Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a vent valve designed to allow
the escape of gases from a hydraulic system.
There are many types of hydraulic systems in which problems
arise from the entrapment of aïr or other gases within the
system. When paxt of the space normally taken up by the
oil or other hydraulic fluid becomes filled with air or any
other gas, the behavior of the system deteriorates because
of the compressibility and elasticity of the air when the
system is pressurized. This air generally enters the system
when the system is depressurized, and is particularly a
~ problem in systems in which the fluid is placed under a less
- than atmospheric pressure so that a negative pressure differ-
ential exists across fluid seals in the system. While this
situation is a particular problem with telescoping hydraulic
cylinders because of their multiple sliding seals, air can
enter other placesl such as through the hydraulic reservoir
and return lines.
Because the air or other gas naturally rises to the highest
; part of the system, it has been a common practice to provide
a bleeder valve at the high point in the system, which can
be manually opened when the system is initially pressurized
for operation and then manually closed after the air has
been expelled and the valve begins to pass hydraulic fluid.
; Because the valve is located at the high point in the
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hydraulic system, there are many situations in which access
to the vent valve for manual operation is difficult and
hazardous, and because it is necessary to determine visually
when the air has been expelled and hydraulic fluid is leaking
from the bleeder valve, there is a tendency to leak excess
amounts of hydraulic fluid, and not only must this fluid be
replaced in the reservoir from time to time, but because of
- its nature it tends to attract dirt and other foreign
material, and therefore requires periodic cleaning of the
surrounding area. Furthermore, because of the difficulty in
conducting the bleeding operation, which may be necessary
as often as every day, and which may require at least two
people to do it efficiently, there is a tendency to neglect
the bleeding operation and operate the system with a certain
amount of entrapped air, which results in decreased efficiency
and even greater wear of certain parts of the hydraulic
system.
The present invention provides a vent valve which operates
automatically whenever the hydraulic system is pressurized
above a certain predetermined, low pressure level well below
the operating range to automatically vent any air or other
trapped gases to the atmosphere, and as soon as the gases
have been expelled and the hydraulic fluid reaches the valve,
it automatically closes and seals to prevent any substantial
leakage of the hydraulic fluid from the system.
According to the valve of the present invention which allows
escape of gases from a hydraulic system including a space
to be filled with hydraulic fluid under pressure, there is
provided a body with first and second chambers in the body
and a first passage connecting the first and second chambers.
The first chamber has a restricted inlet connected to the
space and a first valve seat connected to the first passage.
A first valve member is provided in the first chamber and
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is biased by gravity away from the valve seat. The first
valve member is free]y mova~le between the inlet and the
first valve seat and has a density greater than the
density of the hydraulic fluid. The second chamber has
a second valve seat connected to the first passage, and a
second restricted passage connects the second chamber to
the atmosphere. A second valve member is provided in the
second chamber with means biasing the second valve member
against the second valve seat.
In a specific embodiment of the invention the body has a
bore therein, at the lower end of which is a reduced diameter
orifice plate to restrict the flow of any gas or liquid.
Above the orifice plate is the first chamber in the form of
a cylindrical chamber containing the first valve member in
the form of a ball which, if raised to the upper end of the
chamber, seals against the first valve seat to prevent fluid
flow through the valve. Above the valve seat is the first
passage which is a short passage to the second valve seat
facing in the opposite direction and a second ball forming
the second valve member which is adapted to engage this
valve seat, by both the force of gravity and a relatively
light spring. This second ball lies in the second chamber
which is provided with restricted vent openings to the
atmosphere, and the end of this chamber is sealed by a plug
which is threaded and serves both to adjust the biasing
~; force of the spring and to clamp or force the second ball
against its seat to close and prevent operation of the valve
if this is desired.
The first ball and the chamber in which it is located are
dimensioned such that as air enters the lower orifice plate,
it lifts the ball off the orifice plate and flows around
the ball through the first seat to the second ball. When
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the pressure builds up to a predetermined level such as
50 psi, the second ball opens to exhaust the air through
the vents to the atmosphere. The operation of the first
ball is such that it will not rise sufficiently to engage
its seat under the rate of air flow and pressure at which
the system operates. However, as soon as a liquid such
as hydraulic oil enters the orifice plate, its greatly
increased viscosity overcomes the weight of the ball and
forces it tightly against its valve seat to prevent any
leakage of the oil or hydraulic fluid from the system. The
second ball then closes and prevents re-entry of the air
into the hydraulic system if the pressure should drop below
atmospheric pressure.
The valve is generally mounted in a position close to
vertical because of the requirement of gravity to keep the
first ball away from its seat. However, since the valve
merely requires a single connection to the hydraulic system
at a high point, the valve may be mounted in a remote location
~ and connected to the system by a flexible, hydraulic hose.
:~ 20 BRIEF DESCRIPTION OF THE DRA~INGS
. .
~ These and other aspects and advantages of the invention will
- be more readily apparent upon an understanding of the pre-
ferred embodiments of the invention as shown in the drawings,
wherein:
` 25 Fig. 1 is a fragmentary, cross sectional view through a hydraulic cylinder showing the mounting of a preferred
embodiment of the vent valve of the presen-t invention;
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` Fig. 2 is a vertical, cross sectional view through the
vent valve of Fig. 1, showing the valve in the unpressurized
condition;
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Fig. 3 is a cross sectional view similar to Fig. 2, but
~ showing the valve in a condition where it is venting air
: ~rom the hydraulic system;
Fig. 4 is a cross sectional view of the valve shown in
Figs. 2 and 3, showing the valve closed by hydraulic
pressure;
Fig. 5 is a vertical, cross sectional view of another
embodiment of the present Invention; and
Fig. 6 is a schematic view showing an alternative, remote
mounting of the vent valve.
.: DESCRIPTION OF THE P~EF~RRED EMBODIMENTS
Referring now to the drawings in greater detail, Fig. 1
shows a typical application of the vent valve of this
:~ invention. Shown therein is the fragmentary portion in
cross section of the upper end of a hydraulic cylinder 10
which has therein a cavity 11 normally adapted to be filled
with the operating hydraulic fluid, but which, because it
~ is at the upper end of the system with respect to the forces
`~ of gravity, will tend to collect and retain any entrapped
air in the system
The hydraulic cylinder is shown as having a bore or passage
~ 12 therein opening into the cavity 11 and adapted to receive
: the vent valve indicated generally at 13. Outwardly of the
- bore 12 is a conical seat portion 14, a threaded counterbore
: 25 16, and an end face 17 arranged to provide venting clearance.`. for the valve when it is assembled into operating position. .
s shown.in Fig. 1, the vent valve 13, in operating position,
: may be tilted a certain distanc~ away from the true vertical,
but as will be explained in greater detail hereinafter, for
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proper operation of the valve as an automatic vent, the
vertical axis of the valve member itself preferably should
remain within about 60 degrees of the vertical.
The vent valve 13 is shown in greater detail in Fig. 2,
where it can be seen that the valve comprises a body
me~er 20 which may be machined as a single piece from bar
stock and at its lower end has a cylindrical outer surface
21 adapted to fit within the bore 12u This outer surface
21 has a groove 22 adapted to receive an O-ring seal 23 and
back-up ring 24 to provide proper sealing engayement with
the bore 12 to prevent leakage. Above the surface 21 is a
conical shoulder 26 adapted to seat against the seat 14 in
the hydraulic cylinder to serve as a stop, as well as an
additional seal against leakage. Above the shoulder 26 is
a threaded portion 27 adapted to engage the threaded counter-
bore 16 and above that in turn is a reduced diameter vent
groove 28 and a wrench receiving hexagonal portion 31. The
` top end of the body member 20 is defined by an end face 32,
'~ and to avoid sharp edges it may ~e provided with a chamfer,
~ 20 as indicated at 33.
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:~ At its midpoint, the body member 20 has a central axial bore
35 generally coaxial with the exterior surfaces of the body
member, and this bore 35 serves as a flow path between the
two valving portions of the vent valve. At the lower end
~ 25 of bore 35 is a conical valve seat 36, below which is an
'~ enlarged counterbore or first chamber 37, which will be
seen to have a length approximately equal to twice its
~ diameter, for reasons explained in greater detail herein-
,~ after. At the lower end of the counterbore 37 is a second
enlarged counterbore 38 which receives an orifice plate 40
~ held in place by a spun-over lip 41 on the end of the body
v, member. ~he orifice plate has a centrally located orifice
opening 43 and a generally conical seat portion 44 on its
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inner surface. A ball or valve member 45 having a density
greater than the density of the hydraulic fluid is located
within the counterbore 37 and is able to move freely
between the seat 44 on orifice plate 40 and the valve seat
36.
At its upper end, the body member 20 has an upper counterbore
or second cham~er 48 which is connected to the central bore
35 at a conical valve seat 49. Immediately above the valve
seat 49 are located a plurality of radial vent passages 51
extending from the upper counterbore 48 to the vent groove
28 on the exterior surface of the body member. These
passages are generally arranged symmetrically around the
periphery of the counterbore, but are chosen in number and
diameter so as to provide a predetermined flow restriction,
as will be explained in greater detail hereinafter.
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At its upper endl the upper counterbore 48 connects with a
threaded bore portion 53 extending to the end face 32 and
a second ball or valve member 55 is positioned within the
upper counterbore 48 and adapted to make sealing engagement
with the valve seat 49. A plug 56, preferably in the form
of a dog point setscrew, is positioned within the threaded
bore 53, and is movable axially along the threads to and
from the ball 55. The plug 56 is provided with a hex
socket 57 for rotation by a wrench and has a conical portion
58 and a central projection 60. The central projection 60
has a flat end face 61 and a biasing spring 63 fits around
the central projection 60 to abut at its one end on the
conical portion 58 of plug 56 and at its other end against
the ball 55, thereby providing a biasing force holding the
ball 55 in sealing engagement with the valve seat 49. ~xial
movement of the plug 56 adjusts the force applied by the
biasing spring 63 to determine the opening force required
to move the ball 55 away from valve seat 49. Furthermore,
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the valve can be positively closed by screwing the plug 56
inwardly until the end face 61 oE central projection 60
; positively forces the ball 55 against the valve seat 49.
The operation of the vent valve is seen most clearly in
connection with Figs. 3 and 4~ The vent valve is intended
to operate in a generally vertical position (not more than
60 degrees from the vertical), although it has been found
`~ that the valve will work at an inclination of up to 90
degrees from the vertical. Normally, when the hydraulic
system is ~ot pressurized, the valve is in the condition
shown in Fig. 2, with the upper ball 55 against its seat
to prevent any air entering the system by reverse flow
from the vent passages 51 to the central bore 35. The
lower ball 45 is normally resting on the conical seat 44
of orifice plate 40, but it is not necessary that any seal
exist at this point. Indeed, the valve is also fully
operational if a positive bleed is provided between the seat
44 and the ball 45 by means such as notches in the seat 44
or by making the orifice opening 43 noncircular. However,
whether or not there is a seal at this point does not affect
the operation of the valve, since only the force of gravity
; is holding the ball 45 in this downward position.
When the system is pressurized, the fluid, whether liquid
or gas, lifts the ball 45 off the seat 44, as generally
shown in Fig. 3. Then, when a certain predetermined
pressure, such as 50 psi, is reached, the upper ball 55
moves away from its seat 49 and -the fluid is free to pass
; to the atmosphere through the vent passages 51. As the
pressure in the hydraulic system increases, the rate of air
or gas flow continues to increase in a generally linear
manner, and the ball 45 remains positioned intermediate
the orifice plate and the valve seat 36, without making
any sealing contact with the latter under these conditions.
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However, as soon as a liquid begins to enter the valve
through the orifice opening 43, the greatly increased
viscosity of the liquid, as compared to the gas, now
causes the ball 45 to move into sealing engagement with the
valve seat 36, as shown in Fig. 4, thereby preventing any
~urther escape of any liquid or hydraulic fluid from the
valve, a~ter which the upper ball 55 under the force of
biasing spring 63 moves back into sealing engagement with
its valve seat 49. Thereafter, as long as some pressure
is maintained in the system, the vent valve will remain in
the condltion shown in Fig. 4 and no fluid, either liquid
or gas, will escape from the system.
The exact mode of operation of the valve is not fully under-
stood particularly as to why the ball 45 does not seal
against the valve seat 36 even under relatively high rates
of flow of air. It has been found, as the result of
experimentation, that it is important that the ball 45 be
fairly close to the size of the counterbore 37, and that
the length of the counterbore 37 be such as to allow the
ball 45 to be able to move a distance at least equal to its
diameter between the lower position adjacent the orifice
sea~ 44 and the upper position adjacent the valve seat 36.
Furthermore, it is important to provide a xestriction at
the orifice opening 43 and a further restriction downstream
of the central bore 35. In tests that have been conducted,
the valve has a ball diameter of .375 inches and the
` ~iameter of counterbore 37 is .437 inches. Also, the vent
passages 51 are four in number, and are .140 inches in
; diameter. Under these conditions, with different diameter
orifice openings 43, it has been found that optimum perfor-
mance is obtained when the orifice opening 43 has a
diameter of .187 inches. A further reduction in size of
the orifice opening 43 generally results merely in a
decreased rate of air flow at a given pressure level, and
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an increase in the orifice opening 43 above the optimum
can result in premature closing of the valve by engagement
of ball 45 against valve seat 36. Thus, when the orifice
opening 43 is enlarged to the point of providing substan-
tially no restriction, and the biasing force of spring 63
is adjusted to allow the upper ball 55 to open at 50 psi,
it has been found that while air will flow initially, an
increase in the pressure to lO0 psi will cause the lower
ball 45 to seal against the valve seat 36 and prevent further
escape of air. Furthermore, even with the optimum flow at
- the orifice opening 43 of .187 inches, as described above,
removal of the plug 56 and ball 55, which would allow fluid
entering the central bore 35 to flow straight ahead to the
atmosphere past the threaded bore 53, also causes premature
closing of the valve in the same manner as indicated above.
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` However, if a maximum rate of air flow is not required, the
embodiment shown in Fig. 5 can also be employed for the
same purpose. The embodiment of Fig. 5 is substantially
the same as the embodiment of Figs. l through 4, except that
; 20 the orifice plate 40 is not present. In this embodiment,
the lower end has a counterbore 66 of the same diameter as
the counterbore 37, except the counterbore 66 extends all
the way to the lower end face 67 of the body member 20.
~ To retain the ball 45 in place within the counterbore 66,
-~ 25 the body member is provided with a transverse bore 69
which receives a retaining pin 70 against which the ball
-~ 45 rests in the lower position. It should be noted that
the retaining pin 70 is preferably of such a diameter as
to provide a certain amount of flow restriction to prevent
premature closing of the ball 45, but it is not as effective
in providing high rates of flow as the orifice plate 40
of the embodiment of Figs. l to 4.
Fig. 6 shows an alternative mounting arrangement for either
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of the embodiments of the vent valve for circumstances
in which mounting the valve directly in -the cylinder would
be impractical. In this case, the hydraulic cylinder 72
is provided with a vent fitting 73 which attaches to a
flexible hydraulic hose 74. The manifold member 75 is
secured remote from the cylinder 72 to a suitable vertical
surface, as indicated at 76, by suitable means such as
bolt 77. ~he manifold 75 has a fitting 79 at its lower end
to which is connected the other end of the flexible hose
74 and the vent valve of the present invention, as shown at
80, is mounted in a suitable opening on the upper side of
the manifold, with its lower end exposed to the fluid
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~entering the manifold through the hose 74.
; Although several embodiments of the invention have been
: 15 shown and described in detail, it should be understood that
. various modifications and rearrangements may be resorted
to without departing from the scope of the invention as
deiined by the claims.
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