The HTH Gravity Corer
70 mm or 90 mm gravity corer
The principle is identical between the two versions, only the tube diameter differs. The 90 mm corer has a tube with 90 mm outer diameter. The samples collected are larger compared to the 70 mm corer. Both corers come with 50 cm long tubes as standard, but tubes can be tailored up to one meter. The samples are effectively 40 centimeters as a maximum, with the standard tube.
The Principle
You can vary how deep the corer penetrates into the sediment by selecting one or two of the rings furthest down on the corer.
The corer is lowered until it is 0.5-1m above the sediment surface, then pause for about 10 seconds to allow the corer to stop oscillating and/or rotating.
The corer is lowered until a light tug on the cable is felt, then the closing mechanism is released. When the corer is pulled up, the piston needs to be put in the bottom of the tube before lifting it out of the water.
The tube is then removed from the corer and placed with the piston on the threaded rod. By releasing the lock you can easily evacuate superfluous water at the top and manually move the core tube downwards until the sediment-water interface is a few centimeters below the top of the tube.
Then the lock is fixed and you can attach scraper platform on the top of tube. Samples are pressed out by turning the extruder’s bottom, one turn 360° = 5 mm.
Scrape the samples into a suitable container.
The sediment corer allows water to flow freely through the tube during descent and the closing mechanism is automatic. Penetration into the sediment can be controlled by adding or removing weights from the corer. The tube is made from polycarbonate and the length is 500 mm. The corer is available in two sizes, with a tube diameter (OD/ID) of 70/66 mm or 90/86 mm.
The extruding device gives precision and control when sectioning the sediment. By rotating the lower part of the extruding device 360°, the sediment core is pushed upwards in exact 5 mm increments, 180° gives 2,5 mm thick samples. The lower part of the extruding device can be readily uncoupled from the treaded rod to allow fast, free movement.
The sectioning tray is attached to the top of the tube for scraping sediment into sample containers. While plastic containers are ideal, the tray has a holder to attach plastic sample bags. The tray is made in one piece from polymethylene plastic (POM) and allows easy and solid mounting, free from moving parts.
The piston is made from PE and it is equipped with a rubber disc instead of O-rings to obtain perfect sealing. The piston is buoyant.
Tested under arctic conditions
The corer has been designed for use both in summer- and in winter conditions, at subfreezing temperatures. When used from the ice, the corer will pass through holes made by a standard 150 millimeter auger.
The transport case
The transport case is designed to accommodate all the parts of the sediment corer.
The case is a NEFAB PlyPak box made of plywood. This type of packaging is built to last and the galvanized steel profiles create a very strong design.