GB2064069A

GB2064069A - A Check Valve Operating as a Pressure Limiting Valve and a Make-up Valve

Info

Publication number: GB2064069A
Application number: GB8035402A
Authority: GB
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1979-11-14
Filing date: 1980-11-04
Publication date: 1981-06-10
Also published as: DE2945911C2; IT1134211B; IT8025899A0; DE2945911A1; GB2064069B; SE8007980L

Abstract

The valve has two valve members (16,35) concentric with one another of which the pressure limiting inner valve member (35) is opened by pressure in a load chamber 13 against a spring (43) and has a sliding seal (27,36) which separates a cavity (42) in the outer valve member (16) from a load chamber (13). A throttle (45,39) provides damping of the inner valve member (35) in both directions. From pressure at load chamber 13, the outer valve 16 is subjected to an opening force and, via a spiral groove 34, to a closing force. When the direct opening force on valve 16 due to pressure at outlet 15 is greater than the net closing force due to load pressure combined with spring 32 this valve will open to allow a make up flow from outlet 15 to load chamber 13. <IMAGE>

Description

SPECIFICATION A Directly Controlled Check Valve Operating as a Pressure Limiting Valve and a Make-up Valve The invention originates from a directly controlled check valve as a pressure limiting valve and make-up valve according to the preamble to the main claim. Such a valve is already known from German OS 29 04 403 which is directly controlled and which is suitable for large through flows because, particularly when operating as a kind of make-up valve, pressure medium is sucked past the outer valve member into the load chamber and does not need to flow through the outer valve member. However, with this check valve there is the disadvantage that the inner valve member mounted in the outer valve member is formed as a part-of a pressure limiting valve. Thus, the flow cross-section controlled by the inner valve member is smaller than its pressure influenced area.During operation as a pressure limiting valve, this construction is only suitable for relatively small through flows and requires a large strong spring. A further disadvantage is that the guide for the outer valve cone and its associated valve seat are arranged in different components. Due to the considerable true running error produced thereby a bad seal is achieved at the outer valve member. It is also a disadvantage that no stroke limitation for both valve members is provided which likewise impairs a reliable operation of the check valve. There is a further disadvantage that this check valve cannot be constructed as a releasable valve since, in this case, the valve members are moved in opposite directions during opening. Furthermore, the damping of the inner and outer valve members can only be matched to one another badly which likewise impairs a reliable operation.

Furthermore, a directly controlled working valve operating as a pressure limiting and makeup valve is known from United States specification 3 112 763 and which is also suitable for large pressure medium flows when making-up. However, the disadvantage with this check valve is that the load pressure acting at the load port is conducted from one end of the outer valve member to the other end through the inner valve member. Due to the internal pressure thereby occurring in the valve member on the one hand and on the other hand due to a screwthread arranged in the outer valve member in the region of the mounting for the inner valve member, expansions can occur which lead to jamming of the valve members and thus hinder a reliable operation.The operation is further impaired by the fact that the outer valve member associated with the make-up only permits a slightly effective suction damping in the closing direction.

Moreover, in this case too, the guiding of the outer valve member and its associated valve seat are arranged in different components whereby bad centering and with it bad sealing are achieved. Furthermore, in this case too, no means are provided for producing the check valve as a valve with make-up constructional features.

Furthermore, a check valve operating as a pressure limiting and make-up valve is known from German OS 23 02 043, Figure 6, which is suitable for high through flows. The disadvantage with this check valve is that it is designed as a pilot controlled valve and is consequently of expensive construction. Also, cavities in the outer valve member influenced by the load pressure are provided in the valve which can lead to an expansion and with it a jamming of the valve member and also interferes with its reliable operation.

Advantages of the Invention As opposed to this, the check valve in accordance with the invention comprising the characterising features of the main claim has the advantage that it is suitable for a directly controlled pressure limiting make-up and check valve for large pressure medium flows and at the same time permits a safe and reliable method of operation. Thus, jamming of the valve members as a result of expansion due to internal pressure or due to screwthreads is prevented since the cavity formed in the outer valve member is relieved to the discharge through a duct connection in the inner valve member at least during the pressure limiting and make-up function.Furthermore, sealing between the load chamber influenced by the load pressure and the cavity is effected by a piston section on the inner valve member which is guided in a thick walled region of the outer valve member where the danger of expansion does not exist. Due to the arrangement of the guide and the valve seat for the outer valve member in the same housing part, a high fluid-tightness is achieved. In addition, an effective damping is achieved for the inner valve member which operates with a pressure build-up during opening and during closing of the valve member.The means preventing the jamming and effecting the damping and the sealing provide, with a check valve of that kind performing a plurality of functions with a directly controlled construction suitable for large through flows, an especially advantageous combination which permits a safe and reliable operation of the valve.

Advantageous further developments and improvements of the check valve set forth in the main claim are made possible by the measures set forth in the sub-claims. In order to increase the reliable operation of the check valve still further, it is advantageous to provide stroke limiting for both valve members. A further particularly advantageous arrangement is provided in accordance with claim 6 wherein the check valve can be provided with the constructional features of a releasable valve which, despite its direct control, is not inclined to oscillate and permits a fine control. An arrangement according to claim 8 is particularly preferable for the characteristics of the check valve during its function as a pressure limiting valve.

Drawing Three embodiments of the invention are illustrated in the drawing and are described in detail in the following specification. Figure 1 shows a longitudinal section through a first embodiment of the check valve and Figure 2 shows a longitudinal section through a second embodiment constructed as a releasable check valve and Figure 3 shows a longitudinal section through a portion of a third embodiment.

Description of the Embodiments Figure 1 shows a check valve 10 which can operate as a pressure limiting valve and as a make-up valve. The check valve 10 has a longitudinal bore 12 in a housing 11 which issues into a load chamber 13. A valve seat 14, to which a discharge 1 5 leads, is arranged in an extension of the longitudinal bore 12 in the housing 11.

Thus, the valve seat 14 and the longitudinal bore 12 are formed in the same housing portion so that their position with respect to each other is accurately centered.

An outer valve member 16 is slidingly guided in the longitudinal bore 12 in the housing 11 . This valve member 1 consists essentially of a cylindrical sleeve-like section 17 which, in the region of the load chamber 13, changes into a reduced valve cone 1 8 and at its opposite end is closed by a threaded plug 19. An annular chamber 21 which is in communication with the load chamber 1 3 through radial bores 22 and is in communication with the discharge 1 5 through a valve seat 23 and an axial bore 24, is arranged in the valve cone 18.A multiple stepped bore 26 leads from the annular chamber 21 to a threaded section 25 receiving the threaded plug 1 9. From the annular chamber 21, the bore 26 has at least one first section 27 and then a second section 28.

The outer valve member 16 is sealingly and sliding guided in the longitudinal bore 12 in a region which extends between the load chamber 13 and a distance from the threaded section 25.

By means of its end carrying the threaded plug 19, the outer valve member 16 bounds a space 29 in the longitudinal bore 12 which is closed to the outside by a closure screw 31. A first spring 32 arranged in the space 29 attempts to force the valve cone 18 on the outer valve member 1 6 against the valve seat 14 in the housing 11. The stroke of the outer valve member 1 6 is limited by an abutment 33, which also guides the spring 32, arranged on the outside of the threaded plug 19.

A throttle connection 34 leads from the space 29 to the load chamber 1 3 wherein, in this case, this throttle connection is formed as a spirally extending groove applied to the outer periphery of the valve member 16.

The outer valve member 1 6, which is associated with the make-up functions, accommodates in its interior an inner valve member 35 which is associated with the pressure limiting function. This inner valve member 35 has a piston-like section 36 which is sealingly and siidingly guided in the first section 27 of the bore 26 and projects into the annular chamber 21. In the region of the annular chamber 21 , the pistonlike section 36 changes through a differential surface 37 into a conical section 38 which engages the valve seat 23. Extending from the piston-like section 36, the inner valve member 35 has a throttle flange 39 which co-operates with the second section 28 of the bore 26 to provide a pressure damping during closing of the inner valve member 35. An abutment pin 41 extends from the throttle flange 39.A cavity 42 in the outer valve member 16 and which accommodates a second spring 43 associated with the pressure limiting function, is bounded by the piston-like section 36 of the inner valve member 35. Packing washers 44 are inserted between the second spring 43 and the throttle flange 39 for setting the level of the pressure limiting valve. The cavity 42 is relieved to the discharge 1 5 through a radially extending throttle bore 45 in the abutment pin 41 and a centrally extending blind bore 46. The lower portion of the piston-like section 36 of the inner valve member 35 shows a pure sliding seal which, with low hysteresis takes account of the disadvantage of a high oil leakage, whereas the upper portion of the said section 36 shows as an alternative an O-ring seal which, with low oil leakage, takes account of a large hysteresis.

The method of operation of the check valve 10 is described as follows: When a load pressure which is smaller than the value set at the pressure limiting valve and is greater than the pressure in the discharge 15, prevails in the load chamber 13, then the check valve 10 interrupts the communication from the load chamber 13 to the discharge 1 5. In so doing, the outer valve member 1 6 is also influenced by the load pressure in the space 29 through the throttle connection 34 and is forced onto the valve seat 14 by a force which is produced from the product of the load pressure times the effective sealing area plus the force of the first spring 32.The communication from the load chamber 1 3 through the outer valve member 1 6 to the discharge past the valve seat 23 is blocked by the inner valve cone 35. Only very little pressure medium can leak from the load chamber 1 3 through the slide seal of the piston-like section 36 into the cavity 42 and from there arrive through the throttle bore 45 and the blind bore 46 at the discharge 1 5. The piston-like section 36 is guided in the section 27 with a sliding seal with the least possible clearance in order to maintain such a leakage flow very low. Due to the thick walled construction of the sleeve-like section 1 7 in the said region, the formation of a narrow guiding gap is favoured without the possibility of jamming of a valve member being able to occur.

When the check valve 10 operates as a makeup valve, a lower pressure prevails in the load chamber 13 than in the discharge 1 5 and pressure medium flows from the discharge 1 5 between the valve seat 14 and the valve cone 1 8 through to the load chamber 13. In so doing, the pressure in the discharge 1 5 is high enough for the force on the outer valve member 1 6 resulting therefrom to exceed the force of the spring 32 and the force of the pressure effective in the load chamber times the effective area and to force the outer valve member 17 into an open position against the force of the spring 32. The stroke of the outer valve member 1 7 is terminated when the abutment 33 engages the closure screw 31.

When the check valve operates as a make-up valve, the inner valve member 35 remains forced onto its valve seat 23. During the operation of the check valve 10 as a make-up valve, the pressure effective in the load chamber 13 can build up in the space 29 through the throttle connection 34.

When the outer valve member 17 is raised from the valve seat 14, pressure medium must escape from the space 29 through the throttle connection 34 to the load chamber 13. In that manner, an effective pressure damping may be achieved during opening of the make-up valve. During closing of the outer valve member 1 6, pressure medium must be drawn out of the load chamber 13 into the space 29 through the throttle connection 34. Thus, during the closing operation, a less effective suction damping takes place which permits a relatively more rapid closure and thus prevents an undesirable lowering of a load.

Thus, the outer valve member 17 operates as a non-return valve which safeguards the load chamber 13.

Beyond this, the check valve 10 can also act as a pressure limiting valve. It will be assumed that the valve members 16, 35 are maintained in their initial positions illustrated in Figure 1 by their springs 32 and 43. The load pressure prevailing in the load chamber 13 acts on the differential area 37 on the inner valve member 35. When the resulting force on the inner valve member 35 exceeds the force of the spring 43 then the cone section 38 is raised from the valve seat 23 and pressure medium can escape from the load chamber 1 3 to the discharge past the inner valve seat 23. By providing the inner valve member 35 with a differential area 37, the valve member 35 can control a relatively large cross-section so that the pressure limiting valve is suitable for very large through flows.On opening of the inner valve member 35, the said pressure medium is forced out of the cavity 42 and can only escape through the throttle bore 45 to the discharge 1 5. In that manner, an effective pressure damping is achieved for the inner valve member 35 during opening. The stroke of the inner valve member 35 is terminated when the abutment pin 41 abuts the associated threaded plug 1 9. A narrow annular gap is formed between the throttle flange 39 and the second section 28 of the bore 26, through which, on closing of the inner valve member 35, a pressure medium must escape from an annular space 47. Thus, an effective pressure damping is also achieved during closing.

Thus, despite a simple and compact construction, the present check valve 10 can control large flow cross-sections. Thus, a sliding seal with a very small clearance is possible between the load chamber 1 3 and the cavity 42 relieved to the discharge 1 5 since, due to the considerable wall thickness of the sleeve-like section 1 7 in the region of the bearing of the inner valve member 35 and the smaller inner diameter of the outer valve member 1 6 in the said region, only very slight pressure deformations occur so that no jamming of the valve members can take place.Also, the cavity 42 in the outer valve member 1 7 is permanently relieved to the discharge 1 5 and the threaded section 25 is arranged at a distance from the guiding region so that jamming of the outer valve member 16 as a result of expansion due to internal pressure or due to screwthreads is prevented. The sliding seal by the piston section 36, confers a slight hysteresis on the directly controlled pressure limiting valve.

Furthermore, an effective damping of both valve members in both directions is achieved to a sufficient extent by simple means. The fluidtightness of the check valve is improved not only by the narrow clearance of the piston section 36 but also by the provision of the longitudinal bore 12 and of the valve seat 14 in the same housing portion 11. Stroke limiting of both valve members 16, 35 increase the reliable operation of the check valve 10. The means contributing to the safe and reliable operation of the check valve 10 represent a particular advantageous combination of features.

Figure 2 shows a second embodiment of a check valve 50 of releasable construction in which a fine control during lowering is possible with the aid of a multiway valve. The check valve 50 differs from that according to Figure 1 as follows, wherein like parts are provided with like references: instead of the discharge 1 5 in Figure 1, a first control chamber 52, which is arranged near to the load chamber 13, is arranged in the housing 51. A second control chamber 53 in the housing 51 is arranged at a distance from the first control chamber 52. A release piston 54 is sealingly and slidingly guided in the housing 51 between the two control chambers 52, 53 and concentric to the longitudinal bore 12. Lines 55, 56 lead from the control chambers 52, 53 to load ports of a 4-way 3-position valve 57 which is connected to a pump 58 and to a reservoir 59.A line 61 leads from the line 56 into an annular space 62 of a double acting working cylinder 63.

One piston space 64 of the said cylinder 63 is connected to the load chamber 13 through a line 65. At its valve cone 18, the outer valve member 1 6 of the check valve 50 has a throttle sleeve 66 directed towards the first control chamber 52.

Extending from the valve seat 23, this throttle sleeve 66 has a recess 67 and terminates in a throttle opening 68. A fine control stud 69 is formed on the valve member 35 as an extension of the conical section 38 and which extends through the throttle sleeve 66 into the first control chamber 52 and carries a flange 71 associated with the throttle opening 68. The throttle bore 45 in the inner valve member 35 passes through the fine control stud 69 and the conical section 38 in an axial direction. The release piston 54 engages the free end of the fine control stud 69. In the throttle opening 68, the flange 71 forms a narrow annular gap through which the pressure in the first control chamber 52 and in the recess 67 can be built up.

The method of operation of the check valve 50 according to Figure 2 is as follows: like the check valve 10 according to Figure 1, the check valve 50 can perform its pressure limiting function and its make-up function. Moreover, the check valve 50 can also be operated as a release valve. For this purpose, the control slide of the multiway valve 57 is displaced in the direction of its righthand working position 72. In so doing, the pressure medium coming from the pump 58 is conveyed through the line 56 into the second control chamber 53 with the aid of fine control edges on the control slide and a control pressure is built up in the control chamber 53 which acts on the release piston 54. In addition, pressure medium is delivered through the line 61 into the annular space 62 of the cylinder 63.The release piston 54 influenced by the control pressure forces the inner valve member 35 from its associated valve seat 23.

Depending on the value of the load P acting on the piston rod of the cylinder 63, a pressure prevails in the cylinder space 64 which can then flow away through the line 65, the load chamber 13, the opened cross-section at the valve seat 23, the recess 67, the throttle opening 68, the first control chamber 52, the line 55 and the multiway valve 57 to the reservoir 59. In so doing, pressure medium flowing away from the piston space 64 through the fine control land on the flange 71 is throttled in such a manner that the piston rod retracts only slowly under the influence of the force P. In so doing, the control pressure in the second control chamber 53 remains the same. Thus, the load P cannot run ahead of the supply flow coming through the line 61.Due to the special formation of the flange 71 and the throttle opening 68, a chattering of the inner valve member 35 is prevented during the retraction of the piston rod. The outer valve member 1 6 is forced onto its seat 14 by the load pressure acting on it. In this manner, an osciliation-freb fine control is possible under the action of the load during retraction of the piston rod into the cylinder 63 with the aid of the multiway valve 57.If the control slide of the multi-way valve 57 is displaced fully into its end position beyond the fine control range, then, with a correspondingly large control pressure in the second control chamber 53, the release piston 54 can force the inner valve member 35 into its end position up to the abutment against the force of the spring 43 whereby the flange 71 on the fine control stud comes to rest in the recess 67 and thereby fully opens the throttle opening 68.

For extending the piston rod in the cylinder 63 against the action of the load P, the control slide of the multi-way valve 57 is brought into a left hand working position 73. In so doing, pressure medium flows from the pump 58 through the line 55, the first control chamber 52, past the open outer valve member 1 6 to the load chamber 1 3 and then into the cylinder space 64. In so doing, the outer valve member 1 6 is raised from its valve seat 14 against the force of the first spring 32 and operates like a non-return valve. Should, during raising of the load P, the line 55 between the check valve 50 and the multi-way valve 57 break then the load P is safeguarded by the non-return valve function of the check valve 50.

Figure 3 shows a third check valve 80 which differs from that of Figure 2 chiefly by the fact that the fine control stud 69 with a flange 71 is not arranged on the inner valve member 35 but is rigidly fixed to the release piston 54. This arrangement has the advantage that when the check valve 80 is acting as a pressure limiting valve, the pressure shock acting in the load chamber 13 can be relieved unhindered through the throttle opening 68 since the flange 71 is arranged outside the opening 68. In this instance, the flange 71 only co-operates with the throttle opening 68 during fine control during relief of the inner valve member 35.

Variations in the illustrated embodiments are of course possible without departing from the concepts of the invention.

Claims

1. A directly controlled check valve acting as a pressure limiting and make-up valve comprising an outer valve member associated with the makeup and guided in a bore in a unit fixed to the housing, the valve member accommodating in its interior a coaxial valve member associated with the pressure limiting, wherein both valve members are formed as seat valve members and are each loaded by a spring and both control the communication between a load chamber and a discharge, wherein the outer valve member is forced onto its seat by the pressure in the load chamber and the force of the first spring and during make-up pressure medium flows between the outer valve member and the seat to the load chamber, whereas during pressure limiting pressure medium flows through the outer valve member to the discharge, characterised in that, the outer valve member has a cavity accommodating the spring associated with the pressure limiting function, the cavity is sealed by a piston section on the inner valve member with respect to the load chamber and is in communication with the discharge through bores arranged inside the valve member, that the inner valve member has a differential area influenced by the pressure in the load chamber and that the outer valve member bounds a space in a longitudinal bore, which accommodates the spring associated with the make-up function and is in communication with the load chamber through a throttle connection.

2. A check valve according to claim 1 characterised in that the inner valve member has a throttle flange arranged in the cavity.

3. A check valve according to claim 1 or 2 characterised in that an abutment associated with the outer valve member is arranged in the space and limits the stroke of the valve member.

4. A check valve according to claim 3 characterised in that an abutment pin is associated with the inner valve member and limits the stroke of the valve member.

5. A check valve according to claim 1 or 2 characterised in that the throttle connection is formed as a spiral groove on the outer periphery of the outer valve member.

6. A check valve according to one of claims 1 to 5 characterised in that the outer valve member has a throttle sleeve projecting towards a first control chamber and a release piston is guided coaxially with respect to the valve members and with which is associated a fine control stud actuable by the release piston and co-operating with the throttle sleeve.

7. A check valve according to claim 6 characterised in that the fine control stud is fixedly arranged on the inner valve member.

8. A check valve according to claim 6 characterised in that the fine control stud is fixedly arranged on the release piston.

9. A check valve according to one of claims 6 to 8 characterised in that the fine control stud has a flange which is associated with a throttle opening in the throttle sleeve and that a recess is formed in the throttle sleeve between the throttle opening and the valve seat.

10. A check valve substantially as herein described with reference to Figure 1, Figure 2 or Figure 3 of the accompanying drawings.