Field King 190328 Backpack Sprayer (4 Gallon)

Field King 190328 is a four-gallon manual backpack with an internal piston pump, a twenty-one-inch poly wand, a lockable shutoff and an inline filter. The current manufacturer page also lists a reinforced fifty-inch hose. The internal pump is the feature behind the product's No Leak name: the mechanism sits inside the tank rather than hanging outside it.

That design is relevant to buying, but the name is not a guarantee that no component can leak or that chemicals can never reach the wearer. The manual still requires inspecting hoses and connections and using protective equipment. We have not measured long-term leakage or comfort against competing backpacks. The case for this model is its documented layout and serviceability, not an invented field trial.^[2][6][5]

Four gallons is a reservoir size. It does not establish that a typical lawn takes one or two fills, because solution volume per area changes with the nozzle, pressure and application technique. The current listing advertises a pump capability up to 150 PSI. That figure is not a treatment recommendation or a promise of even coverage at every pressure.

Penn State's calibration method measures output with water while maintaining the same speed and pressure used for the real application. A nozzle change or a different pace changes the relationship between tank volume and treated area. Plan the amount to mix from the product label and that measured output. The backpack's capacity is useful only after those quantities are understood.^[2][3][5]

The retail listing describes use with liquids and wettable powders. The manual is more specific about exclusions: no flammable liquids, caustics, acids or hot water. It calls for goggles, gloves and protective clothing, calm-air spraying and following the label on the material being applied. Broad phrases about doing all applications should not override those limits.

Do not assume a pre-seeding herbicide or a post-germination feed is suitable just because the backpack can spray it. The treatment label determines the target, rate and timing. The internal pump does not establish compatibility with every mixture, remove drift concerns or eliminate the need to prevent cross-contamination between different treatments.^[2][5]

The manual requires cleaning the tank and flushing the pump system, hose, shutoff and nozzle after use. It also identifies the filter basket, gasket, shutoff filter and straps as inspection or maintenance points. Before servicing, release pressure as instructed. Store the sprayer dry, without liquid or pressure left in it, and keep the equipment and chemicals out of children's reach.

The older linked manual includes a generic instruction to empty rinse contents onto gravel or bare soil. Do not treat that as blanket permission for pesticide waste: EPA says disposal must follow the pesticide label and applicable local guidance, and pesticides must not enter household or street drains. A larger tank is worthwhile only when its spraying capacity fits the job and you can complete this cleanup responsibly.^[5][4]