Although the main purpose of the fluid in a parts cleaning unit is to cut the grease and grime, there are other things you may want / should consider.
The Flash Point (related to the vapor concentration that will ignite if exposed to a flame/spark), the Evaporation Rate of the particular cleaning fluid (loss to the air) and is also closely associated with the odor issues.
I believe you may find the water-based cleaner fluids will have a much lower Flash Point and evaporate slower than say a petroleum-based product like Mineral Spirits. I know of a local semi-truck repair shop that uses fuel oil (common diesel fuel, $3/gallon) in their parts cleaner. It works great, but it does evaporate readily (especially on days over 75*F), has a distinct odor and they have lots of air movement inside the bays, so it isn't very noticable anyway. Evaporation rates are closely related to the odor issues. For instance, if you have a "pretty" relatively small (1 or 2 car) garage attached to your house, you wife may not appreciate the distinct odor of diesel fuel or other parts cleaner fluid evaporating into the air and migrating into the house.
Both the evaporation & odor issues can be miminized IF you use a lid to cover the parts cleaner basin while not being used. If you don't use the parts cleaner real often, then you can also use the lid as a secondary work/assembly bench while no parts cleaning is required.
The Flash Point or flammability of the fluid is more of an issue if you're using the unit in a fairly small (1 or 2 car garage) or fairly tight work area. If you can utilize an exhaust fan to the outside located near the the parts cleaner and open a supply/incoming air grille across the room (to allow air in while you are trying to exhaust air out at the fan), that will help reduce any buildup of cleaner fluid vapors & odors within the work space. Chances are you won't need an explosion-proof fan motor, as the vapors likely won't get THAT thick.....
In reviewing your illustrated parts cleaner unit, you may want to consider looking at adding/constructing some 'side curtains' for it to help control any splashed fluid. I constucted an approximate 15" x 15" wire frame and attached flexible plastic 'shower curtain'-like side shields that extend into the basin, allowing any splash to drain back into the basin, and when done, the curtains fold inward & under the lid when not in use.
Of course, you'll likely want to locate the unit under a good, overhead light or plan to install a good light above the unit to allow you to see well with curtains and such in place.
Consider using a good pair of neoprene gloves and a protective apron while working with any of the cleaning fluids. While they remove the grease & grime from your parts, they also remove the oils from the skin on your hands if not protected. In the case of small parts, there are protective hand creams available that will protect your skin to a degree against many petroleum or water-based cleaning products. Check the manufacturer's labels to ensure that the apron, gloves and/or protective hand cream are compatable with the cleaning fluid of choice. No, protective hand cream isn't for sissys.... some of it works VERY well! I have found that it also makes the 'end-of-the-day' or lunchtime wash-up much easier as well.
While this shouldn't be necessary, it is HIGHLY recommended - of course, I'm referring to eye protection. Goggles or at least safety glasses should be worn while using pressurized cleaning fluid. If possible, use a metering valve to regulate the fluid supply pressure to a minumim will help a lot towards reducing the splashing onto yourself and out of the basin. Use of a parts cleaning brush will work much better at removing grime rather than high-pressure cleaning fluid. The fluid only is to rinse away the grime, not power-wash it off............
If you ensure that it has a fluid/particulate filteration system inline before the pump, the pump will last longer. A piece of stiff window screen fastened to a wire framework lying in the bottom of the basin works well to catch small parts and will extend the life of a disposeable filter element.....my friend at the diesel truck repair shop uses coffee filters as a pre-filter in his parts cleaner...

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Good Luck! (sorry, for being soo long...

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RW
