Hydraulic pumps are very simple and have many uses. The basic design is a piston in a cylinder that applies pressure to an incompressible fluid (usually oil) and transfers the force to another piston doing something useful for you.
The force is usually multiplied so that the second piston can do more than the first. To achieve the multiplication of force, the relative size of the pistons is increased. You can also buy hydraulic pumps through various online sites.
Image Source: Google
The oil shouldn't have any air bubbles in it because using the piston when there is a bubble will lose a lot of energy pushing the bubble instead of moving the second piston, which is an ineffective way of thinking.
Most of the damage to pumps has been caused by oil spills of one kind or another. The oil tank should be made of aluminum or stainless steel to prevent corrosion and reduce the possibility of oil spills.
Some hydraulic pumps are manual and others are driven by compressed air, electricity, or gasoline. Manual hydraulic pumps are great. They are portable because they don't require extra power. They are ideal for random duty, but they don't have the power and speed of the pumps they drive.
Hydraulic pumps have many uses, but if you feel the need to buy your own, make sure you do your initial research and find the one best suited for the job.