Scraper flights

Flight scraper type D

Finnchain's D type scrapers are situated above the water surface. The scrapers move along the upper rails over two pair of wheels, skimming scum from the water surface and moving it to a scumbox.


Parts - Scraper Flights

1. Collector chain

Traditional model:
Narrow bearing surface area


  • Bearing surfaces in direct relationship
    top the wear and tear of the chain

Finnchain solution:
Wide bearing surface area


  • Long service life for the chain and wheel

Chain models

Collector chain HA200


  • Small and mid size tanks

Bearing surfaces

  • Joint 2300 mm2
  • Tooth notch 1300 mm2

Collector chain HA205


  • Mid size and large tanks

Bearing surfaces

  • Joint 1300 m2
  • Tooth notch 1640 mm2

Double chain FC-HA205X2


  • For the largest tanks

Bearing surfaces

  • 2 x FC-HA205

2. Patented adjustable pitch drive wheel

The adjustable pitch drive wheel compensates the elongation of the plastic chain.

The weak point of a plastic collector chain is the stretch, particularly as the burden increases. The stretch of the plastic can be decreased by using chain links made from fibreglass. However, it is not recommended to use fibreglass for the bearing surface, since it wears the chain's bearing surfaces and the chain wears faster. The links of all types of chain elongate over the time being in use.

As a result of the stretch the chain and the drive wheel do not match anymore, causing the chain only be drawn by a few teeth or pins. In such a situation, the chain jumps from the drive wheel, causing severe problems (flights may drop to the bottom of the tank, the process has to be interrupted and renovated). For this reason, in all other systems the drive chain has to be kept continually tight, particularly in large tanks.

Life-cycle comparison


Finnchain has compensated the elongation of the chain by a simple and ingenious adjustable pitch drive wheel. By adjusting the pulling pins, the stretched and worn chain link will be able to match the drive wheel sprockets by increasing the diameter of the pitch circle.


Patented Adjustable Pitch Drive Wheel

Get Adobe Flash player

3. Chain watch

When the chain stretches or wears, the chain's division no longer corresponds to the drive wheel's sprockets and the load is distributed onto two or one link at a time. In such a situation, the chain easily skips over the drive wheel, and for this reason the chain is to be kept tight all the time.

The Finnchain system's Chain Watch removes this problem, as the Chain Watch prevents the chain from skipping mechanically. An electric switch can also be connected to the Chain Watch, turning the motor off in overload situations.

Watch Chain Watch's operation-animation

Get Adobe Flash player

4. Scraper flights – variety of choice

Finnchain provides a range of 6 different flights:

  • High profile flights for tanks with a large fluctuation in the water surface
  • Special strengthened flights for wide tanks
  • Steel flights for narrow tanks

For surface scum skimmer, all flights are equipped with easily replaceable rubber blades.

Finnchain flight profiles

  Flight Height, mm Moment of inertia,
Torsnional moment, mm4
files/img/kuvitus/flight-profile-fc-190.jpg FC-190 190 X – X : 3 605 000
Y – Y : 376 100
479 313
files/img/kuvitus/flight-profile-fc-200.jpg FC-200 200 X – X : 5 724 000
Y – Y : 1 152 500
2 520 000
files/img/kuvitus/flight-profile-fc-220.jpg FC-220 220 X – X : 10 881 245
Y – Y : 5 083 635
7 012 345
files/img/kuvitus/flight-profile-fc-300.jpg FC-300 300 X – X : 11 183 000
Y – Y : 1 664 100
2 521 000
files/img/kuvitus/flight-profile-fc-310.jpg FC-310 310 X – X : 19 917 118
Y – Y : 5 600 130
7 013 038

5. The correct attachment of the scraper flights

Practice has shown that the chain links to which the flights are attached and also the neighbouring links tend to have greater wear than the links elsewhere in the chain.

The higher the flight profile is, the more it vibrates and the faster the chain wears. This is more significant in wide basins, with a demand for higher scraper flight profiles to move large load of sludge. Finnchainís patented scraper flight attachment method removes this vibration.

Conventional flight attachment method using bracket links:


The solution is Finnchain's patented flight attachment


Finnchain -attachment vibrationless movement.
Flight FC-220



Finnchain -attachment vibrationless movement.
Flight FC-190

6. Idler wheels – no teeth, smooth wheels

Idler wheel FC-76, on the right double idler wheel FC-80X2 for large tanks.

files/img/kuvitus/idler_wheels_1.jpg files/img/kuvitus/idler_wheels_2.jpg



It has been noted that the idler wheels with teeth wear the chain even more than the drive wheel. Only Finnchain's structure allows the use of toothless, smooth idle wheels.


7. Rails

There are two alternatives for rails that carry scraper flights in Chain & Flight type surface scum skimmers:

- Fibreglass holder and plastic wear rail

- Stainless steel manufactured Z-profile rail

8. Drive machinery

Stainless steel drive shafts, with self-aligning bearings. The ball bearings ease installation and elongates the bearingís service life.


  • Gear drive motor
  • Power 0.18 ñ 0.55 kW

Power transfer
General type is direct from the motor or alternatively chain arrangement with HA44 patented chain or 16B-1 or 20 B-1 standardized roll chains.