GB2188706A

GB2188706A - A 3-port, 2-position directional control valve with pressure balancing for fluids under pressure

Info

Publication number: GB2188706A
Application number: GB08705489A
Authority: GB
Inventors: Werner Reinelt; Karl Krieger
Original assignee: Hemscheidt Hermann Maschinenfabrik GmbH and Co
Current assignee: Hemscheidt Hermann Maschinenfabrik GmbH and Co
Priority date: 1986-03-15
Filing date: 1987-03-09
Publication date: 1987-10-07
Anticipated expiration: 2007-03-09
Also published as: CS264291B2; GB2188706B; GB8705489D0; CS169187A2; DE3608757C2; DE3608757A1

Abstract

A 3/2 directional control valve with pressure balancing for pressure fluids comprises a sliding piston (4) provided with a longitudinal bore (9) which is closed to the exterior, the piston (4) being axially movable in a valve housing (1) into an open position for the connection of a first passage for a pressure medium user connection to a high-pressure conduit lying adjacent this first passage and being movable into a closed position for the connection of a second passage for a pressure medium user connection to a discharge conduit lying adjacent this second passage, wherein the housing (1) is in two parts and comprises an outer housing body (2) and an inner housing sleeve (3) in which the sliding piston (4) is guided, with the high-pressure conduit, the user connection(s) and the discharge conduit being in the form of bores (11, 13, 15) in the outer housing body (2) which terminate in respective ring channels (12, 14, 16) in the housing sleeve (3), there being, in the bottom region of each of the ring channels (12, 14, 16), an outlet for passage openings (18) of slot form lying in one plane on an arc of about 360 degrees, with the first and second passages for the user connection each comprising an outlet from the passage openings (18) in the same ring channel (14). <IMAGE>

Description

SPECIFICATION A 3-port 2-position directional control valve with pressure balancing for fluids under pressure This invention relates to a 3-port, 2-position directional control valve with pressure balancing for pressure fluids, comprising a sliding piston provided with a longitudinal bore which is closed to the exterior, the piston being axially movable in a valve housing into an open position for the connection of a first passage for a pressure medium user connection to a high-pressure conduit lying adjacent this first passage and being movable into a closed position for the connection of a second passage for the pressure medium user connection to a discharge or outlet conduit lying adjacent this second passage.

A control valve of this construction is described in DE-A-28 08 477. In this valve, the first and second passages of the pressure medium user connection(s) are connected with one another, with the first passage in the open position of the piston being separated from the connection of the high-pressure conduit and the second passage in the open position of the piston being separated from the connection of the outlet conduit in a gap region between the valve housing and the piston by respective circumferential seals and each comprising one sealing ring fitted in a ring groove.From the longitudinal bore in the piston-with spacing between them-a forward and a rear row of openings extend radially to the exterior, which openings in the open position of the piston connect the longitudinal bore with the first passage of the pressure medium user connection and the bore of the high pressure conduit. Channels extend around the circumferential surface of the piston, with the forward row of radial openings terminating in a foremost channel and the rear row of radial openings terminating in a middle channel when the piston is in its open position. When, however, the piston is in its closed position, the second passage of the pressure medium user connection and the outlet conduit are connected together by way of the middle channel with the rear radial openings terminating in the middle channel.

A feature of this known control valve is that the connection bores present in the housing open directly into surrounding channels of the piston in which radial bores from the longitudinal bore of the piston terminate. By reason of this construction, pressure medium flow losses occur which limit the range of capacity of the valve. Moreover, the valve throughput is also limited by the fact that the diameter of the passage bores is limited by the width of the circumferential seals.

The aim of the present invention therefore is to improve this form of valve so that flow losses within the valve body are reduced.

In accordance with the invention, this aim is achieved-in a control valve of the construction set forth in the opening paragraph of the Specification-by constructing the housing in two parts so that it comprises an outer housing body and an inner housing sleeve in which the sliding piston is guided, with the user connection(s), the high-pressure conduit and the outlet conduit being in the form of bores in the outer housing body which terminate in respective ring channels in the housing sleeve, there being, in the bottom region of each of the ring channels, an outlet from passage openings of slot form lying in one plane on an arc of substantially 360 degrees, with the first and second passages for the user connection each comprising an outlet from the passage openings in the same ring channel.

Such a construction ensures that, starting from the housing sleeve, the pressure fluid supplied and withdrawn by way of the passage bores is distributed over the entire circumference of the piston, whereby a uniform distribution and thus a reduction of the flow losses are achieved. Furthermore, the surprising effect is achieved that the sealing rings arranged on the circumference of the piston are now no longer subjected to partial pressure action through the outlet openings of the connection bores as in the prior art. Instead, a uniform circumferential loading of the sealing rings occurs so that there is a more uniform load distribution with a range of sealing rings reduced in width.Since the slot width of the passage openings can be less than the diameter of the passage bores in the prior art, a shortened displacement of the piston becomes possible, leading to shorter actuation distances which again cause lower wear. Moreover the shorter actuation distances are also advantageous for the actuation elements necessary for the actuation of the valve and shorter actuation times are achieved.

A further advantage given by the invention is that, by means of an enlargement of the diameter of the piston and the consequent lengthening of the passage openings of slot form, it is possible to obtain larger throughflow cross-sections for the pressure medium, whereby an extension of the range of capacity of the valve becomes possible. In contrast to this, the range of capacity in the prior valve described above is limited by the cross-section of the passage bores which is dependent upon the width of the sealing rings on the circumference of the piston. The valve construction of the present invention now permits the fluid throughflow in the valve to be fixed independently of the thickness of the sealing rings.

Yet another advantage of the invention is that the two-part formation of the housing allows the inner housing sleeve to be easily replaced when worn.

A control valve in accordance with the invention is shown, by way of example, in the accompanying drawings, wherein Figure 1 is a partial longitudinal section through a 3/2 directional control valve with the piston in the closed position; Figure 2 is a partial longitudinal section through the valve shown in Figure 1 with the piston in the open position; and Figure 3 is a section taken on the line Ill-Ill in Figure 1 on an enlarged scale.

As shown in Figures 1 and 2, the illustrated pressure-balanced 3/2 directional control valve, which is especially useful for HFA fluids, comprises a valve housing 1 made in two parts, namely, an outer housing body 2 and an inner housing sleeve 3. A sliding piston 4 is displaceably guided in the housing sleeve 3 so as to be movable between two positions, as represented in Figure 1 and Figure 2, within the housing sleeve 3, the displacement path being indicated by L. The position of the sliding piston 4 in Figure 1 represents the closed position and the position shown in Figure 2 represents the open position of the valve. The sliding piston 4 is displaceable within the valve housing 1 against the force of a return spring 5 and is supported at one end against the return spring 5.

On the external circumference of the housing body 2 there are arranged an entry opening 6 for a high-pressure conduit (not shown), an opening 7 for a pressure supply conduit of a pressure medium user connection (not represented) and an exit opening 8 for a return conduit (likewise not represented) to a tank.

The sliding piston 4 has, in its interior, a longitudinal bore 9 which is closable at one end by means of a closure body 10. From the entry opening 6 a connection bore 11 extends through the housing body 2 and opens into a ring channel 14 of the housing sleeve 3. From the exit opening 8, a connection bore 15 extends through the housing body 2 and opens into a ring channel 16 of the housing sleeve 3. Circumferential seals 17 are arranged in the circumferential surface of the housing sleeve 3 on both sides of the ring channels 12, 14, 16, in order to seal off the axial gap existing between the housing body 2 and the housing sleeve 3 so that, on the one hand, no fluid can penetrate from one ring channel into the other and, on the other hand, a seal to the exterior is guaranteed.In the bottom regions of the ring channels 12, 14, 16 passage openings 18 of slot form are formed as outlets, and in the particular example shown (see Figure 3) four passage openings 18 are formed per outlet, with the openings being separated from one another by ribs 24. The individual passage openings 18 lie in one plane and on an arc of substantially 360 degrees so that the sliding piston guided in the housing sleeve 3 is surrounded over its whole circumference by the passage openings. The housing sleeve 3 has, at one end, an annular collar 19 with which, in the pushed-in condition, it rests against an annular shoulder 20 in the housing body 2. The housing sleeve 3 is made fast within the housing between the latter and the annular shoulder 20 by a screwedin sleeve 21.

A thrust piece 22 is arranged between the screwed-in end of the sleeve 21 and the annular collar 19. The interior space 23 of the screwed-in sleeve 21 at the same time also serves to accommodate the return spring 5 which is formed as a helical spring. A middle channel 25 and a rear channel 26, preferably of the width of the displacement distance L, are formed on the peripheral surface of the piston 4 with a spacing corresponding to the displacement distance L. Into the middle channel 25 there open rear radial bores 27 which issue from the outwardly-closed longitudinal bore 9 of the slider piston 4. Furthermore, from the longitudinal bore 9, there branch forward radial bores 28 which end in a foremost channel 29 on the peripheral surface of the slider piston 4.When the sliding piston 4 is in the open position as shown in Figure 2, the channel 29 is brought into coincidence with the passage openings 18 associated with the ring channel 29. In the ring channel 14 two mutually-spaced outlets are formed in its bottom region from the passage openings 18, as shown in Figure 3, the arrangement being such that, in this position, there is a connection between the channels 25 and 26. In this position there is also a connection between the exit or outlet opening 8 by way of the respective connection bore 15, the ring channel 16 and the respective passage opening 18, and the rear channel 26.Thus, in the closed position as shown in Figure 1, that is the position where there is no connection between the entry opening 6 and the longitudinal bore 9 in the sliding piston 4, a connection is provided between the connection opening 7 for the user and the exit opening, and there is also a connection of these openings with the longitudinal bore 9.

In the open position as shown in Figure 2, that is, in the position where there is a connection between the entry opening 6 and the longitudinal bore 9 by way of the connection bore 9, the ring passage 12, the passage openings 18, the channel 29 and the radial bores 28, the spaced-apart passage openings 18 in the ring channel 14 both open in the middle channel 25 so that a connection is produced between the entry opening 6 and the connection opening 7. The exit opening 8 in this position is not connected with the longitudinal bore 9 so that this exit opening 8 is closed. Circumferential seals 31, 32, 33, 34, 35 are provided in ring grooves (not designated) on the circumferential surface of the sliding piston 4 for the sealing of the longitudinal gap between the housing sleeve and the sliding piston 4 and between the channels 25, 26, 29 and the exterior.These circumferential seals 31 to 35 are so arranged that a sealing of the channel 29 to the exterior is effected by the seals 31 and, in the closed position as shown in Figure 1, a bilateral sealing of the passage openings 18 of the ring channel 12 is effected by the seals 32 and 33. Also, in the same position, a seal is effected between the passage openings 18 of the ring channel 12 and the middle channel 25 by the circumferential seal 33. The circumferential seal 34 is arranged between the middle channel 25 and the rear channel 26 so that, in the open position according to Figure 2, these two ring channels are pressure-tightly sealed against one another. The seal 35 behind the channel 26 serves for sealing to the exterior.

The construction described above achieves the aim that, when a return conduit connected for example to a tank is present, pressure balancing and pressure medium loading of the circumferential seals on the sliding piston take place through the connection openings to the housing so that the sealing rings of the circumferential seals are pressed into their ring grooves. Shearing-off or damage to the sealing rings is thereby prevented. The pressure balancing is effected in the interior of the sliding piston both to the interior and to the atmospheric pressure, for the surfaces which take up the pressure are loaded exclusively in the longitudinal bore 9 of the sliding piston with no pressure being exerted by the pressure medium upon the outer end faces of the sliding piston.This is rendered possible by the guidance of the pressure medium in accordance with the invention for, in the blocking position as represented in Figure 1, the longiudinal bore 9 is blocked off from the entry opening 6. It is to be emphasised further that all circumferential seals are arranged on the sliding piston 4, thus resulting in a simple production of the sliding piston. The circumferential seals for the housing sleeve 3 are also formed on the circumferential surface thereof so that this too can be produced relatively simply.By reason of the association between the connection bores, the ring channels with their passage openings, the channels on the sliding piston, the radial bores in the sliding piston and the circumferential seals on the sliding piston, displacement of the sliding piston out of each position causes a pressure medium charging of the sealing rings of the cirumferential seals of the sliding piston in the passage over the passage openings 28, thereby preventing the possibility of the sealing rings relaxing radially into the passage openings. Due to the relatively small width of opening of the passage openings, pressing of the sealing rings into these openings is additionally made more difficult, and also, due to the circumferential formation of the passage openings 18, a more uniform pressure charging of the sealing rings is effected. Thus, the construction (according to the invention) achieves not only a more favourable throughflow of the pressure medium so that lower pressure losses occur, but also a lower loading of the sealing rings.

Claims

1. A 3-port, 2-position directional control valve with pressure balancng for fluids under pressure, comprising a sliding piston provided with a longitudinal bore which is closed to the exterior, the piston being axially movable in a valve housing into an open position for the connection of a first passage for a pressure medium user connection to a high-pressure conduit lying adjacent this first passage and being movable into a closed position for the connection of a second passage for the pressure medium user connection to a discharge or outlet conduit lying adjacent this second passage, wherein the housing is in two parts and comprises an outer housing body and an inner housing sleeve in which the sliding piston is guided, with the user connection(s), the high-pressure conduit and the outlet conduit being in the form of bores in the outer housing body which terminate in respective ring channels in the housing sleeve, there being, in the bottom region of each of the ring channels, an outlet from passage openings of slot form lying in one plane on an arc of substantially 360 degrees, with the first and second passages for the user connection each comprising an outlet from the passage openings in the same ring channel.

2. A 3/2 directional control valve according to claim 1, in which circumferential seals are arranged in the sleeve circumferential surface on both sides of the ring channels of the inner housing sleeve.

3. A 3/2 directional control valve according to claim 1 or claim 2, in which the radial openings in the sliding piston are formed as radial bores.

4. A 3/2 directional control valve according to any one of claims 1 to 3, in which four passage openings are formed per outlet.

5. A 3/2 directional control valve according to any one of claims 1 to 4, in which the inner housing sleeve is fixed and has an annular collar formed on it within the outer housing body between an annular shoulder of the housing body and a sleeve which is screwable into the outer housing body.

6. A 3/2 directional control valve according to claim 2 or any claim appendant thereto, in which a first circumferential seal comprises two circumferential seals arranged separately from one another on the sliding piston in such a way that, when the piston is in the closed position, the outlet from the passage openings allocated to the high-pressure conduit lies between these sealing rings and the forward ra dial bores are sealed off in relation to the outlet of the high-pressure conduit so that the longitudinal bore is separated from the highpressure conduit.

7. A 3/2 directional control valve according to any one of claims 1 to 6 in which a rear channel is arranged on the peripheral surface of the sliding piston in such a way that, in the closed position of the piston, the second passage of the user connection and the outlet of the discharge conduit terminate at it, and the outlet of the return conduit does so in the open position.

8. A 3/2 directional control valve according to any one of claims 1 to 7, in which the first and second passages of the pressure medium user connection(s) are connected with one another, with the first passage in the open position of the piston being separated from the connection of the high-pressure conduit and the second passage of the pressure medium user connection in the open position of the piston being separated from the connection of the outlet conduit in a gap region between the valve housing and the sliding piston by respective circumferential seals arranged on the piston and each comprising at least one sealing ring fitted in a ring groove.

9. A 3/2 directional control valve substantially as described herein with reference to the accompanying drawings.