Fluid handling – Line condition change responsive valves – With separate connected fluid reactor surface
Patent
1991-05-01
1992-12-08
Nilson, Robert G.
Fluid handling
Line condition change responsive valves
With separate connected fluid reactor surface
137538, 251368, 251900, F16K 1704
Patent
active
051688956
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a pressure-relief valve for the protection of hydraulic units in underground mining, particularly of hydraulic face support systems, against sudden overload due to rock pressure or similar causes, with a valve piston in the valve housing, slidable in the inlet bore against the force of a valve spring and closing off the pressure medium with respect to the outlet bores, this piston having a blind bore and therefrom starting radial bores, which are shaped to correspond with a sealing ring provided in the connection piece.
THE RELATED ART
Such pressure-relief valves, also known as safety valves, are used there where systems, particularly hydraulic struts systems in underground mining are in danger of being damaged by excessive pressures. These hydraulic struts are arranged either as individual struts or as an integrated shield-type support. Because of the particular dangers involved, there are official requirements for providing pressure-relief valves for such shield-type support systems, but also for individual hydraulic struts, in order to prevent permanent damage or even destruction endangering the miners in cases of overload From DE-OS 28 30 891 a pressure-relief valve is known, wherein excessive pressure in the hydraulic system is reduced by means of a valve spring stressed 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 another requirement, the one for a safe response of such mining safety valves is not fulfilled.
From the DE-OS 33 14 837 another pressure-relief valve is known 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 required sealing is provided by an O-shaped annular seal located in a groove. Each time, the O-ring has to be completely overriden by the radial bores of the valve piston, before the pressure medium can exit in case of overload. Due to this excessive load, such O-ring valves have a short operational life. A further drawback of these known pressure-relief valves are the low flow rates of only 40 to 100 liter 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 thickness and have considerable coil diameters in order to counteract the pressure, which again requires corresponding overall valve dimensions. The higher the flow rate, the bigger must be the valve springs, and thereby the entire valve housing. Particularly in underground mining it is already not possible to use such valves, only because of their large dimensions. Also, the required cross sections for the evacuation of pressure medium are not available. Attempts have been made to increase the flow rate by using larger valve pistons and by conferring a special configuration to those valve pistons, as well as by assigning a control piston. However, the response time remains unsatisfactory in this case because the O-rings produce too much friction. As a result of such unsatisfactory closing values, the operation of the valves is too inaccurate. Furthermore, the operational life of such O-rings is very unfavorable.
It is the object of the present invention to create a pressure-relief valve with favorable closing values and with seals insuring effective and long-term operation.
DETAILED DISCUSSION
The problem is s
REFERENCES:
patent: 3482594 (1969-12-01), Simon
patent: 4284101 (1981-08-01), Weirich
patent: 4530373 (1985-07-01), Bork
patent: 4552172 (1985-11-01), Krieger
patent: 4790347 (1988-12-01), Weirich
Dubno Herbert
Nilson Robert G.
Richard Voss Grubenausbau GmbH
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