What Does Pressure Capacity Mean in a Power Steering Pump?

Pressure, and the term “pressure capacity” are widely misunderstood in the power steering world. There is also a lot of misinformation about how pressure works, what it controls, and why you should be thinking about changing the pressure capacity in a power steering pump. We’ll deep dive into pressure in a later post, but for now, let’s look at the basics of pressure capacity and pressure output.

What is Pressure Capacity?

Pressure capacity simply refers to the maximum pressure the power steering pump is allowed to build. Most factory pumps have a pressure capacity set to around 1200 psi. That doesn’t mean that they are always operating at this pressure, it only means that their maximum pressure output is 1200 psi. A pump set to 1800 psi capacity therefore means that the pump is now allowed to build more pressure, if needed.

How Does Pressure Output Work?

Here is where the internet is largely wrong about pressure. Pressure is not a constant output – it is variable. This means the pressure output of a pump is constantly changing as you drive. The pump builds pressure in response to hydraulic load on the steering box (or rack and pinion). So even if you are running at high rpms, but going straight down the road, the pump is barely building any pressure. It doesn’t need to because you, as a driver, don’t need any steering assist.

Compare that to when you throw the vehicle into a very tight, hard corner. The pump pressure output spikes in this condition – again, it is responding to increased hydraulic load on the steering gear, since you are trying to turn the wheels while there is also a lot of grip on the front of the car. The pump pressure spikes so that you maintain steering assist in the hard corner. Once you straighten the vehicle out, the pressure backs off again.

In summary, the pump is never building more pressure than what your vehicle needs. The pump self-regulates its output!

Why You Should NEVER Lower Pressure Capacity

We hear A LOT from people who want to lower their pump’s factory pressure capacity from 1200 psi into the 800 psi range “because my rack can’t handle the higher pressures.”

Any normal OEM-grade steering rack was designed to handle pressures that far exceed 800 psi. If indeed you’re buying a rack that can’t handle even standard factory pressures, then I would look closely at the quality of rack you are purchasing, it may not be a very good investment. And as I just mentioned above, the pump is not always outputting it’s maximum pressure. The pump is already self-regulating it’s pressure output. The pump would only output 800 psi if the rack actually needs 800 psi as you are cornering.

Why You Might Actually Need MORE Pressure Capacity

With today’s restomod and protouring builds and custom vehicle work, it’s a very common to see vehicles that actually benefit from have a pump with a higher pressure capacity. Why would this be necessary or recommended, though?

Vehicle changes, along with driving conditions, change how much force is being applied to the steering gear. Vehicle changes like wider, grippier front tires means that more force is needed to turn the tires. Therefore increasing tire width, changing compounds, dialing in your suspension for better cornering, castor/camber adjustments, adding front downforce or adding a hydroboost system are all changes that mean the pump HAS TO output more pressure to overcome the increase in cornering grip.

The same goes for driving conditions. If you’re street driving, the cornering loads aren’t as high as if you take your car to the local racetrack for track days and start driving hot laps. The hard corning means the pump is outputting more pressure in corners to ensure you’re getting steering assist.

Now that we know vehicle changes + driving conditions can influence pump pressure, you can understand that factory pumps aren’t always up for the job. Even C5 and C6 Corvette pumps had standard tuning of regular passenger cars – they were tuned for street driving. Some vehicles simply need a pump tuned to handle the significant increases in corner grip – which means the pump needs to be able to output higher-than-factory pressure at times.

Need More Assistance?

If you’re still not sure how this directly applies to your vehicle setup, please don’t hesitate to contact one of our Sales & Technical Support Representatives, who will be happy to talk through your specific setup and make power steering recommendations. You can also fill out our online Custom Pump Submission form to get pump recommendations emailed you to.

Stay tuned for more posts related to pressure!