Service manual

REV C 4-8 115615
Test Example: PY (12) Pump
300 psi (21 bar) reading 7 gpm (26 l/min) (1st reading)
1100 psi (76 bar) reading 3 gpm (11 l/min) (2nd reading)
PK (12)
300 psi (21 bar) reading 7 gpm (26 l/min) (1st reading)
1100 psi (76 bar) reading -3 gpm (11 l/min)
(2nd reading)
4 gpm (15 l/min) (the difference)
Subtract the 1st reading from the 2nd.
(In this example, 4 gpm difference would indicate further pump
examination).
Purging Procedures
Due to the affects air has on efficiency in hydrostatic drive
applications, it is critical that air is purged from the system.
These purge procedures should be implemented any time a
hydrostatic system has been opened to facilitate maintenance or
additional oil has been added to the system.
Air creates inefficiency because its compression and expan-
sion rates that are higher than that of oil.
Entrained air in the oil may cause the following symptoms:
1. Noisy operation.
2. Lack of power or drive after short term operation.
3. High operation temperature and excessive expansion of
oil.
Before starting, make sure the reservoir is at the proper oil
level. If it is not, fill to the vehicle manufacturer’s specifica-
tions.
The following procedures should be performed with the vehi-
cle drive wheels off the ground, then repeated under normal
operating conditions.
1. With the bypass valve open and the engine running,
slowly move the directional control in both forward and
reverse directions (5 or 6 times), as air is purged from the
RESTRICTION VALVE
BI-DIRECTIONAL
FLOW METER
CONNECTIONS TO
THE FWD/RVS LINES
DISCONNECTED
FROM WHEEL MOTOR
CONNECTIONS TO
THE FWD/RVS LINES
DISCONNECTED
FROM WHEEL MOTOR
RESTRICTION VALVE
BI-DIRECTIONAL
FLOW METER
WARNING
Potential for serious injury! Certain procedures require
the vehicle be operated and the vehicle to be raised off of
the ground. To prevent possible injury to the servicing
technician and/or bystanders, insure the vehicle is prop-
erly secured. Use only appropriate vehicle stands, with a
maximum weight rating of 2000 pounds to block the unit
up. Use in pairs only. Follow the instructions supplied
with the vehicle stands.