil can be used as hydraulic oil if purchased properly as stipulated in section 8 (3) of the Law on Excise on Oil and Oil Products (Mineralφlsteuergesetz).