Directional control valve device

A recovery check valve 26 and a piston valve 27 are axially slidably disposed within a spool 2 in coaxial relation. An axial fluid passage 32 is formed within a cylindrical portion 27a of the piston valve 27, and a seat portion 33 for the recovery check valve is formed at an open end of the cylindrical portion 27a. The cylindrical portion 37a of the piston valve is formed with a hole 36 through which a hydraulic fluid in the fluid chamber 32 is introduced to a bridge passage 21 when the spool 2 is operated so as to introduce a hydraulic fluid from a hydraulic pump to the bottom side of a hydraulic cylinder. Fluid passages 40, 31 are formed within the spool so that a hydraulic fluid in the bridge passage 21 is introduced to the closed end of the piston valve through the fluid passages when the spool is operated in the opposite direction. With such a structure, the size of the valve apparatus can be set to the same size as the directional control valve not provided with the recovery check valve.

TECHNICAL FIELD
 The present invention relates to a directional control valve apparatus for
 use in a hydraulic drive system of construction machines, and more
 particularly to a directional control valve apparatus wherein a spool
 incorporates therein a recovery check valve for recovering a flow of a
 hydraulic fluid to an arm cylinder of a hydraulic excavator, for example.
 BACKGROUND ART
 As a directional control valve apparatus including a recovery check valve
 which recovers a flow of a hydraulic fluid to a hydraulic actuator, there
 is known one wherein a spool incorporates therein a recovery check valve
 for simplification of the apparatus, as disclosed in JP,Y 7-17841, for
 example.
 DISCLOSURE OF THE INVENTION
 In the directional control valve apparatus shown in FIG. 1, etc. of JP,Y
 7-17841, the side including a recovery check valve is illustrated as
 having substantially the same length as the side not including a recovery
 check valve. In actual design, however, it has been found that when a
 recovery check valve is incorporated in a spool in accordance with the
 same concept as the technique of JP,Y 7-17841, the side including a
 recovery check valve is longer than the side not including a recovery
 check valve. This point will be described with reference to FIGS. 4 to 6.
 FIGS. 4 to 6 show a directional control valve apparatus that is designed In
 accordance with the same concept as the technique disclosed in JP,Y
 7-17841.
 In FIGS. 4 to 6, the illustrated directional control valve apparatus
 comprises a casing 101, a spool 102 axially slidably disposed in a spool
 bore of the casing, and a load check valve 103. In the spool bore of the
 casing 101, there are formed two reservoir ports 104, 105, two actuator
 ports 106, 107, two communicating ports 111, 112, and three center bypass
 ports 108, 109, 110 in the order named from both outer axial ends.
 Further, a bridge passage 121 for interconnecting the two communicating
 ports 111, 112, a center bypass passage 123 for connecting a hydraulic
 pump 122 to the middle one 110 of the three center bypass ports 108, 109,
 110, and a center bypass passage 124 for interconnecting the other two
 center bypass ports 108, 109 and connecting them to a reservoir 125 are
 formed. In addition, a recovery check valve 126 is axially slidably
 disposed within the spool 102 such that, when the spool 102 is operated so
 as to introduce a hydraulic fluid from the hydraulic pump 122 to the
 bottom side of a hydraulic cylinder 150, the fluid returned from the rod
 side of the hydraulic cylinder 150 is recovered to the bridge passage 121.
 The operation of the directional control valve apparatus will be described
 below.
 (1) Neutral (FIG. 4)
 The hydraulic fluid delivered from the hydraulic pump 122 is introduced to
 the directional control valve apparatus. However, because the spool 102 is
 not operated, the hydraulic fluid is introduced to the reservoir 125
 through the center bypass passages 123, 124. Also, the holding pressure of
 the hydraulic cylinder 150 is in a closed condition by lands 113 and 114.
 (2) Extension of Hydraulic Cylinder: Recovery (FIG. 5)
 When the spool 102 is moved to the left in the drawing to extend the
 hydraulic cylinder 150, the communication between the center bypass
 passages 123, 124 is closed by lands 116 and 117. Also, with the leftward
 movement of the spool 102 in the drawing, the communicating port 112 and
 the actuator port 107 are communicated with each other, whereupon the
 hydraulic fluid delivered from the hydraulic pump 122 is introduced to the
 bottom side of the hydraulic cylinder 150 via the load check valve 103,
 the bridge passage 121, the communicating port 112 and the actuator port
 107. On the other hand, the hydraulic fluid returned from the rod side of
 the hydraulic cylinder 150 is drained to the reservoir 125 via the
 actuator port 106 and the reservoir port 104 which are also communicated
 with each other upon the leftward movement of the spool 102 in the
 drawing. At the same time, a hole 129 on the input side of the recovery
 check valve 126 is opened to the actuator port 106, and a hole 130 on the
 output side of the recovery check valve 126 is communicated with the
 bridge passage 121 through the communicating port 111. In the operation
 wherein the hydraulic cylinder 150 is extended under its own load W, a
 pressure of the hydraulic fluid pushed out of the rod side of the
 hydraulic cylinder 150 is higher than that of the hydraulic fluid supplied
 to the bottom side of the hydraulic cylinder 150. Therefore, most of the
 hydraulic fluid pushed out of the rod side of the hydraulic cylinder 150
 enters the hole 129 through the actuator port 106 to push open the check
 valve 126 that is incorporated as a recovery valve in the spool 102, and
 is recovered to the bridge passage 121 through the hole 130.
 (3) Contraction of Hydraulic Cylinder (FIG. 6)
 When the spool 102 is moved to the right in the drawing to contract the
 hydraulic cylinder, the communication between the center bypass passages
 123, 124 is closed by the lands 116 and 117. Also, with the rightward
 movement of the spool 102 in the drawing, the communicating port 111 and
 the actuator port 106 are communicated with each other, whereupon the
 hydraulic fluid delivered from the hydraulic pump 122 is introduced to the
 rod side of the hydraulic cylinder 150 via the load check valve 103, the
 bridge passage 121, the communicating port 111 and the actuator port 106.
 At this time, because the hole 130 is closed by the land 115, the
 hydraulic fluid delivered from the hydraulic pump 122 is prevented from
 leaking to the reservoir 125. On the other hand, the hydraulic fluid
 returned from the bottom side of the hydraulic cylinder 150 is drained to
 the reservoir 125 via the actuator port 107 and the reservoir port 105
 which are also communicated with each other upon the rightward movement of
 the spool 102 in the drawing.
 Thus, the directional control valve apparatus shown in FIGS. 4 to 6 can
 fulfill the recovery function with a simple structure.
 In the directional control valve apparatus having the above-described
 construction, however, when the valve is operated in direction contrary to
 the recovery, i.e., when the spool 102 is moved to the right in the
 drawing as shown in FIG. 6, the spool 102 is required to have a lap
 allowance X1 relative to the lands 115, 118 so that the bridge passage 121
 and the center bypass passage 124 are not communicated with each other.
 The reason is that, if the bridge passage 121 and the center bypass
 passage 124 are communicated with each other, the hydraulic fluid
 delivered from the hydraulic pump 122 would push open the recovery check
 valve 126 via the load check valve 103 and the bridge passage 121,
 followed by escaping to the center bypass passage 124. On the other hand,
 when the valve is operated for the recovery, i.e., when the spool 102 is
 moved to the left in the drawing as shown in FIG. 5, the hole 130 is
 required to have an opening width X2 relative to the communicating port
 111 so that the actuator port 106 and the bridge passage 121 are
 communicated with each other.
 It is here assumed that the left and right communicating ports 111, 112
 have the same length Xa and spool portions projecting from the edges of
 the lands 115, 118 facing the center bypass ports 108, 109 in the neutral
 state of FIG. 4 have the same length Xb. Comparing a length Xh of the land
 115 on the side including the recovery check valve 126 and a length Xm of
 the land 118 on the side not including the recovery check valve 126, the
 length Xh of the land 115 on the side including the recovery check valve
 126 is required to have a value resulted from subtracting the length Xa of
 the communicating port 111 from the sum of a rightward stroke X of the
 spool 102 in the drawing, the lap allowance X1, a leftward stroke X of the
 spool 102 in the drawing, and the opening width X2, whereas the length Xm
 of the land 118 on the side not including the recovery check valve 126 is
 required just to have a value resulted from subtracting the projection
 length Xb from the sum of the stroke X of the spool 102 and the lap
 allowance X1. That is to say:
EQU Xh=(X+X1)+(X+X2)-Xa
EQU Xm=X+X1-Xb
 Further, in actual design, the lands and ports are usually set to have
 necessary minimum lengths for the purpose of making the overall
 construction of the directional control valve apparatus as compact as
 possible. When designing the directional control valve apparatus shown in
 FIGS. 4 to 6 under such conditions, the land 115 on the side not including
 the recovery check valve 126 is longer than the land 118 on the side not
 including the recovery check valve 126 because the lengths Xh, Xm of the
 lands 115, 118 are defined as described above.
 More specifically, let suppose that the spool 102 and the land 115 are cut
 by a length of Xh-Xm to the left, in the drawing, from the edge position
 of the land 115 facing the center bypass port 108 to render the length Xh
 of the land 115 equal to the length Xm of the land 118 while the hole 130
 formed in the spool 102 is positioned so as to surely provide the opening
 width X2 when the spool 102 is moved to the left in the drawing as shown
 in FIG. 5. In this case, when the spool 102 is moved to the right in the
 drawing through the stroke X as shown in FIG. 6, the hole 130 is opened to
 the center bypass port 108, whereby the hydraulic fluid delivered from the
 hydraulic pump 122 pushes open the recovery check valve 126 and is then
 escaped to the reservoir 125 through the center bypass port 108. For this
 reason, the length Xh of the land 115 is required to be longer than the
 length Xm of the land 118.
 Generally, a recovery check valve is provided in a directional control
 valve for, e.g., a hydraulic cylinder having an area difference. In a
 directional control valve apparatus wherein a directional control valve
 not including a recovery check valve for a motor or the like and a
 directional control valve including a recovery check valve for a hydraulic
 cylinder or the like are mixed as encountered in a hydraulic excavator,
 the overall size of the valve apparatus must be set in match with the size
 of the directional control valve including the recovery check valve. This
 means that the size of the valve apparatus is increased.
 An object of the present invention is to provide a directional control
 valve apparatus in which, even in one having a directional control valve
 not including a recovery check valve and a directional control valve
 including a recovery check valve in mixed fashion, the size of the valve
 apparatus can be set to the same as that of the directional control valve
 not including the recovery check valve.
 (1) To achieve the above object, the present invention provides a
 directional control valve apparatus comprising a casing, a spool axially
 slidably disposed in a spool bore of the casing, and a load check valve,
 the spool bore of the casing being formed with two reservoir ports, two
 actuator ports, two communicating ports and three center bypass ports in
 the order named from both outer axial ends toward the center, the casing
 being formed with a bridge passage connected to a hydraulic pump through
 the load check valve and interconnecting the two communicating ports, a
 center bypass passage for connecting the hydraulic pump to the middle port
 of the three center bypass ports, and a center bypass passage for
 interconnecting the other two center bypass ports and connecting these two
 center bypass ports to a reservoir, the spool having a recovery input
 passage and a recovery output passage both formed therein, the spool
 including a recovery check valve axially slidably disposed within the
 spool between the recovery input passage and the recovery output passage,
 the valve apparatus operating such that when the spool is operated in one
 direction, the recovery check valve is opened to communicate the recovery
 input passage and the recovery output passage with each other for
 recovering a hydraulic fluid returned through the meter-out-side port of
 the two actuator ports to the bridge passage via the recovery input
 passage, the recovery check valve, the recovery output passage and the
 communicating passage on the same side as the meter-out-side actuator
 port, wherein piston valve means is provided within the spool for closing
 the recovery output passage when the spool is operated in a direction
 opposite to the one direction.
 With the feature of the piston valve means being provided within the spool,
 in spite of that the length of a land on the side including the recovery
 check valve is set to be equal to the length of a land on the side not
 including the recovery check valve, when the spool is operated in the
 direction opposite to the one direction, the recovery output passage is
 closed by the piston valve means. Therefore, the hydraulic fluid delivered
 from the hydraulic pump is avoided from escaping to the reservoir through
 the center bypass port, and the same function as conventional one can be
 provided.
 (2) In the above (1), preferably, the piston valve means comprises a piston
 valve axially slidably disposed within the spool and being able to open
 and close the recovery output passage, and a fluid passage formed within
 the spool and opened to the meter-in-side port of the two communicating
 ports when the spool is operated in the direction opposite to the one
 direction, thereby introducing a hydraulic fluid in the bridge passage to
 the piston valve to bias the piston valve in the closing direction.
 With those features, the piston valve means closes the recovery output
 passage when the spool is operated in the direction opposite to the one
 direction.
 (3) In the above (1), preferably, the piston valve means comprises a piston
 valve axially slidably disposed within the spool in coaxial relation to
 the recovery check valve and having a seat portion for the recovery check
 valve, the seat portion being positioned at one end of the piston valve on
 the side facing the recovery check valve, and a fluid passage formed
 within the spool and introducing a hydraulic fluid in the bridge passage
 to the piston valve to bias the piston valve toward the recovery check
 valve when the spool -is operated in the direction opposite to the one
 direction, the piston valve having a cylindrical portion opened at the
 side of the seat portion, closed at the opposite side, and including an
 axial fluid passage formed therein, the cylindrical portion having a hole
 formed therein to communicate the axial fluid passage with the recovery
 output passage.
 By so constructing the piston valve means, when the spool is operated in
 the one direction, the seat portion of the piston valve is moved away from
 the recovery check valve, whereupon the recovery check valve is opened to
 recover the hydraulic fluid returned through the meter-out-side actuator
 port to the bridge passage via the recovery input passage, the recovery
 check valve, the axial passage within the cylindrical portion of the
 piston valve, the hole in the cylindrical portion, the recovery output
 passage, and the communicating passage on the same side as the
 meter-out-side actuator port. On the other hand, when the spool is
 operated in the direction opposite to the one direction, the hydraulic
 fluid in the bridge passage, i.e., the pump pressure, is introduced to the
 piston valve through the oil passage within the spool, whereupon the
 piston valve is pushed toward the recovery check valve and the seat
 portion of the piston valve closes the recovery check valve. The recovery
 output passage is thus closed.

BEST MODE FOR CARRYING OUT THE INVENTION
 A directional control valve apparatus provided with a recovery check valve
 according to an embodiment of the present invention will be described
 below with reference to FIGS. 1 to 3.
 FIG. 1 shows a neutral state of the directional control valve apparatus of
 this embodiment, FIG. 2 shows a state in which a spool is moved to the
 left in the drawing (i.e., a state in which the spool is operated so as to
 introduce a hydraulic fluid from a hydraulic pump to the bottom side of a
 hydraulic cylinder), and FIG. 3 shows a state in which the spool is moved
 to the right in the drawing (i.e., a state in which the spool is operated
 so as to introduce the hydraulic fluid from the hydraulic pump to the
 bottom side of the hydraulic cylinder).
 Referring to FIGS. 1 to 3, the directional control valve apparatus
 comprises a casing 1, a spool 2 axially slidably disposed in a spool bore
 1a of the casing 1, and a load check valve 3. In the spool bore 1a of the
 casing 1, there are formed two reservoir ports 4, 5, two actuator ports 6,
 7, two communicating ports 11, 12, and three center bypass ports 8, 9, 10
 in the order named from both outer axial ends toward the center. These
 ports are separated from each other by lands 13, 14, 15, 16, 17, 18, 19,
 20. In the casing 1, a bridge passage 121 and center bypass passages 23,
 24 are formed. The communicating port 11 and the communicating port 12 are
 interconnected by the bridge passage 21. A hydraulic pump 22 is connected
 to the middle one 10 of the three center bypass ports 8, 9, 10 through the
 center bypass passage 23. The other two center bypass ports 8, 9 are
 interconnected by the center bypass passage 24 and then connected to a
 reservoir 25.
 A recovery check valve 26 and a piston valve 27 are axially slidably
 disposed within the spool 2, and at a left end of the recovery check valve
 26 in the drawing, a spring 28 is provided to locate in a spring chamber
 34 formed in the recovery check valve 26 and to bias the recovery check
 valve 26 in the closing direction. Further, in the spool 2, there are
 formed a hole 29 which is closed by a land 14 when the spool 2 is in a
 neutral state (FIG. 1), opened to the actuator port 6 when the spool 2 is
 moved to the left in the drawing (FIG. 2), and opened to the communicating
 port 11 when the spool 2 is moved to the right in the drawing (FIG. 3); a
 hole 30 which is opened to the communicating port 11 when the spool 2 is
 in the neutral state (FIG. 1) and is moved to the left in the drawing
 (FIG. 2), and opened to the center bypass port 18 when the spool 2 is
 moved to the right in the drawing (FIG. 3); and a hole 31 which is closed
 by a land 18 when the spool 2 is in the neutral state (FIG. 1), opened to
 the center bypass port 9 when the spool 2 is moved to the left in the
 drawing (FIG. 2), and opened to the communicating port 12 when the spool 2
 is moved to the right in the drawing (FIG. 3). The hole 29 functions as a
 recovery input passage, and the hole 20 functions as a recovery output
 passage.
 The piston valve 27 comprises a cylindrical portion 27a which is opened at
 one side facing the recovery check valve 26, is closed at the opposite
 side, and has a fluid passage 32 formed therein to extend in the axial
 direction, and a seat portion 33 for the recovery check valve 26, the seat
 portion 33 being disposed at an open end of the fluid passage 32 in the
 cylindrical portion 27a, i.e., at a left end thereof in the drawing. Also,
 the fluid passage 32 and the spring chamber 34 of the recovery check valve
 26 are interconnected through a small hole 35 formed in the recovery check
 valve 26, and the fluid passage 32 of the piston valve 27 and the hole 30
 formed in the spool 2 are interconnected through a hole 36 formed in the
 cylindrical portion 27a of the piston valve 27, allowing the hydraulic
 fluid in the fluid passage 32 to be introduced to the bridge passage 21
 when the spool 2 is moved to the left in the drawing (FIG. 2).
 Further, a fluid passage 40 extending in the axial direction and
 communicating with the hole 31 is formed in the spool 2 and opened to face
 a closed end of the piston valve 27 on the right side in the drawing,
 allowing the pressure (pump pressure) of the hydraulic fluid in the bridge
 passage 21 to be introduced through the fluid passage 40 when the spool 2
 is moved to the right in the drawing (FIG. 3).
 The land 15 and the land 18 have the same length that is equal to the
 length of the land 118 of the directional control valve apparatus, shown
 in FIGS. 4 to 6, not including the recovery check valve.
 More specifically, it is here assumed that spool portions projecting from
 the edges of the lands 15, 18 facing the center bypass ports 18, 19 in the
 neutral state of FIG. 1 have the same length Xb as those shown in FIGS. 4
 to 6, and the spool 2 has the same lap allowance X1 relative to the land
 15 in the operative states of FIGS. 2 and 3 as that shown in FIGS. 4 to 6.
 Comparing a length XH of the land 15 on the side including the recovery
 check valve 26 and a length XM of the land 18 on the side not including
 the recovery check valve 26, both the lands have the same length resulted
 from subtracting the projection length Xb from the sum of a stroke X of
 the spool 2 and the lap allowance X1. That is to say:
EQU XH=XM=X+X1-Xb(=Xm)
 Moreover, the left and right communicating ports 11, 12 have the same
 length that is equal to the length of the communicating port 111 of the
 directional control valve apparatus, shown in FIGS. 4 to 6, not including
 the recovery check valve.
 The operation of the thus-constructed directional control valve apparatus
 of this embodiment will be described below.
 (1) Neutral (FIG. 1)
 The hydraulic fluid delivered from the hydraulic pump 22 is introduced to
 the directional control valve apparatus. However, because the spool 2 is
 not operated, the hydraulic fluid is introduced to the reservoir 25 via
 the center bypass passage 23, the center bypass ports 8, 9 and the center
 bypass passage 24.
 Also, the holding pressure of a hydraulic cylinder 50 is in a closed
 condition by the lands 13 and 14.
 (2) Extension of Hydraulic Cylinder: Recovery (FIG. 2)
 When the spool 2 is moved to the left in the drawing to extend the
 hydraulic cylinder 50, the communication between the center bypass ports
 8, 10 is closed by the land 16, and the communication between the center
 bypass ports 9, 10 is closed by the land 17. Also, with the leftward
 movement of the spool 2 in the drawing, the communicating port 12 and the
 actuator port 7 are communicated with each other, whereupon the hydraulic
 fluid delivered from the hydraulic pump 22 is introduced to the bottom
 side of the hydraulic cylinder 50 via the hold check valve 3, the bridge
 passage 21, the communicating port 12 and the actuator port 7.
 On the other hand, since the actuator port 6 and the reservoir port 4 are
 also communicated with each other upon the leftward movement of the spool
 2 in the drawing, a part of the hydraulic fluid returned from the rod side
 of the hydraulic cylinder 50 is drained to the reservoir 25 via the
 actuator port 6 and the reservoir port 4. At the same time, the hole 29 on
 the input side of the recovery check valve 26 is opened to the actuator
 port 6, and the fluid passage 32 in the piston valve 27, which serves as a
 part of an output side passage of the recovery check valve 26, is
 communicated with the bridge passage 21 via the holes 36, 30 and the
 communicating port 11. In the operation wherein the hydraulic cylinder 50
 is extended under its own load W, a pressure of the hydraulic fluid pushed
 out of the rod side of the hydraulic cylinder 50 is higher than that of
 the hydraulic fluid supplied to the bottom side of the hydraulic cylinder
 50. Therefore, most of the hydraulic fluid pushed out of the rod side of
 the hydraulic cylinder 50 enters the hole 29 through the actuator port 6
 to push open the recovery check valve 26 that is incorporated in the spool
 2, and is recovered to the bridge passage 21 via the fluid passage 32, the
 holes 36, 30 and the communicating port 11.
 (3) Contraction of Hydraulic Cylinder (FIG. 3)
 When the spool 2 is moved to the right in the drawing to contract the
 hydraulic cylinder 50, the communication between the center bypass ports
 8, 10 is closed by the land 16 and the communication between the center
 bypass ports 9, 10 is closed by the land 17. Also, with the rightward
 movement of the spool 2 in the drawing, the communicating port 11 and the
 actuator port 6 are communicated with each other, whereupon the hydraulic
 fluid delivered from the hydraulic pump 22 is introduced to the rod side
 of the hydraulic cylinder 50 via the load check valve 3, the bridge
 passage 21, the communicating port 11 and the actuator port 6.
 At this time, the hole 29 is opened to the communicating port 11 and the
 hole 30 is opened to the center bypass port 8. However, because the hole
 31 is opened to the communicating port 12, the pump pressure in the bridge
 passage 21 acts on the closed end of the piston valve 27 on the right side
 in the drawing, whereby the piston valve 27 and the recovery check valve
 26 are pushed to the left in the drawing to hold the seat portion 33 in a
 closed state.
 On the other hand, since the actuator port 7 and the reservoir port 5 are
 also communicated with each other upon the rightward movement of the spool
 2 in the drawing, the hydraulic fluid returned from the bottom side of the
 hydraulic cylinder 50 is drained to the reservoir 25 via the actuator port
 7 and the reservoir port 5.
 In the directional control valve apparatus of this embodiment, as described
 above, the length XH of the land 15 on the side including the recovery
 check valve is equal to the length XM of the land 18 on the side not
 including the recovery check valve 26. Despite such a structure, when the
 directional control valve is operated in direction contrary to the
 recovery, i.e., when the spool 2 is moved to the right in the drawing as
 shown in FIG. 3, the hydraulic fluid delivered from the hydraulic pump 22
 is avoided from escaping to the reservoir 25 through the center bypass
 port 8, and the same function as conventional one can be provided.
 With this embodiment, therefore, even in a directional control valve
 apparatus wherein a directional control valve not including a recovery
 check valve for a motor or the like and a directional control valve
 including a recovery check valve for a hydraulic cylinder or the like are
 mixed as encountered in a hydraulic excavator, the overall size of the
 valve apparatus can be set in match with the size of the directional
 control valve not including the recovery check valve. Consequently, the
 valve apparatus can be compacted and the production cost can be cut down.
 INDUSTRIAL APPLICABILITY
 According to the present invention, in spite of that the length of the land
 on the side including the recovery check valve is equal to the length of
 the land on the side not including the recovery check valve, when the
 directional control valve is operated in direction contrary to the
 recovery, the hydraulic fluid delivered from the hydraulic pump is avoided
 from escaping to the reservoir through the center bypass port, and the
 same function as conventional one can be provided.
 Therefore, even in a directional control valve apparatus wherein a
 directional control valve not including a recovery check valve for a motor
 or the like and a directional control valve including a recovery check
 valve for a hydraulic cylinder or the like are mixed as encountered in a
 hydraulic excavator, the overall size of the valve apparatus can be set in
 match with the size of the directional control valve not including the
 recovery check valve. As a result, the valve apparatus can be compacted
 and the production cost can be cut down.