Generally, the first step in troubleshooting a surging pressure washer is to check the spray nozzle for dirt. Check the unloader valve for damage or trapped air to see if the nozzle is okay. Check the hose and filter for any leaks or restrictions. If there are none, check your pressure washer's water supply and valves.
Try keeping your pressure hose in a straight line. Make sure there is no loops or wraps in the hose. This creates resistance and may give you this issue.
As the pressure drops off, the valve head in the pressure washer shuts down momentarily until it builds up the pressure again. This is why it appears to pulsate with high and low pressure.
There's a screen where you hook the hose up. Make sure that is clean. Before you hook the hose up run the water for a bit to burp any air out. Once you hook it up hold the trigger on the wand to push out any more air.
If your electric pressure washer turns on and off, a bad unloader valve is probably why. In almost all of the latest models, it is located on the top of the electric pressure washer's pump system. Most times, it has a black handle on top of it.
Common causes of pressure washer surging/pulsing
Kinks and blockages: These can restrict the flow of water, resulting in inconsistent pressure. Plugged nozzle: Over time, debris can build up inside the nozzle, causing it to become plugged and disrupt the water pressure.
If the pressure washer starts and then stalls during its use, first check if the nozzle is clogged and clean it if necessary. If the pressure washer turns off during prolonged use, the problem could be related to motor overheating or a power interruption.
The number one cause of low or no pressure when using a pressure washer is a blocked or worn nozzle. Blocked nozzles will prevent water from escaping, while a worn nozzle will allow too much water to pass through, causing the pressure to drop.
If the valve sticks in the closed position, the thermal relief valve frequently discharges hot water onto the ground because the unloader valve can't open to allow recirculation. If the pressure washer doesn't develop adequate outlet pressure, the unloader valve could be stuck open.
When the pump is pumping faster than water is coming into the well, the pump will quit delivering water until the water rises in the well. Then the pump will start pumping water again causing it to surge.
Is the pump running? The pump may turn on and off several times with very short pauses causing a pulsing sound. This is part of normal operation.
Dirty filter: the filter of your high-pressure cleaner may be dirty or clogged, preventing the smooth flow of water and thus affecting pressure. If you hear strange noises coming from the high-pressure cleaner when in operation, it may mean that the filter is dirty and is causing little water circulation in the system.
Ensure the faucet is fully open, and review and tighten all connectors. If your pressure washer is still pumping, check and remove air trapped in the pump and hose. Check and clean the nozzle, various filters, and the unloader valve.
Your problem is likely that your friend's pressure washer valving is designed for higher flow (less backpressure) nozzles/wands/attachments than your foam cannon. This creates a cyclic feedback loop in the system which is manifested as surging.
As explained above, extended periods in idle can cause damage to the seals, leading to leaks, pressure loss and premature wear of the pump manifold. Shutdown timers prevent unnecessary wear and tear by shutting down the machine after a specified idle time.
Depending on the size of your commercial-grade pump, a full replacement can often cost up to $1,000+. If you can get by with just a repair, expect your cost to be closer to $150 to $300.
Remove any trapped air in the pressure washer by running water through it prior to starting. Trapped air can significantly reduce pressure to the pump. If the pressure appears to be fluctuating, there may be air trapped in the pump.
A Worn Nozzle
Using an old, worn-out nozzle is a common cause of lost pressure. Luckily, it also has one of the simplest fixes. All you need to do is replace the nozzle and make sure you're using the proper size. Don't go by the color of the nozzle; make sure you check the orifice size.
Often times, a machine producing low pressure will surge, cycle on and off, or continue to run. This typically indicates that the machine is losing pressure somewhere, such as a leak in one of the lines or inside the case of the machine.
If the pressure washer is not new, turn off the pressure washer and disconnect the water supply hose. Hold the trigger on the spray gun or wand to release any remaining pressure in the system. Reconnect the water supply hose and turn on the water supply to purge any trapped air from the system.