Fluid handling – Line condition change responsive valves – With separate connected fluid reactor surface
Patent
1991-03-19
1993-01-19
Nilson, Robert G.
Fluid handling
Line condition change responsive valves
With separate connected fluid reactor surface
137538, F16K 1704
Patent
active
051804433
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATION
This application is a national phase of PCT/DE90/00332 filed May 10, 1990 based upon German national applications P39 22 894.0 filed July 12, 1989, P39 29 094.8 filed Sept. 1, 1989 and P39 16 260.5 filed May 19, 1989 under the International Convention.
1. Field of the Invention
The invention relates to a pressure-relief valve for the protection of hydraulic units, particularly the hydraulic face support systems in underground mining and tunnel construction, against sudden overload due to rock pressure or similar causes, with a valve piston arranged to slide longitudinally in the valve housing against the force of a spring and with an inlet opening on the one side of the piston provided with blind bore and with radial bores at the extremity, as well as with outlet holes on the other side of the valve piston, whereby the valve piston is sealed by means of an O-shaped annular seal over which the radial bores can travel.
2. Background of the Invention
Such pressure-relief valves, also known as safety valves, are used where a hydraulic system, particularly a system of hydraulic struts (props) in underground coal mining, can be damaged by excessive pressure. These hydraulic struts are arranged either as individual struts or integrated in a shield-type support. Because of the constant danger, there are official requirements for providing pressure-relief valves not only for such shield-type support systems, but also for the individual hydraulic struts, in order to prevent permanent damage or even destruction endangering the miners, in cases of overload. DE-OS 28 30 891 describes a pressure-relief valve wherein excessive pressure in the hydraulic system is reduced by means of a valve spring braced between the locking screw and the valve piston. On the valve spring cap or the valve spring retainer a conically or spherically shaped valve-closing body is provided which is lifted off the valve seat in case of overload. On the piston a damping cylinder is provided, which limits the flow passage opening. However, such valves do not afford the locking safety required for the use as pressure-relief valves or safety valves in mining. Furthermore an accurate positioning particularly of the spring is very difficult, which means that all of the requirements for a safe response of such a mining safety valve are not fulfilled.
DE-OS 33 14 837 described another pressure-relief valve wherein the valve spring is arranged in the valve housing so that it presses on the valve spring cap and thereby on the valve piston and this way influences the opening of the valve corresponding to the setting. The valve piston is slidably guided on a piston-pin bore formed in the guide, whereby the necessary sealing is provided by an O-shaped annular seal located in a groove. In order to insure reliable operation and a timely response of the valve while ensuring a long life for the sealing rings, the latter have to be completely overridden by the radial bores of the piston. Through the radial bores, the blind hole provided in the valve piston and connected with the piston-pin bore can be reached, so that when the O-shaped sealing rings are overridden the pressure medium can exit the hydraulic unit to be protected. The drawback of these known pressure-relief valves are the low throughflow values of 40 to 60 (maximum 100 ) liters per minute. This is not satisfactory for the required safety and quick response of such valves. Besides, it is disadvantageous that the valve springs involved have to use wire of considerable strength and have considerable coil diameter in order to counteract the pressures; the spring size requires correspondingly large overall valve dimensions. The larger the throughflow, the bigger the valve springs, and thereby the entire valve housing, have to be. In this case, particularly in underground mining, it is not possible to use very large valves, not to mention that the required cross sections for the evacuation of the pressure medium would not be available.
OBJECT OF THE INVENTION
It
REFERENCES:
patent: 3763882 (1973-10-01), Shoop
patent: 4552172 (1985-11-01), Kreger
patent: 4660595 (1987-04-01), Kuster
Dubno Herbert
Nilson Robert G.
Richard Voss Grubenausbau GmbH
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