General information
It is the central task of external gear pumps to convert mechanical energy (torque and speed) into hydraulic energy (flow and pressure). To reduce heat losses, Rexroth’s external gear units offer very high efficiencies. They are realized by pressure-dependent gap sealing and highly precise production technology.
Rexroth external gear pumps are built in four frame sizes: Platform B, F, N and G. Within each platform different displacements can be realized by different gear widths. The pumps are available in the versions Standard, High-Performance, SILENCE und SILENCE PLUS. Further configuration variants are given by different flanges, shafts, valve arrangements and multiple pump combinations.
Construction
The external gear pump consists essentially of a pair of gear wheels supported in bearing bushes and the housing with a front and a rear cover.
The drive shaft protrudes from the front cover where it is usually sealed by the shaft seal ring. The bearing forces are absorbed by slide bearings. These are designed for high pressures and have excellent dry-running qualities, especially at low rotational speeds. The gear wheels have 12 teeth. This keeps both flow pulsation and noise emission to a minimum.
The internal sealing of the pressure chambers is achieved by operating pressure-dependent forces. This ensures optimum efficiency. On the outer face, the movable bearing bushes are pressurized with operating pressure and pressed as seals against the gear wheels. Special seals form the boundary of the pressurized zone. The radial sealing at the tips of the gear teeth against the case is provided by smallest possible gaps that are formed pressure-dependent between the gear wheels and the housing.
External gear pump layout
| 1 | Snap ring | 8 | Housing seal ring |
| 2 | Shaft seal | 9 | Pump housing |
| 3 | Front cover | 10 | Bearing bushing |
| 4 | Slide bearings | 11 | Axial field seal |
| 5 | Centering pin | 12 | Supporting element |
| 6 | Gear wheel | 13 | Rear cover |
| 7 | Drive shaft | 14 | Torx screws |
Gear pumps with integrated valves
In order to reduce piping complexity, a flow control valve or pressure-relief valve can be integrated in the cover of the gear pump. Such solutions are used, for instance, for the hydraulic oil supply of power steering systems. The pump delivers a constant flow or maximum
pressure irrespective of the rotational speed. The residual flow distributed externally to other consumers.
Pressure relief valve, external pressure discharge
p1 = 5 to 250 bar
Pressure relief valve, pressure discharge into suction line
p1 = 5 to 250 bar
3-way flow control valve, residual flow distributed externally, loadable
qconst = 2 to 30 l/min
3-way flow control valve, residual flow returned in suction line
qconst = 2 to 30 l/min
3-way flow control valve with pressure relief valve, residual flow returned in suction line
qconst = 2 to 30 l/min, p1 = 100 to 180 bar