A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy (hydrostatic energy).
Before we begin our introduction to hydraulic pumps by looking at the different types available, it is worth reminding ourselves how hydraulic systems work and the role that a hydraulic pump plays within the system.
Hydraulic systems are designed to transmit power in a controlled way through the use of pressurised liquids. We can trace the use of hydraulic systems back to the Ancient Greeks, but the father of modern hydraulics is Blaise Pascal, a French mathematician who, in 1653, proved that when there is an increase in pressure at any point in a confined fluid, there is an equal increase at every other point in the container.
Understanding this rule made it possible to design systems that use hydraulics to multiply small forces into much bigger forces. All hydraulic systems are based on this principle.
Pressure can be created in a hydraulic system by the careful design of applied forces and the gauge of pipes. Smaller hoses or pipes increase resistance and pressure – as depicted in this image taken from LunchBox Sessions’ training platform.
It’s a common misapprehension that the pump has a role to play in the pressure of a hydraulic system
However, this is not the case; the pump does not play a role in determining the pressure applied to the hydraulic system. Instead, the role of the pump is to ensure the continued flow of fluid.
You can learn more about pressure and flow in LunchBox Sessions’ online learning. These lessons are free for subscribers to their interactive e-learning platform. Delivered in bite-size sessions, they are a fantastic online resource if you want to know more about how hydraulics and other industrial technologies work.
How do hydraulic pumps work?
Since the function of a hydraulic pump in a hydraulic system is to generate flow, it needs to generate flow with enough power to overcome pressure induced by the load at the pump outlet.
A hydraulic pump performs two functions when it operates:
- its mechanical action creates a vacuum at the pump inlet, subsequently allowing atmospheric pressure to force liquid from the reservoir and then pumping it through to the inlet line of the pump;
- its mechanical action delivers this liquid to the pump outlet and forces it into the hydraulic system.
An introduction to hydraulic pumps and the different types available
There are a number of different types of pumps used in hydraulics: gear, piston and vane.
To explain more about these different types of pumps, we’re going to draw on more online hydraulics training resources from Lunchbox Sessions.
In their images below the colour key is as follows: pink = vacuum pressure | blue = atmospheric pressure | yellow = low pressure | orange = medium pressure | red = high pressure.
Gear pumps are strictly fixed displacement pumps
Otherwise known as positive displacement pumps, gear pumps always displace the same amount of fluid on each revolution and don’t offer any control to change this volume. They either come in external or internal gear design. External gear pumps use two external spur gears. Internal gear pumps use an external and an internal spur gear. Moreover, the spur gear teeth face inwards for internal gear pumps.
The image here illustrates an external gear pump (left) and internal gear pump (right).
Piston pumps, on the other hand, are usually variable displacement pumps
This means that you can change the amount of fluid displaced during a revolution, so you can control fluid displacement even when running at the same RPMs. Variable displacement pumps are well suited in circuits where variable speeds or the ability to reverse is needed.
The image below depicts a variable displacement, pressure compensated piston pump.
Vane pumps can come in two different configurations: variable displacement or fixed
The type of displacement supported by a hydraulic pump is an important consideration which will impact the design of your hydraulic system. For example, if you want to change the displacement in a hydraulic system which uses a gear pump, you will need to change the speed of the prime mover in order to change the RPM of the pump.
The image below is of an unbalanced, variable displacement, pressure compensated vane pump.
If you’d like to access more information about an introduction to hydraulic pumps, we highly recommend that you visit LunchBox Sessions’ website and make use of the fabulous resources available there.
Some of the sessions are free; you don’t need to sign up. However, if you are serious about expanding your knowledge of hydraulic systems, we recommend you consider signing up for a subscription to the entire LunchBox Session service. This way, you get full access to all the interactive training materials, tests and simulations for just $29 per month. Students are entitled to a 60% discount off this price when they share their college or university ID.