Page 38
Systems Descriptions
M258 Hydraulic Pump:
Fixed displacement
external gear type hydraulic pump with 12 VDC
electric motor and 76 cubic inch fluid reservoir. The
pressure relief valve is factory set at 2100 psi. The
Braun Pump Code for front or rear mounted 12 volt
M258 pumps is
33
.
Note:
24 Volt pumps are
available for special applications and have a Braun
Pump Code of
34
.
Pump Modules:
Pump mod-
ules are available as a complete quick-service repair
unit. See the Pump Module section for detailed
breakdowns on pages 54 and 55.
Hydraulic Fluid:
Use Dextron III automatic trans-
mission fluid. Make sure the
platform
is
fully
lowered
when checking fluid level or adding fluid.
Fill to within 1/2" of the bottom of the 1-1/2" diameter
fill tube (neck). The maximum fluid level is desig-
nated on the pump reservoir with decal 26735.
DO
NOT
use a solid plug or fill cap without a breather
hole. Doing so will result in pump and/or reservoir
damage.
Contamination:
Fluid should be changed if there is
visible contamination. Inspect the hydraulic system
(cylinder, hoses, fittings, seals, etc.) for leaks if fluid
level is low.
Cold Weather Applications:
The oil can be
thinned with two (2) tablespoons of diesel fuel. The
oil should be changed when warm weather returns.
Note:
We recommend SAE 10 W non-detergent oil
mixed by volume with no more than 30% #1 fuel oil
or kerosene for full time cold weather applications.
Pump Mounted Electrical “Down” Solenoid/
Hydraulic Valve:
The UNFOLD switch circuit
Hydraulics
energizes this solenoid/valve which allows hydraulic
fluid to return from the cylinders to the reservoir at a
limited rate, thus allowing gravity to unfold the
platform. Fluid flows through the internal manifold
valve
before
reaching the Down valve. The Unfold/
Down microswitch is activated when the platform
unfolds fully (reaches floor level), which interrupts
the UNFOLD switch circuit, thereby de-energizing
the solenoid/valve. Releasing the UNFOLD switch
de-energizes this valve also. This stops and holds
the platform at the current position by stopping the
flow of hydraulic fluid from the cylinders to the
reservoir.
When the platform unfolds fully to floor level and the
Unfold/Down microswitch is activated, pressing the
DOWN switch then energizes this solenoid/valve.
The manifold routes the hydraulic fluid through the
manifold internal pressure compensator valve
before allowing it to return to the reservoir from the
cylinders, thus allowing gravity to lower the plat-
form at a reduced rate. The manifold internal
pressure compensator valve allows a limited rate
of hydraulic fluid flow dependent upon platform
load.
Releasing the DOWN switch de-energizes the
solenoid/valve allowing it to close, stopping the
flow from the cylinders to reservoir. This stops
and holds the platform at the current position.
Troubleshooting:
A problem with this solenoid/
valve can be electrical or hydraulic. Follow the
Quick-Check
troubleshooting procedure detailed
the Solenoid/Hydraulic Valve section on page 36
when troubleshooting.
