Why Is My Backpack Sprayer Not Building Pressure?

Backpack sprayers are great for mobility when applying liquid fertilizers, herbicides, or pesticides across the lawn. Like all machines, even simple ones, they need maintenance and might lock up from time to time.

If your backpack sprayer isn’t building pressure, it could be from one of several reasons, including buildup from the products you use or wear on one of the parts or connections along the system. Some quick troubleshooting will help you quickly get to the bottom of the problem.

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How does a pressure sprayer work?

Backpack Sprayer Diagram

There are two main types of backpack pressure sprayers: manual pumps and battery powered.

On a manual pump sprayer, a hand pump is used to pull liquid into the sprayer line with a piston mechanism, and as you spray, the built-up pressure forces the liquid out. Hand pumps allow pressure to be built as needed and must be done while using the sprayer.

Battery-powered sprayers, on the other hand, deliver automatic force when the spray trigger is pulled. This saves you energy as the user, relying on the energy provided by a battery.

If there is a problem with the pressure on a battery powered sprayer, it might be due to low power or a wiring issue, but like manual sprayers, there can be physical problems in the system that are preventing pressure buildup.

When inspecting your unit, keep the model’s instructions close at hand to be sure of the specifications and parts of the sprayer. A Stihl or Roundup backpack sprayer, for example, is a pump technology, but others like Chapin and Solo backpack sprayers have both pump and battery models, and any of their intricacies may vary.

Why does my pump sprayer not work?

If your sprayer isn’t building pressure, it won’t be able to release the liquid that you need to apply. Some of the common problems that occur are easily taken care of after a quick inspection to identify exactly what’s going on. The problem may be:

  • the nozzle is dirty
  • the filter is dirty
  • the sprayer line is blocked
  • the sprayer line has air built up
  • the suction line or sprayer hose has a leak
  • the pump piston is cracked
  • a gasket needs to be replaced
  • a clamp is loose
  • the battery power isn’t working

Before inspecting the sprayer, be sure there isn’t any fertilizer, pesticide, or other solutions in the tank. Consider wearing gloves to handle the inside of the sprayer to avoid getting any of the concentrated substances on your hands.

The Nozzle Is Dirty

Field King 190328 Backpack Sprayer, 4 Gallon,

When the nozzle is not releasing liquid, it might be clogged from buildup. Unscrew the handle from the nozzle, remove the filter, reapply the nozzle, and see if there is a flow.

The spray pattern and pressure release can be disrupted by a clogged nozzle, which results in an uneven stream or application pattern and isn’t as effective, especially when a light spray application is needed for foliar absorption.

The Filter Is Dirty

A dirty filter can also interfere with the pressure system; if it can’t release the pressure, it can’t build more up. There is an interior filter at the bottom of the tank, where the solution is fed into the sprayer’s hose. Disconnect the filter and rinse it off.

This can slowly become clogged from solids in the liquid formulas that you use. It acts as a strainer to avoid those solids building up in the hose or nozzle.

The Sprayer Line Is Blocked

Like the nozzle and the filter, the hose between the tank and the trigger can become clogged from buildup. To rinse the hose, fill the tank with water and spray the water out, or flush the hose with soap and water until the buildup is removed.

The Sprayer Line Has Air Built Up

Airlock can also cause the sprayer to not build pressure due to an inability to release it. There may be blockages in the tank, cracks in the line, or the connection clamps might not be tight enough. These situations can allow air into the sprayer line, which will interfere with releasing and pumping.

Hold the sprayer wand lower or below the tank, and pull the trigger. This should release any built-up air.

The Suction Line Or Sprayer Hose Has A Leak

If there is a crack or leak in the tank’s suction line or the sprayer hose, air may build up, or liquid may escape as you use it. The no-longer-airtight pumping system might not build pressure correctly if there is a leak along the pathway.

The Pump Piston Is Cracked

Like a crack in the hose or suction line, a crack in the piston can interfere with pressure building due to it not being airtight. The piston can be removed from the pressure cylinder to be inspected and replaced if necessary.

The piston usually has an O-ring, a small gasket that sits in a groove in the piston to make the pumping motion air-tight as it pulls in or pushes out to build pressure.

A Gasket Needs To Be Replaced

CHAPIN 61502 4-Gallon Backpack Sprayer with Bonus Foam Nozzle, Translucent White

There are several gaskets along the backpack sprayer system that prevent leaks and provide the air-tight movement required in manual sprayers. There are large gaskets in the tank’s reservoir, the piston, and may be in other spots like the battery engine connection.

These are usually easy to remove and replace as they wear down, become stiff, or crack.

A Clamp Is Loose

Like the sprayer’s gaskets, clamps are used to connect the hose and reservoir lines that must stay in place and remain airtight for the pressure to hold and be released evenly. Ensure the clamp connections are tight and that there isn’t any debris or buildup around those connection points.

The Battery Power Supply Needs To Be Inspected

If you have a battery-powered sprayer, like a Chapin or Solo backpack sprayer, you may need to check the power supply before inspecting the rest of the system to be sure it isn’t a lack of energy. You can troubleshoot the battery sprayer by:

  • verifying the battery isn’t dead and replacing it if it is
  • test the battery connection with a multimeter by removing the cover plate and inspecting the microswitch; the activation engaged by the sprayer wand’s trigger
  • check the pressure dial; if it’s turning without stopping at any setting, it may need to be replaced

How Do You Prime A Backpack Sprayer?

Prime A Backpack Sprayer

Air, debris, or previous liquids may build up or remain in your sprayer’s hose after use. If you don’t make sure this is cleared out, it can cause a problem the next time you go to use the sprayer. When you prime the sprayer, you clear out the hose so it’s ready for new use.

Fill the tank with water and spray it, allowing any built-up air or liquid to be pushed out.

How Do You Clean A Backpack Sprayer?

Like priming, you can clean your sprayer by running water through the system to rinse off and push out any liquids or debris. The tank, reservoir, suction line, wand hose, and nozzle tip can all get dirty over time, and the more regularly you maintain the unit, the longer it will last and the smoother it will work.

Taking your model apart to clean it is a great way to become familiar with the layout in case you need to inspect it for maintenance or repair.