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 life.

Click here to download a comparison between Nitto Kohki Linear shuttle pumps and older style diaphragm pumps in Adobe PDF format.

Principle of linear piston pump

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.

Fewer Components

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.

Easy Maintenance

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 design.

Features of the Linear-motor-driven Free Piston System

  • 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.
  • 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.
  • 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 pulsation.
  • 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.
  • 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.
  • 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.
  • 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.
  • Quick Response Due to the lower starting current, the unit can immediately respond to frequent on-off input signals, even under back pressure conditions.
  • Longer Durability Oil free construction requires no periodical oil-up. This simple mechanism has the fewest number of moving parts possible. Long and stable performance is assured.

How it works

The periodical change of polarity on the coil by AC power supply gives either pull up or push out force to the magnets and thus reciprocating motion to the magnet sets connected to diaphragms, which will repeatedly take in and then discharge air, and achieve electromagnet driven diaphragm pumping function.

  • Stage 1
The coil will attract the left magnet that has the opposite pole, and thus the left diaphragm pushes out the air in the cavity through the discharge valve and further to the outlet port. At the same time, the diaphragm on the right is pulled up by the attraction of the other magnet and air comes in through opened suction valve.

  • Stage 2
In the next stage, the coil polarity is changed and the right magnet is now attracted and the left diaphragm pull up air through opened suction valve while right one push out air through the discharge valve.

Such operating cycle is repeated for 50 times per second with 50Hz supply and 60 times with 60Hz.

Features

  • Use of AC as the switching of suction and discharge makes the structure so simple.
  • Non-contact mechanism in the pump passage gives you clean discharge air.
  • No grating parts in the pump makes the operation quiet.

(Diaphragm Type)

How it works

The set of crank fixed on DC motor shaft and connecting rod converts rotation to reciprocating motion, which will drive the diaphragm back and forth and sending air in and out through valves.

  • Stage 1
Until the crank reaches to the bottom dead center (BDC), the diaphragm pulls up intake air into the enlarged chamber space inside the cylinder.

  • Stage 2
After passing the BDC, the crank start pushing up the diaphragm and thus air in the chamber will push open the discharge valve and go out from outlet port.

The cycle consisting of the said 2 stages is repeated as the motor shaft rotates.

Features

  • Small and lightweight body makes built-in design easy.
  • DC power source makes it easy to build into equipment for electrical control.
  • Non-contact mechanism in the pump passage gives you clean discharge air.

(Cup seal type)

How it works

The set of crank fixed on DC motor shaft and connecting rod converts rotation to reciprocating motion, which will drive the cup-seal on the other side of the rod back and forth and sending air in and out through valves.

  • Stage 1
Until the crank reaches to the bottom dead center (BDC), the cup-seal pulls up intake air into the enlarged chamber space inside the cylinder.

  • Stage 2
After passing the BDC, the crank start pushing up the cup-seal and thus air in the chamber will push open the discharge valve and go out from outlet port.

The cycle consisting of the said 2 stages is repeated as the motor shaft rotates.

Features

  • Small and lightweight body makes built-in design easy.
  • DC power source makes it easy to build into equipment for electrical control.
  • Compared with diaphragm type high discharge pressure is available.

The Next Step in Pump Miniaturization

Revolutionary piezoelectric bimorph technology
The Bimor's driving force, the bimorph, comprises two parallel piezoelectric wafers. Their nature is to expand or contract depending on the direction of the voltage. Therefore when an alternating current is applied, one wafer expands then contracts while the other contracts then expands, causing the bimorph to bend. Repeating the cycle creates the pumping action.
  • Built-in Pulse Absorption Chamber
  • Many build material options for different liquids
  • Self-priming type with air suction acceptable
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