265
PRESSURE CONTROLS
Unloading Relif Valves
C
Unloading Relief Valves
Unloading Relief Valves
These valves are used to operate the pumps with minimum load in
accumulator circuits or in high-low pump circuits.
In accumulator circuits, when the system pressure reaches to a cut out
pressure (adjusted maximum), the valve acts to divert the pump
delivery to the reservoir at low pressure, thus the pump is unloaded
automatically.
When the accumulator pressure drops to the cut in pressure (refer to
characteristic chart on
page 269), the valve directs the pump delivery
to the accumulator and hydraulic system.
An integral check valve prevents reverse flow through the valve from
the accumulator.
In high-low pump circuits, the valve acts to unload the large volume
pump with the same manner as described above during load operation
of the small volume pump.
Special Seals Series Number
Type of
Mounting
Valve
Size
Cut-out Pres.
Adj. Range
MPa (PSI)
High Venting
Pres. Feature
Design
Number
Design Standards
F:
Special Seals
for Phosphate
Ester Type
Fluids
(Omit if not
required)
BUC:
Unloading
Relief Valve
G:
Sub-plate
Mounting
10
06
B:
2.5-7.0
(360-1020)
C:
3.5-14
(510-2030)
H:
7.0-21
(1020-3050)
V:
For High
Venting
Pressure
Feature
(Omit if not
required)
25
30
None:
Japanese
Std. "JIS"
80:
European
Design Std.
90:
N. American
Design Std.
F- BUC G -06 -B V -30
*
Graphic Symbol
Model Number Designation
Use the high-venting-pressure type to reduce the shift time from unloading to onloading.
Model Numbers
Max.
Operating Pres.
21 (3050)
125
(33)
MPa (PSI)
Max. Flow
L/min
(U.S.GPM)
Approx. Mass
kg(1bs.)
BUCG-06-
**
-30/3080/3090
BUCG-10-
**
-25/2580/2590
250
(66)
12
(26.5)
21.5
(47.4)
Specifications
Pilot-drain system
A pilot-drain system is typically configured with an external pilot and an external drain, as
indicated by the right graphic symbol. However, customized pilot-drain systems with an internal
pilot are also available.
For the internal pilot type, the design standard number at the end of the model number is uniquely
assigned. Refer to the table below for the internal pilot type. Please contact us for details.
Pilot &
Drain Conn.
Graphic
Symbols
European Design
Standard
Int. Pitot-
Int. Drain
BUCG-06-
**
-30801
BUCG-10-
**
-25801
N. American Design
Standard
BUCG-06-
**
-30901
BUCG-10-
**
-25901
Japanese Std.
"JIS"
BUCG-06-
**
-3001
BUCG-10-
**
-2501
Int. Pitot-
Ext. Drain
BUCG-06-
**
-30802 BUCG-06-
**
-30902 BUCG-06-
**
-2502
Unloading Relief Valves
266
BUCGM-06-20
BUCGM-10-20
Rc 3/4
Rc 1-1/4
Valve
Model
Numbers
Valve Model
Numbers
M16 55Lg. (2 pcs.)
M16 110Lg. (2 pcs.)
M16 130Lg. (2 pcs.)
M20 70Lg. (2 pcs.)
M20
160Lg. (4 pcs.)
5/8-11 UNC 2-1/4 Lg. (2 pcs.)
5/8-11 UNC 4-1/2 Lg. (2 pcs.)
5/8-11 UNC 5 Lg. (2 pcs.)
3/4-10 UNC 2-3/4 Lg. (2 pcs.)
3/4-10 UNC 6-1/2 Lg. (4 pcs.)
BUCG-06
BUCG-10
Japanese Std. "JIS" and European Design Std.
Socket Head Cap Screw
N. American Design Std.
BUCGM-06-2080 3/4 BSP.F
BUCGM-10-2080 1-1/4 BSP.F
Sub-plate
Model Numbers
Thread
Size
Sub-plate
Model Numbers
Thread
Size
BUCGM-06-2090 3/4 NPT
BUCGM-10-2090 1-1/4 NPT
Sub-plate
Model Numbers
Thread
Size
Japanese Standard "JIS" European Design Standard N. American Design Standard
4.4 (9.7)
7.2 (15.9)
Approx.
Mass
kg (lbs.)
BUCG-06
BUCG-10
Instructions
Mounting Bolts
Attachment
Sub-plate
Sub-plates are available. Specify the sub-plate model number from the table above. When sub-plates are not used, the mounting surface
should have a good machined finish.
To adjust the pressure, loosen the lock nut and turn the pressure adjustment handle slowly clockwise for higher
pressures or anti-clockwise for lower pressures. After adjustments, do not forget to tighten the lock nut.
Take care not to neglect connecting the drain pipe to the reservoir; otherwise not only will the valve fail to operate
properly but also the line pressure will rise infinitely. Extend the end of the drain pipe into fluid.
Limit the pressure drop between the valve and the accumulator in an accumulator circuit below 10% of the cut-out
pressure.
Limit the drain port back pressure below 2% of the cut-out pressure.
267
PRESSURE CONTROLS
Unloading Relif Valves
C
Unloading Relief Valves
DIMENSIONS IN
MILLIMETRES (INCHES)
BUCG-06-
**
-30
BUCG-06-
**
-3080
BUCG-06-
**
-3090
Rc 1/4
1/4 BSP.Tr
1/4 NPT
"A"
Thd.
Rc 1/4
1/4 BSP.F
1/4 NPT
"B"
Thd.Model Numbers
BUCGM-06-20
BUCGM-06-2080
BUCGM-06-2090
M16
5/8-11 UNC
"A"
Thd.Sub-plate Model No.
M16
"B"
Thd.
Rc 3/4
3/4 BSP.F
3/4 NPT
130
(5.12)
127
(5.00)
90
(3.54)
50
(1.97)
Mounting Surface
(O-Rings Furnished)
6(.24)
Dia.
Two Locating Pins
6
(.24)
90
(3.54)
110
(4.33)
128
(5.04)
External Pilot Port
"B"
Thd.
Fully Extended
152
(5.98)
51.5
(2.03)
1
(.04)
Drain Port
"B"
Thd.
Lock Nut
14(.55)
Hex.
Pressure Adjustment Handlle
60.5
(2.38)
83.5
(3.29)
169
(6.65)
52
(2.05)
104
(4.09)
17.5(.69)
Dia. Through
26(1.02)
2 Places
C' bore
Accumulator or
System Port
Pressure Inlet Port
Tank Port
102
(4.02)
78
(3.07)
70
(2.76)
12
(.47)
4
(.16)
35
(1.38)
11
(.43)
33.3
(1.31)
33.5
(1.32)
55.5
(2.19)
46
(1.81)
66.7
(2.63)
27.5
(1.08)
12
(.47)
168
(6.61)
192
(7.56)
11(.43)
Dia. Through
17.5(.69)
Dia. Spotface
4
Places
"A"
Thd. Through
6 Places
7(.28)
Dia.
8(.31)
Deep
2 Places
23(.91)
Dia.
"B"
Thd. (From Rear)
3 Places
40
(1.57)
20
(.79)
145
(5.71)
Pressure Gauge Connection
"A"
Thd.
17.5(.69)
Dia. Through
26(1.02)
Dia. Spotface
4 Places
44(1.73)
Dia.
BUCG-06-
**
-30/3080/3090
Sub-plate
BUCGM-06-20/2080/2090
32.5
(1.28)
88
(3.46)
108
(4.25)
19
(.75)
INC.
Unloading Relief Valves
268
DIMENSIONS IN
MILLIMETRES (INCHES)
BUCG-10-
**
-25
BUCG-10-
**
-2580
BUCG-10-
**
-2590
Rc 1/4
1/4 BSP.Tr
1/4 NPT
"A"
Thd.
Rc 1/4
1/4 BSP.F
1/4 NPT
"B"
Thd.Model Numbers
BUCGM-10-20
BUCGM-10-2080
BUCGM-10-2090
M20
3/4-10 UNC
"A"
Thd.Sub-plate Model No.
M20
"B"
Thd.
Rc 1-1/4
1-1/4 BSP.F
1-1/4 NPT
159
(6.26)
Mounting Surface
(O-Rings Furnished)
6(.24)
Dia.
Two Locating Pins
6
(.24)
External Pilot Port
"B"
Thd.
Fully Extended
154.5
(6.08)
57
(2.24)
Drain Port
"B"
Thd.
Lock Nut
14(.55)
Hex.
Pressure Adjustment Handlle
72.1
(2.84)
107.9
(4.25)
60
(2.36)
120
(4.72)
21.5(.85)
Dia. Through
32(1.26)
C' bore
2 Places
Accumulator or System Port
Pressure Inlet Port
Tank Port
120
(4.72)
92
(3.62)
82.5
(3.25)
14
(.55)
4.7
(.19)
41.3
(1.63)
12.7
(.50)
11(.43)
Dia. Through
17.5(.69)
Dia. Spotface
4
Places
7(.28)
Dia.
8(.31)
Deep
2 Places
28(1.10)
Dia.
"B"
Thd. (From Rear)
3 Places
45
(1.77)
20
(.79)
117
(4.61)
67
(2.64)
137
(5.39)
Pressure Gauge Connection
"A"
Thd.
21.5(.85)
Dia. Through
32(1.26)
Dia. Spotface
4
Places
205
(8.07)
19
(.75)
44.5
(1.75)
38
(1.50)
76.2
(3.00)
51
(2.01)
88.9
(3.50)
204
(8.03)
232
(9.13)
32
(1.26)
14
(.55)
190
(7.48)
"A"
Thd. Through
6 Places
BUCG-10-
**
-25/2580/2590
Sub-plate
BUCGM-10-20/2080/2090
45.5
(1.79)
136
(5.35)
19
(.75)
INC.
Dia.
44(1.73)
269
PRESSURE CONTROLS
Unloading Relif Valves
C
Unloading Relief Valves
BUCG-06,10
Cut-out Pressure
20
MPa
3000
PSI
200010000
15100 5
Cut-in Pressure
18
2500
MPa
PSI
8
4
0
16
12
2000
1500
1000
500
0
BUCG-06
Unloading Pressure
1.0
MPa
PSI
0.8
0.6
0.4
0.2
0
125
100
75
50
25
0
150
L/min
40
U.S.GPM
10050
3020100
Flow Rate
High Venting
Pressure Feature
Standard
BUCG-10
1.2
MPa
PSI
150
1.0
0.8
0.6
0.4
0.2
0
0
0
125
100
75
50
25
0
Unloading Pressure
300
L/min
80
U.S.GPM
200100
6040200
Flow Rate
High Venting
Pressure Feature
Standard
BUCG-06
0.4
MPa
PSI
60
0.3
0.2
0.1
0
40
20
0
150
L/min
40
U.S.GPM
10050
3020100
Flow Rate
Pressure Drop P
0.4
MPa
PSI
60
0.3
0.2
0.1
0 0
0
40
20
0
300
L/min
80
U.S.GPM
25020015010050
6040200
Flow Rate
Pressure Drop P
BUCG-10
Cut-in Pressure vs. Cut-out Pressure
Unloading Pressure vs. Flow
Pressure Drop for Check Valve
Hydraulic Fluid: Viscosity
2
35 mm /s (164 SSU)
, Specific Gravity
0.850
Hydraulic Fluid: Viscosity
2
35 mm /s (164 SSU)
, Specific Gravity
0.850
Hydraulic Fluid: Viscosity
2
35 mm /s (164 SSU)
, Specific Gravity
0.850
Viscosity
2
mm /s
SSU
Factor
15
77
0.81
20
98
0.87
30
141
0.96
40
186
1.03
50
232
1.09
60
278
1.14
70
324
1.19
80
371
1.23
90
417
1.27
100
464
1.30
For any other viscosity, multiply the factors in the table below.
P'= P (G'/0.850)
For any other specific gravity (G'), the pressure drop ( P') may
be obtained from the formula below.
Unloading Relief Valves
270
Spare Parts List
O-Ring28 SO-NB-P6 3
O-Ring29 1
O-Ring30 1
O-Ring31 1
O-Ring32 1
O-Ring33 1
O-Ring34 5
O-Ring35 1
Item Name of Parts
BUCG-06
Part Numbers
BUCG-10
Quantity
SO-NA-P9
SO-NB-P11
SO-NB-P12
SO-NB-P18
SO-NB-P24
SO-NB-P28
SO-NB-P32
SO-NB-P6
SO-NA-P9
SO-NB-P9
SO-NB-P12
SO-NB-P18
SO-NB-P32
SO-NB-P32
SO-NB-P45
Valve Model Numbers Seal Kit Numbers
BUCG-06
BUCG-10
KS-BUCG-06-30
KS-BUCG-10-25
18
2
20
19
21
24
22
23
9
27
BUCG-06-
**
-30/3080/3090
BUCG-10-
**
-25/2580/2590
List of Seals
Note: When ordering the seals, please specify the seal kit number from the table below.
List of Seal Kits
7
8
26
6 5 4 3 16 12 13 14 17
25
15
11
1
10
33
30
34
28
32
31 29
35
