Gate valve to shut off flow of liquid in pipelines

The gate valve has a housing hermetically joined with pipelines and a closing member which is translationally traversable in between the sealing elements of the housing. A bottom end of the closing member having a bevelled edge made so that at the instance when the pipelines get intercommunicated, the passageway is established in between the abovesaid bevelled edge, the housing and the sealing elements, said passageway growing narrow towards the direction of the flow of liquid. The above feature makes it possible to rule out the onset of conditions fraught with cavitation under the closing member and bring the cavitation outside the closing member, thereby adding to the service life of the gate valve.

BACKGROUND OF THE INVENTION 
The present invention relates generally to pipeline fittings and has 
particular reference to gate valves adapted to shut off the flow of liquid 
in pipelines, made use of in diverse fields of industry, such as mining, 
construction, chemical, petroleum production, and the like. 
The invention can find most utility when applied for pipelines laid in 
underground coal winning by the hydraulic method. 
A large number of diverse types of gate valves are known for use currently 
which comprise substantially a housing hermetically joined with pipelines, 
and a closing member translationally traversable in between the sealing 
elements of the housing. 
However, despite a great diversity of gate valves now in use the problem 
how to prolong their service life is yet far from being completely solved, 
especially when the gate valves are used to shut off the flow of liquids 
containing solid impurities, as the closing members and their sealing 
elements are liable to destruct within a short period of time. This is due 
largely to the fact that when the pipelines are shut off or 
intercommunicated, adverse conditions for the closing members and sealing 
elements arise, consisting in that a passageway is established when the 
pipelines are communicated to each other or shut off, said passageway 
being confined within the bottom end of the closing member, the gate valve 
housing and the sealing elements and featuring the same cross-sectional 
area at the entrance and exit thereof. We have been successful in finding 
out that the flow of liquid along such a passageway defines a void space 
situated beneath the closing member close to the entrance to the 
passageway, said void space considerably choking the free passage area 
and, consequently, reducing the hydrodynamic pressure in the flow, thus 
providing the conditions for the onset of cavitation. Before leaving the 
passageway the flow of liquid expands, the hydrodynamic pressure rises and 
the cavities are broken, all this leading to rapid failure of both the 
closing member and the sealing elements. 
SUMMARY OF THE INVENTION 
It is an essential object of the present invention to provide a gate valve, 
wherein favourable conditions would be established for operation of its 
closing member and for longer service life thereof. 
It is another object of the present invention to reduce the mass and 
overall size of the gate valve. 
In keeping with said and other objects in a gate valve to shut off the flow 
of liquid in pipelines, comprising a housing hermetically joined with 
pipelines and having sealing elements between which is interposed a 
closing member translationally traversable normal to the direction of the 
flow of liquid, according to the invention the closing member has a 
bevelled edge at its bottom end throughout the entire length thereof, said 
bevelled edge being so made that, at the instance when communication is 
established between the pipelines, a passageway is defined between the 
bevelled edge of the closing member, the housing of the gate valve and the 
sealing elements, said passageway growing narrow towards the direction of 
the flow of liquid along the pipelines. 
Such a constructional arrangement of the closing device makes it possible 
to gradually compress the flow of liquid thereunder towards the direction 
of its passing and thereby rule out the onset of conditions fraught with 
cavitation and bring the latter outside the closing member towards the 
direction of the flow of liquid. As a result, favourable conditions are 
provided for operation of the closing member and sealing elements, whereby 
the gate valve service life is many times extended. Furthermore, this 
renders it possible to reduce the mass of the closing member and of the 
actuator imparting translational motion thereto. 
In what follows the invention is characterized in that provision is made on 
the end of the closing member for a projection located on the side of the 
bevelled edge thereof and adapted, when in either of its extreme 
positions, to contact with the sealing element which is situated in the 
housing at the end of the liquid flow. This is instrumental in keeping the 
sealing elements against being dislodged by the flow of liquid and doing 
away with their being fixed rigidly in position in the valve housing, a 
feature that simplifies much the gate valve construction. 
It is expedient that the sealing elements be so fitted in the housing as to 
be forced against the closing member through the agency of elastic rings 
interposed between the housing and the sealling element, whereby a 
required contact pressure is developed at the place of sealing in cases 
where the pressure of the flow of liquid is below normal. In addition, 
such an arrangement of the sealing elements provides for a complete 
hermetic tightness when shutting off the pipelines even in case of foreign 
object penetration in between the sealing element and the closing member. 
Thus, the gave valve proposed herein is simple in construction, reliable in 
operation and features long service life.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now referring to the accompanying drawings, the gate valve to shut off the 
flow of liquid is built in to pipelines 1 and 2 (FIG. 1) and comprises a 
housing 3 and a closing member or gate 4. 
The housing 3 is made as a three-way fitting composed of branches 5, 6 and 
7, the diameters of the branches 5 and 6 approximating those of the pipes 
1 and 2, respectively. The branches 5 and 6 of the housing are 
communicated with the pipelines 1 and 2 through a quick-to-release 
coupling 8 of any heretofore known construction providing for a 
hermetically sealed joint. 
The housing 3 accommodates annular sealing elements 9 and 10 between which 
the closing member 4 is interposed with a possibility of translationally 
traversing normal to the direction of the flow of liquid. The closing 
member 4 is made as a slide gate, though it may also be made as one-piece 
structure or be composed of a number of oblong components (not shown in 
FIGS. 1 through 3). 
The closing member 4 with its top end is connected (by any of the 
heretofore known means) to a telescopic rod 11 of an actuator 12 in whose 
capacity use may be made of any hitherto known driving means suitable for 
imparting translational motion to the closing member; the actuator 
consists of a nut 13 and a handwheel 14 in the given particular case. 
A bevelled edge 15 is provided on the bottom end of the closing member 4 
throughout its entire width as it is shown in FIGS. 2 and 3; the abovesaid 
bevelled edge is so made that when the pipeline 1 gets communicated with 
the pipeline 2, a passageway 16 is established between the bevelled edge 
15 of the closing member bottom end, the sealing elements 9 and 10 and the 
housing 3, said passageway growing narrow towards the direction of the 
flow of liquid as indicated by the arrowhead A in FIGS. 1 and 3. It is due 
to the provision of said bevelled edge 15 that a lateral surface 17 of the 
closing member 4 facing the direction of the flow of liquid is of shorter 
length than an opposite lateral surface 18 thereof. 
Such a tapered shape of the passageway 16 is retained throughout the entire 
period of translational motion of the closing member as the pipelines 1 
and 2 are either communicated or shut off; in addition the flow area of 
said passageway 16 at is entrance exceeds that at the exit thereof. 
A projection 19 (FIGS. 1 and 2) is provided on the end of the closing 
member 4 on the side of its bevelled edge 15, said projection being 
adapted to contact the sealing element 9 located in the housing on the 
side facing the direction of the flow of liquid, with the closing member 4 
assuming either of its extreme positions. 
The lateral surfaces of the projection 19 easily turn, as shown in FIG. 2, 
into the surface forming the bevelled edge 15. 
The sealing elements 9 (FIG. 1) and 10 are so mounted in the housing 3 as 
to be forced against the closing member 4 through the agency of elastic 
rings 20 made in any presently known material fit for long-term operation 
in the liquid handled by the pipelines 1 and 2. 
The sealing elements 9 and 10 has annular recesses 21 for the elastic rings 
20 to accommodate; in order to prevent the rings 20 and the sealing 
elements 9, 10 against axial displacement away from the closing member 4, 
annular ridges 22 are provided in the housing 3 on the inner surface 
thereof, for the elastic rings 20 and the sealing elements 9, 10 to bear 
against. 
An access hole 23 is made in the housing 3 on its wall facing the valve 
actuator 12, said hole being adapted for installing the sealing elements 
9, 10 and elastic rings 20 into the housing or withdrawing these 
components therefrom without dismantling the valve housing from the 
pipelines. 
The herein-proposed gate valve operates as follows. 
In order to establish communication between the pipelines 1 and 2 one must 
rotate the gate valve handwheel 14 along with the nut 13, with the result 
that the rod 11 along with closing member 4 moves upward with respect to 
the sealing rings 9 and 10 forced against the closing member 4 by virtue 
of elastic deformation of the rings 20. 
While the closing member 4 is being moved the passageway 16 (FIG. 3) is 
formed in between the sealing rings 9 and 10, the housing 3 and the 
bevelled edge 15 of the bottom edge of the closing member 4, said 
passageway getting narrower towards the direction of the flow of liquid. 
Thus, provision of the bevelled edge 15 and the tapered passageway 16 
enable a gradual compression of the flow of liquid in the passageway 16 
throughout the width thereof, whereby a minimized flow area and minimized 
hydrodynamic pressure therein are ensured at the exit of the passageway 
16. Moreover, formation of cavitation voids occurs outside the closing 
member 4, this being due to the fact that the flow of liquid is widely 
expanded just upon leaving the passageway 16, accompanied by raising the 
hydrodynamic pressure therein and destruction of cavitation voids. Thus, 
the bevelled edge on the bottom end of the closing member and formation of 
the passageway 16 enable one to dislodge cavitation off the closing member 
into the downstream flow of liquid. 
When the closing member 4 is lifted into the topmost position the 
projection 19 restructs the travel of the sealing element 9 caused by 
elastic deformation of the ring 20 and hydrodynamic effect produced by the 
flow of liquid. 
Once the flow of liquid in the pipelines 1 and 2 has been shut off the 
closing member 4 moves down to assume its bottommost position; thus, the 
flow of liquid gets shut off first at the downstream end of the sealing 
element 10, then at the upstream end of the sealing element 9, this being 
due to the provision of the bevelled edge 15 and owing to the different 
length of the lateral surfaces 17 and 18 of the closing member 4. Thus, 
any possibility of the onset of cavitation is obviated in this case as 
well, and the process of cavitation is brought outside the closing member 
towards the direction of the flow of liquid.