Six tips for waterjet troubleshooting and repair

High-pressure waterjets have advanced substantially over the years in terms of longevity and reliability. Still, they need maintenance and repair from time to time. Problems can be avoided or resolved with simple troubleshooting.

High-pressure waterjets are a versatile alternative to cutting methods such as plasma, laser, and mechanical slitting machines. In contrast with thermal cutting, they can precisely cut metal without leaving a heat-affected zone (HAZ). That makes waterjet the preferred method for cutting metal parts for aerospace and construction applications in which metallurgical changes could impact the integrity of the material.

Waterjet Troubleshooting

Like other cutting technologies, waterjet systems have changed quite a bit over the past decade. The newest systems can cut faster and more precisely, and they are more reliable for improved uptime. Engineering advances and advanced system diagnostics that warn of a problem before it starts have made today’s waterjet systems more reliable than those designed even a decade ago, making maintenance more predictable and reducing downtime in general.

Still, as with any mechanical machinery, problems are sure to surface from time to time. Most of them can be quickly resolved with some simple troubleshooting.

The intensifier is probably the hardest-working part of any waterjet system. Because it has more moving parts, more can go wrong. Some of the most common problems are overstroking, water leaks, and short seal life (see Figure 1). Three other common problems with intensifier-based waterjet systems are hydraulic pressure failure, low water pressure, and hydraulic temperature overheating.

1. Overstroking

It is normal for the intensifier to stroke faster during startup and when changing between low pressure and high pressure; however, during normal operation, the intensifier should stroke smoothly to the left and right at the same speed. Sometimes, though, the hydraulic piston travels faster in one or both directions, or more than the pump can support. This is called overstroking. It will trigger an alarm.

Regardless of whether the overstroking is to the left, right, or in both directions, the first thing you should do is reset the alarm. Next:

• Turn off the cutting head.
• Turn on the pump and allow pressure to build.
• Turn on the cutting head.
• Monitor the intensifier stroke rate via the indicator on the operator interface or manually by monitoring the proximity switches.

Sometimes, if the overstroke alarm occurred in error, these steps will reset your system and resolve the problem. If they do not, then monitoring the intensifier stroke rate will indicate how to proceed.

If the intensifier overstrokes in both directions, some steps you can take are:

• Inspect your orifice. Is it worn or improperly installed? Has it failed? If so, reinstall or replace it.
• Inspect the intensifier for leaks from the high-pressure water seals. Are they leaking? If so, replace them.
• Check the water lines, fittings, bleed-down valve, needle, and seat inside the cutting head for leaks. If they are leaking, repair or replace the parts.
• Look at the postfilter water pressure gauge. If it shows the pressure is too low, verify that the cutting water supply is turned on.
• Look at the difference between the values on the pre- and postfilter water pressure gauges. If the difference is higher than 0.7 bar or 69 kilopascals, or 10 pounds per square inch, replace the inlet water filters.
• Look at the prefilter water pressure gauge. If it shows that the pressure of the inlet cutting water is too low, make sure that the cutting water supply is turned on, the low-pressure relief valve or ball valve is closed, and that the inlet cutting water solenoid is allowing water to pass through. To check this, loosen a fitting after the solenoid with the pump running and verify that water streams out.

If the intensifier overstrokes in only one direction, you should:

• Inspect the intensifier for leaks from the high-pressure water seals. Replace if needed.
• Check the low-pressure poppet that corresponds to the overstroke side. If you see overstroking to the left, inspect the poppet on the left side of the intensifier. If the overstroking is to the right, inspect the right poppet. Is the poppet sticking, worn, or damaged? Examine the face of the poppet and the mating face on the check valve. Both surfaces should have a mirrorlike finish. If not, this low-pressure poppet likely needs to be repaired or replaced. After this is done, double-check to make sure the repaired or new poppet fits in the basket without sticking. You may also need to repair or replace the check valve.
• Examine the high-pressure poppets. Overstroking to the left means the high-pressure poppet on the right side of the intensifier has failed. Over-stroking to the right means the high-pressure poppet on the left side of the intensifier has failed. Check for heat from the output adapter on the intensifier end opposite the direction of overstroke. If the output adapter is hot, remove it from the check valve and examine the high-pressure poppet, spring, and seat. If you notice any cracks or discoloration or if the poppet spring is broken, replace the poppet, seat, and spring.

2. Water Leaks

Another maintenance area is water leakage. Damage to the high-pressure water seals and the hoops is the most common cause of water leaks from the intensifier. If you see a drip of water every few strokes, it means that the seals are nearing the end of their life and should be replaced within a reasonable period of time. If you see a drip with every stroke, then you should change your seals at the soonest opportunity. If you see leaks in other areas, that likely indicates a worn part, loose fitting, or damaged seat. It is important to address this leakage right away to prevent further damage to nearby components. There are several things to watch for:

Figure 1
Some of the most common problems with a waterjet intensifier are overstroking, water leaks, short seal life, hydraulic pressure failure, low water pressure, and hydraulic temperature overheating.

• If you notice warm or hot water leaking from the weep hole on the output adapter, a fitting on the high-pressure water tubing probably is not tight enough, the tubing end is cracked or damaged, or the output adapter has failed.
• If you see warm or hot water coming from the weep hole on the check valve, it probably means the output adapter is loose, the high-pressure poppet seat has failed, or the seat face of the check valve is cracked.
• If you notice cold water leaking from the end cap (end bell), it likely means one of the O-rings directing inlet water to the cylinder bore (O-rings on the check valves) has failed and needs replacing.
• Warm or hot water leaking from the end cap indicates the high-pressure seal on the static end of the cylinder has failed and needs replacing.
• Water leaking from the dynamic end of the cylinder means the high-pressure seal on that end has failed.

3. Short Seal Life

If it seems the high-pressure water seals have a short life, some things you can do to help extend the interval between maintenance are:

• Make sure that the water quality is within satisfactory ranges.
• Verify that the water pressure and volume meet minimum requirements.
• When you replace seals, thoroughly clean all parts so that they are free of debris.
• Check for cracks at the ends of the high-pressure cylinder.
• Make sure the plunger bearing (or hydraulic cartridge) is not worn.

4. Hydraulic Fluid Pressure Failure

After intensifier problems, the next most common issue is failure to build hydraulic pressure and, as a result, water pressure. If the pump fails to build hydraulic pressure:

• Double-check the pressure control knob (if manually controlled) to make sure it is set correctly.
• Isolate the pump compensator from the pressure control circuit to verify the compensator can raise pump pressure.
• Measure the temperature of any hydraulic relief valve to ensure it is not opening. Increases in temperature, in relation to surrounding components, indicate the relief valve is opening.

5. Hydraulic Temperature Increases

In addition to hydraulic pressure problems, you might also get a high-temperature warning. The normal operating temperature for hydraulic fluid is based on the fluid weight and determined by the pump manufacturer. If the fluid’s temperature rises above the rated temperature, it becomes too thin and degrades, which decreases the lubricity and protective qualities.

If you see an unexpected increase in temperature, then the likely culprit is the cooling system. Returning the temperature to normal depends on whether your system is water-cooled or air-cooled.

If it is water-cooled, make sure the cooling water is turned on and then adjust the water-modulating valve (if equipped) to increase the water flow, which will decrease the hydraulic fluid temperature.

If you have an air-cooled system, the problem could be caused by the ambient temperature in the shop. It may be too hot, in which case you might want to consider installing an air conditioner or other air-cooling system. The problem may also be that the fan is not generating enough airflow. If you suspect that is the cause, check the heat exchanger fins to be sure they are not dirty or clogged. Clean the fins if necessary. In addition, look at the thermal overload device on the fan motor starter inside the electrical enclosure to be sure it has not tripped. If it has tripped, reset the overload.

If the cooling system is not the cause, measure the hydraulic relief valve temperature. If this valve is cracking open, it will generate a significant amount of heat, potentially overloading the capacity of the heat exchanger or cooler. You can also inspect the cord for the hydraulic fluid temperature and level sensor to be sure it is not unplugged or damaged. Finally, inspect the temperature sensor to ensure that it isn’t faulty or damaged.

6. Low Water Pressure

You may also notice low water pressure, either to or from the intensifier. When water travels away from the intensifier, it is normal for the pump pressure to fall when the cutting head is turned on. However, if the pressure falls too low, you’ll want to take these actions:

• Verify that the orifice is not damaged or defective. Replace if necessary.
• See that the on/off valve is not leaking. If leaking, repair the leak.
• Make sure the intensifier does not stroke when it is at pressure with the cutting head turned off. If it does stroke, check the bleed-down valve and the high-pressure tubing for leaks and repair or replace it if needed. If there are no leaks, make sure the low-pressure and high-pressure poppets are in good condition. Repair or replace the poppets if needed.
• Examine the check valves and repair or replace them if necessary.

When water is traveling to the intensifier, a pressure switch is often present that senses water pressure to the intensifier. If the system senses the pressure is too low, the pump will turn off to protect the system from running without enough pressure to the intensifier. If this happens to you, do the following:

• Make sure that the utility water to the pump is turned on.
• Replace the water filters.
• Check that the inlet cutting water valve has not failed or is not plugged.

Following these troubleshooting tips will save you time and money on a service technician, helping you pocket more profit.

Arion Vandergon is senior product application engineer—waterjet for Hyperthem Inc., arion.vandergon@hypertherm.com, www.hypertherm.com.