4 Description of the micro annular gear pump
Operating manual mzr-11557 Ex
14
Technical data subject to change without prior notice!
Last update: March 2019
Example
: The pump head mzr-11557 Ex has a displacement volume of 192 µl.
On the assumption that the volumetric efficiency is 100%, the flow rate at a
speed of 3000 rpm would be 576 ml/min, according to the above formula.
The following table shows the volumetric displacement, dependent on the
number of revolutions (
η
Vol
= 100 %).
RPM
Q
[ml/min]
Q
[l/h]
300
57.6
3.456
500
96
5.76
1000
192
11.52
2000
384
23.04
3000
567
34.02
4000
768
46.08
5000
960
57.60
6000
1152
69.12
table 6
Theoretical flow rate of the micro annular gear pump
Pressure generated by the pump is determined by the configuration of the fluid
delivery system and results from both the hydraulic pressure and the hydraulic
resistance (tubing, narrow passes etc.). The
volumetric efficiency
of a pump
decreases when the differential pressure rises.
The
viscosity
of the manipulated liquid has an important impact on the
volumetric efficiency. The volumetric efficiency increases for higher viscosity
values because the
internal leakage
values go down.
Cavitation
is an effect which, starting form a certain limit speed value, may
reduce the volumetric efficiency of a pump. In the case of highly viscous liquids
this limit speed value is lower. That happens because of the liquid-specific drop
of vapor pressure in the suction tube which leads to gas formation inside the
pump.
The particularity of the mzr-pumps is their highly precise construction, which
provides for both high operating pressures and a high dosage precision. The
gap between both rotors and between the rotors and the adjacent case parts
lies in the range of a few micrometers. This precision is the key factor enabling
to achieve volumetric efficiency close to 100%.
