DE8312106U1 - PRESSURE LIMIT VALVE - Google Patents

Description

Patent attorney Eichelbaum Michaelstrasse 4 D-4350 Recklinghäusen 2

Since 629 a, b / 83 ".. '· \ . Ί |! - !...".,'. April 14, 1983

Description:

The invention relates to a pressure relief valve with a valve housing within a longitudinal bore slidable along an O-ring inserted in a circumferential annular groove up to a stop and valve piston provided with a stop collar which, when a predetermined setpoint pressure is reached or exceeded is axially displaceable against the force of a spring or a spring system and pressure fluid from an input side of the housing through an axial bore arranged in it and several at approximately the same height radial bores branching off from it can flow through to an output side of the VeKfcilgehäuses and when it is reached or falling below the specified setpoint pressure under the action of the spring or the spring system in his Closed position can be pushed back.

Pressure relief valves of this or a similar type are mainly used to protect corner or cap adjusting cylinders of hydraulic systems used in mining. After the operation of recommendations for the coal industry the demand is made, inter alia, to such pressure relief valves, on the one hand, the closing pressure of the valves less within the first year of operation, the desired set pressure to a maximum of 20% undershot _"n tet and on the other hand, the opening pressure rise

Patent attorney Eichelbaum - Michaelstrasse 40-4350 Recklinghausen 2-7

Da 529 a, b / 83, /. j 'ί ..: ^Γ ' | · * ϊ "ί« j April 14, 1983

at most equal to 150 bar with a flow rate im Range from 0 to 30 liters per minute. These two demands are in a certain contrast to each other, whereupon various problems arise depending on the basic operating mode of the valves. So there is, for example, in the case of pressure relief valves that work with mechanical bourgeoisie, the risk that to Ensuring the required flow rate within the short reaction time, the springs moved to block as a result of which they tire and thus their characteristic curve changes. As a result, the target conditions can no longer be fulfilled.

In the case of pressure relief valves that work with gas springs, on the other hand, hydraulic fluid can enter the gas chamber.

■ 'i5 penetrate. This makes the gas spring harder and can cause it to lead to an increase in pressure on the valve, which in turn is associated with an impermissible pressure increase in the expansion, which leads to deformations and destruction in the hydraulic system and in the steel structure affected by it.

In general it can be said that a hard spring with a short stroke of the valve piston has a high closing force ensures, but also allows only a small flow rate of the hydraulic fluid. In contrast, guaranteed a soft spring has a longer stroke

«Σ of the valve piston and thus a larger flow rate the hydraulic fluid, but then you have the disadvantage of a longer length and a shorter one Closing force.

There is also the case with both types of valve explained above to ensure a large flow rate

Patent attorney Eichelbaurin · Michaelstraße 4 · D-4350 Recklinghausen 2 rt

Da 629 a, b / 83 · _:.; j ::. * ..; .; April 14, 1983

of the hydraulic fluid within a relatively short time Time unit, the risk that the valve piston to clear a flow cross-section to be driven over O-ring literally from the hard jet of hydraulic fluid is sawed open and thus destroyed. Then the valve is inoperable.

In a known pressure relief valve of the type mentioned (according to US Pat. No. 3,548,867) and its Priority-based object according to DE-OS 1 750 834 ' the axial bore is designed to be continuous and is assigned to the outlet side of the valve housing End sealed by the sealing surface of a pressure body, that of a cylindrical helical spring as a support surface serves. When the pressure of the hydraulic fluid rises on the inlet side of the valve housing, the valve piston becomes Moved until its stop collar moves against the stop in the valve housing. Run over it the radial openings the O-ring, so that hydraulic fluid can flow through the axial bore and the radial bores to the outlet side of the valve housing. In the event of a further increase in pressure, the pressure body and thus its sealing surface also move away from the end of the axial bore lifted off, so that hydraulic fluid can also escape from this axial bore / this Pressure relief valve has the disadvantage that, on the one hand, a relatively long stroke from the closed position up to the open position of the valve piston is required and that, on the other hand, the spring acting on the pressure body compresses to block-OQ is cash. The latter leads in terms of the spring

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Patent attorney Eichelbaum · Michaelstrasse 4 - D-4350 Recklinghausen 2

Da 629 a, b / 83. *. : ": '. V' \ \. \ April 14, 1983

to signs of fatigue and to a change in its characteristic curve, while the relatively long stroke has a softer one Requires spring with the disadvantage of a lower closing force. In addition, the pressure in the one receiving the O-ring increases Ring groove abruptly when driving over the radial openings of the valve piston, whereby the O-ring is almost sawed up by the hard jet of hydraulic fluid emerging from the radial openings. In addition, since the relatively long stroke reduces the maximum pressure fluid escaping per unit of time

is subject to a time component, as a result of the longer switching time of the valve, a to Buckling of the steel construction system leading to the load. | In a known pressure relief valve similar | Art (according to DE-OS 2 832 964) the valve piston is at one end over a valve plate from a cylindrical Helical spring and acted upon at its other end by a second spring via a cylindrical sleeve. The two springs work against each other, which means that as the spring force of one spring decreases, | the spring force of the other spring increases and vice versa. The sleeve lies loosely on the Εηάώ des facing it Valve piston on. As soon as this contact point between the sleeve and the valve piston closes the O-ring seal in the valve

2Q has passed the housing, the sleeve is attached to an annular collar held back, whereas the valve piston under the pressure of the pressure fluid, the cylindrical helical spring compresses even more until there is a gap between the two end faces that were previously in contact from the sleeve and the end of the valve piston.

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Patent attorney Eichelbaum Michaelstrasse 4 D-4350 Recklinghausen 2

Da 629 a, b / 83 .: [. ·. ". · '\ ^.: "\''' .. '\. ^{: 14 A} P ^ il 1983

Through this gap, hydraulic fluid can enter the radial emerging outlet openings emerge. In the event of sudden loads, the valve piston can turn the cylindrical Compress the coil spring on a block, which softens the latter, its characteristic curve and thus also changes the target set pressure. It is true that the adjustable abutment of the cylindrical helical spring a readjustment can be made, however, with has the disadvantage of an even faster block compression and a renewed change in the spring characteristic.

At the moment this pressure relief valve is opened only the cylindrical helical spring acts on the valve piston. To achieve the required Closing pressure, this individual spring must therefore be made correspondingly hard. But that in turn has the disadvantage of only a small flow rate through the gap between the sleeve and the end of the valve piston afflicted.

In the case of a pressure relief valve of a different type (according to DE-OS 2 815 919) the last-described one is Gap between the sleeve and the valve piston through an even smaller gap between the axial bore in the valve body and a sealing cone have been replaced. This pressure relief valve has in addition to the aforementioned Disadvantages an even smaller flow cross-section and thus an even smaller flow rate per unit of time.

In the case of a pressure relief valve of a different type (according to DE-GM 7 811 107), the valve piston also plunges one end into a gas space filled with nitrogen

Patent attorney Eichelbaum Michaelstrasse 4 D-435Q Recklinghausen 2 Da 629 a, b / 83 '. ^: \ . I \\. '... '. "'. \ April 14, 1983

of the valve housing. The seal in the valve housing between the radially opening outlet openings and the gas space tends to leak with increasing wear. This causes hydraulic fluid to enter the gas space, causing the gas spring becomes harder, which in turn can lead to an impermissible pressure increase in the expansion. A hardening of the In the case of a pressure relief valve, gas spring is also immediate with a drop in the discharge amount of the pressure fluid connected per unit of time, whereby the valve is at least briefly - in terms of it external forces acting on it can prove to be rigid and can thus increase the burden. In addition, the O-ring is due to the hard Jet of hydraulic fluid emerging from the radial bores arranged downstream in the direction of displacement literally sawed up. Destruction of the O-ring in turn leads to immediate inoperability of the entire pressure relief valve.

Furthermore, from DE-OS 2 408 106 another

on pressure relief valve of another type known, which consists of a There is a multitude of individual parts, a valve piston with a complicated design and a control piston. The valve piston is acted upon by a cylindrical coil spring via a screw plug and a valve plate, the remarks already made on US Pat. No. 3,548,867 and DE-OS 2,832,964 refer to this apply in the same way.

And finally, according to FR-PS 1 493 612, a diaphragm valve of a different type is known in which a combination

pi'essüng the spring by one with a stop " 30th

Patent attorney Eichelbaum · Michaeistraße 4 · D-435Ö Recklinghausen 2 Da 629 a, b / 83 '/ \. \ ::; ... '.'". \ April 14, 1983

collar provided, concentrically arranged between the springs guide rod is prevented. One such Stroke limitation system for the springs cannot be or not simply transferred to the pressure relief valves described above. In the event of a transfer To prevent the valve piston from falling out, its outer diameter must be compared to the Flow cross-section on the inlet side of the valve housing can be increased. That's next to a complicated one Manufacturing associated with a throttling of the hydraulic fluid at the last-mentioned point. Proceeding from this prior art, the invention is based on the object of a pressure relief valve of the type mentioned above, which on the one hand with an extremely short stroke of the valve piston large flow rates of the hydraulic fluid at the permissible Exceeding the target set pressure and which on the other hand ensures a long service life of the O-ring and thus a long-term functional reliability of the valve.

This object is achieved according to the invention in conjunction with the generic term mentioned at the outset by the Combination of the following features solved:

a) The axial bore ends in a manner known per se as a blind hole approximately at the level of the radial bores,

b) in the closed position of the valve, the front edge facing the inlet side overlaps Ring groove the outlet openings of the radial bores and

c) the spring or the spring system has a flat characteristic curve.

Patent attorney Eichelbaum · Michaelstrasse 4 · D-4350 Recklinghausen 2 Da 629 a, b / 83 · *; " ^: · / * ::. ·" · "" April 14, 1983

Through feature a) in conjunction with feature b), the O-ring is pretensioned and consequently presses itself like a plastic mass, but elastic, near the rear edge of the annular groove. This is in conjunction with the feature c) with an optimally small stroke in one direction a momentary large opening and in the other Direction achieved a high closing force of the valve despite the flat spring characteristic. Through this im The principle of multi-stage relaxation is due to the small overall stroke from the closed position to the complete The opening position is soft, but lightning-fast Pressure relief ensured. In tests it has been found that a valve constructed in this way has a passage amount can guarantee up to 60 liters per minute, although according to the operating recommendations for the. Hard coal mining only a maximum of 30 liters per minute are required. Furthermore, it was surprisingly found that that even after 45,000 switching operations the O-ring faces the outlet openings of the radial bores Surface areas showed no signs of wear. Signs of wear were only in those places of the O-ring, the areas with the continuous wall between two adjacent outlet openings of the radial bores had frictional contact. This frictional contact is based on fundamental findings several series of tests, therefore, that a narrow, film-like nose of the O-ring in the due to the sliding fit

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Patent attorney Eichelbaum · Michaelstraßö 4 · D-435Q Recklinghausen 2 Da 629 a, b / 83 '. ^: \. · Y! r. ,! "! \ April 14, 1983

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between the valve piston and the housing required gap is pressed and there a correspondingly high Experience friction. However, contrary to the originally cherished fears of the experts, the preload of the O-ring due to feature b) no wear of the O-ring in the immediate vicinity of the outlet openings of the radial bores, rather an evasion and thus an evasion possibility of the immediate O ~ ring surface areas adjacent to these outlet openings.

According to an advantageous development of the invention In the closed position of the valve, the outermost edge area of the outlet openings of the radial bores is sufficient maximum up to the middle of the pretensioned O-ring. Only when this center of the pre-tensioned, The elastic O-ring allows liquid to pass through. This allows the stroke of the valve piston from its closed position be made even smaller up to the first desired leak. The stroke is advantageously of the valve piston from its closed position to the leak approx. only 1 mm and to its full Open position about 3.5 mm. The size of the sliding fit between the valve piston and the cylinder wall has proven to be Fit h 7 / H 7 plus the corresponding wear allowances the teachings pertaining to this fit have proven to be particularly advantageous. Usually one Fit h 7 / H 7 between two parts does not allow for any relative movement or only with great difficulty. Plus the

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Patent attorney Eichelbaum - Michaelstrasse 4 D-4350 Recklinghausen 2

Da 629 a, b / 83 ·:.; : :: _{r # §} ; ..; .; April 14, 1983

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Speaking wear allowances of the gauges belonging to the fit mentioned could one, all of the requirements satisfactory sliding fit can be achieved. The passage opening is advantageous for the Provide the valve piston in the valve housing with an edge bevel that widens the passage opening in the shape of a funnel. This edge bevel can be designed both 0.5 mm 90 and 0.5 mm χ 120. The wall thickness between the one facing the outlet side of the valve housing The rear edge of the ring groove and the funnel-shaped widening edge bevel is between 1.0 and 0.5 mm.

To ensure a large flow rate through the valve piston is the ratio of the cross-sectional area of its axial bore to the sum of the cross-sectional area of its radial bores about 2: 1. Taking this relationship into account, for example, a Valve piston with an axial bore of 4 mm, eight radial bores with a diameter of 1.0 to 1.2 mm provided, the valve piston having an outer diameter of 5 mm.

An embodiment of the invention is shown in the drawings. Show:

Figure 1: A longitudinal section through the new pressure relief valve,

FIG. 2: the valve piston and the adjoining valve housing parts in an enlarged detail from Figure 1,

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Patent attorney Eichelbaum · Michaelstraße 4 - D-4350 Becklinghausen Da 629 a, b / 83 '/. · | . · ·· _ !. . \ · \ · *. April 14, 1983

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Figure 3: a partial view of Figure 1 at the level of the

O-ring in an enlarged view with preloaded O-ring and

FIG. 4: a section along the line IV / IV of Figure 2.

The new pressure relief valve 1 consists essentially of a valve housing 2, a valve piston 3, a valve spring 4 and a spring chamber 5 End 3 * has a stop collar 9, the edge 9 ^{1 of which} allows a maximum stroke H of the valve piston 3 up to the stop 10 of the valve housing 2.

The valve housing 2 is screwed to an internal thread 12 of the spring chamber 5 via an external thread 11 and is sealed from one another in a pressure-fluid-tight manner by means of the seal 13. The spring chamber is provided with several radial openings 14 and one axial opening 15. The axial opening 15 is located within a nut 16 and an Allen screw 17, via which the spring 4 can be pretensioned. The spring 4 is supported with its one end 4 ¹ against a spring plate 18 adjustable via the Allen screw 17 and with its other end 4 ¹ ′ against a second spring plate 19. The spring plate 19 is provided with a Dürchflußbohrung 20 and on its underside with a! ^ Egg-shaped abutment surface 21 at Q ₃ wherein the semi-spherically shaped end 3 ¹ 'of the

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Patent attorney Eichelbaum · Michaelstrasse 4 · D-4350 Recklinghausen 2 Da 620 a> b / 83 * '.' · · [ . · ··,:. . '. "'. ''. April 14, 1983

Valve piston 3 is applied. The valve piston 3 has a relatively wide axial bore 22 which is in a blind hole 23 ends. Below the blind hole 23, a total of eight branches from the axial bore 22 in the present case Radial bores 24 from.

When a predetermined set pressure is reached or exceeded, the valve piston 3 is acted upon by pressure fluid from the inlet side 25 of the housing in its position shown in FIG. Since the O-ring 8 in this position seals the longitudinal bore 6 of the valve housing 2 against the outer wall 3 ^{flt of} the valve piston 3, the valve piston 3 is raised when the pressure rises. The radial bores 24 pass over the O-ring 8 so that pressure fluid can flow out of the radial bores 24 to the outlet side 26 of the valve housing 2, which in the present case is formed by the interior of the spring chamber 5. From this exit side 26, the outflowing liquid reaches the outside via several, here for example four, radial openings 14 and the axial openings 15. As a result, the pressure of the hydraulic fluid on the input side 25 drops. When the predetermined setpoint pressure is reached or not reached, the spring 4 pushes the valve piston 3 via the spring plate 19 at its adjacent end 3 * 'in the direction of the input side 25 until the radial bores 24 have passed the O-ring 8 again and a new seal is present between the longitudinal bore 6 in the valve housing 2 and the outer wall 3 ^{fM of} the valve piston 3.

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Patent attorney Eichelbaum Michaelstrasse 4 D-4350 Recklinghausen 2 /)

Da 629 a, b / 83. · '. ^'·:::: · ":.': April 14, 1983

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The valve housing 2 and the valve piston 3 are shown in an enlarged view in FIGS. 2 and 3, parts that correspond to those of FIG. 1 being provided with the same reference numerals. The axial bore 22 of the valve piston 3 ends in a manner known per se as a blind hole 23 approximately at the level of the radial bores 24. What is new, however, is that in the illustrated closed position of the valve 1, the front edge 7 'of the annular groove 7 facing the inlet side 25, the outlet opening 27 j 10 of the radial bores 24 overlap. As a result, the interior of the annular groove 7 is constantly under the full pressure of the hydraulic fluid, which can be up to 600 bar, for example. As a result, deforms the illustrated depressurized in Figure 2 O-ring 8 as a plastic mass according to the illustration of Figure 3. In Figure 3, also the gap 28 can be seen, the result of the sliding fit between the outer wall 3 ^{1, 1} 'of the valve piston 3 and the Longitudinal bore 6 in valve housing 2 must be present. Since the O-ring 8 is under the pressure of the hydraulic fluid - as in Figure 3

shown - how a plastic mass behaves, it penetrates into the gap 28 with a thin film 8 '. However, to keep this disadvantageous, in any O-ring of avoidable in issue standing type intrusion as possible _A "small is advantageous at this point \ 25

* located edge 29 of the annular groove 7 is sharp-edged

and the gap 28 is kept as small as possible, because as the film 8 * becomes larger, the friction between the Longitudinal bore 6 of the valve housing 2 and the outer wall

3 ¹ '' of the valve piston 3 increased. To get such a one-30

penetrate a film 8 'occur as briefly as possible

Patent attorney Eichelbaum · Michaelstrasse 4 · D-4350 Recklinghausen 2 Da 629 a, b / 83 'V "; _: ::. _{T m} \>'". \ _{14> April 1983}

In all pressure relief valves of the type in question here, the radial bores 24 were arranged clearly below the groove 7 in the closed position of the valve 1. Associated with this was obviously the hope of the designers that, due to the pressure loss in the gap 28, the O-ring 8 only ^{underwent a disadvantageous deformation in the form of the film 8 1} when the outlet openings 27 of the radial ^{bores 24 reached the front edge 7 1 of} the annular groove 7. According to the invention, exactly the opposite is done, namely that in the closed position of the valve 1, the front edge 7 'of the annular groove 7 facing the inlet side 25 overlaps the outlet openings 27 of the radial bores 24. Nevertheless, the fears regarding premature wear of the O-ring have not been confirmed; on the contrary, this O-ring 8 was still fully functional even after 45,000 strokes. At the same time, with the arrangement described above, the incomparable advantage of an optimal short stroke h from the closed position to the point of leakage or full opening of the valve was achieved. The center of the O-ring 8 in FIG. 3 should be identified by the line 30. Then the relief of the valve takes place essentially in five different-sized strokes h of relaxation. As soon as the outermost edge region 24 'of the outlet openings 27 of the radial bore part 24 exceeds the center line 30 of the pretensioned O-ring 8, a first leak and thus the first relaxation phase of the valve occurs. This hub

2Q is denoted by h ... Reaches the outermost edge area

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Patent attorney Eichelbaum · Michaölstraße 4 · D-4350 Recklinghausen 2 ** y _v

* t «4 · * ·· · C—

Since 629 a, b / 83, · ',' j ·; · ^: ··· · j "·, ': April 14, 1983

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24 'of the radial bores 24, approximately the rear edge 7 ^{11 of} the annular groove 7, further relaxation occurs. At the same time, the film 8 ′, which can expand into the opening 27, is also relieved. For this reason, eight radial bores 24 were not arranged, as was previously the case in the prior art. Fears that the film 8 'and thus also the O-ring 8 could be sheared off by the lower edge 24' * of the radial openings 24 moving upward, have not been confirmed.

As soon as the outermost edge area 24 'of the radial bores reaches the edge 31 of the edge bevel 32, the third relaxation phase occurs at the stroke h ". In this position of the valve piston 3, the valve is not yet fully open. The stroke h .. from the closed position of the valve to the point of leakage is approx. 1 mm, the stroke h "is approx. 2 mm and the stroke h_ is approx. 2.5 mm. The valve is not considered fully open until the stroke h, of 3.5 mm. With a further stroke h, - = H = 4.5 mm, the stop edge 9 ^{1 of} the stop collar 9 of the valve piston comes against the stop edge 10 of the valve housing 2. From the stroke h, at a pressure of 420 bar via the axial bore 22 and the eight Radial bores 24 flow out about 60 liters per minute of the hydraulic fluid.

As soon as the lower edge 24 ″ of the radial bores 24 the rear edge 7 '' of the annular groove 7 on the way to overshoots the full closing opening, the film 8 'of the O-ring 8 is formed again.

As can be seen from Figure 4 in conjunction with Figure 2, is at the level of the radial bores 24

3Q Length of the opened circumference greater than the length

Patent attorney Eichelbaum> Michaelstrasse 4 D-4350 Recklinghausen 2 ", // 1

Da 629 a, b / 83.:!. · .. ^: ' ^: .. ^: ' T ' ^: .. · * ..' April 14, 1983

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the closed circumferential line between the individual radial bores 2 ^. Due to the total of eight radial bores 24, the relatively large axial bore 22 and the small stroke Vi _n . of at most 4.5 mm there is excellent relaxation of the pressure fluid on the input side 25 within a short switching time. Furthermore, the O-ring 8 is less stressed than in the prior art, since according to FIG. of the O-ring 8 is relieved because the circumferential line of the radial openings 24 in this area is longer than the circumferential line of the sum of the webs 33 located between them.

The new one from the valve housing 2, the valve piston 3, the O-ring 8 and the spring plate is particularly advantageous 19 and the spring 4 existing valve as a compact assembly for different types of valves and applications ^ areas used. The O-ring 8 advantageously has a Shore hardness A of at least 100. = »

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Patent attorney Eichelbaum Michaelstrasse 4 D-435G Recklinghausen

Since 629 a, b / 83 'y \ . ; |?.:. . \ "\ _t \ April 14, 1983

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"Pressure relief valve" parts list

Pressure relief valve 1 Valve housing e 2 Valve piston 3 Ends of the valve piston 3 ', V Wall of the valve piston 3 "· Valve spring 4th Ends of the valve spring 4 ', 4 " Spring chamber 5 Longitudinal hole in the valve body 2 6th Ring groove 7th O-ring 8th O-ring film 8 8 ¹ Stop collar of the valve piston 9 Edge of the stop collar 9 ' Total stroke H, h ₅ Strokes h _is h ₂ , h ₃ , h ^ Stop on the housing 2 10 External thread of the housing 2 11th

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Patent attorney Eichelbaurn · Michaelstrasse 4 · D-4350 Recklinghausen Da 629 a, b / 83. · '. ·' *:. ".:. · *."*; April 14, 1983

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internal thread of the spring clip 5 12th poetry 13th Radial openings in the valve piston 3 14th Axial opening in Federkairmer 15th mother 16 Imbus s ehraube 17th Spring plate 18, 19 Flow bore 20th Conical contact surface 21 Axial bore in valve piston 3 22nd Blind hole 23 Radial bores in valve piston 3 24 Entrance side of the housing 2 25th Output side of the housing 2 26th Outlet opening of the radial bores 24 27 Gap between housing 2 in
Valve piston 3 28 Sharp edge of the ring groove 7 29 Center line of the O-ring 8 30th Edge of the edge bevel 31 Edge bevel of the housing 2 32 Bars between radial holes 24 33

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Claims (14)

Patent attorney Eichelbaum. Michaelstrasse 4 · D-4350 Recklinghausen 2 Da 629 a, b / 83 mS .Ί '\ J:' \ '· IJ': April 14, 1983 Applicant: Jörn DAMS Holthauser Strasse 2, 4342 Hattingen-Holthausen "Pressure relief valve" claims 1. Pressure relief valve with an inside a longitudinal bore of a valve housing3 along an in a circumferential ring groove inserted O-ring up to a stop and with a stop collar provided valve piston, which when reaching or exceeding a predetermined set pressure against the force of a spring or a spring system is axially displaceable and pressure fluid from an input side of the housing through a arranged in it Axial bore and several radial bores branching off from it at approximately the same height to an output side of the Can flow through valve housing and when reaching or falling below the specified set pressure can be pushed back into its closed position under the action of the spring or the spring system, 2Q characterized by the combination following features: - 2 30 * * * * «« «Suffered ι * Patent attorney Eiche! Ba <im Michaelstrasse 4 D-4350 Recklinghausen 2 ^ Da 629 a, b / 83 '/ \ ' j ■ \ \ l \ · ■ | "j. \ April 14, 1983 ι a ■ < a) the axial bore (22) ends in a manner known per se as a blind hole (23) approximately at the level of the radial bores (24), b) in the closed position of the valve (1), the front edge (7 ¹ ) of the annular groove (7) facing the inlet side (25) overlaps the outlet openings (27) of the radial bores (24) and c) the spring (4) or the spring system has a flat characteristic curve. 2. Pressure relief valve according to claim 1, characterized in that in the closed position of the valve (l) the outermost edge region (24 ¹ ) of the outlet openings (27) of the radial bores (£ 4) up to a maximum of the middle (30) of the pretensioned O-ring (8) is enough. 3. Pressure relief valve according to claim 1 or 2, characterized. that the stroke (h,) of the valve piston (3) from its closed position to the point of leakage is approx. 1 mm. 4. Pressure relief valve according to the claims 1, 2 or 3, characterized in that that the stroke (h,) of the valve piston (3) of its closed position to its open position is about 3.5 mm. - 3 30 Patent attorney Eichelbaum Michaelstrasse 4 D-4350 Recklinghausen 2 Da 629 a, b / 83 '. ^: · '. . : W: .. '. "'. \ April 14, 1983 ~ * 5. Pressure relief valve according to the claims 1 to Uj, characterized in that the size of the sliding fit between the valve piston (3) and the cylinder wall (6) of the housing (2) is dimensioned h 7 / H 7 plus the corresponding wear allowances of the gauges belonging to the said fit. 6. Pressure relief valve according to the claims 1 to 5, characterized in that the passage opening for the valve piston (3) in the Valve housing (2) is provided with an edge bevel (32) which widens the passage opening in a funnel-shaped manner. 7. Pressure relief valve according to claim 6, characterized in that the edge bevel (32) is designed 0.5 mm χ 90 °. 8. Pressure relief valve according to claim 6, characterized in that the Edge bevel (32) 0.5 mm χ 120 ° is designed. 9. Pressure relief valve according to claims 6 to 8, characterized in that the wall thickness (d) between the output side (26) of the valve housing (2) facing the rear edge (7 ¹¹⁾ of the annular groove (7) and the funnel-shaped widening Randfase (32 ) is between 1.0 and 0.5 mm. - 4 - Patent attorney Eichelbaum Michaelstrasse 4 D-4350 Recklinghausen 2 Da 629 a, b / 83 \. ^: . < . yy ί.ί. . / 'y,'! April 14, 1983 10. Pressure relief valve according to claims 1 to 9, characterized in that the Ratio of the cross-sectional area of the axial bore (22) of the valve piston (3) to the sum of the cross-sectional areas its radial bores (24) is about 2: 1. 11. Pressure relief valve according to claims 1 to 10, characterized in that the Valve piston (3) has eight radial bores (24). 12. Pressure relief valve according to claims 1 to 11, characterized in that the Valve housing (2, 5) with four radial openings (14) and one axial opening (15) for draining the hydraulic fluid is provided. 13. Pressure relief valve according to claims 1 to 12, characterized in that it is as Compact assembly consisting of the valve housing (2), the valve piston (3), the O-ring (8), the spring plate (19) and the Spring (4) consists. 14. Pressure relief valve according to claims 1 to 13, characterized in that the O-ring (8) has a Shore hardness of at least 100 Shore Α | having.