Power-Up/Gravity-Down vs Power-Up/Power-Down
- Differentiate between Circuit 103 single-acting and Circuit 111 double-acting hydraulic power unit operations.
- Identify remote control wiring color codes for blue, red, green, and white conductors.
- Locate and verify primary and secondary relief valve factory settings on double-acting units.
- Digital Multimeter — Check for power at the start solenoid, motor, and solenoid coils during operation.
- Wire Strippers — Prepare remote wiring leads (blue, red, green, or white) for terminal connection.
Circuit 103 (single acting): UP powers start solenoid and motor; fluid goes through the check valve out the P port. DOWN energizes the normally closed 2-way coil to return fluid to tank.
Circuit 111 (double acting): UP powers the motor and the round 4-way coil; DOWN powers the motor and the square coil on the load-holding valve.
Primary relief is factory set at 3200 psi; the 2nd relief on double-acting units is 1500 psi.
Remote wiring: UP = blue or red, DOWN = green, COMMON = white.
How It Works
Circuit 103 Single-Acting Operation
In a Power-Up/Gravity-Down configuration, the UP function powers the start solenoid and motor, sending fluid through the check valve via the P port. The DOWN function does not use the motor; it energizes a normally closed 2-way coil to allow fluid to return to the tank.
Circuit 111 Double-Acting Operation
A Power-Up/Power-Down configuration requires motor operation for both directions. The UP function powers the motor and the round 4-way coil. The DOWN function powers the motor and the square coil located on the load-holding valve.
Relief Valve Specifications
Standard units feature a primary relief valve factory set at 3200 psi. On double-acting units, a 2nd relief valve is present and set at 1500 psi. These settings are factory established and critical for safe operation.
Diagnostic Chart
| Symptom | Check | Spec / Expected | Likely cause & fix |
|---|---|---|---|
| Circuit 103 fails to lift but motor runs. | Inspect fluid flow through the check valve and out of the P port. | 3200 psi | Primary relief valve may be bypassing fluid or check valve is stuck. Basis: KTI DC Power Unit Troubleshooting Guide (Jan 2019) |
| Circuit 103 fails to lower. | Check for power and activation of the normally closed 2-way coil. | Per the applicable manual | The 2-way coil is not energizing to allow fluid return to the tank. Basis: KTI DC Power Unit Troubleshooting Guide (Jan 2019) |
| Circuit 111 fails in the DOWN direction. | Check for power at the motor and the square coil on the load-holding valve. | 1500 psi | Failure of the motor to run or the square coil to energize prevents downward power. Basis: KTI DC Power Unit Troubleshooting Guide (Jan 2019) |
| Circuit 111 fails in the UP direction. | Check for power at the motor and the round 4-way coil. | 3200 psi | Failure of the motor to run or the round 4-way coil to energize prevents upward power. Basis: KTI DC Power Unit Troubleshooting Guide (Jan 2019) |
At the Bay: Diagnose the Case
CASE 1 / 4
Circuit 103 fails to lift but motor runs.
- Test
- Compare
- Correct
Select the next check
Basis: KTI DC Power Unit Troubleshooting Guide (Jan 2019). A likely cause is a hypothesis; confirm it with the applicable service procedure before repair.
Common Bay Mistakes
- ✕ Adjusting relief valves without factory approval.
- ✕ Mistaking the square coil for the round 4-way coil on Circuit 111.
- ✕ Assuming the motor should run during the DOWN function on a Circuit 103 unit.
- ✕ Connecting the green wire to the UP function instead of DOWN.
- ✕ Tampering with relief valves and voiding the warranty.
- ✕ Confusing the 3200 psi primary relief with the 1500 psi secondary relief.
Quick Check
Practice only — not scored.
Hands-on: Shop Test Equipment
Hydraulic Pressure & Relief Gauge
0–5,000 psi gauge on the pump pressure port, DC clamp meter, battery voltmeter
🛠 Equip your bay for this test →Symptom: Routine check before a customer pickup.
Spec limits used
- 3,200 psi — Primary relief (factory preset) (KTI Hydraulics Troubleshooting Manual 2019)
- 1,500 psi — Secondary relief, circuit 111 (KTI Hydraulics Troubleshooting Manual 2019)
- below 9 V — Low-voltage alarm (KTI remote)
- illustrative only — Motor current & voltage drop (General shop practice)
Simulated readings for practice. Always follow the manufacturer's procedure and values on a real trailer.
Source: KTI DC Power Unit Troubleshooting Guide (Jan 2019) — 5–11