Stanley 4 gallon backpack professional sprayer.

Something like this?

https://www.amazon.com/Winters-Economical-Pressure-Internals-Accuracy/dp/B0087UCJ6I/ref=sr_1_7?dchild=1&keywords=stanley+backpack+sprayer+pressure+gauge&qid=1633991257&sr=8-7

It looks like the sprayer is made by Chapin and badged to Stanley.

https://www.google.com/search?q=Stanley+Backpack+Professional+sprayer+61804+parts

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I would like the answer yo that question

Drive out to the country side and look for a ACE or TrueValue hardware store. Bring your sprayer with you. They will likely have the right part for you in stock.

call the 1-800 #

The manual is not available online.......Sorry

The picture looks a lot like a Solo sprayer I have. I wouldn't be surprised if Solo made them for Stanley. Do a search for Solo sprayers. They have a site. My sprayer is a Solo 425

the darker Seal has come off the plunger at the bottom of the unit , easy 5 min fix , just unscrew the allen keys at the bootonm take off the cover and remove the plunger , you'll see the plunger seal still inside you can fish it out with an allen key or similar tool clip it on again and reassemble

Lowes or Home depot sells replacement sprayers. Hose to tip all included.

http://www.alamia.us/Solo_Sprayer_Parts_s/814.htm?gclid=CNvasPXY1ZsCFdVL5Qod3U4hJw

Hose end sprayers are the simplest and least expensive of the category. A sprayer jar is attached to a regular garden sprayer. Concentrated material is added to the sprayer jar. An adjustment on the jar determines the amount delivered. The force of the water through the hose pulls the material up from the jar and mixes and dilutes it with the water. A built-in anti-siphon device prevents unused material from being pulled back into your water supply. Compression or tank sprayers are the most common type of spray equipment. Concentrated material is added to the tank. Water is then added to a marked fill line. The remaining air is pressurized by pumping the handle a designated number of times. A control lever on the wand controls the spray pattern and amount. Compression sprayers provide a precise, on target, non-drift spray good for soil and lawn pests. Adjust the sprayer for a coarse, drenching spray, a concentrated stream or a fine mist. Tank capacities range from 1 quart to over 3 gallon for handheld models. Homeowner type backpack sprayers hold up 4 gallons. The tanks may be made from polyethylene plastic, galvanized steel or stainless steel. In addition to treatments for pests and diseases, compression sprayers are designed for applying cleaning solutions for decks and siding. Backpack sprayers are operated in the same manner as the handheld compression sprayer. The over-the-shoulder configuration makes it easier to carry the heavier load of material. Some backpack models also use a lever-style pump to maintain pressure without removing the unit form your back. Powered sprayers rely on a gasoline engine for spray power. Great for larger yards or gardens due to portability and capacity (12 gallons). Dusters are a slightly different breed. Dry powders (mostly for blooming plants such as roses) are added to a canister and applied by manually pumping. NOTE: Compression sprayers deliver liquid under pressure. Compression sprayers are powerful and efficient tools. This fact also makes them potentially dangerous. Always read the manufacturer's instructions and safety precautions carefully.