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Valves on the crane
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Index
TRAINING
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Valves on the crane
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Index
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Valves on the crane
M1-6
2
1. Hose break valve
1.1 Purpose
The main function of a hose break valve is to stop the crane movements if a hose breaks by stopping
the oil flow.
1.2 Function
If a hose breaks, the oil flow in the broken hose increases. In this case the pressure acting on the ball
in the valve is higher than normal and the force is strong enough to close the connection through the
valve by compressing the spring. In normal case the oil flow is reduced by the throttle in the control
valve and so it is not possible for the valve to respond
.
UV 029
The hose break valve is directly fitted in the cylinder connection so that there is no hose necessary
between the cylinder and the valve.
In the hose break valve shown on the next picture the oil flow is stopped by a shim, if the force on the
shim coming from the oil flow is stronger than the force of the spring.
The actuating oil flow of the valve can be set by adjusting the distance „s“.
s
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Einstellung Schlauchbruchventile
0
10
20
30
40
50
60
70
80
90
0
0,5
1
1,5
2
2,5
3
"s"
l/min
EV-330
EV-358
Adjustment hose break valve
On cylinders with load holding valves it is not necessary to use hose break valves. The load holding
valve holds the load in case of a broken hose.
1.3 Installation
Attention
The hose break valve only works in case the oil flow is much higher than normal. This is not
happening, if the hose has a leakage only.
Special Case
The hose break valves used on timber cranes do not close completely, in case they are acting. These
valves always allow certain flow to tank to lower the load in any case.
Today hose break valves are mainly used at the overload protection
system OSK.
This picture shows the connection used in the overload protection system
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2. Pretension valve
2.1 Purpose
A pretension valve blocks the oil flow through the valve until the adjusted pressure is reached.
2.2 Function
As long as the hydraulic pressure at “P” is less then the spring pressure of the valve, a flow from “P” to
“R” is not possible.
UV 318
The pretension pressure only acts if the oil flows from “P” to the “R” of the valve (look on the valve, the
letters are punched in). The valve has a free flow from “R” to “P”.
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2.3 Application
Pretension valves (pressure raising valves) are normally used to prevent the outriggers against
moving out while driving with the truck.
These valves are also used to control the sequence of some extension boom systems.
Finally pretension valves are used to reduce the working pressure of certain functions, where the
operating pressure given by the port relief valve or the main relief valve is too high.
2.4 Disadvantage
The disadvantage of a pretension valve is that the adjusted pressure gets lost if the oil flows through
the valve.
Furthermore these valves only work in one direction, which is a disadvantage when controlling
extension boom systems.
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3. Pilot operated check valve
3.1 Purpose
A pilot operated check valve blocks the oil flow in one direction through the valve, the other direction is
always open. With the help of the “pilot pressure” the closed direction can be opened as well.
3.2 Function
A)
In one direction the oil flow is always possible (fig. 1).
B)
In the opposite direction the oil flow is blocked because the ball closes the connection back
through the valve (fig. 2).
C)
If the pilot pressure is strong enough to open the valve, the connection back through the
valve is also possible. The pilot pressure is always acting with the help of a certain pilot ratio
which makes it easier to open the valve.
For example:
Locked pressure
300 bar
Pilot ratio
1:3
Pilot
pressure
100
bar
UV 133A
Single acting
pilot operated
check valve
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Valves on the crane
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3.3 Double-Acting Pilot Operated Check Valve
The principle of a double acting pilot operated check valve is similar to two single acting pilot operating
check valves. The pilot pressure of the first valve is always the working pressure of the second valve
(see figure below).
3.4 Application
Double acting check valves are mostly used on the crane equipment (grabs, hydraulic pallet forks ...)
and on the stabiliser system of a crane.
3.5 Return oil utilisation
At some models check valves with integrated return oil utilisation system
are used to get a higher extending speed of the stabiliser cylinder.
V1
extending (connection from control valve)
V2
retracting (connection from control valve)
C1
extending (connection to cylinder)
C2
retracting (connection to cylinder)
The red line shows the oil flow while extending.
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4. Load holding valve
4.1 Purpose
Load holding valves are used where a normal lowering of the crane boom due to normal leakage in
the control valve should be prevented.
In all CE-countries load holding valves are obligatory on the main boom, on outer boom and on the
extension booms of the loading cranes.
The load holding valve controls all movements of the boom. That means the following functions:
Load lifting
Load
holding
Prevent the cylinder from overload
Load
lowering
4.2 Function
Load holding valves are basically pressure relief valves, pressurized or relieved with the pressure of
the opposite side.
The relief pressure of the relief valve is adjustable, the pilot pressure is in a fixed proportion to the
release pressure (it is punched into the valve, e.g. 1:3).
Hydraulic Plan
C
O
C1
V
X
C
connection to the cylinder
V
connection from the control valve
C1
connection of the pilot line
O
connection to the overload protection system
(only at main boom cylinder possible)
X
compensation line
(only at compensated type )
The shown connection (O) is only used on valves for the main
boom cylinder. The pressure is taken between the cylinder and
the load holding valve .
The line to the overload protection system must be protected
with a hose break valve. This connection is similar at all
overload protection systems.
Fig.:
This load holding valve is directly flanged with two pressure
transducer (O1, O2) and passed through lifting and lowering
pipes (C1, C2, V1, V2).
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4.2-1 Load lifting
C
O
C1
V
4.2-2 Load holding
C
O
C1
V
4.2-3 Overload
C
O
C1
V
4.2-4 Load lowering
C
O
C1
V
During lifting the load the oil flows from the connection „V“ to the
connection „C“.
The load lifts free.
The lifting pressure of the crane is adjusted on the control valve.
The set holding pressure of the load holding valve has no
influence to the lifting power of the crane.
The oil is blocked at the connection „C“ until the pressure is
higher than the adjusted pressure.
The load will stay at it’s position.
The load will stay at it’s position also with the pump switched off,
if somebody acts the hand lever on the control valve.
The cylinder pressure is higher than the adjusted pressure.
The cartridge opens from “C” to ”V“.
This may happen because of a peak pressure or a permanent
overload situation.
To lower the load the pilot pressure has to act on the connection
“C1“.
Both, the pilot pressure and the cylinder pressure open the valve
and the load lowers down.
The required pressure to lower the load is not constant. It
depends on the pressure in the cylinder, which may cause
bouncing loads.
See therefore the calculation of the pilot pressure.
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4.3 Mounting
Load holding valves are always mounted with steel pipes to the cylinder or are directly flanged to the
cylinder. Between control valve and load holding valve, hoses are permitted.
1
3
4
6
7
5
2
C1
C
V
O
Legend
1
Pipe for load lowering
2
Pipe for load lifting
3
Hose to overload protection system
4
Hose break valve
5
Load holding valve
6
Pilot oil pipe
7
Cylinder
C
hollow screw into the cylinder
V
“Lifting“ connection / control valve
O
Connection to the overload protection
C1
Connection for pilot line
The number of connections vary on different
types of valves. Some valves have more
connections for pressure transducers and so on.
e.g..:
connection for Paltronic pressure
transducer (O1, O2, M1, M2..)
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4.4 Pilot pressure
4.4-1 Calculation
The pressure which is necessary to open the valve for “lowering” the cylinder is called pilot pressure.
Calculate this as follows:
ruck
Aufsteuerd
erhältnis
Aufsteuerv
linder
DruckvomZy
terDruck
Eingestell
=
−
For example
adjusted pressure:
300 bar
pilot
ratio: 1:3
pressure from the cylinder:
crane without load
30 bar
crane with load
270 bar
pilot pressure:
cylinder without load:
300
30
3
−
=
90 bar
cylinder with load:
300
270
3
−
=
10 bar
4.4-2 Constant pilot pressure
The above example shows, that the pilot pressure depends on the cylinder load. This causes
bouncing loads on bigger cylinders.
At large cylinders this bouncing is an unsolvable problem, which can only be solved by using load
holding valves with constant pilot pressure.
Function
1
2
The mounted relief valve (1) is adjusted at the
highest allowed pressure to protect the cylinder
from overload and peak pressure.
A second valve (2) independent from the relieve
valve is used for pilot operation. By using these
second valve for lowering, the pilot pressure is
constant.
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4.5 Double acting load holding valve with return oil utilisation
This valve is used on nearly all extension boom systems on Palfinger cranes.
Using the return oil utilisation system on extension booms brings a similar extending and retracting
speed on the boom system. As a disadvantage, the extending power is reduced.
For example:
EV 1889, adjusted pressure 210 / 420 bar
The high pressure for retracting the cylinder is necessary to
hold the load in vertical hanging position of the extension
boom system.
The return oil utilisation only works in one (extension) way of the cylinder (see hydraulic plan).
Retracting the cylinder works normal.
Return oil utilisation system with magnetic valve
On large cranes the oil return utilization can be switched on and off with the solenoid valve Y190.
Unsing the system switched off Thereby the extension system is slower but stronger (advantage in
top position).
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4.6 Adjustment of load holding valves
Basically all cranes are delivered preset and sealed.
Only authorized workstations are allowed to change this adjustment. After changing the valves must
be resealed.
4.6-1 Standard Adjustment
Usually, the load holding valve pressure is set ten percent higher than the operating pressure of a
function.
For example:
A lifting cylinder has 300 bar (main pressure) so the load holding valve adjustment is
330 bar.
This gives the following limits to a crane:
a
M = F * a =
10
0%
100%
10
7
%
107%
11
0
%
110%
F
X
100%
The crane has it’s maximum lifting capacity because of the relief valve at the control valve.
107%
Reaching the overload protection system limit switches off all load moment increasing
movements. This system is not obligatory in all countries.
110%
The load holding valve opens at 110%, which causes a lowering of the load. This can
happen because of a peak pressure or wrong operation (e.g. extending the extension booms
too far out).
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4.6-2 Valve on lifting cylinder
To readjust the load holding valve on the lifting cylinder follow these steps:
• At first adjust the valve stronger than normal, therefore remove the seal of the cartridge. Please
not, not all valve types are adjustable.
• Try to lift the maximum allowed load with the crane, therefore use a test weight.
Attention: The crane must be in the strongest position during process (angle on the main
boom as shown on the type shield, outer boom at horizontal level, extension boom distance
correctly calculated).
It must be possible to lift the load stated on the type shield without problems in this position, but
not more!
This checks the main relief pressure.
• If the crane cannot lift the load in this position check and reset the main relief pressure.
• For the adjustment of the load holding valve a 10%-overload situation is necessary. Therefore
extend the extension boom system 10% more.
Attention: If the crane is equipped with an overload protection system only extend the boom
near to the shift point of the OLP-system (7%).
• Switch off the pump.
• Act the lever on the control valve to “main boom down”.
• Unscrew the adjustment screw on the cartridge of the load holding valve until the boom system
starts to move down (during this work the lever on the control valve must be in “main boom down”
position!). Immediately screw in the adjustment screw half a turn (the boom system must stop the
movement down).
• Switch on the pump again. Retract the boom system and try again to extend the system approx.
into a 10%-overload situation. The boom should start to move down there.
• Reseal the cartridge of the load holding valve.
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4.6-3 Adjustment of other load holding valves
The load holding valve on the outer boom, extension boom, slewing system and on the fly-jib can only
be adjusted on a test stand. This is necessary because it is not possible to generate the adjusting
pressure in these systems.
Basically these adjustments should not be changed anyway.
4.6-4 Emergency bypass
The “emergency bypass” is a bypass for the load holding valve in an emergency situation.
If the load holding valve cannot be opened by any reason (e.g. pump fault), the boom system cannot
be lowered anymore. This is a critical situation especially in combination with a workman basket.
The “emergency bypass” solves this problem by creating a bypass way through the valve.
Application
In some countries the “emergency bypass” is obligatory.
Basically it is optional available.
If the crane is equipped with an emergency bypass, a seal must be on the lock valve.
4.6-5 Compensation
C
O
C1
V
Generally there should be an open neutral position or a leakage groove in
the spool. Otherwise it is possible that pressure can be blocked between
the load holding valve and the spool.
If this is not possible, compensated load holding valves should be used.
In case the load holding valve is compensated the pressure between the
control valve and the load holding valve works against the pressure
adjustment (see the red line).
So a closed spool can be used together with a port relief valve.
Beside the fully compensated valves also partly compensated valves are
available, which have a pilot ratio between the adjusted pressure and the
lowering pressure (disadvantage with closed spools).