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Pumps

• Intensifier pumps
• Crankshaft pumps

Intensifier pumps

Early ultra-high pressure cutting systems used hydraulic intensifier pumps exclusively. At the time, the intensifier pump was the only pump capable of reliably creating pressures high enough for waterjet machining.

An engine or electric motor drives a hydraulic pump which pumps hydraulic fluid at pressures from 1,000 to 4,000 psi (6,900 to 27,600 kPa) into the intensifier cylinder.
The hydraulic fluid then pushes on a large piston to generate a high force on a small-diameter plunger. This plunger pressurizes water to a level that is proportional to the relative cross-sectional areas of the large piston and the small plunger.

For Example
If 3000 psi (20,700 kPa) hydraulic fluid acts on a piston with an area of 20 square inches (125 cm2), and that piston pushes on a plunger with an area of only 1 square inch (6.2 cm2), the water that is pushed on by the plunger will be pressurized to 60,000 psi (414,000 kPa) [3000 x 20/1].

The intensifier cylinder is a double-acting cylinder: hydraulic fluid is introduced alternately into one side and then the other. The hydraulic piston pressurizes the water on one side by pushing the small-diameter plunger toward the end of the intensifier cylinder. This motion also directs the water through the check valve and into the outlet manifold. The plunger then retracts and a another check valve allows low pressure water into the plunger cylinder. The same process is done on the opposing side of the cylinder.

The back and forth action of the intensifier piston produces a pulsating flow of water at very high pressure. To help make the water flow more uniform (thus resulting in a smoother cut), the intensifier pump is equipped with an "attenuator" cylinder which acts as a high-pressure surge vessel. The use of this attenuator reduces pressure fluctuations to a few thousand psi per stroke.

Crankshaft pumps

The centuries-old technology behind crankshaft pumps is based on the use of a mechanical crankshaft to move any number of individual pistons or plungers back and forth in a cylinder. Check valves in each cylinder allow water to enter the cylinder as the plunger retracts and then exit the cylinder into the outlet manifold as the plunger advances into the cylinder.




Figure 1: Crankshaft pump

Crankshaft pumps are inherently more efficient than intensifier pumps because they do not require a power-robbing hydraulic system. In addition, crankshaft pumps with three or more cylinders can be designed to provide a very uniform pressure output without use of an attenuator system. Crankshaft pumps were not generally used in ultra-high pressure applications until recently. This was because the typical crankshaft pump operated at more strokes per minute than an intensifier pump and caused unacceptably short lives of seals and check valves. Improvements in seal design and materials combined with the wide availability and reduced cost of ceramic valve components now make it possible to operate a crankshaft pump in the 40,000 to 55,000 psi (280,000 to 379,000 kPa) range with excellent reliability. This represented a major breakthrough in the use of such pumps for abrasivejet cutting.

Today, crankshaft pumps can operate reliably up to 55,000 psi (379,000 kPa).

Experience has shown that an abrasivejet does not really need the full pressure capability of an intensifier pump. In an abrasivejet, the abrasive material does the actual cutting while the water merely acts as a medium to carry it through the material being cut. This greatly diminishes the benefits of using ultra-high pressure. Indeed many abrasivejet operators with 60,000 psi (414,000 kPa) intensifier pumps have learned that they get smoother cuts and more reliability if they operate their abrasivejets in the 40,000 to 50,000 psi (276,000 to 345,000 kPa) range. Now that crankshaft pumps easily produce pressures in that range, an increasing number of abrasivejet systems are being sold with the more efficient and easily maintained crankshaft-type pumps.

A Comparison Between Intensifier and Crank Drive Pumps