the pump makes a loud knocking or banging noise, especially when i pull the trigger

Diagnosis

The loud knocking or banging noise occurring specifically when the trigger is pulled on a Briggs & Stratton S2200 is a classic symptom of cavitation. This happens when the pump's internal pistons create a low-pressure zone that causes dissolved air or water vapor to form bubbles. When these bubbles move into the high-pressure side of the pump, they implode violently. This "water hammer" effect creates the metallic banging sound you hear and can quickly pit the internal valves or crack the pump housing. This occurs because the pump is demanding a higher volume of water than the supply line can provide. This is rarely a failure of the pump itself, but rather a failure of the "feed" system. If you are using a standard 5/8" garden hose instead of a high-flow 3/4" hose, or if there is a partial blockage in the inlet screen, the pump will starve. You can confirm this by checking if the noise disappears when the engine is at a lower RPM or if the noise stops immediately after you release the trigger, indicating the pressure spike is the catalyst.

How to Fix It

To eliminate cavitation and stop the banging, you must ensure an unrestricted, high-volume flow of water into the pump. Follow these steps precisely:

1. Shut down the engine immediately. Do not run the pump while it is knocking, as this can lead to permanent seal failure.
2. Inspect the Inlet Filter Screen. Unscrew the water inlet coupling. Locate the small mesh screen inside the intake port. Use a soft brush or compressed air to remove sediment, algae, or mineral buildup. If the screen is torn, replace it with a genuine Briggs & Stratton replacement part to prevent debris from entering the pump.
3. Upgrade the Supply Hose. Replace any standard 5/8" diameter garden hose with a heavy-duty 3/4" diameter hose. The S2200 requires a high volume of water to maintain prime; a narrow hose creates too much friction and restricts flow.
4. Check for Kinks and "Soft" Hoses. Ensure the hose is not kinked and is not a "cheap" expanding hose. Expanding hoses often collapse internally under the suction of the pump, cutting off water flow.
5. Verify Faucet Flow. Fully open the outdoor spigot. If you are using a quick-connect fitting, ensure the O-rings are seated properly and not obstructing the flow path.
6. Test with the 40-degree Tip. Reassemble and start the engine. Use the white 40-degree nozzle first. This tip has the lowest pressure drop and allows the pump to move water more freely, confirming if the issue was a restriction.

If That Didn't Work

• Check for an Air Leak in the Suction Line. Even a tiny pinhole in the garden hose or a loose connection at the pump inlet can allow the pump to suck air instead of water. This introduces air pockets that cause rhythmic banging. Replace the hose washers with new, thick rubber gaskets to ensure an airtight seal.
• Inspect the Unloader Valve. If the knocking persists even with a high-flow hose, the internal unloader valve may be sticking. This valve manages the bypass of water when the trigger is released. If it is fouled with calcium or debris, it can cause pressure surges. Spray a small amount of pump lubricant into the unloader assembly to see if the noise diminishes.
• Verify Water Source Pressure. If you are pulling water from a rain barrel or a low-pressure gravity feed, the S2200 pump will cavitate because it is designed for pressurized municipal water. You will need to install a booster pump or move the unit closer to a pressurized main.
• Check for Nozzle Blockage. A partially clogged spray tip creates excessive backpressure that can cause the pump to "stutter." Soak the nozzles in a vinegar solution for 24 hours to remove mineral deposits.

Heads Up

• NEVER run the pump dry. Running the S2200 without water for even 30 seconds can overheat the pump head and destroy the internal seals.
• Always connect water before starting. Establish a full prime of the pump by squeezing the trigger for a few seconds before starting the engine.
• Winterize the pump. Use a pump protector/antifreeze solution before storing the unit for winter; frozen water inside the pump housing will crack the manifold, leading to leaks and cavitation.
• Avoid "Expanding" Hoses. These are the primary cause of pump starvation in residential pressure washers due to their tendency to collapse under suction.