How Do Hydraulic Pumps Work?

Hydraulic pumps are extremely useful in business applications because they have the ability to convert mechanical power into hydraulic energy, which consists of flow and pressure. The pump itself will generate sufficient flow to overcome any pressure that is induced by a load right at the pump outlet. Most hydraulic systems in operation today require the use of hydraulic pumps so as to accomplish tasks necessary for the machinery that they drive.


Hydraulic pumps – what are they?

A hydraulic pump is a device that converts mechanical energy from some moving agent (like a truck engine) into hydraulic energy, which can then be used by some kind of system. Hydraulic energy results when pressure and flow are applied by actuators, which can then be harnessed to perform useful tasks. Hydraulic energy is a combination of both flow and pressure, and unless both are present, no work can actually be done. Ordinary flow would have no energy behind it to move fluids, and standalone pressure would just be trapped fluids, so it’s clear that the two must work in tandem in order for any useful work to be accomplished.

The function of a hydraulic pump is to push against fluid and cause it to be moved through some type of machinery until it actually moves against actuators so that some kind of load can be driven. A hydraulic pump might be pushing on ball bearings, sand, or any type of solid medium that has the ability to assume the shape of its container so that the net result is force being transmitted.

This transmission of force is the essential core of hydraulics, and as any student of hydraulics can tell you, pressure is the force that makes something move, and flow is simply the rate at which pressure is created. Pressure will generally rise as high as it has to in order to overwhelm resistance downstream, but it’s good to keep in mind that if pressure doesn’t start at the pump, the fluid will then move backward.

As it relates to hydraulics, pressure is a perfect example of Newton’s Third Law of Motion, which states that every action has an equal and opposite reaction. In this case, the opposing force might be a flow control or possibly some kind of loaded cylinder, and it doesn’t make any difference to the pump as to which it is.

The pump will continue to move fluid in accordance with rising pressure so that resistance can be overcome. This is true even if the prime mover ends up being overloaded, or if it causes something to simply blow up. The key point to remember in all of this is that all energy originates from the pump, and once this is understood, everything else about a hydraulic system will begin to make much more sense.

How do hydraulic pumps work?

During normal operation, a hydraulic pump has two functions, the first of which is to create a vacuum at the point of the pump inlet, thereby allowing atmospheric pressure to push some type of liquid from a tank or reservoir into the inlet line and up to the pump itself. The second function of a hydraulic pump is to deliver that liquid to an outlet, which then forces it into the entire hydraulic system.

A hydraulic pump does not generate pressure of any kind; it merely produces flow, or liquid movement. That flow is necessary to create pressure, which functions as a resistance to the flow of fluids throughout the system. This means that the pressure of fluid at the pump outlet itself is zero when the pump is not connected to any kind of load.

When the pump does deliver to a specific system, the pressure will only increase to whatever level is necessary in order to exceed the resistance of the load. All hydraulic pumps will fall into one of two categories: positive-displacement pumps or non-positive-displacement pumps. The vast majority of pumps that are currently used in most hydraulic systems today are of the positive-displacement variety.

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Hydraulic pump types

The most popular types of hydraulic pumps used in most hydraulic systems today are gear pumps, vane pumps, and piston pumps. All of these pumps will either be uni-rotational or bi-rotational in nature, referring to their ability to operate in either a single direction or both directions of produced by shaft rotation.

Gear pumps are commonly used in truck-mounted hydraulic systems. Because they have fewer moving parts, they are easier to maintain, and they’re much more tolerant of contaminants. On top of that, they’re also fairly inexpensive, which makes them appealing to a great many users. Gear pumps are rated in terms of their maximum pressure rating, their maximum input speed rating, or their cubic inch displacement.

Piston pumps are often used in high operating-pressure systems because they can withstand those higher pressures better than gear pumps. The downside of using piston pumps is that they generally cost more, and they don’t have the same kind of resistance to contamination as gear pumps do. They are often used in applications such as snow and ice removal or on truck-mounted cranes because these are situations where it will often be necessary to modify system flow while maintaining engine speed at a constant. There are more moving parts to piston pumps, and that makes them somewhat more difficult to maintain and service, but they are invaluable when high operating pressures are necessary.

Vane pumps are small displacement pumps that are most commonly used on utility vehicles. However, they are less popular today than they once were, because many applications now use gear pumps in their place. Vane pumps operate by having the input shaft rotate, which causes oil to be picked up between the vanes of the pump, and that oil is then pushed to the outlet side of the pump.

Final Thoughts

It can be somewhat confusing when you try to understand the precise nature of hydraulic pumps in any kind of hydraulic system. However, if you keep in mind that all hydraulic pumps have two functions — create a vacuum and deliver liquid to an outlet — you’ll be well on your way to understanding their operation.

There are a wide variety of hydraulic pumps in operation today, only a few of which have been described in this discussion. Because there is such a tremendous range of operating conditions, however, there will always be a need for a diverse number of hydraulic pumps to satisfy those particular business requirements. Be sure to learn about the types most relevant to your business’s needs!