Shut-off valve with spherical plug

A shut-off valve assembly includes a housing which has a spherical plug arranged in a chamber. The housing has an internal thread into which a support element for a sealing member is screwed. On the outer end face of the support element is supported a flange bushing by means of a retaining nut. The pitches of the internal thread and of an external thread for the retaining nut are directed in opposite directions, so that the support element cannot be loosened when the retaining nut is unscrewed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to a shut-off valve with a 
spherical plug, and more particularly to a shut-off valve assembly having 
a housing which defines a chamber and has at its two ends external 
threads. Retaining nuts for holding flange bushings are screwed onto the 
external threads. Sealing members are arranged on both sides of the 
spherical plug, wherein at least on one side the sealing member is mounted 
on a support element which is screwed into an internal thread of the 
housing. At least one flange bushing has sealing contact with the outer 
end of the support element facing away from the plug. 
2. Description of the Prior Art 
A shut-off valve of the above-described type is known from DE-C2-3044201. 
When the retaining nut is unscrewed in the valve of this type, turning of 
the flange bushing causes a screwed-in part to be simultaneously turned, 
particularly due to the great play of the thread, so that the sealing 
member is lifted from the spherical plug and the shut-off valve is no 
longer tight. This may be dangerous particularly when the shut-off valve 
is used with aggressive media. The shut-off valve is therefore only usable 
to a limited extent. 
It is, therefore, the primary object of the present invention to provide a 
shut-off valve of the afore mentioned type which affords a tight sealing 
action even when a flange bushing at the outlet side is unscrewed and the 
connected pipe is loosened. 
In accordance with another object of the invention, the sealing action of 
the spherical plug is to be self-tightening within a certain range in case 
of wear. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, the internal thread for the 
support element for the sealing member has a pitch which is directed in 
the opposite direction of that of the external thread for the retaining 
nut. 
As a result of the oppositely directed pitches of the internal thread for 
the support element for the sealing member and the external thread for 
mounting the retaining nut on the housing, the support element cannot move 
away from the spherical plug even when the support element rotates 
together with the retaining nut when the retaining nut is unscrewed, so 
that the shut-off valve remains tightly sealed even when the pipe on the 
outlet side is removed. 
In accordance with another feature of the invention, the threads are 
trapezoidal threads which is advantageous with respect to the manufacture 
by injection molding and provides excellent properties with respect to 
movement and strength. The internal thread for the support element is 
advantageously a left-handed thread. 
In accordance with yet another feature of the invention, round rubber rings 
are provided between one sealing member and the support element and 
between the other sealing member and the housing. In addition, an annular 
groove provided in the support element affords an advantageous resiliency 
of the support element, so that the sealing elements for the spherical 
plug can be pretensioned and, consequently, the sealing action of the 
sealing members is maintained even after wear of the sealing members. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the drawings and descriptive matter in which there is 
illustrated and described a preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION 
As illustrated in the drawing, the valve according to the present invention 
includes a housing 1 which has a tubular projection 11 which defines a 
bore hole 12. In bore hole 12 is rotatably mounted a spigot 3. A handle 4 
is placed on and connected to the end of spigot 3 which extends out of 
projection 11. 
The housing further has a cylindrically shaped chamber 13 in which a 
spherical plug 2 is arranged. Plug 2 is in engagement with the end of 
spigot 3 which extends into the chamber 13, so that plug 2 can be rotated 
by means of handle 4 through spigot 3. Sealing members 20 are provided on 
both sides of plug 2 so as to contact plug 2. One sealing member 20 is 
arranged on a recess 14 of housing 1 and the other sealing member 20 is 
arranged on a support element 5. 
Support element 5 has an external thread 51 which engages an internal 
thread 15 at the outer end of chamber 13, so that the support element 5 is 
screwed into housing 1 until the sealing members 20 make contact with plug 
2. Round rubber rings 21 are provided between one sealing member 20 and 
support element 5 and between the other sealing member 20 and recess 14. 
When the support element 5 is screwed in, the rubber rings 21 are 
compressed, so that they press the sealing members 20 against the plug 2 
in a prestressed condition. 
Support element 5 has a through bore 56 and a cylindrical portion 52, with 
a sealing ring 53 provided on the outer circumference of cylindrical 
portion 52. An annular groove 54 is provided on the outer circumference of 
the support element 5 between the cylindrical portion 52 and the external 
thread 51. The depth of groove 54 is at least one third, preferably up to 
one half, of the annular thickness of the support element 5. As a result, 
cylindrical portion 52 is resilient in such a way that when the support 
element 5 is tightened by means of external thread 51, sealing member 20 
is still pressing against spherical plug 2 even when the sealing member is 
worn. 
The outer end 55 of support element 5 extends out of housing 1. A sealing 
ring 58 is arranged in an angular groove formed in end face 57 of the 
support element 5. 
Housing 1 has external threads 19a and 19b, respectively, at its two ends. 
A retaining nut 6a holding a flange bushing 7a is screwed onto thread 19a. 
A retaining nut 6b holding a flange bushing 7b is screwed onto thread 19b. 
The flanges of flange bushings 7a and 7b are directed inwardly toward plug 
2. Flange bushing 7a rests sealingly against end face 57 of support 
element 5 and flange bushing 7b rests sealingly against an end face 17 of 
housing 1 provided with a sealing ring 18. 
Through bore 56 of support element 5 and through bore 16 arranged on the 
other side of housing 1 and, in the position of plug 2 illustrated in FIG. 
1, a through bore 26 of plug 2 form a continuous opening for flow of a 
medium through the valve. The flow of the medium is stopped when the plug 
2 is turned by 90 degrees. 
For screwing the support element 5 into the housing, the element 5 has on 
its end face 55 two oppositely located recesses 59, as illustrated also in 
FIG. 2. The removable handle 4 may serve as a screwing tool. For this 
purpose, it has on its upper side a web 8 which, as can be seen from FIG. 
3, has such a length and width that it can be inserted into the two 
recesses 59, so that the support element 5 can be rotated by means of 
handle 4. 
The pitch of the internal thread 15 and the pitch of the external thread 19 
are oppositely directed. For example, the external thread 19 intended for 
the retaining nuts 16 may have a conventional right-handed pitch and the 
internal thread 15 intended for the support element 5 may have a 
left-handed pitch. Both threads may be trapezoidal threads which provide 
the necessary play for manufacture and assembly. 
In order to be able to use the shut-off valve in accordance with the 
invention for aggressive media, its parts are manufactured, for example, 
from polyvinyl chloride which is resistant to these media. Most parts, 
even the threads, can be manufactured by injection molding without 
requiring subsequent mechanical machining. 
The shut-off valve according to the invention may also have a symmetrical 
configuration, that is, it may have support elements for sealing members 
on both sides of the plug. In that case, both support elements are screwed 
into the housing with threads which have opposite pitches from the threads 
intended for the retaining nuts. 
While the specific embodiment of the invention has been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles.