Snapper 1650 Series User Manual

HYDROSTATIC TRANSMISSION (1650 & 1855 SERIES)
This hydrostatic transmission is composed
of four major components: A charge pump, a
variable displacement radial ball-piston
pump, a fixed displacement radial ball-piston
motor and a system of valves located bet¬
ween the pump and motor.
The charge pump draws oil from the rear
axle housing and performs three functions:
1. Maintains pressure (30-50 psi) on the
low pressure side of the circuit to charge the
variable displacement pump.
2. Supplies oil lost due to internal leakage
in the loop circuit.
3. Provides a source of auxiliary hydraulic
power to operate double-acting cylinders.
The variable displacement ball-piston
pump consists of five "free" ball-pistons,
each contained in a single piece five bore
rotor unit. Like the charge pump, it is con¬
trols the amount of oil being pumped by in-
finate movement from neutral to a maximum
off center position.
The fixed displacement ball-piston motor is
similar in appearance to the pump. Its cam
ring is permanently fixed in an off center
position. The motor turns only when the
pump is pumping oil and since the pump can
pump oil in either direction, it can make the
motor rotate in either direction, it can make
the motor rotate in either direction. Also, sin¬
ce the pump output volume of oil can be con¬
trolled by the pump cam ring it can make the
motor turn fast or slow and any infinate
speed in between.
The motor is connected to the rear axle in¬
put shaft and thus the Tractor moves for¬
ward, backward, slowly or swiftly.
FIG. 4.25-SCHEMATIC OF HYDROSTATIC DRIVE SYSTEM
stant running unless disconnected from the
engine. The ball-pistons travel within a
radius controlled by a moveable cam ring.
The cam ring is controlled by the operator.
When the cam ring is centered around the
rotor unit the ball-pistons do not move in or
out within the bores thus, no pumping action
takes place and the transmission is con¬
sidered to be in neutral. Moving the cam ring
off center around the rotor unit will cause the
ball-pistons to move in and out within their
bores and oil will be pumped.
Since the cam ring can be moved off center
in either direction from neutral, the pump
can pump oil in either direction without a
change in rotation. The cam ring also con-
The valve system located between the
pump and motor consists of check valves, ac¬
celeration valves, a charge pump relief valve
and dampening pistons. Fig. 4.25 shows the
complete hydraulic circuit on the Tractor. On
3-point hitch equipped tractors there would
be an extra valve, cylinder and two con¬
necting lines.
IMPORTANT NOTE
This transmission does not contain an im¬
plement relief valve. Implement relief valve
is located in the auxiliary hydraulic control
valve.
4.6
J.2

Snapper 1650 Series Specifications

General

Brand	Snapper
Model	1650 Series
Category	Lawn Mower
Language	English