Contact Us

This procedure tells you how to make a slight adjustment to an Hydraulic Power Unit (HPU) that is noisy, vibrates, or has pressure that fluctuates wildly.

 Note: Only perform this procedure after you have investigated all other possible causes in the Haas Hydraulic Power Unit - Troubleshooting Guide. This procedure is only necessary in very rare cases for HPU's with Nachi pumps, usually with dual spindles or chuck and tailstock manifolds. Nachi pumps can be identified by two product labes located on the fan shroud of the pump. One is for the motor [1] and one is for the pump [2].

Tools Required:

• Marker
• Flat-head screwdriver
• 5 mm and 8 mm allen wrench
• 11/16" and 15/16" wrench
• 600 psi pressure gauge (part number: 58-0741) with a snubber (part number: 58-0936)
• Adapters (part number: 58-0864 and 58-0116)
• T-fitting (part number: 58-0040)

Power the machine on and adjust the chuck, second chuck (if equipped), and tailstock (if equipped) pressure adjusting valves to the maximum pressure setting and power the machine off. Refer to Chuck and Tailstock - Recommended Maximum Pressure.

Install a pressure gauge [3] as shown between the pump outlet fitting [2] and the pump outlet hose [1].

Note: Older style HPU's have a 90 degree swivel elbow fitting.

Remove the black cap [4] that says "DON'T REMOVE" by prying it off with a flat-head screwdriver.

Note: For older style HPU's with the manifold blocks on the HPU tank lid, loosen the elbow fitting from the pump bypass output fitting and rotate it so that the bypass hose is not over the black cap that says "DON'T REMOVE" and retighten the fitting.

Mark a line from the center of the 8 mm allen screw [1] across the 15/16" hex jam nut [2] and on to the pump body to mark the initial position. Loosen the Slide Kit adjustment 15/16" hex jam nut [2] around the Slide Kit adjustment allen screw [1].

Loosen the pressure adjustment 11/16" hex jam nut [3] around the pressure adjustment 5 mm allen screw [4].

Power on the HPU.

Observe the pressure at the pressure gauge at the pump outlet. The pressure should be approximately 450 psi for newer HPU's (without manifolds mounted on the tank lid) or 550 psi for older style HPU's. If the pressure is not correct, adjust the pressure by turning the 5 mm allen screw [4] counterclockwise to reduce the pump pressure or clockwise to increase the pump pressure.

If the pump is still noisy and the pressure is fluctuating, turn the Slide Kit adjustment 8 mm allen screw [1] clockwise 1/12 of a turn. This increases the pump pressure.

Caution: Only adjust in steps of 1/12 of a turn. Turning the Slide Kit adjustment screw too much can raise the pressure too high and cause damage.

Turn the pressure adjustment 5 mm allen screw [4] counterclockwise to reduce the pump pressure until the pressure is correct.

Note: The pressure should be approximately 450 psi for newer HPU's (without manifolds mounted on the tank lid) or 550 psi for older style HPU's.

Repeat this step if the pump is still noisy and the pressure is fluctuating until the noise has been eliminated and the pressure no longer fluctuates.

Record the approximate clockwise rotation of the Slide Kit adjustment screw [1] from its original position.

Tighten the hex jam nuts on both of the adjustment screws, reinstall the black cap, remove the pressure gauge from the pump outlet, make sure all fittings are tight, and return the bypass hose to the original routing if changed.