How Do Hydraulic Pumps Work?

What exactly does a hydraulic pump do? You clearly know what it is, else you wouldn’t be here. Every hydraulic system has to have some sort of pump, or all it would do is just sit there. But what exactly does it do, and how do hydraulic pumps work?

A hydraulic pump creates flow in a hydraulic system. It’s commonly mistaken that the pump creates the pressure in a system, but pressure is really just a by product of having flow (usually measured in gallons per minute). The pump simply generates flow, and the size & speed of the pump determines how much fluid it can move. If a pump is moving fluid through an open system with no resistance, there would be no pressure, but pressure is created when a load is introduced. If you are familiar with electrical systems, there are a lot of parallels to hydraulics. Flow (GPM) would be similar to voltage, while pressure (PSI) would be the equivalent of amperage.

Types of Hydraulic Pumps

There are several different types of hydraulic pumps, mainly gear pumps, vane pumps, piston pumps and hand pumps. Each type uses a different method to deliver the same effect but are typically used for different applications, as they have different attributes.

Gear Pumps

(Click to see animation) Photo courtesy: Wikipedia
How a gear pump works. Gear pumps are the most common & versatile of all types, typically having the widest range of uses and are economical & efficient. They work by meshing 2 gears together which creates flow by causing lower pressure on one side. I would compare a gear pump to the good old combustion engine. Maybe a little noisy & may have a bit more vibration, but reliable, efficient and easy to maintain.

Vane Pumps

Vane pumps use a series of “fins” or vanes to create flow. The fluid is swept around a crescent-shaped housing cavity and flow is created by the difference in volume by the variation in the housing. Vane pumps are typically smoother & quieter than gear pumps, so they commonly work well in industrial systems and hydraulic units that will be used indoors. They have no metal-to-metal contact & self-compensate for wear, since the vanes self extent to fit the housing. They are also very effective in fluid transfer, thanks to excellent suction characteristics.

Piston Pumps

Piston pumps are typically much more complicated and are often available in wither fixed or, commonly, variable displacement configurations and with pressure compensation. These are big words that mean that piston pumps can usually adapt to the system pressure, providing maximum efficiency and flexibility. They are often used in “closed center” systems where the pump displacement varies to meet the needs of the work being done. Piston pumps use a “swashplate” to move the pistons and the angle of the swashplate & bore of the pistons determines the displacement. Variable displacement systems are beyond the scope of this article, but will be covered in an upcoming post. Pressure compensation regulates outputs in response to variations in the system. Piston pumps are typically the most efficient type of hydraulic pumps.

Those are the main types of hydraulic pump used in mobile, industrial & agricultural hydraulics. There may be a few other types, but this covers about 99% of all pumps being used out there. Each type has it’s own strength/weaknesses & are available in a variety of configurations, especially when you consider that there are double & triple pumps that use these same principles. So now you have a pretty good idea of how hydraulic pumps work.