Frequently Asked Questions


HNPM is the abbreviation for the company name HNP Mikrosysteme GmbH.

HNP Mikrosysteme GmbH was founded in 1996 and then in 1998 started business at Parchim with 5 employees.

Since 2013 the headquarters are located in Schwerin, a city in northern Germany.

In addition to the headquarters in Schwerin there is a sales office in France. As a subsidiary, HNP Mikrosysteme USA is responsible for the distribution in USA and Canada. The office is located in Highland Park, Illinois. In several foreign countries HNP Mikrosysteme works with distributors.

Basics in Microfluidics

The displacement volume is the calculated (theoretical) volume that is moved from the inlet to the outlet side of the pump during one rotation of the pump shaft and inner rotor.

The effective volume is the volume of liquid that actively passes through the pump head.

The total volume specifies the total internal volume of the pump head and is made up of the effective volume and the dead volume.

The dead volume is the volume of liquid inside the pump head where no active flow exists and which does not actively pass through the pump.


»mzr« is the abbreviation for »Mikrozahnring« the German translation of micro annular gear. mzr® is a registered German trademark of HNP Mikrosysteme GmbH.

The outer rotor is referred to as annular gear because of its annular shape and inner toothing (indentations).

The abbreviation »mzr-pump« stands for »Mikrozahnringpumpe« and can be translated into micro annular gear pump.

Micro annular gear pumps are used in applications where small amounts of liquids or volume flows need to be dosed or metered with low pulsation. Pumping of aggressive, corrosive or crystallizing liquids is also possible as is metering of high viscous fluids.

Overview Applications

The first two numbers - for mzr-115xx the first three numbers - of pump nomenclature stand for the root circle diameter of the outer rotor. They provide information about the size of the rotor set and the displacement volume of the pump. The term mzr-2500 means that the root circle of the outer rotor measures 2500 µm (ø 2.5 mm). Other rotor sizes are: mzr-2900 (ø 2.9 mm), mzr-4000 (ø 4.0 mm), mzr-4600 (ø 4.6 mm), mzr-6300 (ø 6.3 mm), mzr-7200 (ø 7.2 mm) and mzr-11500 (ø 11.5 mm)

No. Micro annular gear pumps are designed for liquids, they cannot meter gases. However, liquids containing gas bubbles can be pumped with mzr-pumps.

See also: Are mzr-pumps self-priming?

Yes. Micro annular gear pumps are self-priming. Operating pumps for a longer period of time without liquid should be avoided to minimize wear.

The recommended mounting orientation of the pump depends on the pump design. For pumps of the Modular Series and Low pressure pump series the favorable mounting orientation is vertical with the motor pointing upwards above the pump head.

For pumps of the High performance pump series the mounting position can be horizontal or vertical with the motor pointing upwards above the pump head.

For pumps of the Hermetic inert pump series the recommended mounting orientation is horizontal or vertical with the motor pointing downwards below the pump head.

Pumps of the Magnetic hermetic pump series can be mounted either vertically or horizontally.

To select the right pump series and pump size three parameters have to be taken into account: pressure conditions at the inlet and outlet side of the pump, minimum and maximum volume flows or dosing volumes, and the viscosity characteristics of the liquid.

Pressure conditions determine the pump series: for low pressures, pumps of the Low pressure, Modular or Magnetic Hermetic Series will be selected. For higher pressures, pumps of the High Performance or Magnetic Inert Pump Series will be selected. The volume flow range or dosing volume define the pump size. The chemical properties of the working liquids determine the materials of the wetted parts to be used in the pump. They also determine if a hermetic pump is necessary for the application or if a pump with shaft seal is suitable enough.

Our Technical Sales team will help you to select the right pump.

The suction side (inlet) of the pump is marked with a "S", the delivery side (outlet) is marked with a "D". An arrow on the pump head's front side indicates the flow direction and rotors' rotation direction inside the pump.

First, the optimal flushing liquid has to be selected. It is important that the working liquid and the flushing liquid are mixable and precipitation inside the pump is avoided. Precipitates inside the pump can lead to blockage of the rotor set. In each case, only flushing liquids compatible with pump materials can be used. The flushing liquid flow has to be high enough to ensure an exchange of liquid in areas of the pump head that are not easily accessible. The time frame of the flushing procedure depends on the properties of liquid residues inside the pump and properties of the flushing liquid. Additional information regarding the flushing process can be found in the pump manual.

Filters, complementary modules, controllers

A filter is used to protect the micro annular gear pump from particles and contaminants which might cause the pump to block. HNP Mikrosysteme recommends to use a filter with a mesh size of 10 μm.

Should there be any technical reason why a filter cannot be used, please contact HNPM to discuss a solution.

In case of a pressure gradient between the inlet and outlet side of the pump, the use of a check valve or shift valve prevents backflow through the pump.

The heat insulation module is used for thermic decoupling of pump head and motor. It prevents transfer of heat between motor and pump head in both directions. The use of such module enables the operation of the pump with liquids over wider temperature ranges, i.e. -20 °C to +150 °C or even +200 °C.

The heat insulation module is made out of a plastic material with low thermal conductivity and is located between pump head and motor. It is available for pumps of the High performance pump series and Hermetic inert pump series.

The fluidic sealing module is used when pumping crystalizing or air and moisture sensitive liquids, respectively. It prevents contact between the pumped liquid and the surrounding air through the shaft seal. It also increases the suction capacity of mzr-pumps when pumping out of the vacuum.

By installing an additional shaft seal on the motor side of the pump, a chamber is formed between the shaft seal on the pump head side and the one on the motor side. This chamber has to be filled with liquid compatible with the pumped liquid. The liquid used in the sealing chamber will depend on the application and has to be selected accordingly.

The fluidic sealing module is available for pumps of the High performance pump series as well as the mzr-724x of the Modular pump series.

No. Every pump requires its own controller because every pump has its own closed loop speed control.

If several pumps with their controllers are required to be controlled by one central controller, this can be done via a serial interface (daisy chain) or CAN-Bus.

The minimum achievable motor speed depends on pump configuration and pump type. The minimum achievable motor speed is directly dependent on encoder resolution, type of integrated hall sensors, and quality of the speed controller inside the motor controller. For some pumps the minimum speed is 10 rpm. If a high resolution encoder is used, 1 rpm can be achieved. For speeds below 1 rpm the motor speed can be reduced further by a reduction gear box.

The possibilities for controlling micro annular gear pumps depend on the motor and configuration of the different controllers.

Micro annular gear pumps with direct current (DC) servo motors can be controlled via 0-10 V, 0(4)-20 mA, or RS-232. For selected motors a CANopen-controller is available.

For the control of alternating current (AC) motors, a frequency converter is necessary.

Overview controller mzr-pumps

Materials and Liquids

A general statement to this question is not possible, HNPM should be consulted. Basically, alkaline liquids with a pH-range 12-14 can be handled with pump parts made of hard metal (tungsten carbide).

For acidic liquids with a pH-range 1-3 ceramics are better suitable.

In general, it is advisable to consider each individual case.

Product inquiry

Chloride ions in aqueous solutions can result in pitting corrosion of steel. How fast the corrosion progresses will depend on chloride concentration, additional components in the liquid, and temperature. Hydrochloric acid is a highly corrosive liquid because, in addition to chloride ions, the low pH supports corrosion. Special care has to be taken for selecting the right pump materials.

Service and Troubleshooting

If the pump stops, it can be due to an electrical or mechanical cause. Please check if the electrical wiring is correct and that the supply of power is ensured in accordance with the pump manual.

If electrical errors can be ruled out, a mechanical cause is likely. In this case please contact Technical Sales or directly Technical service. Do not open the pump.

For disassembling the pump special tools are required. Incorrect disassembly can result in damage to sensitive and precision-made pump parts.

Contact Technical Service

Please contact your sales contact. They know your application, configured a suitable pump, and will help provide answers to your questions and solutions to your problems.

Contact Technical Sales

Service of HNPM pumps requires the following steps:

1. You inform us by telephone or email about the return of a pump for service.
2. You fill out the »Declaration of Media Contact« form and send it back to us along with the pump.
3. As soon as we receive the pump, we check contents and completeness of the package.
4. Your micro annular gear pump is examined and assessed by our service team.
5. Shortly afterwards, results of the analysis and a quotation for the service will be sent by email.
6. You issue the service order and clear the repairs with it.
7. The pump will be carefully repaired and will pass a quality check.
8. We promptly ship the repaired micro annular gear pump back to you.

Contact Technical Service

After receiving, we need approximately 4-6 working days to inspect the pump and prepare a service quotation which we send to the respective contact person.

After receiving the order for the repairs we need approximately 10-14 working days depending on the extent of repairs before returning the pump.