Fluid handling – Removable valve head and seat unit – Threaded into valve casing
Patent
1998-10-28
2000-08-08
Michalsky, Gerald A.
Fluid handling
Removable valve head and seat unit
Threaded into valve casing
13759617, 25112918, 25112919, F15B 13044, F16K 3110
Patent
active
060986530
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The invention relates to an electrohydraulic control unit for a hydraulic self-advancing support with a 3/2 directional control valve connectable to a high-pressure line and with an electromagnet connectable to an intrinsically safe power supply to operate a stopper which in the closing position is held on a sealed seat by a closing spring and by the hydraulic fluid and is shiftable to the opening position by the control plunger of the electromagnet, a spring buffer with a pressure element which is subjected to initial pressure by spring force being arranged between the control plunger and the stopper.
A switching device for a hydraulic directional control valve which can be precisely set for specified switching force and travel is known from DE 3717403 C1. This switching device is being successfully used in underground mining for controlling hydraulic self-advancing supports. The operation of these supports involves high supporting forces, generated by jacks working at high pressures. The control valves are switched by electromagnets, which are connected to intrinsically safe power supplies for safety reasons. Converting the inherently small switching forces which can be obtained with electromagnets in the intrinsically safe range to the high pressure of the hydraulic fluid present in the valves makes it necessary for the valves to respond and operate very precisely under the specified conditions.
To transmit the switching force produced by the pulse generator (the electromagnet) to the hydraulic directional control valve, this switching device uses a double-armed lever mounted in the manner of a balance beam, with lever arms of equal length on either side. On the directional control valve side, the lever arm is fitted with a spring buffer with a pressure element which is urged in the opposite direction to the direction of operation and is guided in an axially displaceable manner in a bush displaceable in the direction of operation. The spring buffer imparts to the switch pin of the directional control valve a specified switching force whose magnitude can be altered by the initial compression of the spring. The spring buffer is fitted, with the bush, in a tapped hole in the lever, and is adjustable in the direction of operation with respect to the directional control valve, which is fixed in the valve casing, so that the necessary switching travel can be precisely defined. Careful adjustment in the direction of operation is imperative, as the switching behaviour of the valve is affected considerably by the play due to the manufacturing tolerances of the individual components of the valve on the one hand and by the play present in the electromagnet on the other hand. The switching force of the electromagnet increases disproportionately as the switching travel increases. Consequently the valve has to be switched in the upper range of switching force. If the switching travel is set too tightly, with too little play, the force is insufficient to open the valve, as full switching force is not attained. If there is too much play, the control plunger of the electromagnet, connected to the armature, travels to the end position without switching the valve.
The aforesaid switching arrangement is in need of improvement. The construction necessary for transmitting the switching forces and for accommodating an adjustable spring buffer in a two-armed lever is complex, and therefore costly. Adjustment and replacement of components are time-consuming.
DE 4122982 C2 describes a switching device in which an electromagnet and a 2/2 spool valve are arranged one behind the other on a common axis, with the valve spool resting against the control plunger of the magnet. The valve body is screwed to the casing of the electromagnet with adjustable clearance so that the lap between the spool and a control bore in the valve body can be varied, thus allowing adjustment of the effective orifice for pressure regulation. This variation has no effect on the switching force which is exerted by the electromagnet on the valve.
REFERENCES:
patent: 5427142 (1995-06-01), Peters et al.
Kobow Wolfgang
Reinelt Werner
DBT Automation GmbH
Michalsky Gerald A.
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