Yanmar YM155d Service Manual page 152

7.
HYDRAULIC SYSTEM
P.
Trouble
1 . Implement cannot
be
lifted, or lift
speed is slow.
!
Probable cause
1. Hydraulic pump drive shaft damaged.
2.
lnsufficient hydraulic pump discharge.
3.
Hydraulic fluid (Use transmission
oil) has excessive viscosity.
lnsufficient hydraulic fluid.
4. Filter clogged.
5.
Spool n o t functioning correctly.
6.
Faulty stop valve " 0 ring.
7. Relief valve (safety valve) w o r n or
damaged.
Improper pressure setting.
Din
i n relief valve seat.
Remedy
Replace drive shaft.
Clean or replace.
Change hydraulic oil.
A d d transmission oil.
Clean.
Replace completely.
Replace.
Replace spring.
Adjust setting.
Clean.
I
(
n o t drop.
(
pool
return spring damaged.
1
Replace spring.
I
Push rod does n o t function Clean o r replace.
smoothly.
I
I
1
2.
Stop valve seat seized.
/
Replace.
3. Rate of free descent
Je
3.
Hydraulic cylinder piston seized.
1. Spool worn.
lnsufficient free travel when spool
is at a neutral position.
2.
Faulty valve seats.
D i n i n valve.
Faulty " 0 ring.
3.
Stop valve
"0
ring defective.
Faulty seats.
4. Hydraulic cylinder piston or cylinder
damaged or worn.
Broken
" 0
ring.
5.
Safety valve seat seat faulty.
D i n i n valve.
Broken " 0 ring.
Faulty control valve o r hydraulic
Replace.
Clean o r replace.
Replace
Replace.
Replace.
I I
/
Pump improperly fined.
I
cylinder
"0"
rings;
1
3. Control valve lift position
(
Adjust stroke b y control lever turnbuckle.
1.
Pump gear faulty.
1
Replace.
4.
2.
A i r being drawn i n (cavitation)
because of insufficient oil.
Excessively high oil viscosity.
A I
regulation is excessive.
Strange noises.
Bleed air or change oil.