Determine the gallons per minute (GPM) rating for your hydraulic system. Most basic systems will have pumps that move from .5 to 1 gallon per minute. If you have additional equipment or clamps attached to the unit or you have an increased capacity, this may increase or decrease slightly, depending on the tax of these additional pieces.
Note the size and power of the motor in your hydraulic system. The horsepower of the pumping unit will be the primary element that determines the pressure needed for your hydraulic system.
Measure the size of the pump reservoir. This is typically anywhere from 1 to 5 gallons in capacity. The reservoir capacity will not only help you determine the hydraulic pressure needed, but it will also indicate just how long your hydraulic system can work without being depleted.
Review the instruction and owner's manual for your particular hydraulic lift system. These documents have important data about your specific machine's pressure requirements and should be your primary information source for all adjustments to your lift. For instructions, you can also try Autoquip, a major retailer of hydraulic lifts that has a special literature page with manuals in PDF format (see Resources below).
Maintain relief-valve settings. These settings are set by the manufacturer to specific design and code requirements, so adjusting them can destabilize the entire system.
Calculate the compressibility of the fluid you are using. You should always use the specific fluids outlined in the users manual of your hydraulic system for best performance. However, if you find it necessary to use some other fluid, you can use a relatively simply equation to determine the compressibility for your hydraulic system. You can find this equation, along with many other useful equations, in the Precision Fluid Power website glossary (see Resources below).