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| Posted on 5/17/08 at 08:53 AM | |
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Using a garden hose with a nozzle.... is not even close to being the same as a pressure washer. Street water pressure in most towns and cities is roughly 50-60 psi. The only benefit you get from using street pressure is that you actually get a higher volume of water flow to carry away junk than you would out of an actual pressure washer. This is why when developing or degreasing you use standard garden hose water volume and pressure to carry away degeraser and wet the emulsion faster. Cheap junk pressure washers from a discount store advertize an average of 1000 psi. Read the fine print. That is usually at about 0.5-0.7 gallons perminute. This is why they do not feel like they are doing much. Get a proper industrial pressure washer....one that puts out a bare minimum of 1200 psi at 1.0 gallons per minute....and its a different world. Yes they are more expensive up front....but what they save you in time,chemicals and screens you didn't have to discard... will generally pay for the equipment in about 3 months. Most mid-sized to large shops run pressure washers that average 2,000 psi at about 1.5-1.8 gallons per minute. they ahve to. The cheap cheezy pressure washer made for cleaning your driveway of washing your car....generally cnanot stand up to the hours of use it requires to go through 75-100 screens per day of more. I have installed numerous 3,000 psi pressure washers in large graphic shops. Most of them use 380 mesh all day long. They then use a fraction of the chemicals they used to....and no...it will not hurt your mesh having that much pressure. The only time that happens is if you have a hole or a broken thread...which means the screen was doomed anyway on an automatic press. For a for-instance reference to pressure as to why 2,000-3,000 psi will NOT hurt your screens....a 23" x 31" frame with 40ncm of tension (say a 156 mesh) has approximately 1,428 pounds of force locked up in it just sitting still. If you print with 1/16" of off-contact.....that force is multiplied to approximately 3,100 psi every time the squeegee strokes. With the right pressure washer (albeit not cheap)...you can strip a screen that has been permanently cross linked by emulsion remover from the squeegee side in about 2 minutes. Ray [Edited on 5/17/08 by raygreenwood] | ||
 
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