The hydraulic piston sampler is designed for taking undisturbed samples in very soft to stiff clays. The necessary hydraulic load for operating the equipment is generated from the hydraulic power unit on a drilling rig, or by using a purpose-designed hydraulic power pack available from Archway. An operating pressure of 1200 p.s.i. is usually more than adequate for taking samples in the soil conditions for which the unit was designed. The piston has a maximum stroke length of 1 metre.
The piston sampler is of the stationary type. The entire unit is rigid and of fixed length – approx. 2.85 m. – from the rod connection at the top to the piston head at the bottom. The only moving part is the hydraulic cylinder which slides up and down the central rods. The sample tube is attached to a steel bush at the lower end of the hydraulic cylinder by means of 3 grub screws. Hydraulic oil flowing through hose inlet B enters the hydraulic cylinder through oil port B and causes the cylinder with attached sample tube to move downwards into the ground during sampling. At the end of the stroke the whole apparatus is lifted out of the ground and the full sample tube is replaced with an empty one.
The flow of hydraulic oil is then reversed. Oil flowing through port A causes the hydraulic cylinder to move upwards. When the cylinder has moved to its highest extent, the piston head is then visible close to the bottom end of the sample tube, and the apparatus is lowered into the ground ready for taking the next sample.
To ensure a good seal against the bore of the sample tubes, the pressure exerted by the piston seal can be adjusted by tightening or loosening the Allen-cap screws on the back-plate of the piston head. (The back-plate is designed to compress the seal when it is tightened up). Operating instructions for the hydraulic piston sampler are here and an exploded diagram and parts list is here.
The equipment is designed to be used with thin-wall aluminium sample tubes 1 m long. Standard sample tubes are 105.1 mm O.D. x 101.6 mm (4M) I.D. with an area ratio of just 7%, but kits can be supplied to allow the piston sampler to be used with sample tubes of alternative diameters. Hydraulic hose and extension rods can also be supplied for direct connection to the piston sampler.
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