Haas Hydraulic Power Unit - How it Works and Troubleshooting Guide

How it Works

A: Haas HPU for most lathes made before 2016.

B: Haas HPU for most lathes made after 2016.

note: Not all lathes will have all of the components shown.
[1] Hydraulic pump [7] Pressure filter
[2] Chuck and Tailstock pressure adjustment valves [8] Intake screen
[3] Chuck and Tailstock pressure gauges [9] Pressure sensor
[4] Oil fill cap [10] Heat exchanger (can be mounted remotely, with or without fans)
[5] Oil dip stick/Oil sight glass [11] Cooling fans
[6] Solenoids [12] Return filter

The Haas HPU is powered from the I/O PCB with 240 VAC 3-phase.

Pressurized oil is supplied from the HPU pump thru a pressure reducing valve then a solenoid control valve to the chuck or tailstock.

Some models have the HPU filter in the main pressure line and some have it in the return line. If the main pressure filter is clogged it can cause erratic or poor performance.

The pressure reducing valve allows the user to set the appropriate force desired for the chuck or tailstock. Do not exceed the limits for the specific chuck installed (see chart in Section 4) or machine damage will occur.

The solenoid valves are electrically controlled by the Haas control with 120 VAC to open or close the chuck, advance or retract the tailstock, or speed up the tailstock.

After the solenoid valve the oil flows to the rotating union that is attached to the chuck (for example). It then returns to the tank via the return line. The return line has a filter on some models. This filter is inside the tank and normally does not need servicing. It has a bypass feature, and cannot cause any symptoms in the system.

The union also has a drain line that is a gravity drain, non pressurized line. This drain line must be clear and flow downhill or oil will back up into the rotating union creating leaks. This line collects the oil deliberately leaking past the rotating union joints and returns it to the tank. Oil in this line will sometimes be very foamy, caused by air mixing with the oil as it is expelled from the union. This is normal and does not cause problems if not excessive.

If chips or debris are allowed to obstruct the coolant drain under the rotating union, the coolant level can rise and get inside the union and contaminate the hydraulic oil. It can even overfill the hydraulic tank causing an oil spill.

Inside the oil tank some models have a box shaped baffle to contain the air bubbles introduced by the union to a small area of the tank. The air rises to the top inside the baffle & out the open corners above the oil level. The denser non aerated oil sinks to below the baffle & is mixed with the oil already in the tank.

It is rare that the entire HPU system needs to be replaced. Individual components are available parts.haascnc.com.

Symptom Possible Cause Corrective Action Section
Oil leaks The hoses are split or the fittings are loose. Tighten the fittings or replace the hoses. 1
The oil tank overflows. Diagnose the cause and drain the oil to the correct level.
Coolant contaminated the oil. Check the coolant collector for blockage. 10
Chuck or tailstock does not operate correctly.

or

Incorrect chuck or tailstock clamp force or pressure.

The solenoid system does not operate correctly. Troubleshoot the system. 2
There are air bubbles in the oil. Reduce the clamp force, RPM, or duty cycle. 4
Inspect for oil leaks on the intake pipe. 5
Re-configure the return and pick-up pipes. 11
The oil level is low. Fill the HPU to the correct oil level. 6
A filter is clogged. Check the pressure filter and the intake screen for clogs. 8
The adjustment valve is contaminated. Open the adjustment valve to purge the system. 9
Coolant contaminated the oil. Check the coolant collector for blockage. 10
Pressure fluctuates wildly. Pump oscillates and vibrates.

or

Noisy

There are air bubbles in the oil. Reduce the clamp force, RPM, or duty cycle. 4
Inspect for oil leaks on the intake pipe. 5
Re-configure the return and pick-up pipes. 11
The oil level is low. Fill the HPU to the correct oil level. 6
The fans do not operate. Make sure the fans operate. 7
Coolant contaminated the oil. Check the coolant collector for blockage. 10
Overheating. Check for signs of overheating. See symptom "Overheating"
A filter is clogged. Check the pressure filter and the intake screen for clogs. 8
Overheating The oil level is low. Fill the HPU to the correct oil level. 6
The fans do not operate. Make sure the fans operate. 7
There are air bubbles in the oil. Reduce the clamp force, RPM, or duty cycle. 4
Setting 216 is not enabled. Enable Setting 216. 3
A filter is clogged. Check the pressure filter and the intake screen for clogs. 8
Low or no hydraulic pressure. Incorrect power phasing - the pump motor is running backward. Check the phasing indicators and change the incoming power cables, if necessary. 12

Section 1

Symptom: Oil leaks.

Possible Cause: The hoses are split or the fittings are loose. The oil tank overflows.

  • If the tank was filled while the HPU was in operation, the oil can overfill when the machine returns to inactivity.
  • There is an excessive amount of foamy oil (refer to Section 3).
  • Coolant leaks into the oil.

Corrective Action:

If the oil tank overflows, find the cause, and fill the oil to the correct level. If the oil is contaminated with coolant, drain and replace the oil (refer to Section 10).

Make sure the hoses are routed correctly [4] and are secure. Tie them together with zip ties [3]. Damage can occur to the hoses if they rub [1] against other components, have sharp bends, or are kinked [2]. Replace the hoses if they are damaged.

Check the condition of the hydraulic hose fittings: Look for leaks at both ends of the hose. If a fitting has cracks [5], wear, or a leak, the hose must be replaced.

Do not over-tighten the fittings.

For hose replacement instructions, click the link for Lathe - Hydraulic Power Unit (HPU) - Hoses and Fittings - Maintenance, or search for the document by keywords on diy.haascnc.com.

Section 2

Symptom: Chuck or tailstock does not operate correctly.

Possible Cause: The solenoid system does not operate correctly.

Corrective Action:

It is normal for the solenoids to be hot to the touch. Check the voltage to the solenoid.

  1. Pull the solenoid connectors partially apart so you can access the leads with your needle-tip probes while the solenoid is connected.
  2. With the chuck or tailstock in operation, measure the voltage to the solenoid. The measured voltage must be 120 VAC.
If there is no voltage, go to diy.haascnc.com to troubleshoot the I/O PCB.

If the solenoid receives voltage, but it does not operate correctly, clean the valve:

  1. Turn off the power to the machine.
  2. Remove the solenoid valve. Use compressed air to clean the solenoid valve.
  3. Reinstall the solenoid valve.
    caution: Do not lose the (4) o-ring when you reinstall the solenoid valve.
  4. Test for correct operation.

Section 3

Symptom: Overheating

Possible Cause: Setting 216 is not enabled.

Corrective Action:

Make sure Setting 216 SERVO AND HYDRAULIC SHUTOFF is set to (120) seconds or less. If it is set to (0), the HPU will not turn off, and will create unwanted air bubbles and heat. This setting will power-down the HPU when the machine is idle. This helps dissipate the air bubbles in the oil.

Section 4

Symptom: Pressure fluctuates wildly. Pump oscillates and vibrates. Noisy. Overheating.

Fluctuations of up to 50 PSI is normal for HPU operation, and does not affect machine operation or performance.

Possible Cause: There are air bubbles in the oil .

Foamy oil, or air bubbles that disolved in the oil, mix with the inlet oil that goes to the pump. This causes the pump to compress the aerated oil and create foamy oil. The different oil densities vary the load on the pump, and cause it to vibrate and oscillate.

The rotating union on lathes has a slip joint that allows pressurized oil to actuate the piston and move the draw tube. The oil that escapes the slip joint is aerated when it goes through the support bearings. The oil that is normally clear then turns to foamy white oil. The foamy oil flows back into the tank through the drain on the union housing. Normally, the foamy oil will dissipate the air bubbles over time.

Prolonged operation at high spindle RPM and chuck pressure will cause the oil in the reservoir to turn foamy white. The foamy oil enters the pump. The pump is not able to compress both the oil and the air evenly.

Corrective Action:

Always make sure the oil level is correct and the filter is clean (refer to Sections 6 and 8).

Push EMERGENCY STOP. Wait half an hour while the air and oil separate. Resume machine operation. Check if the normal pressure returns while the operation resumes. If the symptom occurs again:

  • Reduce the hydraulic clamp pressure by about 25 PSI to reduce the rate of the hydraulic union leak at the slip joint.
  • Reduce the cycle time with higher feed rates.
  • Reduce the spindle RPM.

Maximum Chuck Operating Pressures

Type psi Bar
5" Chuck 330 23
6" Chuck 330 23
8" Chuck, 2" Bore 330 23
8" Chuck, 2.5" Bore 260 18
10" Chuck 330 23
12" Chuck, 3" Bore 400 28
12" Chuck, 4" Bore 250 17
15" Chuck 340 23
18" Chuck 300 21

caution: Do not add anti-foaming agents. These agents are already present in the HPU oil.

Section 5

Symptom: Pressure fluctuates wildly. Pump oscillates and vibrates. Noisy.

Possible Cause: There are air bubbles in the oil.

Corrective Action:

Check for oil leaks at the intake pipe [1]. If there are leaks, clean the threads on the intake pipe [1]. Reapply thread sealant, and install the intake pipe [1].

If the symptom persists, go to Section 11 to reconfigure the pipes.

Section 6

Symptom: Pressure fluctuates wildly. Pump oscillates and vibrates. Noisy. Overheating. Incorrect chuck or tailstock clamp force or pressure.

Possible Causes: The oil level is low.

Corrective Action:

Check the gauge [1] or dipstick [2] to make sure that the HPU has enough oil. If the oil level is low, check for a leak. If there is a leak, repair the leak. Refill the oil.

Section 7

Symptom: Pressure fluctuates wildly. Pump oscillates and vibrates. Noisy. Overheating.

Possible Causes: The fans do not operate.

Corrective Action:

If the HPU oil overheats: Some HPU assemblies have fans installed on the back. Make sure the fans operate when the spindle is in operation.

Make sure the spindle motor fan operates.

If the machine has a heat exchanger, make sure the heat exchanger is clean and its fan operate correctly. Not all heat exchangers have a separate fan. Some machines have remotely-mounted heat exchangers with integral fans.

Section 8

Symptom: Overheating. Incorrect chuck or tailstock clamp force or pressure.

Possible Cause: The filter is clogged.

Corrective Action:

Clean or replace the pressure filter [1] on the pump assembly. Make sure the intake filter [2] is not clogged. Clean it if necessary.

Test the hydraulic components for the correct pressure.

Some models have a return line filter. This filter cannot cause any symptoms.

Section 9

Symptom: Incorrect chuck or tailstock clamp force or pressure.

Possible Cause: The adjustment valve is contaminated.

Corrective Action:

Check the adjustment valve for debris: Open and close the adjustment valve fully to flush any contamination out. Remove the adjustment valve. Inspect the o-rings for damage. Damaged o-rings can also cause incorrect pressure.

If the adjustment valve is damaged, replace it. For adjustment valve replacement instructions, click the link for ST/DS Lathe - Chuck and Tailstock Pressure Adjusting Valve - Replacement, or search for the document by keywords on diy.haascnc.com.

Section 10

Symptom: Oil leaks. Pressure fluctuates wildly. Pump oscillates and vibrates. Noisy. Incorrect chuck or tailstock clamp force or pressure.

Possible Cause: Coolant contaminated the oil.

Corrective Action:

Find the coolant return line under the spindle. If chips block the coolant return line, coolant floods into the hydraulic union and will contaminate the HPU oil and cause it to foam. It can also cause the tank to overfill.

Unclogg the coolant return line.

Drain the HPU and blow shop air through the hoses. Clean or replace all HPU filters. Clean the HPU and refill it with new oil. Cycle the chuck and tailstock several times. Check the oil again.

Section 11

Symptom: Pressure fluctuates wildly. Pump oscillates and vibrates. Noisy.

Possible Cause: There are air bubbles in the oil.

Corrective Action:

Reconfigure the return and pick-up pipes to separate them. This gives the oil more time to dissipate the bubbles.

Remove the elbow fitting [1] from the intake line [2] and the intake filter [3]. Install the new intake screen [4] (Haas P/N 58-1832) on a new nipple (available locally). The new nipple length must be long enough so the new intake screen [4] is 1/4" from the bottom of the tank.

Remove the return line [5] from the return drain [6]. Install an elbow fitting [7] between the return line [5] and the return drain [6]. Install a new pipe nipple (available locally) to the elbow fitting [7] that reaches approximately 1" from the side of the tank.

Section 12

Symptom: Low or no hydraulic pressure.

Possible Cause: Incorrect power phasing - the pump motor is running backward.

Corrective Action:

The power supply PCB has a phase detect with neon indicators on the top center portion of the board. Make sure that the electrical power is phased correctly:

  • Green Light: The incoming power is phased correctly.
  • Orange Light: The incoming power is incorrectly phased.
  • Both Lights: A phase is missing (there is a loose cable in the system).

If the electrical power is phased incorrectly:

Set the main circuit breaker to the OFF position.

Lock the main circuit breaker. Use an approved lock with an approved safety tag.

Swap the #74 and #75 incoming power cables at the main transformer.

Be aware: Many service and repair procedures should be done only by authorized personnel. The service technicians at your Haas Factory Outlet (HFO) have the training, experience, and are certified to do these tasks safely and correctly. You should not do machine repair or service procedures unless you are qualified and knowledgeable about the processes.

Danger: Some service procedures can be dangerous or life-threatening. DO NOT attempt a procedure that you do not completely understand. Contact your Haas Factory Outlet (HFO) and schedule a service technician visit if you have any doubts about doing a procedure.

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