Platform (mast) won’t stay elevated, Overview of procedure, Check for these obvious conditions first – JLG 15VPSP Service Manual User Manual

Page 89: Manual descent valve is closed tight, Table 3-29. platform (mast) won’t stay elevated, Platform (mast) won’t stay elevated -35

SECTION 3 - TROUBLESHOOTING

3120728

– JLG Lift –

3-35

Platform (Mast) Won’t Stay Elevated

Overview Of Procedure

The following procedure requests that the lift down, dump, and pump internal valves be checked to see if any are stuck
open, it also examines the lift down and dump valve circuits. Also suggests that the lift cylinder packing could be leaking
internally.

Check For These Obvious Conditions First:

• Manual descent valve is closed tight.

Table 3-29. Platform (Mast) Won’t Stay Elevated.

STEP

ACTION

SPEC

YES

Is the lift down valve stuck open?

—

Repair or Clean

Valve

Go to Step 2

Check the valve inside the pump, it could be stuck open.

—

Replace Pump

Go to Step 3

Lift down valves could be open due to incorrect electrical signal.

—

Check Pump

Valve Electrical

Circuit

(Table 3-22)

Go to Step 4

Dump valve could be open due to incorrect electrical signal.

—

Check Pump

Valve Electrical

Circuit

(Table 3-22)

Go to Step 5

Oil could be passing around the lift cylinder bore packing.

—

Replace or

Rebuild the Lift

Cylinder

—