Nozzle and focusing tube choice

• Whether you are cutting with water only i.e. soft materials like Foam, rubber, cardboard, foodstuffs, leather or textiles, or water and abrasive i.e. hard materials like metal alloys, glass, ceramics, stone, laminates or Granite.

• Quality and speed of cut required.

• Volume of cutting. In the case of a fixed displacement pump, there is only one choice of nozzle as the volume of water delivered is constant and the pressure delivery is influenced by the orifice diameter. Therefore the nozzle diameter and the focusing tube diameter must be chosen so that the pump delivers the required cutting pressure.

With an intensifier pump the orifice diameter and the pressure of the water determine the volume of water being used. With pure water cutting the cutting head design is very simple as you can see in the diagram above. For abrasive water jet cutting the high velocity water jet creates a vacuum in the cutting head and if abrasive is required, the vacuum draws the abrasive material into the mixing chamber where it is accelerated by the water jet and then aligned with the water in the focusing tube.

An abrasive water jet must be perfectly formed to provide the optimal cutting capacity. The shape of the nozzle must allow a perfect, thin jet of water to be formed. The cutting head must be designed to allow even mixing of the abrasive with the water jet and the focusing tube must be of sufficient length to accelerate and align the abrasive particles.

Increasing the diameter of the orifice greatly increases the cutting power of a water jet, the maximum nozzle size being limited by the capacity of the pump. Typically for a 50hp intensifier pump, the optimum orifice size is 0.35mm, with a 1.1mm focusing tube, which gives optimum cutting power and cutting speed.