For product & service enquiries pleace contact or call +44 (0) 1924 271446.

Rotajet Float Sink Tanks


Rotajet HKS series float sink tanks

Rotajet Float Sink Tanks

        Rotajet HKS50 float sink tank   Rotajet HKS70 float sink tank


Rotajet manufacture the HKS range of float sink tanks.

Principle of operation:

The Rotajet float sink tanks are used for density separation of various types of plastics and also to remove contaminates prior to upstream processing. Water is generally used in float sink tanks, as the density media. The specific gravity water is (1000kgs / M3), which makes it ideal for the separation of polypropylene polyethylene from PVC`s, ABS etc….Other contaminates such as glass, grit, dirt, etc…have specific gravities greater then 1, so sink.
In some applications the specific gravity of the water can be increased by the addition of various chemicals. This then allows a series of Rotajet float sink tanks to be operated for the separation of a range of plastics.

List of Specific Gravities of Various Plastics:

Below is a list of the specific gravities of various plastics.

Material Specific Gravity

LDPE 0.91 - 0.93
HDPE 0.94 - 0.97
PP 0.90 - 0.91
PS 1.04 - 1.07
PVC 1.35 - 1.45
ABS 0.99 - 1.10
Polyester 1.38 - 1.39
PC 1.2
Nylon 66 1.13 - 1.15
Teflon 2.1 - 2.2

Particle feed size:

We recommend that in the in feed material is a shred or granulate with a particle size less then <40mm, this allows the Rotajet float sink to operate effectively and produces the optimum environment in which the contamination and different plastics can be separated.

Feeding material into to Rotajet float sink tank:

The Rotajet float sink tanks are typically fed via. Belt conveyor, screw auger or blower. Depending on the application the material can be discharged onto to the surface of the tank, or fed via a screw feeder. The screw feeders, are mounted above the surface of the liquid and are submerged into the tank, this gives a uniform flow into the tank, breaks up any lumps, and ensures that all materials are fully submerged at the start of the process and have to either float or sink. The separation in force fed float sink tanks generally produces a high purity product.

Sinking Fraction Discharge:

The standard Rotajet float sink tanks are fitted with bottom screw discharge augers, the augers are manufactured completely in stainless steel and fully welded. The screws are located in a trough in the bottom of the tanks; the troughs are fitted with easy to replace wear plates. The number and diameter of the screws depend on the model of machine and throughput requirement. The torque on the screws is mounted and feeds back to the PLC. Once the sinking fraction is discharge from the Float sink, we normally recommend drying the material in a Rotajet mechanical dryer, the water can then be pumped back to the float sink tank.

​Rotajet float sink tank discharge screws

Floating Fraction Discharge:

The floating fraction is driven along the surface of the float sink by a series of rotating paddles; each paddle is mounted so the floating fraction is completely submerged as it driven along the surface of the float sink tank by the rotating paddles. The speed of the rotating paddles can be changed by the PLC to increase the agitation and discharge speed within the float sink tank. The floating fraction is transferred into the incline discharge screw via. a weir at the discharge end of the Rotajet float sink tank. The incline discharge screw body in manufactured with easy to replace sceens; these screens allow the water from discharge weir to be screened from the floating fraction. The screen water is fed via. Gravity into a Rotajet vibratory screen, this is normally fitted with a 300 micron sieve. The filtered water is pumped into a holding tank, ready for reuse in the float sink tank. We recommend that the floating fraction is discharged into a Rotajet mechanical dryer, the filtered water is normally pumped back to the vibratory sieve for filtering and reuse.

The level of working fluid level has to be maintained in the Rotajet float sink tanks; this is done by reusing the filtered solution in the storage tanks, and also introducing fresh solution if required.

Rotajet HKS40 float sink weir plate

Other options available for the Rotajet HKS float sink tanks:

  • Automatic chemical analysis
  • Automatic chemical dosing
  • Additional filtration
  • Frost protection
  • Automatic infills
  • Integrated feeding systems for difficult products


Rotajet float sink tank processing AD waste plastic  Rotajet HKS70 float sink ready for production

Rotajet HKS40 float sink tank being shipped to customer   Rotajet HKS70 Float Sink For PET bottles