[0001] There exist various types of work machines and industrial plants which are activated
by hydraulic apparatus in which one of the mobile organs (e.g. the arm of an excavator,
the lift arm of a crane or a lift truck, etc.) is moved via two hydraulic cylinders
which work contemporaneously in parallel, either because the thrust required would
actually necessitate a cylinder of excessive proportions, or in order to share the
stress forces in two different points, with a consequent advantage in terms of size
and construction.
[0002] In many cases, security standards require that each of these cylinders be equipped
with a device of its own, typically a block and control valve of the load descent,
in order to avoid uncontrolled falls in a case of breakage of the oil pipes. It follows
that in order to activate the descending or lowering movement of the load, the command
system of the machine has to send a signal, for example a piloting pressure, which
contemporaneously opens the two block and control devices of the descent in each of
the two cylinders.
[0003] It often occurs, even when the two cylinders are connected in parallel to one another
and are connected to the same structure, that the hydraulic pressure induced in the
cylinders is not identical, for example due to asymmetry in the lifted weight, or
due to elasticity of the structure, or because the two cylinders are positioned distant
from one another, or because the machine is inclined with respect to the horizontal,
or for other reasons.
[0004] If the pressures in the cylinders are considerably different from each other, the
opening of the two block and control devices of the oil flow cannot be perfectly synchronised,
which is a generally necessary condition in order to for the operator to have fine
and sensitive control of the movement.
[0005] To obviate this drawback, generally there is a connecting tube between the two cylinders,
which functions as a balancing tube, such that the two pressures are balanced with
one another. On the other hand this connecting tube represents, in turn, a source
of danger. If there is a breakage, there could be an uncontrolled loss of oil. In
order to avoid this problem, each cylinder affords small-diameter choke orifices,
in general comprised between 0.8 and 1.0 mm, such as very much to limit any oil leakage
in a case of pipe breakage. These chokes, however, enable only static pressure balance,
as the limited oil flow which they allow through is not sufficient to guarantee balance
under dynamic conditions too.
[0006] The aim of the present invention is to provide a device which enables the drawbacks
in the balancing circuits of known type to be obviated.
[0007] The set aim is attained by a pressure balancing valve for two cylinders activated
in parallel according to the present invention.
[0008] An advantage of the valve is that is provides excellent response characteristics
in both static conditions and dynamic load conditions.
[0009] A further advantage of the valve is that in case of a breakage of the connecting
conduit between the two cylinders, the loss of oil is limited to very small amounts.
[0010] Further characteristics and advantages of the present invention will better emerge
from the following description, provided by way of non-limiting example in a preferred
but not exclusive embodiment of the pressure balancing valve, made with reference
to the accompanying figures of the drawings, in which:
figure 1 is a first version of the valve of the present invention;
figure 2 is a second version of the valve of the present invention;
figure 3 is a third version of the valve of the present invention.
[0011] The valve of the present invention is particularly useful internally of a hydraulic
control circuit for two cylinders 31, 32 activated in parallel. This circuit comprises
a first supply conduit circuit V2-C2 predisposed for supplying an operating fluid
to supply port C2 of the base of the two cylinders 31, 32, with the aim of causing
extension of the stem of the two cylinders and, consequently, raising of a load. A
second conduit circuit V1, C1 is predisposed to supply the operating fluid to the
supply port C1 of the annular chamber (the chamber in which the stem is arranged)
of the two cylinders, with the aim of determining return of the stems and consequently
the descent of the load. Two valves 33, 34 for control of the descent are interposed
between the supply port C2 of the base of the two cylinders and the pressurised fluid
source, indicated by V2 in the figures. The valves 33, 34, widely available on the
market, have the function of preventing the discharge of the operating fluid from
the bottom of the respective cylinder in the absence of a load descent command, such
as to guarantee that the load stays in a stationary position. In the presence of a
load descent command, the valves 33, 34 for load descent control enable a controlled
discharge of the fluid from the bases of the two cylinders, such that the descent
of the load is initially done at a contained speed. To this end, the load decent control
valves 33, 34 are provided with shaped obturators which can take on a closed position,
in which they do not enable discharge of the operating fluid from the base of the
cylinders, and an open position, in which they enable discharge of the fluid from
the bases of the cylinders 31, 32. Elastic means push the two obturators towards the
closed position, while the displacement towards the open position is normally determined
by means of a piloting pressure exerted by a piloting fluid supplied via a conduit
Pil. Alternatively the piloting fluid could be directly sourced from the conduit V1-C1.
The description that follows, and the accompanying figures of the drawings, for the
sake of simplicity refer to a case in which the two cylinders 31, 32 support a load
or, in any case, generate a thrust by sending a pressurised fluid into the bases of
the two cylinders. The balancing valve of the present invention could also be used
in a case in which the support of the load or the force transmitted are generated
through the sending of pressurised fluid into the annular chambers of the two cylinders,
i.e. when the two cylinders work in traction rather than in thrust. The balancing
valve 1 of the present invention comprises a main conduit 21, 22 predisposed to be
connected to a first cylinder and to be connected to a balancing conduit 40 which,
in turn, is predisposed to connect to a second cylinder 32. The balancing tube 40
can comprise a flexible tract, or can be entirely flexible.
[0012] An obturator 3, preferably of a two-way two-positioned type, is interposed between
a first tract 21 and a second tract 22 of the main conduit 21, 22. The obturator 3
is mobile between a closed position, in which the first and the second tract of main
conduit 21, 22 are not in mutual communication and the main conduit 21, 22 is closed
to fluid passage, and an open position, in which the first and the second tract of
the main conduit 21, 22 are in mutual communication. In the open position of the obturator
3, the main conduit 21, 22 is open to fluid passage such that the base of the first
cylinder 31 and the balancing conduit are in mutual communication. Thrust means 4,
preferably of an elastic type, are predisposed to push the obturator 3 towards the
closed position. In a preferred embodiment, the thrust means 4 are constituted by
an spring having an adjustable or fixed calibration, located in a low-pressure environment
by means of an opening to air or a connection to the operating fluid tank, as illustrated
in the figures. Piloting means 5, 6 are predisposed to push the obturator 3 towards
the open position, exerting an antagonistic action to that of the thrust means 4 by
means of a piloting pressure. In the absence of a piloting pressure, the piloting
means 5, 6 exert no thrust, so that the obturator 3 is brought into a closed position
by effect of the thrust exerted by the thrust means 4.
[0013] The piloting means comprise a first piloting conduit 5 which places the second tract
22 of the main conduit 21, 22 in communication with a thrust surface of the obturator
3, such that the pressure internally of the second tract 22 of the main conduit 21,
22 exerts a force which acts on the thrust surface of the obturator in order to push
the obturator 3 towards the open position. In this way, the presence of pressurised
fluid internally of the balancing conduit 40, which is in communication with the second
tract 22 of the main conduit 21, 22 of the valve, maintains the obturator 3 in an
open position. In these conditions the base of the first cylinder 31 is in communication
with the balancing conduit 40 and, consequently, it is in communication with the base
of the second cylinder 32.
[0014] The presence of pressurised fluid internally of the balancing conduit 40 is typical
of a condition in which there is a load present which is acting on the two cylinders
31, 32 and creating pressure internally of the bases of the two cylinders .This pressure
is transmitted to the obturator 3 which stays in the open position such that the bases
of the two cylinders 31, 32 are in communication with one another and the pressures
present internally thereof equal out perfectly. The perfect equalling-out between
the pressures present internally of the two bases enables a perfectly similar response
to be given to the two cylinders 31, 32 to a command to descend.
[0015] In a case in which fluid leaks from the balancing conduit 40, for example during
a breakage of the conduit 40 itself, the pressure in the balancing conduit 40 drops
and with it also the piloting pressure which, via the first piloting conduit 5, acts
on the obturator 3. The drop in piloting pressure which acts on the obturator 3 leads
to the obturator 3 itself moving into the closed position by effect of the thrust
exerted by the thrust means 4. In this way, the fluid in the base of the first cylinder
31 cannot discharge through the balancing conduit 40. In order to prevent the operating
fluid from unloading from the base of the second cylinder 32 in these conditions,
a second balancing valve 1a is interposed between the second cylinder 32 and the balancing
chamber 40 in a same way as for the first balancing valve 1. In a case of operating
fluid leakage from the balancing conduit 40, the obturator 3 of the second balancing
valve 1a too, entirely similarly to the first balancing valve1, is brought into the
closed position by effect of the thrust exerted by the thrust means 4. If, on the
contrary, there are no leakages from the balancing conduit and internally thereof
there is pressurised fluid, both the obturators 3 are kept in the open position and
perfect fluid communication is maintained between the bases of the two cylinders 31,
32.
[0016] The piloting means 5, 6 preferably comprise a second piloting conduit 6 which places
the first tract 21 of the main conduit in communication with the first piloting conduit
5. The second piloting conduit 6 might be afforded through the valve body, but alternatively
might be afforded through the obturator body 3, or it could be constituted by a small
passage of fluid between the obturator 3 and the sliding seat of the obturator 3.
The presence of the second piloting conduit 6 enables a very rapid opening of the
obturator 3 to be obtained, as soon as the operating fluid is supplied to the bases
of the two cylinders 31, 32, even in a case in which the pressure internally of the
bases and the balancing conduit 40 is initially nil, as happens for example when the
load is rested on the ground.
[0017] The second piloting conduit 6 is provided with a fixed choke 7 (figures 1 and 2)
or a flow rate regulator 7a (figure 3) predisposed to limit the flow of fluid which
can transit through the second piloting conduit 6. These two devices enable the oil
flow which can discharge through the second piloting conduit 6 in a case of leakage
from the balancing conduit 40 to be limited to a very small amount. In particular,
the flow rate regulator 7a can be compensated, i.e. able to limit the maximum flow
rate of fluid that can discharge from the second piloting conduit 6 independently
of the fluid pressure in the base of the cylinder 31, 32.
[0018] The first tract 21 of the main conduit 21, 22 can also be provided with a fixed choke
8 (figure 1) or a flow rate regulator 8a (figures 2 and 3), possibly of the compensated
type, predisposed to limit the fluid flow rate which can transit through the first
tract 21 of the main conduit 21, 22. The choke 8 or flow rate regulator 8a enable
excessive movement of oil between the two cylinders to be limited. The choke 8 or
the flow regulator 8a of the first tract 21 of the main conduit 21, 22 can be combined
equally with the choke 7 or the flow regulator 7a of the second piloting conduit 6.
In order to guarantee a quick communication of fluid between the first cylinder 31
and the second cylinder 32, including during a malfunctioning or at sudden pressure
peaks, the valve of the present invention can be provided with a by-pass conduit 9
provided with a check valve 10. In the case of the valve applied to the first cylinder
31, the check valve allows the operating fluid to flow only from the second cylinder
32 towards the first cylinder 31. Vice versa, in the case of the valve applied to
the second cylinder 32, the check valve 10 allows fluid to flow only from the first
cylinder 31 towards the second cylinder 32. In both cases the by-pass conduit is arranged
in parallel with the main conduit 21, 22 of the valve. The valve of the present invention
provides important advantages. Firstly, it enables a very rapid and precise balancing
of the pressure in the bases of the two cylinders. The presence of a balancing conduit
which is substantially lacking in chokes enables rapid transmission of fluid between
the two cylinders. On the other hand, while offering the possibility of connecting
the two cylinders substantially without interposing chokes, the valve can greatly
limit any fluid leakage due to a breakage of the balancing conduit. This is due to
the presence of the obturator 3, piloted to open by the pressure internally of the
balancing conduit which, should there be a drop in pressure due to breakage of the
balancing conduit, is rapidly brought into the closed position, blocking the transmission
of the fluid towards the balancing conduit. The very small leakage of residual oil
is discharged via the first piloting conduit 5 of the obturator, which fluid leakage
can be further reduced with the use of the fixed choke 7 or the compensated flow regulator
7a.
[0019] The valve is further simple to use and install, as it can be applied directly to
the bases of the two cylinders.
1. A pressure balancing valve for two cylinders operated in parallel, characterised in that it comprises: a main conduit (21, 22) predisposed to be connected to a first cylinder
(31) and to connect to a balancing conduit (40) connected to a second cylinder (32);
an obturator (3), interposed between a first tract (21) and a second tract (22) of
the main conduit (21, 22), which is mobile between a closed position, in which the
first tract and the second tract of the main conduit (21, 22) are not in mutual communication
and the main conduit (21, 22) is interrupted, and an open position, in which the first
tract and the second tract of the main conduit (21, 22) are in mutual communication;
thrust means (4), predisposed to push the obturator (3) towards the closed position;
piloting means (5, 6), predisposed to push the obturator (3) towards the open position,
which comprise a first piloting conduit (5) that places the second tract (22) of the
main conduit (21, 22) in communication with a thrust surface of the obturator (3),
such that the pressure internally of the tract of the second tract (22) of the main
conduit (21, 22) exerts a force which acts on the thrust surface of the obturator
(3) in order to push the obturator (3) towards the open position.
2. The valve of claim 1, wherein the piloting means (5, 6) comprise a second piloting
conduit (6) which places the first tract (21) of the main conduit in communication
with the first piloting conduit (5).
3. The valve of claim 2, wherein the second piloting conduit (6) is afforded in the body
of the pressure balancing valve (1).
4. The valve of claim 2, wherein the second piloting conduit (6) is afforded through
the obturator body (3).
5. The valve of claim 2, wherein the second piloting conduit (6) is constituted by a
space arranged between the obturator (3) and a sliding seating of the obturator (3).
6. The valve of one of claims from 1 to 4, wherein the second piloting conduit (6) is
provided with a fixed choke (7).
7. The valve of one of claims from 1 to 4, wherein the second piloting conduit (6) is
provided with a flow regulator (7a) predisposed to limit a fluid flow which can transit
through the second piloting conduit (6).
8. The valve of one of the preceding claims, wherein the first tract (21) of the main
conduit (21, 22) is provided with a fixed choke (8).
9. The valve of one of claims from 1 to 7, wherein the first tract (21) of the main conduit
(21, 22) is provided with a flow regulator (8a) predisposed to limit a fluid flow
which can transit through the first tract (21) of the main conduit (21, 22).
10. The valve of one of the preceding claims, comprising a by-pass conduit (9), arranged
in parallel to the main conduit (21, 22) provided with a check valve (10).
11. A balancing device for balancing pressure of two cylinders activated in parallel,
characterised in that it comprises: a balancing conduit (40); a first valve (1) and a second valve (1a)
according to one of the preceding claims, connected to ends of the balancing conduit
(40) by means of the second tract (22) of the main conduit (21, 22).