Except for very fine grain media (e.g. 45-90 micron), most Dana-Ridge wetblast machines give best results at around 25%-30% by volume of media to water.
Too much media can overload the machine. Too little media results in inefficiency, ie. poor cleaning ability and long cleaning times.
So how do you tell the media concentration level?
Very easily…simply take the plastic media concentration jar that comes with every machine and fill it with a typical sample of the slurry coming from the process gun (with the air off). To fill it, direct the gun flow across the hole on the side to fill the flask gradually.
Prolonged filling will result in an invalid sample, more and more media sinking to the bottom, while the water overflows. It is best to stop once the top black line is reached as per the photo.
Once the sample has been collected, allow the bottle to stand to permit the media to settle to the bottom. For finer media you may need to wait longer as it settles.
The media level should be very evident.
For efficient results, the height of the media should be about 1/4-1/3 of the total height. (Near where the double black lines are on the bottle pictured).
The test only takes about 20-30 seconds to perform and should be done regularly. If you don’t keep the media topped up, you will find that the work takes longer than it should. It is easy to lose track of time while concentrating on the pieces being processed.
For a full load of media, you may find it difficult to get the slurry to flow on pump start-up ie. the pump the pump runs but does not pump. This is not a bad sign. In fact, it may be a good sign, indicating a high concentration of media. If cavitation occurs, stop the pump and loosen up the bedded media by opening the sump fill water valve located at the back of the machine and injecting water into the bend below the pump. This is only required for a few seconds immediately prior to starting the pump. Make sure you turn the valve off.
Note: If you leave the valve turned on you will cause an unnecessary amount of water to continue filling the sump. In turn, this will cause excess media to be washed out the overflow as you blast, increasing the media consumption rate. Therefore, make it a rule, that you keep your hand on the valve while it is turned on. Only take your hand off the valve after you have turned it off.
During operation some media will be deposited around the cabinet interior, necessitating a further compensatory addition to maintain the strength of the slurry concentration.
Media breakdown will also occur at a rate depending upon a number of variables such as air pressure, gun angle, nozzle distance from and nature of the work piece. It will be necessary therefore to make periodic additions of media in order to maintain performance.