Many people ignore the importance of water quality & temperature in a waterjet cutting system even though water can have a tremendous effect on the life of waterjet components.
Let's look at how to save money by controlling water quality and temperature to extend the life of waterjet parts.
Total Dissolved Solids
The first hurdle in water quality is to filter out impurities before it can reach the high pressure line or cutting head. Impurities in water are measured in parts per million, or ppm, and consist of dissolved and suspended solids. The total dissolved solids (TDS) in average American tap water ranges anywhere from 140-400 ppm, with 500 ppm considered unsafe for human consumption.
The quality of the water supplied to the intensifier pump can directly influence the service life of waterjet components. A high concentration of TDS causes accelerated wear of any components that come in contact with the high pressure water because of the increased abrasiveness of the water from the TDS.
Although it would seem logical that zero parts per million is the desired quality water for a waterjet, it is actually counterproductive to remove all impurities from the water. Pure water (H2O) is considered 'the universal solvent' and its presence in a waterjet can cause major issues including metal pitting and other damage. Instead, most waterjet experts recommend aiming for low total dissolved solids in water, with 60 - 70 ppm of total dissolved solids optimal.
Reverse Osmosis (RO) and Deionization (DI) units are available as add-on's for waterjet owners interested in regulating the total dissolved solids. There are many different brands of RO and DI systems on the market and the waterjet manufacturer can recommend which will work best with a machine. Many manufacturers also offer closed-loop systems, such as the WARDJet WRS-3000 water recycler, which uses the same water over and over again. Typically, these systems have built-in water treatment to manage TDS.
In addition to the concern for total dissolved solids, water must be filtered for suspended solids. These are solids in water that can be trapped by a filter, whereas dissolved solids would pass through a filter. Suspended solids constitute a wide variety of material, including silt, decaying plant matter, industrial wastes, etc.
Suspended solids can also cause shortened pump life as well as difficulty with seals and nozzles. Also, if suspended solids make it into the high pressure stream, they can act as an abrasive and damage high pressure equipment. There are both pre-filtration and final filters designed for this purpose, depending on the size of the particle that needs to be removed. These filters are located inside of the pump prior to the intensifier and can be easily changed by hand. Generally, the pump PLC will send a notification when it is time to replace a clogged final filter.
Water pH is just as important as total dissolved solids and suspended solids. If the inlet water has a low pH, its acidic properties can damage the high pressure tubing which would cause it to be replaced more often than necessary. Similarly, if the inlet water has a high pH, its basic properties can cause scaly buildup of calcium carbonate on the inside of high pressure tubing. This calcium carbonate buildup will eventually break off, move through the high pressure tubing gaining momentum, and damage the waterjet orifice. Water used in a waterjet cutting system should ideally have a pH level of 7 which is neither acidic nor basic. The addition of a water softener to regulate the pH level of inlet water is an easy fix that is strongly recommended by waterjet technicians.
Water temperature also has a big effect on the life of waterjet components. Water entering the high-pressure pumps must be kept cold (below 70* F) or else is can effect seal longevity. Water right out of the tap may already be cool enough for some companies, but if not, manufacturers often suggest a chiller system.
Environmental factors like rainfall and temperature of the climate can also affect the initial water temperature. In this case, waterjet professionals often recommend a closed-loop system with chillers to keep everything at a constant temperature.
WARDJet has found that the use of a good quality water softener in conjunction with a 0.2 absolute final filter to be successful for treatment of water for the intensifier. Since 2003, WARDJet has installed hundreds of waterjet systems using this setup without any shortened component life. In the worst case scenario, if seal life does not live up to expectations, then a DI or RO system can be installed.
Currently, WARDJet is the only manufacturer of waterjet systems that includes a 0.2 final filter standard with all pumps. The WARDJet Parts Department is also able to supply consumable 0.2 final filters for use on nearly any brand of pump.
As part of installation planning, a water quality analysis should be performed by a commercial company that specializes in water conditioning equipment. The minimum information one should obtain from this analysis is TDS, silica content and pH value. Each waterjet manufacturer has different requirements for water quality. Check with the manufacturer to obtain the specifications for a particular machine.
As many waterjet technicians will attest, one of the best ways to improve machine life is to invest in water analysis and then incorporate the recommended water conditioning system into the machine. Although water quality should be analyzed by all waterjet owners, there are also instances where treatment is not necessary to have a well-functioning waterjet system.