The hydraulic piston sampler is designed for taking undisturbed samples in low strength fine soils, such as silt and soft to stiff clays.
The necessary hydraulic load is generated from the hydraulic power unit on a drilling rig, or by using a purpose built Hydraulic Power Pack. An operating pressure of 1200 p.s.i (80 bar) is usually adequate for taking samples in the soil conditions for which the unit was designed.
The piston sampler is of the stationary type. The entire unit is rigid and of fixed length (2850 mm) from the drill rod connection at the top end to the piston head at the bottom. The only moving part is the hydraulic cylinder which slides up and down the central rods. The stroke length is exactly 1 metre.
The sample tube is attached to the lower end of the hydraulic cylinder by means of 3 screws. Hydraulic oil flowing through the piston sampler causes the cylinder with attached sample tube to move downwards into the soil. At the end of the stroke the apparatus is lifted out of the ground and the full sample tube is removed, replacing it with an empty one.
The direction of flow of hydraulic oil is then reversed, causing the cylinder with attached sample tube to move upwards. When the cylinder has moved to its highest extent, the piston head is visible at the bottom end of the sample tube. The apparatus is then lowered into the ground ready for taking the next sample.
To ensure a good seal against the bore of the sample tube, the pressure exerted by the piston seal can be adjusted by tightening or loosening the screws on the back-plate of the piston head. (The back plate compresses the seal when it is tightened up).
The standard sample tube is 4" bore (101.6 mm) made from aluminium and is 1000 mm long. With a wall thickness of just 1.75 mm, these tubes produce a soil sample with minimum disturbance. The area ratio is just 7%.
