Understanding Different Types Of Hydraulic Pumps

Hydraulic pumps are undoubtedly critical pieces of equipment used in various industries. These pumps are used on every conceivable industrial or mobile hydraulic machine, including cranes, tractors, excavators, loaders, and vacuum trucks. Consequently, hydraulic pumps are commonly used by businesses in the mining, vehicle, oil and gas, forestry, marine, agriculture, and construction industries. As such, it is no surprise that Technavio estimates that the global hydraulic pump market will increase by $3.53 billion (£2.82 billion) from 2021 to 2026.

You can think of hydraulic pumps as the heart of hydraulic systems. A hydraulic pump's function is to turn mechanical energy into hydraulic energy, a combination of flow and pressure. Basically, a hydraulic pump is any device that you can input force into to generate pressure, creating flow as a result.

Hydraulic Pump Types

There are three primary types of hydraulic pumps: gear, piston, and vane pumps. These pump types are further classified based on their functions. For instance, there are fixed displacement and variable displacement pump types.

Fixed Displacement Pumps

A fixed-displacement pump is a positive displacement type where the displacement amount can't be varied because there are no controls for this. It has a fixed flow rate- each motor stroke moves the same fluid amount. Fixed displacement pumps are easier to maintain, relatively cheap, and simple. It is used in open centre hydraulic systems. The gear pump is perhaps the simplest type of fixed-displacement pump out there. In this pump, rotating gears push the hydraulic gears. However, the gears are interlocking in a more efficient version. The screw pump is another excellent variation of a fixed displacement pump. It uses the famous Archimedes screw to move the fluid. Fixed displacement pumps are known for their high flow rate at relatively low pressure.

Variable Displacement Pumps

Variable displacement pumps convert mechanical energy to hydraulic energy, but the hydraulic flow requirements will differ based on operating conditions. A variable displacement pump's swashplate is not fixed, and you can adjust its angle by a pressure signal, unlike their fixed displacement counterparts. The swashplate angle changes if more flow is required, creating a longer piston stroke that increases pump displacement. Unlike the fixed displacement pump, the variable displacement pump is used in closed centre systems. In a closed centre system, the variable displacement pump's swashplate angle decreases as flow requirement reduces, preventing excess flow or hydraulic horsepower loss.

Electric Pumps

Electric hydraulic pumps are driven by electric motors designed to supply power to hydraulic systems. Many modern electric pumps are best for small to medium-sized hydraulic tools and ideal for easy pump transport applications.

Hydraulic Hand Pumps

Hydraulic hand pumps use the mechanical force a manually-operated actuator generates to transmit fluid. A handle, lever, or toggle could be your manually operated actuator. Hydraulic hand pumps can be used for water pumping, hydraulic fluid distribution, and many other applications.

Air Hydraulic Pumps

These are hydraulic power devices that leverage compressed air to trigger a pump action, generating energy from pressurised liquids. They are also called pneumatic hydraulic pumps and are used in various industries to lift heavy goods and transport materials with less initial force.

Cordless Battery-Powered Hydraulic Pumps

High-pressure cordless battery-powered hydraulic pumps are best for safety, speed, and portability tasks. These cordless pumps are ideal for remote locations without power access. However, your business can also use them indoors when size, trip hazards, and ergonomics are key factors.

Gear Pumps

The gear pump is perhaps the simplest and most common type of hydraulic pump being used today. They are one kind of positive displacement pump, also known as fixed displacement pumps. In this pump, fluid moves by enclosing a defined fluid volume using interlocking gears and then transporting it as the gear rotates. Also, there are usually two gears in a gear pump; the driver or power gear and the driven or idle gear. The driver gear is linked to any mechanical energy source or some prime movers. A gear pump offers a pulse-free flow directly proportional to the gears' rotational speed. It is generally used for developing high pressure.

Generally, these pumps are utilised in open centre hydraulic systems. They trap oil in the areas between the pump's body and its two gears' teeth, send it around the gear cavity's circumference, and force it through the outlet port when the gears mesh. A tiny amount of pressurised oil behind the wear plates pushes it tightly against the gear's ends to boost pump efficiency. Gear pumps are widely rated by the pump's maximum input speed limitation, maximum pressure rating, and cubic inch displacement. Also, it is estimated that the swept volume of gear pumps for hydraulics is between 1 to 200 millimetres. Another interesting fact about gear pumps is that their volumetric efficiency is the lowest of the three main pump types.

Advantages of Gear Pumps

  • They are quite simple and compact with few moving parts
  • Incredibly affordable
  • Low maintenance costs
  • They can be used to generate high pressures of up to 3000 psi.
  • They can pump highly viscous liquids like oils with a low chance of leakage.
  • They run in both directions, so they are appropriate for loading and unloading alike
  • Gear pumps are less sensitive to contamination

Disadvantages of Gear Pumps

  • They are notoriously noisy.
  • Limited sizes, making them not ideal for large bulk flow rates
  • Abrasive fluids can't be used in the gear pump because meshing gears are used.

Piston Pumps

A piston pump, also known as a reciprocating pump, is one of the most popular hydraulic pumps. It is a type of positive displacement pump where the high-pressure seal corresponds with the piston. They compress gases or move liquids at high pressure without significantly affecting the flow rate. As such, they are commonly used in water irrigation or delivery systems. An electric motor, steam, turbine, electric motor, or drive mechanism can power a piston pump. They can deliver different very high levels of pressure up to 10,000 psi and are leveraged to transport lubricant fluid along the machinery axis. During this process, pressure build-up forces the fluid through the pump and causes it to pulsate due to the piston movement. Fixed and variable displacement pumps are both available.

Advantages of Piston Pumps

Piston pumps have an enormous and wide pressure range, so they can reach incredibly high pressures that can be regulated without affecting the flow rate. Additionally, they have a steady discharge rate, allowing them to move high gas volumes and viscous liquids throughout the machine. Furthermore, piston pumps are incredibly durable and will serve your business well for a long time if maintained properly.

Disadvantages of Piston Pumps

Cost is a significant disadvantage of piston pumps, as they are expensive to acquire upfront. Admittedly, they pay for themselves in the long term, but their initial costs can be too large due to their size and complexity. Another huge disadvantage of piston pumps is their numerous and stringent maintenance demands. For instance, a piston pump's mechanical parts are likely to wear down due to the intense pressure they undergo and the high psi they generate if you don't lubricate them properly.

Furthermore, piston pumps are pretty heavy due to the components used in their manufacturing, and they are also quite bulky. Finally, their valves must be kept intact and remain abrasive-resistant to allow the passage of large and thick solids and liquids.

Vane Pumps

Charles C. Barnes invented vane pumps in 1874. They are positive displacement pumps used to increase the pressure of flowing fluid with vanes mounted to a rotor. They can be used to transport fluids from one point to another at high pressures. Vane pumps maintain a steady flow rate under different pressures and are self-priming. The vane pump's vanes can be tensioned to maintain contact with the pump's wall as they rotate. Many of today's vane pumps have replaced line contact with rotor and stator contact. They are commonly used in air conditioners, cars, and the power steering of automobiles.

Advantages of Vane Pumps

  • They are self-priming, robust, and supply constant delivery at a fixed speed.
  • High volumetric and general efficiencies.
  • They provide uniform discharge with insignificant pulsations.
  • They don't need check valves
  • Lightweight and compact
  • Their vanes can be easily replaced
  • Can handle liquids containing gases and vapours
  • Their discharge is less sensitive to pressure and viscosity variations
  • Robust and compact design

Disadvantages of Vane Pumps

  • Not ideal for abrasive fluids
  • Relief valves are necessary to protect the pump in case of sudden delivery stoppage.
  • They require good seals.
  • They need good filtration systems or will be severely damaged by foreign particles.
  • Not ideal for high-pressure or high viscosity applications.