The Difference in Pressure Washer Pumps - Direct Drive

Why won't my pressure washer pull from a tank? What do you mean by "Direct Drive?" Why do I keep destroying pressure pumps? Let's talk about direct drive pressure washers and their advantages and limitations. Many companies start out with direct drive pumps, and often times keep them as back-ups in their mobile cleaning business.

However, there are some facts you need to know about these types of pumps before you run out and purchase one. Often times they will not "pull" of draw from a tanks and will need to be force fed from a water spigot. There are also some very simple tips you can do to maximize the longevity of these pumps and gety the most out of them.

Whether you are downstreaming, using and x-jet or justy looking for a pressure type application, these pumps will work.

[GHohn]

One major advantage of the belt setup is the ability to tune the pump speed and engine speeds to operate optimally. This allows the same engine to run a slightly larger pump effectively.

For example, consider little GX270 pulling a Cat 66DX at rated power. With a 3.5gpm pump, it can hit 4000psi. With a 4gpm, it can only hit about 3200psi. With a 5gpm, it's limited to about 2250psi. And if you try to run much higher pressures than those values with those three pumps, you'll pull down the engine speed and reduce flow to where the smaller pump would actually outperform.

The 5gpm CAT is rated 3250 prpm, the smaller pumps are 3400prpm for rated speed. If I ran a belt setup setup on the GX270 to drive the 5gpm pump at 2750rpm while the engine was at 3600, I multiply the engine's torque output by 30%. This will push the 5gpm pump to 3000psi, but at the reduced flow of 4.25gpm. A minor improvement over the 4gpm pump, but still an improvement.

But the real advantage is the ability to target a peak pressure range (torque) and optimize flow for that. Say your sweet spot is 2500psi. Cat says that at this pressure the 5gpm DX66 needs 13.8lb-ft. Which means the 12.8lb-ft of the GX270 needs another 10% more torque, roughly. So you setup your GX270 on a 10% underdrive and get 14lb-ft to the pump at 3240pump rpm. The pump's rated speed is 3250rpm.

Presto, you have a 5gpm setup with usefully sufficient pressure (2500psi) running off a GX270! Remember, you can reduce pressure with a larger nozzle orifice, but you cannot increase flow. A belt setup lets you tune the drive ratio (via pulley sizes and belt length).

So if you are running a setup that is capable of 4000psi, you are wasting engine power to hit a potential pressure range you almost certainly don't need. And you are giving up GPM that you actually DO need to get it! That's not a good tradeoff.

Not all "cleaning units" are the same. Once you have enough pressure, you have enough pressure. More pressure won't clean more effectively or faster. Flow will. I'd suggest therefore that you consider something like 3000psi to be a hard ceiling of capability you do not want. Get all the flow you can that still lets you pull 3000psi. Or 2500, or whatever your personal experience suggests is the most pressure you need.

[dbac]

This is exactly what I needed. Thank you

[scottspooner]

The problem with the direct drive is RPM's. If the pump max rpm is 3500 and the 14hp engine runs at 5000 rpm's it will kill the pump. That's why a 2 for 1 gear reduction box is so important.

[DETAILINGDETAILING-hbbj]

Thanks for post - if possible could you create a tutorial video setting up (external/12V) pump, and fittings to pressure washer? finding proper fittings seems to be most issue from 1/2 to 3/4

[kdalbakri]

Thank you Sir for this useful information

[improvementoptions]

My maintenance personnel adviced that I should just tie the trigger permanently, to save my pump, and off engine at any slight stop.

[kkutube]

Once you go to commercial grade, very hard to ever go back to regular.

[SOB_]

I just installed the General Pump EZ4040G on my Honda GX390 and when I pull & let go of the trigger the seems to want to cut out. What PSI is the pump rated?

[gopowerwashatl]

Instead of adding a 20ft hose and running it into a tank could you disconnect one end of that looping hose and let the water run out on the ground? If so, wouldn't the water coming in from the garden hose or tank run out where you disconnected the hose? You didn't mention what to do there. Should there be a plug to put in place of where the hose was? I'm new to this and I have a direct drive pw with a pump that looks like that one. I want my pump to last as long as possible. 🙂 Thanks for your feedback in advance.

[dtman]

How much does that exact pressure washer cost?

[rubenguerrero]

Not true, I’ve made several different direct drive pull from a tank no problem, you just have to know what your doing.

[chad]

You seem to be confusing "direct drive" with positive displacement pump (the pump type in your video), in your tutorial. The drive input does not determine what kind of pump it is, only what type of input it has.
The drive input has little to do with whether a pump will gravity draw its water, that's determined by your pump/tank set up. I've had experience with both Direct drive and centrifugal pumps for almost 30 years, using hundreds of pumps and have NEVER had a pump not draw from a tank because I understand how gravity works.