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A waterjet pump primer

Choosing the right pump technology for the application

Figure 1
The application typically drives which waterjet pump technology is needed for the job. For example, if a shop is using only one cutting head and it wants to speed up cutting, it might consider more powerful pumps that can deliver at least 75,000 PSI.

Selecting a waterjet pump can be a confusing undertaking. There are so many choices:

  • Direct-drive or intensifier pump technology
  • 36,000 PSI, 60,000 PSI, 75,000 PSI, or greater
  • Horsepower, which can range from under 30 to well over 200

How do you know what you need if you’ve never owned a waterjet? It all comes down to what you want to accomplish (see Figure 1).

Waterjet pumps are a lot like vehicles. Lower-cost direct-drive pumps or low-horsepower intensifier pumps get you from point A to point B on a budget. Higher-pressure pumps (75,000 PSI or more) get you there really fast and in style. The bulk of the other pumps are built strictly for utility. Like vehicles, most pumps can be loaded up with options.

So which pump do you need, a hatchback, a sports car, or a pickup truck? It depends on what you want to do.

Starting With the Basics

The goal in selecting a waterjet is to find the most efficient and cost-effective pump technology within your budget that will cut your parts at the lowest possible cost. To determine that, the waterjet technology provider needs to know what materials you are cutting and how fast you need to cut them. This helps to determine flow rates and how many nozzles you need, and that drives horsepower requirements.

Nine out of 10 times, pump horsepower is determined by the number of cutting heads. The rule of thumb for abrasive cutting is 50 HP per cutting head, but if you are cutting 4-in. or thicker material more than 50 percent of the time, you may want to consider 75 to 100 HP per head to help with throughput.

Pump Types

Two major types of pumps are available on the market today: hydraulic intensifier pumps and direct-drive pumps. Both of these pumps produce ultrahigh-pressure water by moving a piston or plunger assembly back and forth. Hydraulic intensifier pumps use a dual-acting hydraulic cylinder to drive the plungers (see Figure 2), and direct-drive pumps use a crankshaft to drive pistons (see Figure 3).

Hydraulic intensifier pumps continue to be the pump of choice for shops that run multiple nozzles and process high volumes of material or thick material. Hydraulic intensifiers are less expensive to maintain and last longer, but cost more upfront.

Direct-drive pumps are less expensive to purchase upfront and use less electricity, but require more maintenance as intensifiers stroke at less than 60 strokes per minute, while direct-drives stroke at more than 1,000. Each cycle consists of a pressure cycle that goes from 60 PSI to the ultrahigh pressure.

In terms of pressure, most shops continue to run traditional 55,000- to 60,000-PSI pumps. (Traditional 60,000-PSI pumps with 100 to 150 HP are suitable for shops that need to run multiple cutting heads.) However, a growing number of shops are selecting pumps capable of 75,000 PSI or more for their efficiency gains. These higher-pressure pumps are most attractive for shops that run a single cutting head, but need to increase throughput.

Figure 2
While costing more upfront, hydraulic intensifier pump technology actually requires less maintenance than direct-drive pump technology because hydraulic intensifiers do not need the pump to stroke as many times per minute.

Operating Costs

Operating cost is an important consideration when investing in a waterjet system. An abrasive waterjet costs about $17 to $48 per nozzle per hour to operate (excluding labor), depending on horsepower and pressure, type of pump, local utility rates, and, most important, the amount of abrasive required. Garnet abrasive costs an average of 24 cents per pound and is the biggest cost in abrasive waterjet system operation, considering that a typical abrasive jet uses 0.5 to 1.5 lbs. of garnet per minute.

Hydraulic intensifier pumps are much less expensive to operate than direct-drive pumps. For example, a single-nozzle abrasive waterjet system powered by a 30-HP, 55,000-PSI direct-drive pump costs about $36 per hour to operate, excluding labor, assuming you use 1.3 lbs. of abrasive per minute. A single-nozzle abrasive waterjet system powered by a 30-HP, 60,000-PSI hydraulic intensifier pump costs about $17 per hour to operate, excluding labor, assuming you use 0.6 lbs. of abrasive per minute.

Higher-pressure, 75,000-PSI systems can achieve up to 50 percent faster cutting speeds than traditional 55,000- to 60,000-PSI systems, and as a result, they consume less garnet, water, and power. Compared to a 60,000-PSI pump, a typical 75,000-PSI system uses 30 percent less water, 30 percent less power, and up to 50 percent less abrasive, resulting in up to a 40 percent reduction in operating costs.

By cutting faster, these higher-pressure waterjets also free up your machine for other jobs. Higher-pressure pumps naturally use more consumable parts, so you should consult with your waterjet manufacturer to determine if a higher-pressure pump has adequate return on investment for your application.

Speaking of cutting speeds, one of the first questions those new to waterjet cutting ask is “How fast will it cut?” Cutting speed varies tremendously depending on the quality of the cut desired, the material and its thickness, water and abrasive flow, and the pump pressure. For example, a 100-HP, 75,000-PSI waterjet can cut 0.25-in. aluminum as fast as 149.3 IPM at its lowest quality setting using 1.5 lbs. of garnet per minute, while a 50-HP, 60,000-PSI waterjet can cut 0.25-in. aluminum as fast as 90 IPM at the same quality level. Both speeds could be reduced by as much as 80 percent by cutting at the highest quality.

Powering the Pump

Before you purchase a waterjet system, you need to make sure you have adequate power. Minimum power requirements depend on the voltage and horsepower of the pump. For example, at 230 VAC, a 50-HP pump requires a 200-amp disconnect and a 30-amp disconnect for the motion system, so a standard 400-amp service would be adequate with additional capacity for other equipment. However, if the facility has 460-VAC service, the amperage requirements are cut in half, leaving even more capacity.

Shops with limited power do have some new options. Hydraulic intensifier pump technology has been unveiled that draws only 37 full-load amps at 460 VAC (60 Hz) or 74 full-load amps at 230 VAC (60 Hz). It is capable of producing 0.6 GPM of ultrahigh-pressure water at a continuous operating pressure of 55,000 PSI.

Direct-drive pump technology, designed specifically for rural and remote areas with limited power, also has emerged in recent years. One such direct-drive pump uses a tractor power takeoff to produce up to 0.9 GPM of 55,000-PSI ultrahigh-pressure water (see Figure 4).

A Final Note on Maintenance

All waterjet pumps require maintenance. Pump maintenance costs average $3 an hour over 10,000 hours, but can vary from less than $2 an hour to more than $9 an hour, depending on the type of pump. Following a manufacturer’s waterjet maintenance schedule and taking advantage of training programs help to keep operating costs in line over the equipment’s lifetime.

For instance, with ultrahigh-pressure waterjets, maintenance is extremely important. If you ignore a small leak, it could become a costly or time-consuming problem if you allow it to wear a groove into an expensive high-pressure component. Now you have to either resurface or replace that part.

In the end, you want to make sure you keep your pump cool, your water clean, and replace your seals and hydraulic fluid as needed.

A new take on waterjet pump technology

A new take on waterjet pump technology

Servomotor technology is no stranger to metal fabricating, having made its way into press brakes and stamping presses over the past decade. So it should be no surprise that the same has occurred in waterjets.

Techni Waterjet debuted a waterjet pump that uses an electric servomotor to power the plunging action that draws, pressurizes, and ejects the water from a sealed chamber. More specifically, the electric servomotor is attached to a high-load precision ball screw, which drives the plungers.

With this pump design, the only energy used is the power required to run the plungers. In hydraulic intensifier pumps, energy is needed to run hydraulic oil through the heat exchanger to prevent overheating; also in this type of system, the oil has to be directed through a relief valve to stop the plunging action when the intensifier pump is idle. In a direct-drive system, the pump has to consistently drain water via a dump valve every time the cutting head is closed.

This electric servo pump technology allows the operator to dial in a specific pressure, which is delivered almost instantaneously. The advanced control of the servomotor and precision of the ball screw enable precise control over the output pressure and volume of displaced water. There is no need for extra time to ramp up or depressurize as a fabricator might find with a hydraulic intensifier pump design. Direct-drive crankshaft pumps are not suitable for running varying pressures.

Information provided by Jim Fields, national sales manager, TECHNI Waterjet, 15301 W. 109th St., Lenexa, KS 66219, 888-832-4643, www.techniwaterjet.com.

About the Authors

David Arthur

Southeast Regional Manager

12070 43rd St. NE

St. Michael, MN 55376

800-538-3343

Deron Roberts

Parts and Service Director

12070 43rd St. NE

St. Michael, MN 55376

800-538-3343

Jeff Schibley

Regional Manager

12070 43rd St. NE

St. Michael, MN 55376

800-538-3343

Nancy Lauseng

Marketing Manager

12070 43rd St. NE

St. Michael, MN 55376

800-538-3343