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  • Gears, Pistons, and Vanes: The Ingenious Trio Powering Hydraulic Systems

Gears, Pistons, and Vanes: The Ingenious Trio Powering Hydraulic Systems

Date: 02-10-2023

Hydraulic systems and what powers them, the unsung heroes of modern machinery, rely on a trio of crucial components: gear, piston, and vane pumps. These mechanical wonders work in harmony, translating fluid power into mechanical motion with precision and efficiency. In this article, we'll delve into the roles and significance of each of these essential elements.

Gears

Define the gear pump.

The gear pump is a PD (Positive displacement) pump. It helps to develop a flow by carrying the fluid between repeatedly enclosing interlocking gears or cogs, transferring it automatically using a cyclical pumping action. So, the hydraulic gear pumps provide a smooth pulseless fluid flow whose rate depends on its gears’ rotational speed.

How does the gear pump work?

The gear pump uses rotating gears or cogs action to move fluids. Its rotating part forms a fluid seal by the casing of the pump and creates suction at the inlet of the gear pump. Fluid pulled into a gear pump is surrounded by the rotating gears or cogs cavities and shifted out to discharge.

Types of Gear Pump

The gear pump is classified into two major types:

➣ External Design Gear Pump

➣ Internal Design Gear Pump (Figure 1).

1. External Design Gear Pump

External design Gear pump contains two identical and interlocking gears that are supported through separate shafts. The motor is used to drive the first gear which drives the second gear. In a few cases, electrical motors can drive both shafts that are supported with bearings on every side of the casing.

  1. When gears move out from the mesh on the pump’s inlet side, they form an extended volume, Fluid flows into the pump’s cavities and is entrapped by the edges of the gear while gears carry on rotating against the casing of the pump.
  2. The entrapped fluid comes out from the Pump’s inlet towards the discharge side around the region of the casing.
  3. When gear’ edges get interlocked on the Pump’s discharge side, the volume decreases and fluid forces out underneath pressure.

The fluid cannot be transferred back over the center, amongst the gears, as they got connected. Close tolerances amongst the casing and the gears let the external gear pump extend suction over the inlet and prohibit fluid from going back from the pump’s discharge side (Though the low viscosity fluids have more tendency for fluid leakage).

The external designs gear pumps can utilize herringbone, helical, or spur gears.

2. Internal Design Gear Pump

The Internal Design Gear Pump works the same as of External Design Gear Pump except that it’s both interconnected gears have different sizes where one rotates inside of the others. It has a larger internal gear which is called the rotor i.e. its edges projecting from the inside. The other external gear of small size is mounted into the center of the rotor which is called the idler.

It is designed for interconnecting with the outer rotor in a way that the edges of the gear engage at one end. The bushing along with a pinion is attached to the casing of the pump which holds the inner idle into its location. A crescent shape fixed divider fills the vacant place which is created by the idler’s irregular mounting position. It works like the seal amongst outlet & inlet ports.

  1. When gears move out from the mesh on the pump’s inlet side, they form an extended volume, fluid flows into the pump’s cavities, and is entrapped by the edges of the gear while gears carry on rotating against the partition and casing of the pump.
  2. The entrapped fluid comes out from the Pump’s inlet towards the discharge side around the region of the casing.
  3. When gear’ edges get interlocked on the Pump’s discharge side, the volume decreases and fluid forces out underneath pressure.

The internal design gear pump can only use the spur gears.

Piston Pumps

When high operating pressures are required, piston pumps are often used. Piston pumps will traditionally withstand higher pressures than gear pumps with comparable displacements; however, there is a higher initial cost associated with piston pumps as well as a lower resistance to contamination and increased complexity.

This complexity falls to the equipment designer and service technician to understand in order to ensure the piston pump is working correctly with its additional moving parts, stricter filtration requirements, and closer tolerances.

 

Piston pumps are often used with truck-mounted cranes but are also found within other applications such as snow and ice control where it may be desirable to vary system flow without varying engine speed.

A cylinder block containing pistons that move in and out is housed within a piston pump. It’s the movement of these pistons that draw oil from the supply port and then force it through the outlet. The angle of the swashplate, which the slipper end of the piston rides against, determines the length of the piston’s stroke.

While the swash plate remains stationary, the cylinder block, encompassing the pistons, rotates with the pump’s input shaft. The pump displacement is then determined by the total volume of the pump’s cylinders. Fixed and variable displacement designs are both available.

Quick Look

  • Withstand higher pressures
  • Higher initial cost, lower resistance to contamination and increased complexity
  • Additional moving parts, stricter filtration requirements and closer tolerances
  • Truck-mounted cranes
  • Good when desirable to vary system flow without varying engine speed
  • Fixed and variable displacement designs available
  • Encompasses cylinder block containing pistons that move in and out – this movement draws oil from the supply port and forces through the outlet
  • Angle of swash plate determines the length of the piston’s stroke
  • Swash plate remains stationary
  • Displacement determined by total volume of pump cylinders

Fixed Displacement

With a fixed displacement piston pump, the swashplate is nonadjustable. Its proportional output flow to input shaft speed is like that of a gear pump and as a gear pump, the fixed displacement piston pump is used within open center hydraulic systems.

Vanes

Vane pumps were, at one time, commonly used on utility vehicles such as aerial buckets and ladders. Today, the vane pump is not commonly found on these mobile (truck-mounted) hydraulic systems as gear pumps are more widely accepted and available.

Within a vane pump, as the input shaft rotates it causes oil to be picked up between the vanes of the pump which is then transported to the pump’s outlet side. This is similar to how gear pumps work, but there is one set of vanes – versus a pair of gears – on a rotating cartridge in the pump housing.

As the area between the vanes decreases on the outlet side and increases on the inlet side of the pump, oil is drawn in through the supply port and expelled through the outlet as the vane cartridge rotates due to the change in the area.

In conclusion, the synergy of gears, pistons, and vanes in hydraulic systems powers our modern world. Gears provide speed control and torque amplification, while pistons convert fluid pressure into mechanical motion with precision. Vanes ensure a continuous flow of hydraulic fluid, making these systems efficient and reliable. Together, these components form the backbone of hydraulic engineering, driving innovation and propelling industries forward with their unwavering strength and precision.