EXTRU - The reliable melt pump for extrusion







Melt pump for extrusion processThe EXTRU is mainly used in conjunction with extruders or kneaders. It reduces the natural pulsation and irregular conveyance, particularly in single-screw extruders, added to which, the build up of pressure in the gear pump is more efficient in comparison to the extruder. Because of this, less energy or heat is transferred into the polymer and the product is conveyed in a gentle manner. The EXTRU melt pump is indispensable for the manufacture of precision films or micro granulate.

The robust construction and low wear materials make the EXTRU indispensable for extrusions. Special versions are available for conveying natural rubber and soft PVC. The WITTE quick colour change version lends itself particularly to master batch applications with frequent changes of colour.


 In order to prevent the extrusion pump's drive shaft from being driven/pushed out of the housing when there is a high pressure on the suction side (extruder conveying pressure), the drive shaft must be relieved. It protrudes from both sides of the housing and is sealed, so that atmospheric pressure predominates on both sides of the drive shaft. The shaft is thus relieved.


Melt pumps different versions

Melt pump EXTRU II -
round version

Melt pump EXTRU III -
edge design

Melt pump - quick color change version for masterbatch applications

Melt pump for extrusion tasks Melt pump edge design for extrusion process Melt pump quick color change version

Technical Features

Heat resistant carbon steel, e.g. 1.6582 · rust-free stainless steel 1.4313 · with optional coating

Tool steel · nitrated steel · special steel · with optional surface coating · helical gearing · herringbone gearing (for extremely low-pulsation conveyance)

Friction Bearings
Tool steel · NiAg (nickel-silver) · Al-bronze · special materials · with optional surface coating

Shaft Seal
Viscoseal · stuffing box

Heating Systems
Electrically with heating cartridges · optional cover heating

Operating Parameters

up to 40000 Pas

up to 400°C (752°F)

Inlet pressure
Up to max. 120 bar (1740 psig)

Differential Pressure
Up to 250 bar (3625 psig) · special models also available for higher pressure differentials

The values listed are maximum values and must not coincide under certain circumstances.

Pump Sizes
From 22/22 (4.7 cm3/U - 10 kg/h) up to 280/280 (12000 cm3/U). Intermediate sizes, with narrower gear wheels for higher differential pressure, are possible, e.g. 140/90 (690 cm3/U).

Application Examples




Food industry
Liquorice · chewing gum

Type of Seals

viscoseal extrusion melt pumpViscoseal (VS)
The viscoseal is the standard seal for WITTE EXTRU and BOOSTER pumps. This is a dynamic seal for high viscosities and suction pressures. It can be provided with heating or cooling. The dynamic seal is suitable for high pressures and temperatures. Its range of use is limited by the suction pressure and the viscosity of the medium being conveyed (at least 10 Pas). The viscosity can be increased by an additional cooling system if necessary.

max. temperature: 450°C (850°F)
Viscosity: 10000 to 40000000 mPas (cP)



stuffing box fo melt pumpsStuffing Box
The stuffing box is a simple (static) seal for WITTE gear pumps. It can be provided with buffering if so desired. The range of application is similar to that of the viscoseal. The standard material used for the packing rings is made of expanded pure graphite with structural textile fibes. But it goes without saying, that other materials are also available.

max. temperature: 350°C (660 °F)
Viscosity: up to 40000000 mPas (cP)



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