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Basic Guidelines for Hydraulics for Beginners

If you’re fairly new to the area of hydraulics or you have an intern working with you then you may find the following information useful to read or share with others.

Before we get started – hydraulic principles are not easy or straightforward until you’ve delved in and learnt a few things. Fluid dynamics, hydraulic mathematics, circuitry and related matters can be downright complicated and that’s why it’s necessary to share information of the type that you find in these blog posts. Goodness knows what any of us did prior to the development of the internet. We would have had to go out of our way to build relationships with others in the industry in order to have free access to their knowledge.  But we do have access and thank heavens for that.

With much gusto, let’s look at the basic fundamentals of hydraulics.

It was knowledge founders such as Newton, Pascal and Galileo who first discovered phenomena that was considered interesting, and actually formed the basis of some of what we know today. Way back in 1650 Pascal came across and then formalised the ‘Law of Hydraulics’. It took another 150 years to actually start using and applying that knowledge for practical purposes.

Hydraulic devices operate based on his law which states that confined liquid will carry the power of any external force that is exerted upon it. So much so that it will be carried to every part of the interior of the vessel that liquid is in.  

When a hydraulic pump is in use by a mechanic and he is exerting force to confined liquid, then that power will be transmitted through the liquid, whether it’s in a pipe or a hose right up to the piston which will then be forced to move.

Although what you read above is a simplified version, today’s hydraulic machines use the exact same principles, but the mechanics may be replaced by an electric motor or even a gasoline engine. There could be more hoses, some relief and check valves to go through on the way. There could even be a few return lines and a reservoir of fluid to cross. Whatever the case, the action and the result remains the same; movement.

When it comes to how much force is either input or output from devices of hydraulic nature, a pressure measurement is used. This is recorded in the format of pounds per square inch, or psi.

To put this into perspective, 1 psi is equal to one pound of weight put onto an area of 1 square inch.

If 10 pounds of force were put onto 10 square inches, then the result would be the same – 1 psi. If there is a liquid pressure creating a force against a piston then it will be measured either in tons or pounds. A pressure of 100 psi on a piston that has an area of 10 sq inches will be 100 psi x 10 (square inches) or 1000 pounds.

Although there will not be a lot of fluid displacement when a small piston is pushed down in the pump cylinder. Therefore, it will only be enough to move the larger piston a little or short distance. Although a large advantaged is gained in terms of force, there is not much advantage in ‘distance’.

This can be illustrated as follows. Imagine a man pushing his hand against a wall. He can push as much as he likes, but the wall is going to be opposing him with resistance. Without that resistance he would not be able to push, as his hand would just move through the air. This is something that applies to hydraulics too. Without the same resistance, there won’t be the expected result. For example, although a pump might be rated to deliver an output of 10,000 psi if it doesn’t meet with an equal resistance from a cylinder, it won’t output that 10,000 lbs of pressure.

When it comes to hydraulic pumps, there is a variety of different designs including:
·   Piston pumps
·   Vane pumps
·   Gear pumps

When it comes to cylinders, you can expect to come across:
·   Spring return
·   Gravity return
·   Double-acting
·   Single-acting
·   Pull-type
·   Push-type

Valves are also is use, and this is what performs the large variety of functions that hydraulic machines are capable of.

For example, the lowering and raising of a barber’s chair, brakes in cars, the hydraulic raising and lowering of the landing gear in planes and even the jack that is used by many lay persons and mechanics to change the tyre on their car.

Years ago, low pressure is what was popular and in use in hydraulic systems, but these days there are far more high pressure hydraulics being utilised. Strangely enough the safety factors involved are similar, with higher pressure ranking as being slightly safer than lower pressure. The largest benefit of using high pressure equipment is that it is usually smaller compared to a lower pressure device, but will deliver the same amount of force.

This has been a rather eclectic collection of facts about hydraulic systems, but together they should give a deeper insight into how this very clever power delivery system works.

Keep following our blog for more insights into hydraulic systems.


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