Driven by electricity, gas or powered by hand, hydraulic pumps turn mechanical energy (speed, torque) into fluid power (flow, pressure). They are often used in hydraulic machines to open, close, lift, lower and move components.
Hydraulic pumps are either uni-rotational (they operate in one direction) or bi-rotational (they can operate in either direction). There are three main types of hydraulic pumps used for mobile hydraulic applications including gear pumps, piston pumps and vane pumps.
The basic types of hydraulic pumps include:
Hydraulic Piston Pumps
Piston pumps are capable of withstanding large volume flows and high hydraulic system pressures. Piston hydraulic pumps can operate at such high pressures due to the outstanding sealing properties of the pistons and low fluid leakage. Often used in the construction and marine industries, piston pumps tend to be more complex than gear pumps as they feature more moving parts and have more stringent filtration requirements.
As their name suggests, piston pumps feature sliding pistons that utilise movement to transport fluid from the supply port to the outlet port. The length of the stroke of the pistons is determined by the angle of the swash plate that they move against.
There are two types of piston pumps: fixed displacement pumps and variable displacement pumps. In fixed displacement piston pumps, the swash plate is non-adjustable. Just like in gear pumps, fixed displacement pumps are usually used in open centre hydraulic systems since they feature an output flow that is proportional to the input shaft speed.
Normally utilised in closed centre systems, variable displacement piston pumps feature an adjustable swash plate. If more flow is desired, the swash plate can be adjusted to increase the pump displacement and piston strokes. This type of piston pump is often used in situations where it may be beneficial to change system flow without changing engine speed, such as ice and snow control. Variable displacement piston pumps can be flow compensated, pressure compensated or both flow and pressure compensated.
Hydraulic Gear Pumps
These gear pumps use the movement of interlocking cogs and gears to transfer liquids such as oils or even highly viscous fluids. They are simple in design and require little maintenance.
Usually used in open centre systems, hydraulic gear pumps are both economic and easy to use, a factor that makes them one of the most popular pump types on the market. They are designed with few moving parts and are simple to service. In addition, they operate well at pressures of around 210 bar and can reach speeds in the vicinity of 3000-6000 rpm.
Gear pumps work by trapping fluid in the teeth of the gears and the body of the pump. They then transport the liquid around the meshing gears, forcing it through the outlet port. Gear pumps are classified as fixed displacement pumps (they are also sometimes called positive displacement pumps). This essentially means that the same volume of liquid is generated with the rotations of the pump’s shaft.
Hydraulic gear pumps come in four types:
- External gear pumps
- Internal gear pumps
- Gear ring pumps
- Screw pumps
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There is a wide range of hydraulic pump accessories on the market. These include various parts and service tools such as hydraulic pump flanges, hydraulic cylinders, pancake cylinders and rod end bearings.
Hydraulic gear pumps are designed with interlocking cogs and gear wheels that transfer fluid as they rotate, creating a seal through the suction generated at the inlet. The pump’s flow depends on the speed of the gear rotations. Hydraulic gear pumps are fixed displacement pumps meaning that each rotation generates the same volume of flow.
There are four different types of hydraulic gear pumps. External gear pumps where one gear is connected to a motor and the other rotates in the opposite direction. When they interlock, volume is created between the gears, walls and bearing blocks. Internal gear pumps also come with two gears but this kind of hydraulic pump has one large gear with teeth on the inside that rotates a smaller one. Meanwhile, gear ring pumps feature a stator and a rotor that creates flow through movement. Last but not least, screw pumps come with two or three worm gears.
Hydraulic gear pumps are relatively inexpensive and feature very few moving parts, which makes them both easy to operate and service. To sum up, they have a simple design, yet are highly effective. Gear pumps boast a smooth function, handle contaminates well and operate well at pressures levels of around 210 bar. Plus, they are suitable for pumping various types of fluids including oils and even viscous liquids. As such, they are often used as a source of power for a diverse range of machines in industrial, commercial and domestic applications.
External hydraulic gear pumps are primarily used in industrial and mobile applications that involve log splitting or lifting vehicles and heavy equipment. Internal gear pumps, on the other hand, are usually utilised in non-mobile hydraulic applications such as vehicles that operate in indoor spaces such as electric forklifts.
Meanwhile, gear ring pumps are often used in hydraulic power steering systems and pressure lubrication in various machines and combustion engines. Screw pumps have a low operating noise level” making them suitable for hydraulic systems in areas such as opera houses and theatres.
Hydraulic hand pumps convert mechanical energy — or manual effort usually activated by a lever — into hydraulic pressure and flow that generates energy in a cylinder. Pushing the lever down generates pressure that displaces fluid through an outlet. Meanwhile, pulling the lever up sucks up fluid from an inlet. Hand-operated hydraulic pumps are equipped with safeguard valves to stop fluid from being sucked back up through an outlet.
Since hydraulic hand pumps are extremely portable and don’t require a power source, they are usually used in the field to test, calibrate and load machinery and other heavy objects. They are often utilised in the gas and oil industry where the use of electrically-powered equipment can be risky and cost-prohibitive.
There are two types of hydraulic hand pumps — single action hand pumps and double action hand pumps. Single action hand pumps generate fluid force on every downstroke (to generate energy in a single acting cylinders) of the lever while double action pumps generate force on both the upward and downward lever strokes (to generate energy in a double acting cylinders). As such, double-action hand pumps are more efficient than their single-action counterparts. While double action pumps are more common, single action pumps can be found on hydraulic jacks such as toe jacks and bottle jacks since they are simple and easy to maintain.