The Wilson Auto-Siever, initially designed in the late 1980's, was constructed in 1990, and has since undergone several modifications. The fabrication of the Wilson Auto-Siever was undertaken in order to standardise sieving operations between surveys and personnel, and to reduce the total number of field personnel required on any given project by improving the efficiency of sample handling. The unique and revolutionary design enables its employment in the reduction of most sediment types including heterogenic and cohesive substrates.
Since its construction, the Wilson Auto-Siever has been used extensively in commercial surveys around the world by Gardline Surveys OED. Areas include the UK (North Sea and English Channel), Southern Europe, South East Asia and West Africa.
The Wilson Auto-Siever is based primarily on a stainless steel table which acts as a sieve stand. Its extended height provides a comfortable working level for field operations. A large (450mm) stainless steel sieve is positioned in the centre of the table with a tarpaulin chute and pipe fixed below to discharge sieved sediments over the side of the vessel. Directly beneath the sieve, a heavy duty plastic sieving head assembly is served via a pipe network and control valves on the upper side of the table. The top of the sieve is covered with a removable lid with handle, perspex window and central filter.
During operations, the underside of the sieve mesh is continuously swept by a curtain of water, under very low pressure, which maintains sediment fluidity at the sieve interface. This not only acts to keep the sieve pores from blocking, but also momentarily suspends the sediment, allowing the finer particle size fractions to pass through the sieve aperture.
In cases where the sediment type is coarse, mixed or cohesive, the pressure of water can be altered as follows:
Cohesive sediments: Where sample volumes are large (i.e. > 10 litres) or particularly cohesive, such as muddy sands, the larger lumps should be lightly broken down with sea water directly within the sample tray, prior to pouring into the Wilson Auto-Siever. By ensuring that the rotary arm is already sweeping the mesh when the sample passes into the sieve, all of the suspended sediments should pass immediately though leaving only cohesive lumps at the interface.
By fitting the sealing lid, the pressure of the spray can be increased to lightly wash the remaining sediments within the sieve. In the event that the sample should momentarily overflow, then the excessive water will be allowed to pass directly through the centre of the lid, whilst a 500 Ám filter guards against the loss of any suspended fauna. The progress of sample breakdown is observed through the Perspex window and after a few minutes, the lid removed and lightly sprayed down to remove any fine biota. Any remaining sediment (usually gravels or clays) can finally be dealt with by hand.
Fine sands: Fine sands are poured directly into the sieve and allowed to pass through at low pressure (or by increasing the pressure slightly). The sealing lid is not usually required for this operation.
Mixed sediment: Mixed and coarser sediments are poured directly into the sieve and the spray run at intermediate to high pressure. If the proportion of residual material is substantial, then the lid will not be required as the sediment is allowed to "boil".
|Dimensions (cm)||Weight Boxed|
|70 x 70 x 100||30 x 105x 78||57|