Pressure washer nozzles, how to decrease pressure?

great white

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This is kind of a hydraulic quesion, so this seems like the right forum. the mods can feel free to move the thread if it's not the right place.

Several years ago, when my Dad passed on, I inherited his old pressure washer. I had to clean it up and set some things right when I got it as Dad was a "use it until it ides and buy another one" kind of guy. I doubt he even changed the oil in the years he owned it. He didn't use it much, but every year he would just push it into the shed and leave it there in freezing temps. I still don't understand how it didn't freeze and burst, but it's still working today so it must be a fairly tough little thing.

When I got it I did the required maint and then just used it, figuring it wouldn't last much longer. I've used it for about seven years now and this year, I decided to give it a little "refresh" beyond the seasonal maint. I took it apart, cleaned it up and did all those little things like required seasonal maint, touched up paint chips, cleaned out the mud wasp nests in the cooling fins, ultrasonic the carb, painted the muffler shroud etc. the engine internals and pump I left alone. Working fine, no need to pull it apart and jsut incur added costs for nothing. Besides, it's old enough now that I didn't want to risk ruining some "unobtainable" part from inside it.

It's nothing special. Somewhere around 20 years old and (at the time) an entry level K'Archer G2000Mk. Gas engine, 2000 psi, 2.0 gpm.

Cleaned up:

fr_4431_size1024.jpg

As it's given me reasonable service over the years, I decided to "kit it out" a little more. I added a 50 foot "Flexilla" hose and a new gun/wand. I also added some quick connects as well as buying a "foam cannon" and an undercarriage washer.


But, Seems I didn't pay attention when ordering the new gun as it came with 4000 psi nozzles. On anything besides the "soap" nozzle, the pump will run for a short while and then the overloader valve in the pump will pop. It will cycle though the pump for a few seconds and then build pressure again. the cycle will repeat every minute of so. 20-30 seconds or so.

Can be a little bit of an annoyance, but more importantly, not good for the pump.

I can get the overloader to stop it's cycling by reducing the engine rpms (and reducing he subsequent pressure in the pump), but running a small engine on less than the spec'd rpms isn't a good idea with it's simple splash lube oil system. I'd rather keep it running at the spec'd 3400 rpm (governed) rather than risk it not lubing itself properly. It's made it this long, last thing I want to do is spin a rod bearing surface or something like that. .

The foam cannon and the undercarriage washer are no problem. They don't build a lot of pressure on the pump because they are such high flow.

I've found a website with a chart specifying nozzle diameter per flow rate/pressure and it seems I should be using a 0.043" orifice.

Charts are here: https://www.ultimatewasher.com/nozzles-size-pressure-washer.htm

Seems a 4000 psi nozzle at roughly 2.0 gpm is 0.034".

It also appears these newer style interchangeable nozzles don't come as low as 2000 psi in my little unit's 2.0 gpm rate. Or at least I can't find any down around 2000 psi that use the 1/4" connectors on the newer guns/wands.


So, now we get to the questions:

Anyone think I can chuck the nozzles up in my mill and enlarge the orifice to the 0.042/0.043" I need for my Dad's little pressure washer?

If yes, would a drill be sufficient or should I ream? Can you even get a reamer that small?


I do have two sets of the 400 psi nozzles (the foam cannon also came with a set of the same nozzles). I guess I could sacrifice one set to see what happens....
 
OI used to work on carwash pumps (a long time ago) and one thing I remember is that the nozzles (that I worked with) were hardened.
 
Looks identical to the one I just scrapped out . Mine froze and blew the pump out . I kept the Honda motor as it runs great still . I would think you could drill the holes out , and yes , they make reamers that small .
 
Hmm, looking under the lighted magnifier, it seems the orifices might not all be round. which would make sense as they do produce different spray "cones".

So it may not be as simple a matter as I thought to increase the orifice size with a drill/reamer.

Off to continue searching for a set of 2000 psi nozzles.....
 
Anyone think I can chuck the nozzles up in my mill and enlarge the orifice to the 0.042/0.043" I need for my Dad's little pressure washer?

If yes, would a drill be sufficient or should I ream? Can you even get a reamer that small?


I do have two sets of the 400 psi nozzles (the foam cannon also came with a set of the same nozzles). I guess I could sacrifice one set to see what happens....
Nice restoration!

With regard to modifying a nozzle, it would be easier to center in a lathe than a mill. More importantly, just increasing the orifice diameter probably isn’t going to do what you’re looking for: nozzles are not simple devices and the relationships between the hole size and location & angle of the slot can be critical.

Check out Spraying Systems, they probably have a nozzle in stock that will work. While it has been decades, they were always very helpful recommending what I needed for a specific application, even if it was just one or two nozzles.
 
Hmmm, further internet reading seems to indicate I'm not really understanding how the nozzles work. It seems that the rating on teh nozzle is a maximum, not what pressure it builds in the washer pump.

That woudl seem to indicate that perhaps my G2000 is running over the rpm it should and building too much pressure, kicking the overloader into action. I can choke the engine to reduce the rpm (has no throttle on it, it's all out or off) and the overloader valve doesn't activate.

I've checked the RPM with my "sirometer", but perhaps I wasn't reading it right. Planning to install an hour meter/rpm gauge on it anyways. I have a couple of the "tiny tach" style ones laying around so might as well toss on on it and see what I get.....
 
Northern Tool has a fantastic selection of nozzles! Plenty of on line vendors too.
 
My interpretation of the charts is a bit different. As I see it the lower the pressure the pump puts out the smaller the nozzle orifice has to be for the machine to reach the rated pressure. The larger the nozzle orifice allows a larger volume of water to flow through thus not maintaining enough back pressure for the pump to reach the rated pressure. A higher pressure/capacity pump can maintain the rated pressure with a larger orifice.

I'm guessing you have internal pump problems. I have 2 pressure washers. The older electric one is about the same age with close to the same pressure and volume rating as yours. It started having problems a few years ago. When I tore down the pump It was obvious what happened. Pumps of that era have ceramic coated steel pistons. Over time the ceramic wears and starts to chip off. The chips get caught in the valves and either hold them open so little pressure is developed or clog the ports. When the ports are clogged the pump reaches the overload pressure in short order. Then the motor idles down.

I ended up replacing the pump with a General like this:

At first, I thought about rebuilding the pump. I contacted General for a kit and was advised that they did have them, but I should completely disassemble the pump before ordering one. If the cylinder bores showed any signs of scoring the kit would not last long. I did as suggest and found the cylinders were a mess. Rather than throw good money after bad I bit the bullet and ordered a new pump. Unfortunately, today they cost close to $750.00 a copy. That's more than double the price of a few years ago. I'm sure you can replace the entire unit for far less.
 
Are you triggering the gun when the unloaded is cycling? Or is it when the machine is simply running standby?
 
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