How to keep pressure washer patio cleaners like the T-Racer working optimally

TL;DR

If you have such a spinny drum pressure washer attachment and it fails to spin its sprayer arm, and you have tried everything except adding a slippery water-soluble substance to the detergent reservoir: try that before replacing or buying new parts, you may be surprised. Just some glycerine diluted with water should already work well.

The Long Story

After working fine for several years, the patio cleaner attachment that came with our Kärcher pressure washer would suddenly no longer spin, or only do so at a very low speed. The result was “line art” on the surface, worsened by the fact that the slowly turning or even stationary nozzles were cleaning the same tiny area ultra-effectively while leaving everything else dirty.

Eventually I managed to restore the attachment to its normal performance, by going through the following steps. The most essential one proved to be the final step, but you should always go through this entire list to rule out every possible problem.

1. The first thing to check is whether the pressure washer itself is not to blame. If it is not delivering the required pressure, the attachments won't work properly. Try the different attachents like the regular lance, and see if it still produces the expected strong jet of water at its maximum setting. If not, the washer itself may need repair.
2. Check whether the attachment's nozzles are not clogged: it will not work properly on a single nozzle. Obviously, do not point the thing at anyone's face, including your own, in an attempt to check this. Best is to just remove and check the nozzles right away. On the Kärcher model, they can be easily removed by taking out the 2 large metal “staples” that hold them in place. Remember how they were mounted, or see the image below. Then pull out the nozzles, if need be with some minor twisting action. You must be able to see light coming through the nozzle. If not, use a fine piece of wire to remove the obstruction, and flush the nozzle with clean water from both directions. Reassemble, taking care to mount the nozzles in their original orientation.
   
3. Take the axle apart and clean it. Dirt, grit, or even limescale may get in between the tightly fitting parts. If you suspect that limescale may have accumulated, soak the axle in some vinegar, and also try to descale the bearing, if need be by inserting a paper towel soaked with vinegar and letting it sit for several minutes. You could apply grease, but this is rather futile as it will be flushed out by water in no time. However, if the cleaner does spin nicely albeit temporarily with some grease applied, you should definitely check the last point below.
4. Replace the axle or whole assembly. This should be a last resort, but may be the only solution if there is obvious fatal wear. However, check the next point first if you don't notice any real damage and wonder why the thing no longer spins well.
5. Add a diluted slippery water-soluble substance to the pressure washer's detergent reservoir. Really, this can work wonders, as it did for me. I tried a natural soap that had glycerine as an additive. Just plain glycerine will probably also work fine. Just avoid using random synthetic detergents. The detergent sold by your pressure washer's manufacturer is probably a good option, albeit likely overpriced as usual. You don't need a lot of the slippery substance. Its only real goal is to make the water going through the system slightly slippery. Of course, using an actual detergent may help with overall cleaning performance as well. Just make sure it feels slippery even when heavily diluted with water.
   Why this works: the Kärcher patio cleaner, and I suspect other models as well, rely on water to act as a kind of lubricant, evidenced by tiny deliberate slots in the gaskets embedded in the axle. Those slots direct a bit of the water pressure around the axle bearing, to prevent the surfaces from touching each other. However, water on its own is not a great lubricant, which is why adding something slippery, even in small amounts, can make the difference between the sprayer arm having difficulty moving or spinning freely.
   It is best to empty the reservoir and run the washer for a while with some plain water in it before storing it for a long time, to avoid that the substance dries up and clogs something.

Even with all problems fixed, washing a really dirty surface may throw up enough dirt that it gets inside the bearing and jams the spinning assembly. Usually, stopping and starting again a few times will clear this. If not, flush the axle with clean water, if need be by using the lance attachment, to clear out the grit. In the worst case you may need to unscrew the axle to clean it.