Assembly, commissioning and maintenance of hydraulic systems
1. General
1.1 Long service life and functional reliability of hydraulic systems and their components are dependent on correct handling.
Ensure fault-free operation by taking note of:
–The special installation and operating instructions for the components
–In individual cases the special instructions
–The technical data contained in the catalogue sheet We would also like to draw your attention to:–…Commissioning and maintenance of oil hydraulic systems“ (VDI 3027)
–German standard …Hydraulic systems“ DIN 24 346
–ISO standard ISO 4413
2. Assembly
2.1 Assembly preperation
–Ensure that the system is clean!
For the environment:
Power units, pipe connections, components (e.g.
pickling may be necessary if a hot process has
been carried out, e.g. welding, hot bending, etc.),
are to be kept clean, e.g. cleaned!
For the pressure fluids:
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Watch out for contamination, dampness;
contamination from the environment must not be
allowed to enter the tanks! Fill oil tanks only via a
filter – preferably via system filters or portable filter
stations with fine filters.
Protective internal paint coatings, if used, must be
resistant to the pressure fluid to be used!
For stock parts:
Storage of parts which have not been filled or
treated with anti-corrosion fluid can lead to the
build-up of resin. Dissolve the resin and renew the
lubricating film.
–Check to see that all of the parts required for assembly are available!
–Take note of any transport damage!
2.2 Carrying out assembly
–Make use of lifting facilities and transport equipment!–Do not use force, to minimise shearing forces and tension on pipelines and components. The valve
mounting surfaces must be flat. The fixing bolts have to be evenly tightened to the stated torque. Take care to ensure that the pipes are adequately fixed (pipe
clamps)!
–When selecting pipes, hoses and fittings/flanges, the correct pressure rating has to be selected (wall
thickness, material). Only cold drawn seamless tube
is to be used.–Do not use hemp and putty as sealing materials, as these can lead to contamination and thus to malfunctions!
–In order to avoid external leakage, take note of the installation instructions of the pipe fittings‘ manufacturer.
We recommend the use of fittings with flexible seals.
–Make sure hose lines are correctly laid! Rubbing and abutting of the lines must be avoided.
–Having the correct pressure fluid available
Mineral oils: DIN 51 524 part 2 HLP – hydraulic oils are generally suitable for use with series production systems
and components.
Fast bio-degradable pressure fluids: VDMA 24 568.For these fluids the system and components have to be
matched.
Fire resistant fluids: VDMA 24 317. For these fluids the system and components have to be matched. (Before
filling the special medium it must be checked to ensure
that the system is compatible with the intended fluid.) Selected according to system requirements, please note:
–Viscosity of the hydraulic fluid
–Operating temperature range
–Type of seals used on the components fitted
3. Commissioning
When assembly has been carried out correctly, it is possible to proceed with commissioning and functional testing.
3.1 Preparations for a trial run
– Tank
cleaned?
–Pipelines cleaned and correctly fitted?
–Fittings, flanges, tightened?
–Pipelines and components correctly connected in line with installation drawings or circuit diagram?
永远的谭嗣同–Is the accumulator filled with nitrogen? Nitrogen is to be filled until the pre-charge pressure p0 , as stated in the
circuit diagram, is reached. (On the fluid side the system
has to be at zero pressure!) It is recommended that the gas pre-charge pressure is noted on the accumulator (e.g. self-adhesive label) and in the hydraulic circuit so that a
compartory check may be made later if required.
Attention! Only use nitrogen as the pre-charge gas!
The accumulator must comply with the safety regulations
which apply at the place of final use.
–Are the drive motor and pump correctly assembled and aligned?
–Is the drive motor correctly connected?
–Does the filter comply with the required filter rating?
–Is the filter fitted in the correct direction of flow?
–Has the specified pressure fluid been filled up to the maximum oil level?
As the pressure fluid often does not meet the required cleanliness, filling must take place via a filter. The absolute filter rating of the filling filter should be at least that of the filter which is fitted in the system.
3.2 Trail run
–For safety reasons only personnel from the machine manufacturer and possibly maintenance and
operating personnel should be present.
–All pressure relief valves, pressure reducing valves and pump pressure controllers are to be set to zero.
The exception to this are TÜV set valves.
–Are the isolator valves fully open!
–Switch on briefly and check so see that the drive motors direction of rotation matches that of the pump.–Check the position of the directional valves and, if necessary, move them into the required switched
position.
–Set the control valves to by pass.
–Open the pump suction valves. If necessary, dependent on the design, fill the pump housing with
pressure fluid, to avoid the bearings and rotary group components from running dry.
–If there is a pilot oil supply pump this should also be commissioned 1)
–Start the pump, move it out of its zero position and listen for any noises.
–Swivel the pump out a little. (approx. 5°) 1)
–Bleed the system Carefully loosen fittings (at high points in the system) or bleed screws. When the
escaping fluid is free of bubbles then the filling
process is complete. Re-tighten the fittings.
–Flush the system, if possible by short circuiting the actuators, until the filters remain clean; Check the
filters! With servo systems the servo valves are to be
removed and replaced by flushing plates or directional valves of the same nominal size. The actuators are to be short circuited. During flushing the pressure fluid
within the hydraulic system should reach a
大明湖的传说temperature that is at least as high as the subsequent operating temperature. The filter elements are to be replaced as required. Flushing continues until the
required minimum cleanliness class is reached. This
can only be achieved by continuous monitoring using
a partical counting unit.
–Check the system functions without load, if possible control by hand; Cold test the electro hydraulic
controls.
–After the operating temperature has been reached, test the system under load; slowly increase the
pressure.
–Check monitoring and measuring devices!
科学家发现迄今最小恐龙–Check the housing temperature of the hydraulic pumps and motors –Listen for noises!
–Check the oil level, if necessay top up!
–Check the settings of the pressure relief valves by loading or braking the system.
1)As far as possible using the built-on controller, otherwise operate with the full flow. With combustion engines they are to be run at the idle speed.–Check for leaks
–Switch-off the drive
–Tighten all fittings even if there is no evidence of leakage. Attention! Only tighten when the system is not under pressure!–Is the pipe fixing adequate even under changing pressure loads?
–Are the fixing points correct?
–Are the hoses so laid that they do not rub, also under pressure?
–Check the pressure fluid level
–Full functional test of the system. Compare the measured values with the permissible or required data (pressure,
speed, setting further control components.)
–Jerky movements indicate, amongst other things, the presence of air in the system. By briefly swivelling the
pump in one or both directions with the actuator in the
loaded or braked condition, it is possible to eliminate
certain air pockets. The system is completly bled when all functions can be carried out jerk-free and smoothly and
there is no foaming on the surface of the pressure fluid. In practice it has been found that foaming should have
ceased one hour after start-up.
–Check the temperature
–Switch-off the drive
–Remove filter elements, off-line and main filters and inspect for residues. Clean the filter elements or replace. Paper or glass fibre elements cannot be cleaned.
–If further contamination is found then additional flushing is required in order to prevent premature failure of the system components
–All of the settings carried out should be documented in an acceptance certificate.
3.3 Commissioning of fast running systems
Such systems can often not be commissioned using the normal measuring instruments (e.g. pressure gauge, thermometer, electrical multi-function measurement unit, etc.) and standard tools. Optimisation is also not possible.
These systems are, for example forging presses, plastic injection casting machines, special machine tools, rolling tools, crane controls, machines with electro hydraulic closed loop control.
For commissioning and optimising these systems it is generally necessary to have a larger requirement for measurement and instrumentation so that more than one parameter (e.g. more than one pressure, electrical signals, position, speeds, flows, etc.) can be simultaneously measured.
3.4 The most common faults occuring during commissioning
In conjunction with maintenance, commissioning is very desisive for the service life and functional safety of the hydraulic system.
That is why faults must, as far as possible, be minimised during commissioning.
The most common faults are:
–The fluid reservoir has not been checked.
–The operating fluid was filled unfiltered.
–The installation was not checked before
commissioning (subsequent conversion with loss of
fluid!).
–System components were not bled of air.
–Pressure relief valves are set too close (slightly higher) to the working pressure (switching pressure
differentials not taken into account).
–Hydraulic pump pressure controllers are set higher or to the same pressure as the pressure relief valves.
–The flushing time for servo systems was not adheared to.
–Abnormal pump noises were not taken into account (cavitation, suction line not air tight, too much air in
the pressure fluid).
–Shear loads on cylinder rods not taken into account (installation error!).
–Hydraulic cylinders were not bled (seal damage!)
–Limit switches adjusted too close.
–The pressure switch switching hysteresis was not taken into account during setting up.
–Hydraulic pump and hydrualic motor housings were not filled with pressure fluid before commissioning.
–The set values were not documented.
–The adjustment spindles were not secured or sealed.–Unnecessary personnel were present at the system during commissioning
4. Maintenance
According to DIN 31 051 the term …Maintenance“ contains the following areas of activity:
–Inspection
Measures to recognise and assess the actual
situation and thereby recognise how and why the
deteriation of the so called wear reserve continues.
–Service
Measures to ensure that the nominal condition is held, precautionary measures that ensure that the wear
reserve during the usable service life is held as low as possible by applying suitable measures.
–Maintenance
Measures to re-obtain the nominal condition to
compensate for performance reduction and to top up
the wear reserve. Maintenance has to be planed and
carried out taking into account the duty, the
conseqences of a failure and the required availability.
4.1 Inspection
The individual inspection points should be colated for a specific system in so called inspection lists. This is so that personnel with differing degrees of training can adequantly carry out individual inspection points
Important inspection points are:
–Pressure fluid level in the reservoir.
–Check heat exchangers (air, water) for effectivness.–Check for external leaks (visual).–Check the pressure fluid temperature during operation.
– Check
pressures
–Check the amount of leakage taking place
–Check the cleanliness of the pressure fluid
Attention!
A visual check can only give an approximation (clouding of
the pressure fluid, it looks darker that when originally filled, sediment in the fluid reservoir).
If partaical counting is not possible then there are three methods of determining the cleanliness:
Partical counting via electronic counting and sorting equipment.
Microscopic examination
Gravimetric determination of the solids via fine filtration of
a specific quantity of fluid (e. g. 100mL) and weighing the
filter paper before and after the filtration process. This
makes it possible to determine the amount of solids in
mg/L.
–Checking filter contamination. A visual check of todays, increasingly used, depth filters is no longer possible.
–Check the chemical characteristics of the pressure fluid.
–Check temperatures where bearings are located.
–Check the development of noise
–Check performances and speeds
–Check pipework and hoses
Attention!
Damaged pipes and hoses must be immediately replaced.–Check accumulator stations
4.2 Servicing
Inspection, servicing and maintenance are often in practice not as severely separated as the defenitions describe. Servicing is often done in conjunction with inspection.
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Due to safety considerations pipe fittings, connections and components must not be loosened as long as the system is pressurised.
Important service work is:
–Create a maintenance book It is recommended that a maintenance book is created to define which specific
components have to be checked.
–Checking the fluid level
Continuously during commissioning
For a short period after commissioning
Later, weekly
–Checking the filter
During commissioning, in intervals of two to three hours and, if necessary replace.
During the first week daily and if necessary clean.
After the first week the filter should be cleaned as required.
Suction filter maintenance:
Suction filters require particulary careful maintenance.
After
start-up they should be checked at least once a week and cleaned if necessary.
–System fluid mainentance
Maintenance intervals are dependent on the following operating factors:
-Pressure fluid condition (e.g. water in the oil, considerably aged oil)
-Operating temperature and system volume
We recommend that a fluid change is carried out in relation to an oil analysis. With systems where no regular analysis is carried out the fluid should be changed every 2000 to 4000 operating hours.
The system fluid should be drained at its operating temperature and then renewed.
Severely aged or contaminated system fluid cannot be improved by adding new fluid!
Only fill via a filter that has at least the same filtration rating as the filter installed in the system, or via the
system filter.
Take laboratory probes of the system fluid and have the probes analysied, for partical type, size and
amount. These values whoud be documented.
–Check the accumulator pre-charge pressure, for this the fluid side must be de-pressurised.
Attention!
Work on systems that incorporate accumulators must only be carried out after the fluid has been depressurised.
It is not permissible to carry out welding, soldering or mechanical work on an accumulator.
Incorrectly carried out repairs can lead to severe accidents. Repairs to hydraulic accumulators must therefore only be carried out by the responsible Service Department personnel.
–The operating temperature must be measured. An increase in operating temperature points towards
increased friction and leakage.
–Leakage within the pipework Leakage, particularly underfloor piping, means in conjunction with the loss
of pressure fluid, danger to the components and
concrete floor.
Sealing work carried out on pipework must, due to
safety reasons, only be carried out when the system
is de-pressurised. Leakage at points where soft seals (O-rings, form seal rings, etc.) are used cannot be
repaired by tightening as these sealing elements are
either destroyed or hardened. Sealing is only possible by replacing the sealing element.
–Check the main and pilot pressures
Check interval: one week
Document pressure corrections in the maintenance book
Increased pressure adjustment points to, amongst other things, wear to the pressure relief valve.4.3 Maintenance
Determining and rectification of faults and damage.
– Fault
localisation
A prerequisite for maintenance is a
systematic fault search.
For this it is, in each case, necessary to have detailed
knowledge about the design and operation of the individual components as well as the entire system. All necessary
documentation has to be available and be easily
accessible.
The most important measuring equipment (thermometer,
electrical multi-function measuring instrument, industrial
stethoscope, stopwatch, speed measurement device, etc.) should be, especially for large systems, easily accessible
< in the vicinity of the system.
– Fault
correction
–For any work carried out cleanliness is of great importance.
Before loosening fittings the surrounding area has to be
cleaned. Defective components should not be repaired on site, due to the fact that normally on site the required tools and necessary cleanlines is not available. On site as fas as possible only complete
components should be replaced,
The system should only be left open to the surrounding ambient conditions as briefly as possible,
Fluid loss should be held to a minimum,
By replacing with re-conditioned and tested components it is possible to ensure that the system is only out of service for the shortest possible time. It is very important to check, after the fault has been localised, to see whether the
faulty component has contaminated a part or the entire
system with broken parts or if large quantities of metallic
particals caused by friction have been given off.
4.4 Repair and general maintenance of hydraulic components It can be normally determined that the general service and repair can only be carried out economically and correctly by the component manufacturer (same quality standard, trained personnel, test facilities, guarantee, etc.).
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