Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a hydraulic valve assembly
for use with, for example, hydraulic lifting apparatus.
There are many applications where hydraulic cylinders
are used to raise loads. A typical example is a tractor
mounted back hoe. Commonly, the cylinder is connected by
flexi~le hoses to control valves at a spaced location, e.g.,
the trac~or ca~. However, if a hose fails while the cylinder
is supporting a load, the load will be dropped with attendant
danger.
The invention provides a hydraulic valve assembly com-
prising a unitary structure having first and second ports for
selective connection via respective flexible hoses and control
valves to a source of pressurized fluid and third and fourth
ports for connection to a hydraulically-powered actuator.
A first valve means interconnects the first and third ports
and a second valve means interconnects t~e second and fourth
ports. The first valve means is adapted to permit free flow
from the first port to the third port and to permit flow from
the third port to the first port only on receipt of a pilot
pressure greater than a predetermined value. The second valve
means is adapted to permit free flow from the fourth to the
second port and to permit ~low from the second to the fourth
port when a predetermined pressure difference exists in that
direction. A pilot passage extends from the second port to
the first valve means to provide a fluid pressure which is a
function of the pressure at the second port as the pilot
p~essure.
This structure provides safer operation in the event
of a hydraulic hose or simi~ar failure.
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An em~odLment of the invention will now be described,
by way of example, with reference to the accompanying drawings,
in which:
Figure 1 is a schematic hydraulic circuit of a valve
assembly according to the invention;
Figure 2 is a detailed cross-section of a valve assembly
incorporating the circuit of Figure 1.
Referring now to Figure 1, the valve assembly is housed
in a single metal block indicated a~ 10, and has ports 16 and 18
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1 for connection to n lift" and "lower" sides respectively of a
2 hydraulic cylinder 20 and ports 12 and 14 for connection via
3 conventional hoses and control valves to a source of pressurized
4 fluid. Port 12 is pressurized and port 14 connected to exhaust
for a "lift" operation and port 14 is pressurized and port 12
6 connected to exhaust for a "lower" operation. Preferably, the
7 assembly is mounted on the cylinder such that one of the ports
8 16, 18 is coupled directly to the respective cylinder port,
9 the other being connected via a metal tube (not shown) secured
to the exterior of the cylinder. In this way, the use of
11 flexible hoses between the valve assembly and the cylinder is
12 avoided.
13 The cylinder 20 may be the boom cylinder of a tractor
14 mounted backhoe.
The ports 12 and 16 are interconnected by valves 22 and
16 24 arranged in parallel, and the ports 14 and 18 are inter-
17 connected to valves 26 and 28 in parallel. The valves 22 and
18 26 are one-way check valves. The valves 24 and 28 are loaded
19 by adjustable springs and are each responsive to a pilot pres-
sure, as will be explained.
21 A circuit relief valve 30 interconnects the ports 16
22 and 18. The function of this valve is to protect the cylinder
23 20 against peak pressures caused by overloading from externa~
24 sources, for example, dynamic shocks during road transport in
the case of tractor mounted equipment. ~or this purpose, the
26 valve 30 is biased to open at a given high pressure, suitably
27 3500 p.s.i.
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1 A passage 32 in the block 10 connects the port 12
2 via a one-way check valve 34 to vent the spring chamber of
3 valve 38 and thereby provide a drain passage for fluid leakage
4 valve 28. A pilot passage 36 couples the pressure at the
port 14 to the valve 24 which is so constructed that it will
6 open only when a given pilot pressure is available in the
7 passage 3~.
8 In normal operation, three modes are available, namely
9 "lift", "hold" and "lower. n
For "lift", oil is supplied under pressure to port 12,
11 is blocked at valves 24 and 34, flows through valve 22, is
12 blocked at valve 30, and flows out at port 16 to pressurize
13 the rod side of cylinder 20. Oil displaced from the piston side
14 of the cylinder 20 flows in at port 18, is bloc~ed at valve 28,
and flows through val~e 26 to be discharged to reservoir from
16 port 14.
17 In "hold" operation there is no oil flow to or from
18 ports 12 and 14. The weight of the apparatus, and payload if
19 any, attached to the piston produces a pressure in the rod side
of the cylinder 20, which is maintained by the ~locking action
21 of valves 22, 24 and 30.
22 To effect "lower", oil i9 supplied at port 14 and is
23 bloc~ed ~y a ~alve 26 and, initially, ~y valve 28. When a
24 predetermined pressure has ~een reached, the valve 28 opens
2~ to permit flow into the piston side of cylinder 20. At the
26 same time, the pressure at port 14 acts ~ia the pilot passage
27 36 to open val~e 24, thus permitting displaced oil from the rod
28 side of cylinder 20 to return to the reservoir from port 12.
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1 In the event of failure of the hose coupling port 12
2 or port 14 to the operator's control valves, the cylinder 20
3 will assume either the "hold" or "controlled" condition as
4 detailed in the following table:
Resulting Effect on Operation
6 Failed "Liftn nHold" nT~ower"
7 ~ose
8 Port 12 Lifting will No effect Displaced oil
9 cease as supply will lea~ to
of oil is im- atmosphere in-
11 paired. 'hold' stead of to tank
12 situation ta~es via control valve.
13 over.
14 Final condition Final condition Final condition
System in 'hold' System in 'hold' controlled 'lower'
16 Port 14 Displaced oil No effect Ability to lower
17 will leak to will cease. 'Hold'
18 atmosphere in- Qituation taXes
19 stead of to tank over.
via control valve.
21 Final condition Final condition Final condition
22 controlled 'lift' S~stem in 'hold' Svstem in 'hold'
23 Ports 12 Final condition Final condition Final condition
24 and 14 System in 'hold' ~stem in 'hold' System in'hold'
Thus, in no case will the load be able to fail.
26 Figure 2 illustrates a practical realization of the circuit
27 o~ ~igure 1 using commerically available cartridge type valves.
28 In Figure 2, like reference numerals denote like parts to those
29 of Figure 1.
The valves 22, 24 and 30 are combined in a single bore
31 in the bloc~ 10. The valve 30 comprises a valve mem~er 38
32 biased against a seat 40 by Belleville springs 42. The outer
33 face of ~he valve member 38 is in communication with the port 16
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1 via apertures 44 in a cup-shaped member 46. Thus, if the
2 pressure at the port 16 becomes sufficiently high to over-
3 come the force of the springs 42, oil is spilled to the
4 port 18.
The cup-shaped member 46 is biased by a coil spring 48
6 into engàgement with the free end of a cylindrical portion S0
7 of a member 52 to form the valve 22 of Figure 1. The interior
8 of the cylindrical portion 50 communicates via apertures 54
9 with the port 12 and the chec~ valve 34. When the pressure
at port 12 is higher than that in port 16, the cup-shaped
11 member 46 is forced back against the spring 4~ to permit flow.
12 The member 52 is also biased towards the cup-shaped
13 member 46 by a coil spring 56 to act as the valve 24. The
14 pilot passage 36 extends from an opening 58 in the port 14
to an annular space 60 around a sleeve 62 in which the valve
16 members are mounted. Apertures 64 in the sleeve 62 provide
17 communication between the space 60 and an annular space 66.
18 An internal cylindrical portion:68.of the member 52 communicates
19 with the port 12 via passages 70. Thus, when the pressure at
the port 14 is sufficiently high, this pressure acts in the
21 space 66 against a sleeve i2-secured to the member 52 to mo~e
22 the latter, against the force exerted by the spring 56 and the
23 fluid pressure within the cylindrical portion 68, away from the
24 cup-shaped member 46 to permit fluid flow bPtween ports 12 and
16. The force of the spring 56 may be adjusted by rotation of
26 a screw-threaded adjuster 74.
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1 The valves 2~ and 28 of Figure 1 are combined within
2 another bore in the block 10. A mounting member 76 threaded
3 into the bore has a sleeve 78 secured thereto. A piston 80
4 is slidable within the sleeve 78 and is biased by an adjustable
coil spring 82 to a position in which a shoulder 80a abuts
6 the end of the sleeve 78. The other end of the sleeve 78 is
7 open to the port 14, and has a cylindrical member 84 slidable
8 therein. The member 84 is biased by a spring 86 to abut a
9 stop 78a on the sleeve 78, at which position it also engages
the end of the piston 80.
11 An annular space 88 is formed between the sleeve 78
12 and the end of the piston 80 adjacent the member 84, and this
13 space 88 communicates via a port 90 with the port 18. Thus,
14 when pressure at the port 18 is raised, the cylindrical member
84 is forced against the spring 86 to permit flow to the port 14,
16 providing the function of valve 26.
17 The other end of the pistcn 80 is subjected to the
18 force of the spring 82 and also to hydraulic pressure by virtue
19 of a drilling 92 in the mounting member 76 which permits com-
munication with the one-way valve 34. When the pressure applied
21 at port 14 is sufficiently high to overcome these forces (and
22 therefore is higher than the pressure in port 12), the piston 80
2- moves to the right as seen in Figure 2 to uncover the port 90
24 and permit flow to the port 18, thus fulfilling the function of
the valve 28.
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1 Although the above preferred embodiment uses a single
2 metal block in which the valves and pilot passages are housed,
3 the invention may be embodied by providing these in another
4 form of unitary structure, for example, two blocks housing
S valve assemblies similar to those of Figure 2, the blocks
6 being connected by metal tubes welded or screw-threaded thereto.
7 Provided the valves, ports and pilot passage(s) form a unitary
8 structure, the failure of a flexible hose elsewhere will not
9 result in a situation of danger.
