Medo Pumps Information Page
The Linear-motor-driven Free Piston System (Pat.) has an
internal piston inside the cylinder which is driven by an electro-magnet and spring system
controlled by the alternating input current cycle. The piston thus forms a single
combined structure of two usually different devices; motor and pump. The system is quiet
and vibration free, and offers the advantages of easy maintenance and a long operating
Linear Pump Operating Principle
The activated electro-magnet attracts the piston against
the return spring, while air is taken into the cylinder through the opened inlet valve. When the
electro-magnet is deactivated, the return spring pushes the piston back, and the
compressed air is brought out of the cylinder through the now open outlet valve. The
system can function as either an air compressor or as a vacuum pump.
The pump's unique and simple structure has no
complicated transmission mechanism such as a crankshaft, connecting rods, ball bearings,
etc., which are widely used in between the motor and compressor in conventional pumps.
Replacement of the piston is easily achieved by simply
removing the end cap connected to the pump housing by unscrewing the four screws which
hold the cap in place.
Completely oil free construction is achieved by the
combination of smooth Teflon® seals with superior resistance against abrasion on sliding
piston surfaces and the "air bearing effect" created by the unique air path
1) Self-cooling design. Cool intake air is blown
onto the electro-magnetic coils through an orifice, making sealed construction possible
and preventing the escape of operating noise.
2) Low noise level. The machine has no complex transmission system. This results in
the lowest noise level possible due to the absence of rotating parts or ball bearings.
Operating noise is also quelled due to the pump's sealed configuration.
3) Small output air pulsation. Piston reciprocation is synchronised with input
power frequency regardless of load (i.e.; 3000 rpm for 50Hz and 3600 rpm for 60Hz). Such
high RPM adversely reduces each discharge volume and eliminates any problems caused by
4) Low Power Consumption. The piston is the only component in the system which
moves. The absence of transmission usage to pass the power to the piston means that there
is a large reduction in energy loss, and an improvement in efficiency over other pumps.
5) Compact composite structure. This unique system enables direct reciprocation of
a single part which consists of composite piston and armature. The incredibly compact and
lightweight design was achieved by combining what are two different functions in other
pumps - motor and piston - into a single structure.
6) Anti-overpressure mechanism. When the output pressure exceeds the rated value
the piston stroke will automatically diminish and prevent over-pressurising. At the same
time, the current and power consumption will also be automatically reduced, thus
eliminating possible failure caused by tentative overload.
7) Low vibration., The aluminium die-cast piston produces very little vibration or
kick-backs. Little or no damage from vibration stress is therefore sustained during
operation. Even secondary vibrations are absorbed by special soft rubber feet.
8) Quick Response. Due to the lower starting current, the unit can immediately
respond to frequent on-off input signals, even under back pressure conditions.
9) Longer Durability. Oil free construction requires no periodical oil-up. This
simple mechanism has the fewest number of moving parts possible; one. Long and stable
performance is assured if usage complies with its specification.