Hydraulic Circuit Operation and Pressure Safety

Before work on a hydraulic system, ensure the hydraulic lines are depressurized. Hydraulic injection can initially feel like a bee sting but can cause loss of fingers or death; go directly to an emergency room if injection occurs. Relief valves are factory set. Do not adjust them without consulting the factory, and obtain KTI's written approval for field adjustments. Tampering can cause catastrophic failure or serious injury.

Circuit 103 is Power Up Gravity Down. Pressing UP on the yellow hand control powers the start solenoid and DC motor. The motor drives the gear pump, and fluid passes through the check valve and out port P to extend the cylinder. At full stroke or maximum load, fluid bypasses to the tank through the primary relief, which is factory set to 3200 PSI.

For Circuit 103 retraction, DOWN energizes the coil on the normally closed two-way valve. Opening that valve lets fluid return to the tank. An optional flow control in the manifold can regulate retraction speed. The documented DOWN sequence energizes the valve coil rather than the start solenoid and motor used for extension.

Circuit 111 is Power Up Power Down. UP powers the start solenoid, motor, and cylindrical coil together. The directional valve shifts, sending fluid through the load-holding valve and out port A to extend the cylinder. Pump pressure pilots the lowering valve open so fluid from the cylinder's rod end can return to the tank. The lowering valve pilot ratio is 2.5:1, and the primary relief is factory set to 3200 PSI.

On Circuit 111, DOWN powers the start solenoid, motor, and square coil. Pressure travels through the directional valve and lower portion of the load-holding valve, then out port B to retract the cylinder. Energizing the square coil opens the return path through the lowering valve. At the end of retraction, fluid bypasses through a secondary relief set to 1500 psi; this protects against rod-end overpressurization and thermal expansion.

Relief valves limit overpressurization, while check valves prevent reverse flow toward the pump. A directional valve changes the flow path when its energized coil shifts the spool. The load-holding valve checks both cylinder ends, and its solenoid-operated section allows retraction without the additional flow-restricting orifice described for a dual pilot-operated check valve.

Installation scope matters: Single-Acting-Installation-Instructions-INST0001.pdf, pages 1–4, routes the cylinder base to P. Double-Acting-Installation-Instructions-.pdf, pages 1–4, routes A to the base and B to the rod end. Single-Double-Acting-Installation.pdf, pages 1–5, adds both powered and gravity lowering; identify the actual installed controls rather than assuming that every DOWN command runs the motor.

NEWDouble-Double.pdf, pages 1–5, covers two independent double-acting circuits: A/B serve UP/DOWN, and A1/B1 serve OUT/IN, with each A-side at its cylinder base and each B-side at the rod end. Prime each cylinder separately, keep at least half-full fluid during startup and recheck fluid with both fully retracted. Although it references a page 6 bleed procedure, the supplied file contains only five pages; obtain the missing applicable instructions instead of inventing them.

The installation documents specify 18 ft-lb for their 9/16-18 SAE ORB / SAE #6 fittings, and 3 ft-lb for the specified upper battery-connection nut while holding the lower nut. Do not transfer these torques to different fittings or motor terminals. Their cable tables list 4 AWG at 1–2 ft, 2 AWG at 3–4 ft, 1 AWG at 5–7 ft, 1/0 at 8–9 ft, 2/0 at 10–12 ft, 3/0 at 13–15 ft and 4/0 at 16–19 ft. The troubleshooting guide’s current-and-length table is different: confirm which table applies instead of averaging sizes.

The new dc-power-unit-troubleshooting-guide.pdf, pages 3–4, reinforces electrical-first diagnosis, contamination control and factory-only relief authorization. It substantially overlaps the 2019 guide already used here, so it is corroborating material, not a new circuit or proof that earlier model-specific instructions are obsolete.