Pump Technology
The pump is the heart of the waterjet system. The pump pressurizes the water and delivers it continuously so that a cutting head can then turn that pressurized water into a supersonic waterjet stream.
Two types of pump can be used for waterjet applications — an intensifier based pump and a direct drive based pump.
Direct Drive Pump
The direct drive pump operates in the same manner as a low-pressure "pressure washer" that you may have used to pressure wash a house or deck prior to repainting.
It is a triplex pump that gets the movement of the three plungers directly from the electric motor.
These pumps are gaining acceptance in the waterjet industry due to their simplicity.
At the time of this writing, direct drive pumps can deliver a maximum continuous operating pressure 10 to 25% lower than intensifier pumps units (20k to 60k for direct drive, 40k to 94k for intensifiers).
Though direct drive pumps are used in some industrial applications, the vast majority of all ultra-high pressure pumps in the waterjet world today are intensifier based.
Intensifier Pump
Two fluid circuits exist in a typical intensifier pump, the water circuit and the hydraulic circuit.
The water circuit consists of the inlet water filters, booster pump, intensifier, and shock attenuator.
Ordinary tap water is filtered by the inlet water filtration system – usually comprising of a 1 and a 0.45 micron cartridge filter.
The filtered water then travels to the booster pump, where the inlet water pressure is maintained at approximately 90 psi – ensuring the intensifier is never "starved for water."
The filtered water is then sent to the intensifier pump and pressurized to up to 94,000 psi.
Before the water leaves the pump unit to travel through the plumbing to the cutting head, it first passes through the shock attenuator.
This large vessel dampens the pressure fluctuations to ensure the water exiting the cutting head is steady and consistent. Without the attenuator, the water stream would visibly and audibly pulse, leaving marks on the material being cut.
The hydraulic circuit consists of an electric motor (25 to 200 HP), hydraulic pump, oil reservoir, manifold, and piston biscuit/plunger. The electric motor powers the hydraulic pump.
The hydraulic pump pulls oil from the reservoir and pressurizes it to 3,000 psi. This pressurized oil is sent to the manifold where manifold’s valves create the stroking action of the intensifier by sending hydraulic oil to one side of the biscuit/plunger assembly, or the other.
The intensifier is a reciprocating pump, in that the biscuit/plunger assembly reciprocates back and forth, delivering high-pressure water out one side of the intensifier while low-pressure water fills the other side. The hydraulic oil is then cooled during the return back to the reservoir.
The advanced technology in the pump is found in the intensifier.
As mentioned briefly in the description of the water circuit, the intensifier pressurizes the filtered tap water to up to 60,000 psi. Intensifier pumps utilize the “intensification principle.”
Hydraulic oil is pressurized to a pressure of, say, 3,000 psi. The oil pushes against a piston biscuit. A plunger with a face area of 20 times less than the biscuit pushes against the water. Therefore, the 3,000-psi oil pressure is “intensified” twenty times, yielding 60,000-psi water pressure. The “intensification principle” varies the area component of the pressure equation to intensify, or increase, the pressure.
Pressure = Force /Area
If Force = 20, Area = 20, then Pressure = 1. If we hold the Force constant and greatly reduce the Area, the Pressure will go UP. For example, reduce the Area from 20 down to 1, the Pressure now goes up from 1 to 20. In the sketch below, the small arrows denote the 3,000 psi of oil pressure pushing against a biscuit face that has 20 times more area than the face of the plunger. The intensification ratio, therefore, is 20:1.
In the illustration below, the biscuit and plungers are in the green section and outlined in red. The biscuit contains the small arrow suggesting movement to the left. The two water plungers extend from either side of the biscuit. High-pressure water is delivered out the left side while low-pressure water refills the right. At the end of travel, the biscuit/plunger assembly sequence is reversed.
(click image for larger version)
Sophisticated check valves ensure the low pressure and high-pressure water is only allowed to travel one direction. The high-pressure cylinders and end caps that encase the plunger and biscuit assembly are specially designed to withstand the enormous force and the constant fatigue.