Kubota B1830, Workshop Manual, Page: 236 / 548

TRANSMISSION B1830,B2230,B2530,B3030, WSM
3-S12
Readjustment of Relief Valve (When the HST does not work
due to its loose hexagon socket head screw)
IMPORTANT
• The KUBOTA does not recommend the readjustment of
relief valve. And KUBOTA will recommend to replace with
genuine parts.
• As the HST may be damaged if the pressure is set to higher
by mistake, be careful when adjusting it.
NOTE
• The relief pressure is set in between 33.3 to 36.3 MPa (340
to 370 kgf/cm
2
, 4836 to 5262 psi) when shipped from the
factory. But, for the purpose of after-sales services, as it is
impossible to reset the pressure precisely as set in the
factory, its setting range is defined as a slightly wider range
between 31.4 to 35.3 MPa (320 to 360 kgf/cm
2
, 4551 to
5120 psi).
1. Measure the pre-adjustment distance "A" .
2. Compress the spring of the relief valve with a relief valve
assembling tool (3).
3. Then, find the distance "A" by turning the poppet (4) with a
screwdriver.
Reference: The distance
"A" changes by about 0.5 mm
(0.0197 in.) per one turn of the poppet (4).
4. Repeat the same operation a few times to find the distance "A"
as it is difficult to acquire at the first time.
5. After finding the distance "A" , hold the setscrew (6) to a vice
and fasten the hexagon socket head screw (2) with specified
torque.
On this occasion, use a copper plate, etc. for the vice jaws not
to damage the setscrew (6).
6. Install the relief valve in the HST.
7. Check the relief pressure as indicated in pages 3-S8 and 3-S9.
The distance "A" is for refresh only. Make sure to check the
relief pressure after readjustment.
8. If the relief pressure does not fall within the readjustment
pressure range, repeat the processes of the above item 1
onward.
Reference: The pressure changes by 1.47 MPa (15 kgf/cm
2
,
213.3 psi) per 0.1 mm (0.0039 in.) in distance "A" .
9Y1210003TRS0008US0
Tightening torque Hex. socket head screw
24.5 to 29.5 N·m
2.5 to 3.0 kgf·m
18.1 to 21.7 lbf·ft
Relief valve readjusting
pressure
Factory specification
31.4 to 35.3 MPa
320 to 360 kgf/cm
2
4551 to 5120 psi
Distance "A" Reference value
37.9 to 38.0 mm
1.4921 to 1.4960 in.
(1) Relief Valve Assembly
(2) Hexagon Socket Head Screw
(3) Relief Valve Assembling Tool (4) Poppet
(5) Valve Seat
(6) Setscrew
KiSC issued 05, 2012 A