Information
-
Patent Grant
-
6823669
-
Patent Number
6,823,669
-
Date Filed
Wednesday, April 2, 200321 years ago
-
Date Issued
Tuesday, November 30, 200420 years ago
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Inventors
-
Original Assignees
-
Examiners
- Yu; Justine R.
- Leslie; Michael
Agents
-
CPC
-
US Classifications
Field of Search
US
- 060 430
- 060 405
- 060 428
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International Classifications
-
Abstract
A hydraulic transfer valve system has a main valve selectively placing one of a primary and secondary hydraulic system in communication with a hydraulic load. A pilot valve provides a toggling action between the primary and secondary systems with respect to pressure changes in such systems.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to hydraulics, and more particularly to transfer valve systems for aircraft hydraulics
(2) Description of the Related Art
In an aircraft, a transfer valve (also known as a switching valve) is used to direct pressure and flow from one of two available hydraulic supply systems to a downstream circuit. The valve switches between supply systems based on the relative magnitudes of the system pressures and a pressure bias built into the valve. The bias is often achieved by providing different pilot areas on each end of the valve, the larger of the pilot areas being on the end acted upon by the preferred, or primary, system. A spring is also sometimes used to provide a bias. With both supply pressures at normal operating pressure, the forces acting on the valve are such that the preferred (primary) system is connected to the circuit and the other (secondary/back-up) system is blocked. The purpose of a transfer valve is to allow the back-up system to take over for a failed or failing primary system. The transfer valve also isolates one hydraulic supply system from the other. As the primary system pressure decays, the force balance on the valve favors the primary system less and the back-up system more, until eventually the valve shuttles from the initial primary position to the back-up position. In the back-up position the valve connects the back-up system to the circuit and blocks the primary system.
Once pressures reach the switchover condition, the transfer valve advantageously shuttles with a snapping action, without interruption, hesitation, or instability. The snapping action is advantageous for two reasons. First, it minimizes transient pressure spikes as the valve closes off flow from one system and opens flow from the other. Second, it prevents the forces acting on the valve from achieving equilibrium when the valve is mid travel. If the valve stops mid travel it could block both supply systems and create a hydraulic lock in the downstream circuit. This snapping action can be enhanced through the use of a mechanical, hydraulic or electric detent mechanism.
Two well known styles of transfer valve are solenoid-operated and pressure-operated valves. Solenoid-operated transfer valves provide a high degree of control. The transfer valve can be switched from one system to the other by energizing and dc-energizing the solenoid. Because the solenoid controls when the valve shuttles, this design does not require a detent mechanism. This approach is generally relatively complicated and requires a suitable electronic computer or system to control the solenoid. In addition to the computer system, some means of sensing pressure is required. Because this approach is more complicated, it requires a higher level of redundancy and is generally more expensive.
Pressure-operated valves shuttle based on the relative pressures of the two supply systems and the pressure bias and detent action designed into the valve. This style or transfer valve may require no inputs from other devices. Pressure-operated transfer valves may make use of a hydraulic or mechanical detent to achieve the desired valve behavior. With a mechanical detent, a mechanism holds the valve in position until sufficient shuttling force is developed to overcome the detent. Once the detent is overcome, the valve moves away from the detent and the detent force no longer acts to hold the valve in position. With the detent force suddenly removed, the forces acting on the valve are no longer in equilibrium and the valve shuttles with a deliberate motion. Mechanical detents are typically spring-loaded devices. The mechanical detent may introduce friction and side loads on the valve spool, both of which have a negative effect on the valve's switching characteristic.
BRIEF SUMMARY OF THE INVENTION
Accordingly, one aspect of the invention involves a hydraulic transfer valve system for coupling one of primary and secondary hydraulic systems to a hydraulic load. The hydraulic systems each have a source and a return and the load has an input and a return. The system has first and second valves and a passageway coupling the first valve to the second valve and having first and second ports at the first and second valves, respectively. The first valve has a first condition in which it provides communication between the primary hydraulic system source and the hydraulic load input, provides communication between the primary hydraulic system return and the hydraulic load return, blocks communication between the secondary hydraulic system source and the hydraulic load input, provides communication between the secondary hydraulic system return and the hydraulic load return, and blocks the passageway first port. The first valve has a second condition in which it provides communication between the secondary hydraulic system source and the hydraulic load input, provides communication between the secondary hydraulic system return and the hydraulic load return, blocks communication between the primary hydraulic system source and the hydraulic load input, provides communication between the primary hydraulic system return and the hydraulic load return, and does not block the passageway first port. The second valve has a first condition in which it blocks the passageway second port and a second condition in which it does not block the passageway second port and herein, with the first valve in its second condition, the passageway permits a flow from the primary hydraulic system source to the primary hydraulic system return.
In various implementations the valves may be sliding spool valves. The valves may be spring-biased in a direction from their second conditions to their first conditions. Pressure from the primary hydraulic system source may bias the valves in the directions from their second conditions to their first conditions. Pressure from the secondary hydraulic system source may bias the valves in directions from their first conditions to their second conditions. With the valves in their first conditions, a recirculating flow from the secondary source to the secondary return may be permitted through the second valve. A pressure sensor may be coupled to the second valve and output a signal indicative of a pressure in the secondary hydraulic system.
Another aspect of the invention involves a hydraulic transfer valve system with means for piloting a first valve so that with primary and secondary hydraulic systems initially operating normally and the first valve in its first condition, a decrease in a pressure of the primary hydraulic system source relative to the secondary hydraulic system source causes the first valve to toggle to its second condition. With the secondary hydraulic system initially operating normally and the primary hydraulic system source initially operating with an insufficient pressure and the first valve in its second condition, a sufficient increase in the pressure of the primary hydraulic system source relative to the secondary hydraulic system source causes the first valve to toggle to the first condition.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a partially schematic view of a transfer valve system in a normal operating condition.
FIG. 2
is a partially schematic view of the system of
FIG. 1
in an intermediate condition before switching to backup operation.
FIG. 3
is a partially schematic view of the system of
FIG. 1
in a backup condition.
FIG. 4
is a partially schematic view of the system of
FIG. 1
in an intermediate condition before returning to normal.
Like reference numbers and designations in the various drawings indicate like elements.
DETAILED DESCRIPTION
FIG. 1
shows a transfer valve system
20
coupling a hydraulic load or circuit
22
to primary and secondary hydraulic systems
24
and
26
. The circuit
22
has an input
30
for receiving hydraulic fluid from an engaged one of the systems and a return
31
for returning fluid to such engaged system. The primary system.
24
has a source
32
and a return
33
. The secondary system
26
has a source
34
and a return
35
. The system sources and returns may respectively be coupled to associated pumps and reservoirs (not shown). The transfer valve system
20
includes a main valve
40
and a pilot valve
42
. In the exemplary embodiment, both valves are spool-type valves having spools
44
and
46
and pistons
48
and
50
. The spools are mounted for reciprocal motion within sleeves or cylinders
52
and
54
. Likewise, the pistons are mounted for reciprocal movement in sleeves or cylinders
56
and
58
at proximal ends of the associated spool cylinders
52
and
54
. Springs
60
and
62
extend from the opposite ends of the piston cylinders and into the associated pistons to bias the pistons toward their associated spools.
FIG. 1
shows a normal operating condition of the system
20
. In this condition, the system input
30
and return
31
are respectively coupled to the primary source
32
and primary return
33
. Both valve pistons are in relatively distal positions. In this condition, a conduit branch or passageway
70
, communicating with the primary source
32
, has a port on the main spool cylinder
52
at the proximal end of an annular chamber or cavity
72
of the spool
44
. A conduit
74
leading to the circuit input
30
has a port on the cylinder
52
at the distal end of that chamber. Thus the circuit input
30
communicates with the primary source
32
via the annular chamber
72
. Additional conduits
76
and
78
communicating with the primary source
32
provide communication between the primary source
32
and proximal volumes
80
and
82
of the piston cylinders
56
and
58
. A restriction
83
(described below) is located in the conduit
76
at an inlet to the volume
80
. In the normal condition, pressure from the primary source
32
acting on the pistons
48
and
50
along with the compression force of the associated springs
60
and
62
biases each piston toward its distal position. A conduit
84
in communication with the circuit return
31
has a port on the cylinder
52
near a proximal end thereof and in communication with a distal headspace
86
of the cylinder
56
in the normal condition. A conduit
88
in communication with the primary return
33
has a port on the cylinder
56
also communicating with the headspace
86
. Thus normal condition communication between the circuit return
31
and primary return
33
is via the headspace
86
.
Adjacent the annular chamber
72
, the lands
100
and
102
of the spool have smaller annular chambers
104
and
106
communicating with a central proximal compartment
108
within the spool by associated ports or apertures. The compartment
108
is vented to the headspace
86
via an aperture
110
near the proximal end of the compartment
108
. In operation, high pressure leakage out of the chamber
72
will be vented into the compartment
108
via the chambers
104
and
106
and then passed to the headspace
86
via the aperture
110
. This helps isolate the flow within the primary system and prevents leakage and cross-communication between the primary and secondary systems. Similar features (discussed below) are provided for the secondary system. A conduit
120
communicating with the secondary source
34
has a port on the cylinder
52
at a proximal end of an annular chamber
122
located immediately distally of the land
102
. A conduit
124
communicating with the secondary return
35
has a port in the cylinder
52
at an annular chamber
126
located distally of the chamber
122
and separated therefrom by a land
128
. In the normal condition of
FIG. 1
, the chambers
122
and
126
are not in communication with any other ports on the cylinder
52
. A conduit
130
communicating with the circuit return
31
has a port on the cylinder
52
. This port and thus the conduit
130
is normally blocked by the land
128
. Annular channels
132
and
134
immediately distally and proximally of the chamber
122
respectively in the lands
102
and
128
communicate with a central distal compartment
136
of the spool
44
via associated apertures. The distal compartment
136
communicates with the chamber
126
and thus with the secondary return
35
. Accordingly, secondary source leakage from the chamber
122
passes through the chambers
132
and
134
and into the compartment
136
to return to the secondary return
35
via the chamber
126
so as to, thereby, isolate the secondary system.
Conduits
140
and
142
in communication with the secondary source
34
have ports at the respective distal headspaces of the spool cylinders
52
and
54
. The exemplary spool cylinders are of smaller diameter and cross-section than their associated piston cylinders. Pressure from the secondary source
34
acting on the headspaces
144
and
146
produces a smaller counterforce than the force from the primary source
32
on the volumes
80
and
82
(which primary source force is also augmented by the relatively small associated spring force). In the normal condition this pressure balance maintains the piston distal ends contacting the associated spool proximal ends and maintains the spools at distalmost positions determined by stop shoulders
148
and
150
separating a wall surrounding the normal condition headspaces
144
and
146
from main body portions of the cylinders
52
and
54
.
In the exemplary embodiment, the distal end
152
of the primary spool
44
is sealed. The pilot spool
46
has a passageway
160
extending through its distal end
161
and communicating with a distal annular chamber
162
between a distal end land
163
and an adjacent land
164
via a port in the spool. At a distal end of the chamber
162
, a conduit
165
in communication with the secondary return
35
has a port on the cylinder
54
. In the normal condition, the passageway
160
permits a recirculating flow of fluid from the secondary source
34
to the secondary return
35
. A constriction
166
is located within the passageway
160
to limit the rate of the recirculating flow. At a proximal end of the chamber
162
, a conduit
168
has a port on the cylinder
154
and provides communication with a pressure sensor
170
. In this normal operating condition, the pressure sensor
170
thus outputs a signal indicative of the operating pressure of the secondary system. If the secondary system were to fail or otherwise shutdown, the pressure sensor
170
would provide an indication of the associated pressure drop.
A number of additional conduits are inoperative or less relevant in the normal operating condition. A conduit
180
in communication with the secondary return
35
has a port on the cylinder
54
at an annular chamber
182
separated from the chamber
162
by the land
164
. The conduit
180
provides a return path for leakage over the land
164
from the chamber
162
. To minimize leakage/contamination it may be advantageous that source pressure from one system not be adjacent to a return of the other in any of the valves. A conduit
190
has a port at the main piston cylinder headspace
86
and a port on the pilot spool cylinder
54
at an annular chamber
192
located proximally of the chamber
182
and separated therefrom by a land
194
. A conduit
196
has a port on the cylinder
54
at the chamber
192
and a port at the headspace
198
of the pilot piston cylinder
58
. In the normal operating condition, the conduits
190
and
196
serve to expose the pilot piston cylinder headspace
198
to the pressure of the primary return
33
. A conduit
200
having a restriction
202
has a port on the main piston cylinder
56
. In the normal condition, this port is blocked (just barely overlapped) by a proximal land
204
separated by a chamber
206
from a distal land
208
. The piston
48
has apertures
210
providing communication between a volume
80
and the chamber
206
. The conduit
200
has a second port, at its opposite end, on the pilot spool cylinder
54
. In the normal condition, this port is blocked (just barely overlapped) by a proximal land
212
of the spool
46
adjacent the chamber
192
.
In a failure of the primary system, the pressure of the primary source will drop. The nature of the drop will depend upon the nature of the failure. For example, a normal operational pressure of the sources may be in the vicinity of 4000 psi. As the primary source pressure begins to drop, the distal biasing force from primary system fluid in the chambers
80
and
82
will drop. The valve geometries and spring forces are such that this has a greater initial impact in the pilot valve than in the main valve. At a moderate reduction in pressure (e.g., from 4000 psi down to 3500 psi) the proximally-directed forces on the piston
50
(including the force from the secondary source acting on the spool
46
in the headspace
146
) is sufficient to overcome the distally-directed forces (including those from the primary source and spring
62
). Over a very small further pressure drop, the pilot valve shuttles proximally to the condition of
FIG. 2
with the piston
50
and spool
46
in proximal positions. In these positions, the valve condition is such that the distal land
163
blocks the port of the conduit
164
and the proximal land
212
is clear of the pilot piston cylinder port of the conduit
200
so that the conduits
190
,
196
, and
200
all communicate with the chamber
192
. In this condition, the main piston cylinder port of the conduit
200
is still blocked by the proximal land
204
of the piston
48
. In this condition, the secondary recirculating flow through the conduit
164
is blocked. This interruption may initially cause a slight increase in the pressure from the secondary source
34
as measured by the sensor
170
. This pressure increase is also felt in the headspace
144
of the main spool cylinder. This pressure increase, along with any further decrease in primary source pressure (e.g., below 2,530 psi) will cause the primary spool and piston to be shifted slightly proximally so that the land
204
begins to underlap the main piston cylinder port of the conduit
200
. This port opening provides a venting of primary fluid from the chamber
80
through the apertures
210
and annular chamber
206
and into the conduit
200
. From the conduit
200
, this flow passes through the annular chamber
192
, through the conduit
190
and through the headspace
86
and conduit
88
to the primary return
33
. This flow contributes to a sharp drop in the pressure difference across the piston
48
. The resulting force imbalance from the pressure drop causes the primary piston to rapidly shuttle to a distalmost position of
FIG. 3
with the primary spool following. This final shuttling of the main spool
44
makes the switch between primary and secondary systems. During the shuttling, the land
100
blocks the main spool cylinder port of the conduit
84
to block communication between the primary return
33
and circuit return
31
. An initial substage of this shuttling also causes the land
102
to block the main spool cylinder port of the conduit
74
thus blocking communication between the circuit input
30
and the primary source
32
. In a final substage of this shuttling to the distalmost position, the land
102
again underlaps the main spool cylinder port of the conduit
74
establishing communication between that conduit and the annular chamber
122
which remains in communication with the conduit
120
. This establishes communication between the system input
30
and secondary source
34
via the chamber
122
. Similarly, in this final substage the land
44
will underlap the main spool cylinder port of the conduit
130
establishing communication between the conduit
130
and the annular chamber
126
which remains in communication with the conduit
124
. Thus this substage also establishes communication between the circuit return
31
and the secondary return
35
via the annular chamber
126
. With the secondary hydraulic system
26
thus active, flow from the secondary hydraulic system
26
to the circuit
22
will slightly decrease the pressure measured by the sensor
170
. In this condition, if there is residual pressure in the primary hydraulic system
24
there can be a recirculating flow through the main piston
48
, pilot spool cavity
192
, and main cylinder headspace
86
.
Should full functioning of the primary hydraulic system
24
be reestablished, the exemplary implementation provides for toggling back to use of the primary system. As primary system pressure increases, initially the flow through the piston apertures
210
prevents this pressure change from shuttling the primary valve distally. Thus, although the primary valve shuttled to its distal position after the pilot valve shuttled, it does not shuttle back before the pilot valve does. As the primary source pressure increases to a threshold value (e.g. an exemplary 2930 psi) the pressure balance on the pilot valve permits the pilot valve piston and spool to shuttle back to their initial distal positions (FIG.
4
). This shuttling, inter alia, causes the pilot spool proximal land
212
to overlap the associated port of the conduit
200
thereby terminating the recirculating flow of the primary system through the piston apertures
210
. This termination can further increase primary system pressure. Additionally, the shifting of the pilot spool reestablishes flow through the conduit
164
, slightly decreasing pressure in the secondary system. These pressure changes along with a further increase in primary source pressure and along with any associated drop in the pressure at the headspace
86
, cause the primary valve piston and spool to rapidly shuttle back to their distal positions of
FIG. 1
breaking communication between the secondary hydraulic system
26
and the circuit
22
and establishing communication between the primary hydraulic system
24
and the circuit
22
.
Accordingly, it is seen that the exemplary system provides a two-way toggling of the operation of the main valve: both in transferring from the primary system to the secondary system and in transferring back to the primary system.
The pressure sensor or switch
170
may advantageously be used to detect latent failures of the pilot valve. If the pilot valve were stuck, the transfer valve might continue to operate, although not at proper pressure thresholds and the aircrew or control system would be otherwise unaware of the failure. The state of the sensor may be periodically checked during a flight or mission to determine that the pilot valve is in the appropriate position. The sensor may be checked during preflight operations when the secondary system is pressurized and the primary system is not. Under these conditions, the pilot valve should be positioned that it blocks the connection to return, causing the sensor to be pressurized. In flight, the pilot valve should be positioned such that it opens the connection to return, causing the sensor to be unpressurized. The value at which the sensor trips may not be particularly critical as it may behave like a binary on-off switch. The size/geometry of the orifice
166
substantially determines the flow through the secondary system when the secondary system is inactive. This may be dictated or influenced by the performance characteristics of the secondary system. The relationship (e.g., size ratio) between the orifices
83
and
202
substantially determines the pressure at which the transfer valve shuttles in the event of a failed (e.g., jammed) pilot valve. The orifices
83
and
202
in series determine the inactive primary system flow, similar to the role of the orifice
166
for the secondary system. In operation, it is anticipated that the spool and piston of each valve will maintain their engagement to each other and thus may be further integrated. The geometry and spring bias will advantageously be such that under no anticipated conditions will return pressure transients be large enough to cause spool/piston separation. The two-piece construction aids maufacturability.
The relationship between: (a) the ratio of (i) the cross-sectional area of the pilot valve piston acted upon by the primary system pressure to (ii) the cross-sectional area of the pilot valve spool acted upon by the secondary pressure; and (b) the ratio of (i) the cross-sectional area of the main valve piston acted upon by the primary system pressure to (ii) the cross-sectional area of the main valve spool acted upon by the secondary system pressure will influence the shuttling action of the primary valve. The former should be smaller than the latter. This causes the pilot valve to shuttle first so as to give the transfer valve an advantageous snapping detent action characteristic when shuttling from primary to secondary systems. For example, at exemplary normal operating source pressures of 4000 psi (and return pressures essentially zero), the valves may be configured so that the initial shuttle of the pilot occurs when the primary source pressure drops to a first threshold in the range of 2200-3200 psi (55-80% of normal), more narrowly 2700-3000 (67.5-75%) psi. The main may then shuttle at a lower pressure in the range of 1700-2600 psi (42.5-65%), more narrowly 2300-2500 psi (57.5-62.5%). A resumption in primary source pressure may shuttle the valves back nearly simultaneously at one or more thresholds in the range of 2700-3400 psi (67.5-85%), more narrowly 2900-3100 psi (72.5-77.5%). If the pilot is jammed in its second position, the main may shuttle back as a somewhat higher pressure in the range of 2800-3500 psi (70-87.5%), more narrowly 3200-3500 psi (80-87.5%). With another normal pressure (e.g., 3000 psi), the shuttling pressures could be at similar percentages.
One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, if applied as a redesign or retrofit of an existing transfer valve system, various features of the existing system may influence the implementation. Accordingly, other embodiments are within the scope of the following claims.
Claims
- 1. A hydraulic transfer valve system for coupling one of primary and secondary hydraulic systems, each having a source and a return, to a hydraulic load having an input and a return, the hydraulic transfer valve system comprising:a first valve; a second valve; and a passageway coupling the first valve to the second valve and having first and second ports at said first and second valves, respectively, the first valve having: a first condition in which the first valve: provides communication between the primary hydraulic system source and the hydraulic load input; provides communication between the primary hydraulic system return and the hydraulic load return; blocks communication between the secondary hydraulic system source and the hydraulic load input; provides communication between the secondary hydraulic system return and the hydraulic load return; and blocks the passageway first port; and a second condition in which the first valve: provides communication between the secondary hydraulic system source and the hydraulic load input; provides communication between the secondary hydraulic system return and the hydraulic load return; blocks communication between the primary hydraulic system source and the hydraulic load input; provides communication between the primary hydraulic system return and the hydraulic load return; and does not block the passageway first port; and the second valve having; a first condition in which the second valve blocks the passageway second port; and a second condition in which the second valve does not block the passageway second port and wherein with the first valve in its second condition, the passageway permits a flow from the primary hydraulic system source to the primary hydraulic system return.
- 2. The hydraulic transfer valve system of claim 1 wherein:the first valve is a sliding spool valve; and the second valve is a sliding spool valve.
- 3. The hydraulic transfer valve system of claim 1 wherein:the first valve is spring-biased in a direction from its second condition to its first condition; and the second valve is spring-biased in a direction from its second condition to its first condition.
- 4. The hydraulic transfer valve system of claim 1 wherein:pressure from the primary hydraulic system source biases the first valve in a direction from its second condition to its first condition; pressure from the primary hydraulic system source biases the second valve in a direction from its second condition to its first condition; pressure from the secondary hydraulic system source biases the first valve in a direction from its first condition to its second condition; and pressure from the secondary hydraulic system source biases the second valve in a direction from its first condition to its second condition.
- 5. The hydraulic transfer valve system of claim 1 wherein:with the first valve in its first condition and the second valve in its first condition, a recirculating flow from the secondary source to the secondary return is permitted through the second valve.
- 6. The hydraulic transfer valve system of claim 1 further comprising a pressure sensor coupled to the second valve and outputting a signal indicative of a pressure in the secondary hydraulic system.
- 7. A hydraulic transfer valve system for coupling one of primary and secondary hydraulic systems, each having a source and a return, to a hydraulic load having an input and a return, the hydraulic transfer valve system comprising:a first valve; a second valve; and a passageway coupling the first valve to the second valve and having first and second ports at said first and second valves, respectively, the first valve having: a first condition in which the first valve: provides communication between the primary hydraulic system source and the hydraulic load input; provides communication between the primary hydraulic system return and the hydraulic load return; blocks communication between the secondary hydraulic system source and the hydraulic load input; and provides communication between the secondary hydraulic system return and the hydraulic load return; and a second condition in which the first valve: provides communication between the secondary hydraulic system source and the hydraulic load input; provides communication between the secondary hydraulic system return and the hydraulic load return; blocks communication between the primary hydraulic system source and the hydraulic load input; and provides communication between the primary hydraulic system return and the hydraulic load return; and at least one of the first and second valves having means for piloting the first valve so that: with the primary and secondary hydraulic systems initially operating normally and the first valve in the first condition, a decrease in a pressure of the primary hydraulic system source relative to the secondary hydraulic system source causes the first valve to toggle to the second condition; and with the secondary hydraulic system initially operating normally and the primary hydraulic system source initially operating with an insufficient pressure and the first valve in the second condition, a sufficient increase in the pressure of the primary hydraulic system source relative to the secondary hydraulic system source causes the first valve to toggle to the first condition.
- 8. The hydraulic transfer valve system of claim 7 wherein:the means are configured so that: said decrease causes said second valve to shift from a first condition to a second condition at a first threshold pressure between 2200 and 3200 psi; and said decrease causes said first valve to shift from its first condition to its second condition at a second threshold pressure, less than the first threshold pressure and between 1700 and 2600 psi.
- 9. The hydraulic transfer valve system of claim 8 wherein:said first threshold pressure is between 2700 and 3000 psi; and said second threshold pressure is between 2300 and 2500 psi.
- 10. The hydraulic transfer valve system of claim 8 wherein the means are configured so that:said increase causes both the first and second valves to shift to their first conditions at one or more third threshold pressures between 2700 and 3400 psi.
- 11. The hydraulic transfer valve system of claim 10 wherein said one or more third threshold pressures between 2900 and 3100 psi.
- 12. The hydraulic transfer valve system of claim 8 wherein the means are configured so that if the second valve is jammed in its second condition:said increase causes the first valve to shift to its first condition at a third threshold pressure, greater than the first threshold pressure, and between 2800 and 3500 psi.
- 13. The hydraulic transfer valve system of claim 8 wherein said third threshold pressure is between 3200 and 3500 psi.
- 14. The hydraulic transfer valve system of claim 7 wherein:the means are configured so that: said decrease causes said second valve to shift from a first condition to a second condition at a first threshold pressure between 55 and 80% of a normal operating pressure of at least one of the primary and secondary hydraulic systems; said decrease causes said first valve to shift from its first condition to its second condition at a second threshold pressure, less than the first threshold pressure and between 42.5 and 62.5% of said normal operating pressure; said increase normally causes both the first and second valves to shift to their first conditions at one or more third threshold pressures between 67.5 and 85% of said normal operating pressure; and if the second valve is jammed in its second condition said increase causes the first valve to shift to its first condition at a fourth threshold pressure, greater than the first threshold pressure, and between 70 and 87.5% of said normal operating pressure.
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Kind |
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A |
3913324 |
Miller et al. |
Oct 1975 |
A |
4164119 |
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Aug 1979 |
A |
6173728 |
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