When both gears are rotating, the opening teeth are creating a larger volume, sucked the liquid into the pump. The liquid is then transported in the gap between two teeth and pushed to the outlet side when the teeth of the gears connect again.
The Gear pump can be divided in 2 basic types:
The external gear pump
The external gear pump has a more simple design and is more often used than
the internal gear pump. When viewing fig.2 You can see the liquid being sucked
in the space between the two teeth. The liquid is then carried to the delivery
side and the teeth of the other gear fills up the space between the two teeth.
To achieve maximum volumetric efficiency, the leakage should be brought back to
an absolute minimum. When fluid is trapped between two teeths, this can cause
increased friction and lower mechanical efficiency.
Preventing internal leakage, losses and slip in a gear pump is nearly impossible.
Slip is affected by the vicosity-level. With a higher viscosity the slip tends
to decrease, but there is more power required to achieve the same speed / capacity.
There are a number of standard gear diameters for standard gear pumps. A gear pump
with a high diameter reduces bearing loads. The smaller the diameter gets, the less
leakage will occure.
(1) The liquid is being sucked into the space empty space between two teeth.
(2) The liquid, trapped between the tooth spaces is being transported to the output side.
(3)
After the liquid arrives at the output side, the teeth of the two gears,
fill each others empy spaces up, and the liquid is pumped into the outlet.
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| (1) | (2) | (3) |
The internal gear pump
The internal gear pump is recognizable on it's outer ring. The principle of
the internal gear pump, the opening between the teeth is getting wider as
the gear rotates, and because this space is getting wider, the liquid is
sucked into it. When the gear reaches the output side, the space is getting
smaller, pushing the liquid into the outlet.
(see picture).
The internal gear pump is particularly suitable for liquids that have a wide range of viscosity, because of their relatively low speeds. The internal gear pump has some advantages over the external gear pump. Because the two gears rotate in the same direction, the friction is substantiable lower than with the external gear pump. The localized fluid pressures are substantial lower, and so are the shearing forces on the fluid. The noise an internal gear pump produces, is also notably lower.
Internal gear-within-a-gear pump
When the gear rotates, the empty space between the teeth is getting free,
sucking the liquid into it's space. Trapped in this space, the liquid is transported
to the outlet. When the liquid reaches the outlet, the space between the teeth is being
filled up by a tooth from the outer gear, pushing the liquid out of the space, into
the outlet. (see picture below)
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| Gear-within-a-gear principle | |||