General
Gear flow meters are positive displacement meters, similar in design to
a gear pump. The measuring medium rotates two gears, which are
engaged with minimum play. The medium is forced along through closed
measuring chambers between gears and housing. The gears, which run
idle, lose no power. The r.p.m. of the gears is proportional to the instantaneous
flow rate. The gear flow meters are fitted with pickups which will
precisely detect the r.p.m. through the body of the meter without
contact to the fluid. Pulses per volume unit will finally serve the
evaluation (in addition, an analogue signal 4 to 20 mA will be available
when using the local display unit VTM).
Evaluation
The K-factor (calibration factor) of the gear flow meter defines the exact pulse
rate per litre. The K-factor can be taken from the calibration record, which is
supplied with each flow meter. Among others, our calibration records include
the following specifications:
• Max. measuring error referring to the instantaneous flow rate
• Max./min. frequency with corresponding flow values
• K-factors for different flow rates
• Average K-Factor valid for the entire flow range
The following equation applies:
Q = flow rate in litres per minute
f = output pulse frequency in Hz
K = K-factor of the gear flow meter in pulses per litre
Preparation
Mechanical and electrical installations, start up and maintenance shall only be effected by qualified and
authorised personnel. Please make sure that the measuring range of the ZHM cannot be exceeded by more
than 20%. Before installation the pipe system has to be purged. Particles must not get into the gear flow
meter as they could block the gears. This is particularly important with small sizes ZHM 01–ZHM 02. As a
precaution use filters for the measuring medium:
ZHM 01–03: 120 micron
04–05: 200 micron
06–07: 300 micron
Installing the Flow Meter
The gear flow meter should be mounted in flow direction (calibration direction). It can be mounted either
horizontally or vertically. The flow direction is indicated by an arrow on the flow meter.
The mounting direction is not relevant with reverse flow as in this case the flow meter will have been calibrated
for both flow directions.
Our standard gear flow meters are bored to suit Ermeto screwed fittings. No additional sealing is necessary
and never should fibrous sealants such as hemp or teflon strip be used when different connections require
additional sealing.
Maintenance
• Gear flow meters have to be purged with an adequate solvent if there is no permanent flow or if
the meters will not be used for a long period of time. Purging is particularly important when fluids are
likely to harden with particles remaining in the flow meter.
• The calibration of the gear flow meter should be checked after about 8,000 hours of permanent operation.
• The battery of the fibre-optic pickup type FOP 60 is to be exchanged after approx. two years.
