Model 425L SOLO 4 Gallon (15.1 liters) Professional Piston Backpack Sprayer, Made in USA. It includes the original packaging and the Operator's Manual & Parts List. It has been used, but it in very good/excellent condition. You can test it here if you'd like since it hasn't been used lately.
It has a diaphragm pump, suitable for liquids and powders. This model is designed for applying fertilizers, herbicides, and pesticides with a wide pressure range of up to 90 psi. It has a long spray wand and pre-attached top buckles shoulder straps.