So you need to use a higher volume of water to clean your car/porch/elephant than your machine can currently handle. The solution: A bigger pump. The problem: You don’t know if it’s possible.

**You can replace the pump in your pressure washer with a larger pump without damaging it. However, if you want it to perform at the same PSI it did before, you will also need to replace the motor with a stronger one.** **Otherwise, you risk damaging both the motor and the pump.**

Sounds expensive, but it’s a better answer than no, right? So how do we figure out how much horsepower we need to keep our current PSI?

## Why Does It Work?

In order to talk about why the different parts of a pressure washer are so interchangeable we need to talk a little bit about how the machine works as a whole.

**Pressure washers are actually not terribly complicated on the the whole. **Essentially, there are four parts to it that affect whether and how well it will work.

The first and possibly the most important is the pump. The pump works in about the same way as a hand pump for a well would. It draws water in and then quickly pushes it out to create the effect of shooting pressurized water.

The pump determines how much water will be used each minute. We measure this number in Gallons per Minute (GPM). **It is the pump which determines GPM, not the motor.** This is because GPM is mostly a function of how large the pump’s chamber is.

The motor is what makes the pump able to push hard enough and quickly enough to pressurize the water. The maximum PSI that a pressure washer is able to put out is a combination of the Horse Power (HP) of the motor and the GPM of the pump.

The other two parts are the hose and the nozzle. These don’t really effect things like GPM or PSI, but that doesn’t make them unimportant.

**If you change the size of your pump, you will need to get a new nozzle to compensate for the increased flow rate.** If the hose or the nozzle break, then no matter how big your pump is your machine will still be useless.

## Figuring Out What You Need

So how do you know what you’re going to need to run your pressure washer optimally? Well, unfortunately I can’t actually tell you how much GPM you need to wash your elephant.

But since you are the one who sought this article out and decided to read this far, I figure you probably already know what you need on that front.

The hard question is **how much Horsepower do you need to keep your current PSI running**. That’s something I can help you with! And actually, once we know how to do that, we can use the same formula to learn a bunch of other really useful things.

So here we go. The equation that we use to figure out the amount of Horsepower we need looks like this:

**[(PSI * GPM)/1450] * 1.5 = HP**

Yeah, I know. It’s incomprehensible. Fortunately, the only work that you need to do is to plug in the numbers for what you already know (the PSI that your washer works at and the GPM your new pump can do) and then have a calculator do the rest.

Trust me, I wouldn’t touch these calculations with an eighteen foot pole unless I were doing it for you beauties.

We can re-arrange this equation for even more utility though. If you want to figure out how to get to a certain PSI, you can use this formula:

**[(HP/1.5) * 1450]/GPM = PSI**

With this equation, increasing the GPM will usually decrease the resulting nummber, while increasing HP will increase it. If you want to solve for GPM instead, you can simply switch its place with PSI for a formula that looks like this:

**[(HP/1.5] * 1450]/PSI = GPM**

You can use this formula if for some reason you want to figure out what GPM you need to prevent your PSI from rising when you increase your motor’s horsepower. Why would you do this? I don’t know. But with this formula, you can figure out what you need to do it right.

## How Big Can The Pump Get?

A quick search for the biggest pump that you can attach to a pressure washer doesn’t yield any reasonable results that answer the question, so I think that we can safely assume that the largest pump that you could possible turn into a pressure washer is the same as the largest possible pump.

This is good news if your goal is to build a pressure washer that can move all of the water in the ocean to the moon. The GPM you’d need has got to be pretty high, since if Superman catches you before you’re done he’ll probably try to stop you.

**The largest pump in the world is the Pentair Fairbanks Nijhuis HP1-4000.340 in The Netherlands**. It’s currently used to prevent the country from flooding by taking the seawater that’s trying to get in and pushing it back out into the ocean.

It operates at about 951,019 GPM, using a motor with 5,364 HP. Using our formula, **we can determine that its PSI is somewhere in the ballpark of 5,277,171 (if we attached it to a pressure washer hose.)** Is that enough to send water to the moon?

Escape velocity on Earth is 11.19km/s. That’s pretty fast I guess. We don’t need to worry about many variables here, since we will be using a chain of 50,440,000 twenty-five for hoses to reach from the surface of the ocean to the moon.

We can figure out the rate of acceleration that we can get from the device using the PSI and then the Force formulas.

This is a lot of math, so the quick version is we end up accelerating our water about 18.2 km/s after accounting for gravity (I’m not a physicist, I’m probably wrong about this.)

**This is fast enough to increase the speed of the water to escape velocity in less than a second**, meaning that if you were to hijack the PFNHP-14000.340 and attach it to a hose that goes from the pump to the moon turning it into a giant pressure washer, you might be able to move a significant amount of seawater before Batman shows up to stop you.

Hopefully you’ve planned ahead to stop any pesky superheroes from stopping your entirely innocent plan.