Patent GB-955149-A (GB)
Title: Gas pressure operated blasting cartridges
IPC: F42B3/06
Filed: 1960-08-22
Abstract: 955,149. Blasting devices. OLIN MATHIESON CHEMICAL CORPORATION. Aug. 22, 1960 [Sept. 24, 1959; March 11, 1960], No. 29004/60. Heading F3A. A gas pressure operated device for blasting or like purposes comprises a cartridge having a main chamber and a control chamber for retaining compressed gas, ports leading from said main chamber to the exterior of said cartridge for exhausting the compressed gas from said main chamber, a first valve sealing said ports normally held in sealing position by said compressed gas, said first valve being positioned between said chambers, means for equalizing pressures within said chambers, and a resiliently mounted lift valve sealing said control chamber, said lift valve being exposed to gas pressure within the cartridge and directly responsive thereto to release the gas pressure from said control chamber and thereby reduce the pressure on one side of said first valve which is thereby unseated. A cylinder 5, Figs. 1 and 2, is attached by an adaptor 2 to a casing 1 to which gas under pressure is supplied and the cylinder 5 is closed by a cap 12 fixed to a plug 9. The ports 15 in the cylinder 5 are normally closed by a sleeve valve member 17 which, at one end, seats on the knife edge 23 of a seating member 22 and, at the other end, is engaged by a flange 26 of a control piston 24 loosely slidable within the sleeve 17 and biased to the position shown in Fig. 1 by a spring 44, one end of which is fixed to a plate 45 screwed on to an adjustable stem 38 which extends into a tubular extension 36 of the piston 24. Within the piston 24 is a valve chamber 29 closed by a plug 27 and containing a ball valve 33 loaded by a spring 35 against a seat 34. The main chamber 30 is connected to the valve chamber 29 via passages 16, 31 and the control chamber 25 is connected to the valve chamber 29 via ports 32. The item 38 has a centrally extending pin 41 and a bore 42 connected by ports 43 to the bore 37 of the control piston extension 36. The ball valve 33 normally closes the passage 37. As gas under pressure is supplied to the chamber 30 it passes via passage 16, ports 31, chamber 29, ports 32 to the chamber 25 and the sleeve valve 17 is maintained against its seating by virtue of the greater area of its right-hand face exposed to pressure. The piston 24 has a differential effective area such that as the supply pressure increases it moves to the right until the ball valve 33 abuts the pin 41. The piston remains in this position until the gas pressure increases sufficiently to unseat the ball valve 33 to vent the chamber 25 via ports 32, passage 37, ports 43, passage 42 and vents 14. The sudden reduction of pressure on the right hand face of the sleeve 17 allows the sleeve to move quickly to the right to open the exhaust ports 15. In another example, Fig. 4, the ports 15 are closed by the piston valve member 17 having a port 55 and the control piston 24 has a tubular extension 61 which defines the valve chamber 29 containing a ball valve 33 loaded by a spring 35 against a seat 34. The stem 38 extends from a cap 12. As the gas pressure increases within the chambers 30, 25 the valve member 17 is urged with greater and greater force against the seat member 20 and the control piston moves to the right against the force of the spring 44. The piston 24 stops when the ball valve 33 meets the abutment 41. When the gas pressure increases sufficiently to unseat the valve member the chamber 25 is vented and the valve member 17 moves quickly to the right to open the exhaust ports 15. In other two examples (not shown) the movement of the control piston is caused solely by an increase in pressure within the control chamber, and in one case the valve member 17 is loaded by a spring and the control piston has a short stroke.