Internal Gear Pump

INTERNAL GEAR PUMP

1. Introduction

The operation of internal gear pumps is very much similar to external gear pumps, but they are very efficient and produce less noise. The gears rotate in the same direction, with the inner gear rotating at a higher speed. Generally the internal gear pumps are used for low output applications at pressures below 70 bar. This pump is also known as crescent seal pumps.

2. Construction

Internal gear pump consists of an internal spur gear, a outside ring gear, a crescent shaped spacer, and an external housing, as shown in Fig.4.6. The internal spur gear drives the outside ring gear which is set off-center (i.e., both gears are eccentric to each other). The inner and outer gears are separated by a crescent shaped spacer, which is a stationary part of the housing around which oil is carried. The inlet and outlet ports are located in the end plates between where the gear teeth mesh and un-mesh at the two ends of the crescent shaped spacer.

3. Operation

The operation of the internal gear pumps is similar to external gear pumps. Oil is transferred from the inlet to the outlet port. The internal gear drives the external gear and affects a fluid tight seal at the place where the teeth start meshing. Rotation causes the teeth to un-mesh near the inlet port, the cavity volume increases and the suction occurs. The oil is trapped between the internal and external gear teeth on both sides of the crescent shaped spacer and is carried from the inlet to-the outlet cavity of the pump, as shown in Fig.4.6. Meshing of the gear teeth reduces the volume in the high pressure cavity near the outlet port and exits from the outlet port.

4. Advantages and Disadvantages of Internal Gear Pumps

• The advantages and disadvantages of internal gear pumps are the same as listed in Table 4.4 for external gear pumps.

• Unlike in external gear pumps, the gears in an internal gear pump rotate in the same - direction.

• The slow relative rotation and the rolling contact between the gears reduce friction, wear, and turbulence.

• These pumps also permit pumping of liquids that are more shear sensitive.

5. Ranges

Internal gear pumps are available with capacities upto 70 Lps and the discharge pressures are limited to 7 bars.