The main difference between the two is that the Chapin 61900 Tree/Turf Pro Backpack sprayer has a stainless steel wand, and the Chapin 61800 Pro Series 4 Gallon Backpack sprayer has a plastic wand and nozzle.Typically, if this were to be used for a company at a customers house, they would want the 61900 Pro Sprayer because the stainless steel looks slightly more professional but doesn't necessarily mean it sprays any better.
The 61800 and the 61900 both have a pressure gage. The 61900 does come with the deluxe padded shoulder straps while the 61800 comes with the basic unpadded straps. Below is a link that will allow you to see a side by side comparison of the sprayers:
http://www.domyownpestcontrol.com/product_compare.php?prod_696=1&prod_1150=1&x=50&y=10
Typically, the Chapin 61900 Tree/Turf Backpack sprayer can reach only about 10 feet if you turn the nozzle to the pinstream setting which just shoots a thin stream of water. We do carry a Chapin Slide Pump Sprayer which can reach targets over 30 feet away.
The only difference between the Chapin 61900 and the Chapin 62000 is the gun and the wand. The 62000 is the premium model and comes with a brass gun and a brass wand. The 61900 comes with a plastic gun and a stainless steel wand. All the other components including the pump are the same.
The Chapin Tree/Turf Pro Commercial Backpack Sprayer - 4 Gal sprayer will spray as high as any other hand pump sprayer, which is only about 10 feet. If you need to spray higher than 10 feet, you should look at the Chapin Slide Pump Sprayer, which can reach up to 30 feet.
Yes, the Chapin 4 Gallon Tree/Turf Pro Commercial Backpack Sprayer can be used for spraying commercial pesticides. It features a large 4 gallon capactiy tank and hands-free operation which gives you the power to handle even the largest spray jobs.
Chapin 4 Gallon Tree/Turf Pro Commercial Backpack Sprayer (61900) will not reach 25 ft. We would suggest the Chapin Slide Pump Sprayer (6002).