GB2041172A

GB2041172A - Bellows seal for push rod

Info

Publication number: GB2041172A
Application number: GB8001665A
Authority: GB
Original assignee: Elektrowatt AG
Current assignee: Siemens Building Technologies AG
Priority date: 1979-01-26
Filing date: 1980-01-17
Publication date: 1980-09-03
Also published as: SE433966B; DE3001834A1; GB2041172B; CH638327A5; DE3001834C2; SE8000148L

Abstract

As a sealing element between valve regulating push-rod (12) and housing (11), a metal bellows (40) is secured at one end to an end wall (16) and at the other end to the push-rod (12). In order to leave the metal bellows (40) uninfluenced by any pressure drop between the spaces (38, 39), the regulating push-rod (12) is widened out following on said metal bellows (40) and surrounds another metal bellows (45) which is disposed coaxially and of which the end adjacent to the first-mentioned metal bellows (40) is secured to the push-rod (12) and of which the end remote from the first-mentioned metal bellows (40) is secured to the other end wall (21) of the housing (11). The spaces (43, 48) surrounded by the metal bellows (40, 45) on the one hand and the spaces (44, 49) surrounding the metal bellows (40, 45) on the other hand are each in flow communication with one another. <IMAGE>

Description

SPECIFICATION Wall entrance for a regulating device The invention relates to a wall entrance for a regulating device having a longitudinally displaceable regulating push-rod which extends through a housing and having a metal bellows which is secured at one end tightly to the inside of an end wall of the housing and at the other end tightly to the regulating pushrod, surrounding this in the housing.

A regulating device is understood to mean a device which comprises a regulating drive which is coupled to a regulating unit through a regulating push-rod. Thus the invention relates to the essential parts which are present between the regulating drive and the regulating unit.

In known wall entrances of the kind referred to at the beginning a leakage-free sealing between the side of the regulating push-rod adjacent to the regulating drive and the side adjacent to the regulating unit is ensured by the metal bellows. In addition, a displacement of the regulating push-rod which is practically free of friction is possible, although against a slight spring force originating from the metal bellows.

If a pressure drop prevails between the side adjacent to the regulating drive and the side adjacent to the regulating unit, however, then with the known wall entrances of the kind referred to at the beginning, the metal bellows tends to be deformed axially, that is to say to lengthen or shorten depending on the direction of the pressure drop and accordingly to displace the regulating push-rod also. Now if the regulating drive cannot withstand the forces originating from the pressure drop, a displacement of the regulating push-rod may occur and hence an unwanted change in the position of the regulating unit.

It is therefore an object of the invention to provide a wall entrance of the kind referred to at the beginning, wherein a pressure drop between one side and the other of the wall entrance has practically no influence on the position of the regulating push-rod, which can thus be coupled to a regulating drive which can only apply small regulating forces.

The present invention is a wall entrance for a regulating device and comprising a housing, a longitudinally displaceable regulating pushrod extending through said housing, a first metal bellows around the push-rod and secured at one end to the inside of an end wall of the housing and at the other end tightly to the regulating push-rod which then broadens to surround a second metal bellows which is disposed coaxailly with said first metal bellows and of which the end adjacent to said first metal bellows is secured tightly to the regulating push-rod and of which the end remote from said metal bellows is secured tightly to the inside of the other end wall of the housing, the spaces surrounded by the metal bellows on the one hand and the spaces in the housing surrounding the metal bellows on the other hand being each in flow communication with one another.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is an axial section through a wall entrance; and Figure 2 is a section on the line ll-ll of Fig.

1.

The wall entrance 10 illustrated has a housing 11 and a regulating push-rod 1 2 which extends through this and is disposed in this for longitudinal displacement. The housing 11, which comprises a substantially cylindrical inner wall 13, comprises a tubular section 1 4 which ends at one end in an end wall 1 6 comprising a bore 1 5 and merges at the other end into an outwardly projecting flange 17, for example with an external hexagonal. The flange 1 7 is followed by a socket 1 9 provided with an external thread 18. This socket 19 is tightly screwed into the wall 20 of the housing of a valve (not illustrated) for example a regulating or mixing valve.The socket 1 9 ends in an end wall 21 in which there are two arcuate, through slots 22, 23 (Fig. 2), so that the central portion of the end wall 21 remains connected to the socket 1 9 through two webs 24, 25.

The regulating push-rod 1 2 comprises an upper shaft-shaped section 26 which extends with clearance through the bore 1 5 in the end wall 1 6 and is provided with an external thread 27 at its upper end. The clearance between the bore 1 5 and the section 26 serves to establish a flow communication. If the section 26 should not be permitted'gny deflectability in the radial direction, the bore 1 5 may also be so dimensioned that the section 1 6 is guided with a sliding fit. Then one or more further bores 15' must be provided close to the bore 1 5 to establish the flow communication.The external thread 27 serves to couple the regulating push-rod 1 2 to a regulating drive (not illustrated), which displaces the regulating push-rod 1 2 in the longitudinal direction and holds it in a specific displaced position.

An annular disc 28 is anchored, for example by screwing, on the section 26 at its end appearing at the bottom in Fig. 1. In this annular disc 28, close to the anchoring point of the section 26, a ring of through bores 29 is present which likewise serve to produce a flow communication.

Pulled over the periphery of the annular disc 28 as a further part of the regulating push-rod 1 2 is a tube section 30, the external diameter of which is smaller than the internal diameter of the inner wall 1 3. The tube sec tion 30 is divided by two slots 32 extending in the axial direction into two tongues 33, 34 of cylindrical shell shape which engage with clearance through the slots 22 and 23 in the end wail 21. The webs 24 and 25 also serve for the straight guiding of the tube section 30. At the lower end, the tube section 30 is closed by a stopper 35 which merges into a shaft-shaped section 36 provided with an external thread 37. The external thread 37 serves to secure one or more regulating members (not illustrated) for example a piston valve or a valve disc on the regulating pushrod 12.

A metal bellows seal serves to seal off the space 38 at the one side of the wall 20 from the space 39 at the other side. A first metal bellows 40 surrounding the shaft-shaped section 26 of the regulating push-rod 1 2 is secured at one end 41 in a sealing manner to the inside of the end wall 1 6 so that in any case it surrounds the bore 1 5 and possibly the bores 15'. At the other end, the bellows 40 is secured at 42, that is to say at a line surrounding the ring of bores 29, with a sealing action, to the annular disc 28. The space between the section 26 and the bellows 40 is designated by 43, the space surrounding the bellows 40 in the housing 11 is designated by 44.A second metal bellows 45 is secured at one end at 46 tightly to the opposite side of the annular disc 28, that is to say likewise along a line surrounding the bores 29 and at the other end at 47 tightly to the central portion of the end wall 21. The interior of the bellows 45 is designated by 48 and the space between bellows 45 and the inner wall 1 3 by 49. Thus the two adjacent ends of the bellows 40, 45 are secured to the annular disc 28 of the regulating push-rod 1 2 and at their ends remote from one another to the opposite end walls of the housing 11.

The spaces 43 and 48 are in flow communication with one another through the bores 29 and with the space 38 through the bore 1 5 or 15'. On the other hand, the spaces 44 and 49 are in flow communication with one another through the slots 31, 32 and with the space 39 through the slots 22, 23.

The two bellows 40 and 45 are preferably identical, that is to say they have the same internal and external diameter and also the same number of folds. In addition, both bellows 40, 45 are installed in the precompressed state so that neither of the two bellows 40, 45 is stressed in tension independently of the position of the regulating pushrod 1 2. The bellows 40, 45 may, for example, be of stainless steel with a thickness of about 0.04-0.07 mm-according to the pressure difference to be expected between the spaces 39 and 38. Other metallic materials, for example Be-bronze, are also suitable for the bellows 40, 45.

From what has been said, it follows that on a movement of the regulating push-rod 1 2 upwards, the bellows 40 is axially compressed whereas the- bellows 45 is extended. Since the bellows 40, 45 are of a very thin material, the spring force originating from them is very slight and is practically negligible.

A pressure drop acting from the space 39 towards the space 38 would, in itself, tend to compress both bellows in the axial direction.

Since the two bellows are connected to a certain extent so as to counteract one another, such a pressure drop leads to practically no displacement of the regulating push-rod 1 2.

In the wall entrance described, the regulating push-rod 1 2 is suspended floating between the bellows 40 and 45, which mutulally compensate one another, and so is displaceable without friction and without hysteresis in the spindle housing 11. The only forces which the regulating drive acting on the external thread 27 has to withstand are the spring forces originating from the bellows 40, 45 which-as mentioned-are practically negligible. Thus a solenoid can be provided as a regulating drive, the stroke of which depends on a regulating signal.

It will naturally be understood that instead of the slotted tube section 30, a plurality (at least two) of parallel rods may be provided which are secured at one end at regular angular distances apart to the periphery of the annular disc 28, lead with clearance through corresponding bores in the end wall 21 and are secured at the other end to the periphery of the stopper 35.

On the other hand, it is also conceivable, although it involves more problems from the production point of view, to use a one-piece bellows seal wherein the two actual bellows 40 and 45 follow on at both sides of a foldfree, cylindrical central section to be secured tightly to the outer wall of the shaft section 26. In this case the tube section 30 or the above-mentioned rods must be secured to the section 26 by means of a strap or the like spanning the said central section. On the other hand, the flow communication between the spaces 43 and 48 would have to be established by an axial bore in the shaftshaped section 26 of the regulating push-rod 12, closed by a transverse bore.

Claims

1. A wall entrance for a regulating device and comprising a housing, a longitudinally displaceable regulating push-rod extending through said housing, a first metal bellows around the push-rod and secured at one end to the inside of an end wall of the housing and at the other end tightly to the regulating push-rod which then broadens to surround a second metal bellows which is disposed coaxially with said first metal bellows and of which the end adjacent to said first metal bellows is secured tightly to the regulating push-rod and of which the end remote from said metal bellows is secured tightly to the inside of the other end wall of the housing, the spaces surrounded by the metal bellows on the one hand and the spaces in the housing surrounding the metal bellows on the other hand being each in flow communication with one another.

2. A wall entrance as claimed in claim 1, in which the two metal bellows have the same external and internal diameter and the same number of folds.

3. A wall entrance as claimed in claim 1 or claim 2, in which the two metal bellows are equal in length in the position of rest.

4. A wall entrance as claimed in any preceding claim, in which, following on the firstmentioned bellows, the regulating push-rod comprises a tubular section which is provided with at least one slot through which there extends a web of the other end wall of the housing.

5. A wall entrance as claimed in claim 4, in which the slotted portion of the tubular section extends with clearance through a slot in the form of a circular sector formed in the other end wall.

6. A wall entrance as claimed in claim 1, in which the two metal bellows are installed in the housing with precompression.

7. A wall entrance for a regulating device substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.

8. A wall entrance as claimed in any preceding claim in combination with a regulating device, the regulating drive of which is a solenoid with a stroke depending on a regulating signal.