Pressure washer pump?

[zmoz]

I was out having a great old time pressure washing the driveway today when I heard a clunk and the engine stopped. Something seized up, either the pump or the engine, not sure yet. I'm guessing it's the pump, since it's a cheap oilless POS...

If the engine is still good, I want to replace the pump with a nicer one. The pressure washer has a 5.5hp Honda and was rated at 2600 PSI and 2.5GPM. I'm looking at getting a Cat pump rated at 4000PSI/3.9GPM. They say it requires 14hp for full output.

Obviously if I attach that to my 5.5hp engine it won't have full power. Does that mean it would still work but at lower pressure? (more like the original) Since I'm buying a good rebuildable pump, it will probably last longer than the engine, which can be replaced in the future with a bigger one.

 

[J_J]

I don't think that 5.5 will run that pump, for this reason. The pump will try and build up to the 4000 psi, and that takes more HP. While spraying, pressure washer pumps never put out the max pressure. When you let off the trigger, that is when the pump will try and build up to it's max pressure, and I believe that it will stall out the motor. The regulator/relief valve will try and relieve.

Even with that 2600 psi pump, that is not the pressure coming out the nozzle. That will be dictated by the orifice of the nozzle. If you put a gage in the system, you can see what is happening.

My 13 HP Honda will run a 3000/4000 psi pump, but ever now and then, it will try and choke out the engine when I let off the trigger.

 

[J_J]

There are ways to trick just about anything, so if you put an extra large nozzle on the end, and adjusted the regulator down to a lower pressure, you might be able to use that pump.

 

[SPYDERLK]

how do you know the pump is oiless. My Karcher that rating has oil. Found out when I took it apart to reseat the valves.
larry

 

[zmoz]

There are ways to trick just about anything, so if you put an extra large nozzle on the end, and adjusted the regulator down to a lower pressure, you might be able to use that pump.

That's kinda what I was thinking...but I guess I don't know enough about it. They say you can use a smaller engine than 14hp and get less output...but I was wondering if the engine would stall. They probably mean more like 12hp.

how do you know the pump is oiless. My Karcher that rating has oil. Found out when I took it apart to reseat the valves.
larry

In the manual it says something about the pump being oilless and "not repairable" or something like that. That's why I want to buy a higher quality rebuildable pump this time. I think they're only supposed to last a couple hundred hours at the most, but mine doesn't even have that much time on it...

 

[rScotty]

If the engine is still good, I want to replace the pump with a nicer one. The pressure washer has a 5.5hp Honda and was rated at 2600 PSI and 2.5GPM. I'm looking at getting a Cat pump rated at 4000PSI/3.9GPM. They say it requires 14hp for full output.

Well lets see....math to the rescue.
theoretical flow HP = gal/min*psi*(7/12000).
Multiply it out as 2.5*2600*7/12 and you get about 4 hp theoretically required to run the pump you've got to its full specs. Throw in an efficiency factor of 70% - which is about right for the various loses and it comes out darn close to 5.5 hp. So that 5.5 hp Honda monster motor should have been able to run that oilless pump to its full specs. and I reckon it did.

So what will happen with the larger pump? Well, those are positive displacement pumps, so the pump has no choice but to pump as much gal/min as it is sized for....but the 5.5 hp motor won't let it both pump that much flow and also develop that much pressure. And unfortunately larger pumps are less efficient than small ones. More like 60%.

You'd best check to make sure that the larger pump has a pressure adjustment. Most pumps do, but it's critical for what you are trying to do. Basically you just start turning that pressure adjustment down until your 5.5 hp Honda will rev out. High flow is less efficient than high pressure, so you will lose about another 10% there. But it should work......it might require drilling out to a very slightly larger orfice on the pressure wand to handle enough flow at a the new lower pressure. Just for ball park I'd say that your existing motor ought to be able to run the larger pump at a little under 1400 psi.

 

[gizmo]

What Scotty said. Also don't forget that the Honda motor speed is set by a governor and not by simply opening the carb. Don't use the Cat pump unless it has a pressure regulator. Start with it all the way open and the motor set to normal running speed, and gradually increase pressure until the motor just starts to drop RPM. At that point the speed governor will be at maximum.

 

[J_J]

That cat 4000 psi pump probably cost more than a new 2600 pressure washer. I don't think you will be satisfied with the results, using that 4000 psi pump on a 5.5 HP motor.

Most all pressure washers have an unloader/relief valve.

 

[zmoz]

That cat 4000 psi pump probably cost more than a new 2600 pressure washer.

Actually they're only a little over $200. I could buy another cheap low quality pressure washer for $3-400, but I already learned my lesson on those...they're cheap for a reason! The only good part of mine was the cart and the engine - now I know why I see so many of those for sale used - no pump!

I'd rather buy a professional ~14+hp washer with a nice pump, but I'm not looking to spend the cash right now. I just need something to finish the driveway, it looks like it's half painted now....

I was looking at another cat pump rated at 2700 PSI that would probably be a direct bolt on for my engine...but it's hardly any cheaper than the bigger pump.

I guess in the end, I'll have to buy both.....

 

[Big Wave D]

If the preceding post and numbers by rScotty is correct:

You'd best check to make sure that the larger pump has a pressure adjustment. Most pumps do, but it's critical for what you are trying to do. Basically you just start turning that pressure adjustment down until your 5.5 hp Honda will rev out. High flow is less efficient than high pressure, so you will lose about another 10% there. But it should work......it might require drilling out to a very slightly larger orfice on the pressure wand to handle enough flow at a the new lower pressure. Just for ball park I'd say that your existing motor ought to be able to run the larger pump at a little under 1400 psi.

I'd say forget it.

I've used commercial 3-4K PSI units, I've used heavier duty home units 2.5-3.2K PSI, and the throw away light duty that just died on you. From the top to the bottom is night and day difference. It's the combination of PSI and GPM that truly make a good Power Washer.

To only get 1400 PSI and spend that kind of money will be VERY disappointing on cleaning performance. The lighter units can't put out the volume of water to wash away effectively what your pressure is removing. Even the heavier home owner units with 2.5 GPM are rather uninspiring in their performance.

Don't buy another cheap washer(whether it is gas or electric) to finish your drive

My real advice would be to rent or borrow one (preferably a true commercial unit so you know what the greener grass is like and therefore know what your future purchase should compare too) to finish and put any real money towards a good used commercial unit that WILL last and CAN be rebuilt.

:2cents: