POLY - Discharge Gear Pump

discharge gear pump for polymer melts


POLY high-pressure gear pump for the discharge of medium to high viscosity media from the reactor. The extra large inlet opening guarantees an even flow of product to the gearwheels even under vacuum or extremely low NPSH conditions.

Offered with either a round inlet port, by means of which the suction flange of the pump is directly connected to the outlet flange of the reactor or as a low NPSH version, where the pump is connected between the pump and reactor flanges, in order to achieve an even larger and shorter inlet port.

Technical Features

Non-alloyed and alloyed steels · cast steel · with optional surface coating

Nitrated steel · tool steel · special steel · with optional surface coating · helical gearing · herringbone gearing

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

Shaft Seals
(Vacuum) viscoseal · stuffing box · combination of viscoseal and stuffing box · double-action, buffered mechanical seal

Heating Systems
Heat transfer oil · steam

Operating Parameters

up to 40000 Pas

up to 350°C (662°F)

Inlet pressure
Vacuum to max. 15 bar (218 psig)

Differential Pressure
Up to 250 bar (3225 psig)

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 (12,000 cm3/U - 30,000 kg/h). Intermediate sizes, with wider gear wheels for lower differential pressure, are available as standard, e.g. 152/254 (3,170 cm3/U).

Application Examples

Polymer processing


There are two types of Poly:
a) Standard design: The suction flange is also the fastening flange to the reactor.
b) The Low NPSH design: In this case, the fastening flange is designed as an alifning flange and is seated on the delivery side of the pump. The pump is clamped between the aligning flange and the reactor flange. This design provides an extremly large and short suction opening, promotin product flow. The opening can be circular, squate or rectangular.

Low NPSH Version

The loss of pressure on the suction side of the pump is dependent upon a number of factors. Parameters like viscosity and flow rate are largely predetermined by the process. According to the Hagen-Poiseuille equation, the pressure loss is linearly proportional to the length of the inlet path and inversely proportional to the fourth power of the diameter. The unique WITTE low NPSH version utilises this knowledge and offers an extremely large diameter, short suction inlet.

With the Low NPSH version, the connecting flange is foreseen as a loose flange and is located on the pressure side of the pump. The pump itself is connected between the loose flange and the reactor flange. This configuration allows an extremely large diameter, short suction inlet to be incorporated into the housing. The shape of the inlet is variable and can for example be round, quadratic or square.

Due to the fact that the pressure losses at the suction side have been reduced to a minimum, even critical applications can be reliably realised, e.g. discharging high viscosity or foaming melts.

Types of Seals:

viscoseal for polymer discharge gear pumpVacuum viscoseal with stuffing box
The vacuum viscoseal is a special version of the viscoseal and can also be provided with heating or cooling. The return flow to the suction side is adjusted by means of a needle valve, so that the choked product forms a barrier. This makes it possible to operate the pump with vacuum conditions on the suction side. Due to the fact that it is a dynamic seal, it is often combined with a buffered stuffing box. This combination prevents air from entering the reactor, even when the pump is at a standstill.




stuffingbox for gear pump


Stuffing 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 graphite but it goes without saying, that other materials are also available.








Vacuum viscoseal with lip seal
As an alternative, the vacuum viscoseal can also be combined with a lip seal instead of a stuffing box. The buffer fluid of this static shaft seal acts as barrier. If the pump is stopped for a short time this design prevents air getting sucked in the pump through the shaft seal.


Download Brochure