HETTON COLLIERY. 301' 



allow the passage of the rods and core barrel through it, and 

 carries at its lower end a chuck, which clamps the rods firmly 

 to the spindle. After feeding the spindle forward through 

 its full run, the chuck is released, and the spindle fed very 

 rapidly back to grip the rods higher up. For underground 

 work, extension screws may be fitted into the top of the two 

 parallel columns for jacking up against the walls of a tunnel, 

 in which case the back legs are removed. To save pumping 

 by hand, the pump may be mounted on one of the columns, 

 and be worked by an eccentric on the main crank shaft, as 

 shown in the figure. 



Stockton Borehole Colliery (Boolaroo). 



This was formerly known as Black's colliery, and was 

 worked by the Sneddons. It now belongs to the old Stock- 

 ton Co., and is under the management of Mr. A. Hindley. 



The borehole seam is thin in this part of the field, being 

 3ft. 9in. to 3ft. lOin. thick, so is worked on the longwall sys- 

 tem. There are two shafts, about 750ft. deep, the downcast 

 being 16ft. in diameter, and the upcast 14ft. 



The air shaft is protected with light wooden roof-shaped, 

 doors, counterbalanced by weights connected to them, by 

 ropes, so that in case of a gas explosion in the mine they can 

 be easily blown open. While sinking, the usual lorry or 

 running bridge was used as a shaft cover, on to which the 

 buckets were landed. Two wire-rope guides were used for 

 the cross-head, while sinking, which terminated about 50ft. 

 from the bottom of the shaft. These rope guides were 

 lowered as required from reels, with the assistance of differen- 

 tial block and tackle, and when at the desired depth, they 

 were held By an iron clarnp connected to an eyebolt, which, 

 was fixed in concrete. 



The hoisting engine is duplex, with 22in. diamerer cylin- 

 ders and a 5ft. stroke. It has a conical wood-lagged drum, 

 with .12ft. Gin mean diameter. Cornish valves are used for 

 both steam and exhaust, and are actuated by trip gear. 

 Cornish valves have a quicker admission and cut off than-' 

 elide valves : the main objection to the Cornish type being the 

 hammer on the valve due to it dropping by its own weight, 

 and if the valve is badly packed, it may hang up, and become - 

 unreliable. The steam cylinders have spring relief valves at 

 their ends to let any water escape that may have collected by 

 the condensation of steam, thus saving damage to the cylinder 

 in case the pet cocks are not properly attended to. They 

 have Cornish, Lancashire, and Babcock and Wilcox boilers for 

 raising steam. 



