Chemically inert control valve

A control valve, the internal wetted working parts of which are made of corrosion resistant material and which are completely enclosed by and easily removed from a steel or stainless steel pressure vessel, and which is capable of tight shut-off when subjected to fluid differential pressure.

BACKGROUND OF THE INVENTION 
This invention relates to a flow control or modulating valve commonly used 
in chemical process plants or paper mills. Specifically, this invention 
also relates to a further improvement of the Chemically Inert Control 
Valve now patened under U.S. Pat. No. 4,214,730. The major improvement of 
my new invention over the previous patent is the increase in available 
flow capacity by providing a direct "line of sight" valve construction 
and, in addition, providing a valve design where the sealing mechanism is 
pressure assisted, that is, the seal tightness is improved with increase 
in valve differential pressure. 
Valves of this type are usually positioned by pneumatic disphragm actuators 
in response to a positioning signal from a control instrument of 
conventional art. The control of highly corrosive media used for the 
control of the PH level for bleaching paper or waste water, for example, 
poses special problems for the process control engineer, since very few 
materials will resist the strong chemical attack by those media. Plastic 
materials, such as Teflon*, show nearly perfect inertness, yet are not 
capable to serve as pressure vessels, i.e., to withstand the working 
pressure of the controlled medium nor the mechanical stress imposed by the 
connected piping. It has, therefore, been customary to clad inert valve 
parts with metal, i.e., to place all working parts of such a valve in a 
metal shell, usually Type 316 stainless steel. 
FNT *Tetrafluoroethylene 
Prior art valves of this type have conventional plug and seat rings, both 
made from rigid Teflon. The conventional shape of such valves poses great 
difficulties on the metal cover design and the supporting metal cover or 
shroud is usually composed of several separate and interconnecting parts, 
in order to be able to properly support and protect the internal or wetted 
valve portion. Such relatively complicated arrangements are, therefore, 
neither safe nor economical to produce. 
My invention has for an important object to provide for a chemically inert, 
or Teflon valve which is simple to insert into a one piece shroud or metal 
cover. 
A further object is to provide a flangeless or wafer style valve which is 
easy to install in a pipe system and without need for additional pipe 
flange gaskets. 
Furthermore, my invention allows the use of a fluid pressure actuated valve 
seat which is self-adjusting, if slightly worn, without need to remove the 
valve from service. 
Finally, yet another objective of my invention is the ability to provide a 
valve capable of regulating even very minute amounts of flow without being 
affected by the limitations posed upon conventional Teflon valve plug-seat 
combinations, i.e., stickiness caused by thermal expansion or seizing due 
to interference fit of these identical material parts.

DESCRIPTION 
The subject invention comprises a metal valve housing 1, preferably made 
from corrosion resistant steel such as AISI Type 316. The housing serves 
as a retainer and pressure supporting frame for plastic insert 2 made from 
a chemically inert material such as Teflon. Note, that the insert 2, 
fitting tightly into a perpendicular bore of housing 1, extends slightly 
above the width of housing 1 at one end portion 4, in order to serve as 
contact or gasket surface against adjacent line flanges 5 (shown here 
dashed) constituting parts of a pipeing system. Insert 2, in turn, has a 
horizontal bore 27, which is occupied by a sliding spool 28 connected by a 
flexible wall section 29 to a flanged portion 30 whose inner surface 31 
abutts the second end portion of insert 2. A central port opening 32 
extends through the length of spool 28 and constitutes a valve orifice 
capable of conducting field from inlet pipe 33 to outlet pipe 34. The 
outer surface 35 of flange portion 30 extends slightly above the width of 
housing 1 in order to serve as inlet gasket surface. 
Both flanges 5 are connected by conventional tie rods 6 which, when 
tightened, compress gasket surfaces 4 and 35 to form an effective seal to 
prevent fluid from leaving the pipe system, in addition to retaining 
housing 1 within the pipeing system. Guiding slots 7 are provided within 
housing 1 for the tie rods 6 (shown in FIG. 2) to serve for centering 
housing 1 in relation to flanges 5. 
Referring back to FIG. 1, a vertical central bore 8 intersects both housing 
1 and insert 2 to receive a number of stacked V-shaped packing rings 9, 
preferably made from Teflon and having a reduced diameter bore 10 which 
extends into the lower parts of insert 2 and which engages a sliding valve 
plug 11. Plug 11 is made of a highly corrosion resistant material such as 
Titanium or preferably Tantalum, not excluding materials such as glass or 
ceramics. The smaller bore 10 located co-axial with bore 8 extends through 
packing rings 9, insert 2, and spool piece 28 to allow downward travel of 
plug 11. In the retracted position of plug 11, as shown, port opening 32 
is unblocked to permit fluid to pass freely through the invented valve. 
Upon downstroke of plug 11, fluid passage 32 is blocked successively till 
shut-off is achieved. 
It has to be realized that inserting sliding cylindrical valve plug 11 into 
conduit 10 will not in itself provide drop tight closure. It is for this 
tightening purpose that spool piece 28 is allowed to be motivated against 
the outer cylindrical surface of plug 11 by fluid forces acting on the 
flexible portion 29 extending inwards from recess 37. A similar recess 38 
in insert 2 allows such freedom of motion of flexible portion 29 which, in 
turn, forces spool piece 28 towards the downstream side, and to cause 
tight and intimate contact of wall surfaces 39 and 40 against plug 11. It 
should be realized that the higher the fluid differential pressure, the 
higher the contact or sealing pressure is against plug 11. This capability 
of movement of spool piece 28 will also compensate for wear of surfaces 39 
and 40. 
The fluid flow is stopped, whenever plug 11 is brought down by means of a 
suitable actuating device 26 of conventional art connected through a valve 
stem 17, and when the fully cylindrical shape of plug 11 closes the 
passage 32 which now serves a function comparable to a valve port in a 
conventional plug and orifice type valve. 
All packing rings 9 are of commercially available design and are called 
"Chevron Rings." They have elastically deformable lips on their outer and 
inner circumferences which increase their sealability with increased 
pressure differential. The use of these commercially available and 
inexpensive packing rings allows for low cost seal ring replacement in 
case of wear. While the lowest packing ring serves to seal insert 2 
against housing 1, the upper rings prevent escape of fluid along the upper 
portion of valve plug 11. 
The compression of packing rings 9 is accomplished by means of valve bonnet 
18, the lower portion 19 of which is threadingly engaged with housing 1 
and the lower terminating end 20 of which contacts packing rings 9. A 
recess 21 within the lower bonnet portion is cooperating with a metal 
washer 22, suitably fastened to the upper part of plug 11, to serve to 
limit the upward stroke of plug 11. 
For any given inlet pressure, rotation of bonnet 18 by means of a hex 
portion 23 enables the valve assembler to compress packing rings 9 
sufficiently to prevent leakage by plug 11. Such adjustment is possible 
even while the valve is in actual service as part of a piping system, thus 
enabling the user to compensate for minor wear of packing rings 9 due to 
severe operating conditions. The final location of bonnet 18 in respect to 
packing 9 is then fixed by means of a locknut 24. 
As added safety feature, bonnet 18 may incorporate a conventional 
stuffingbox arrangement 25 primarily used to seal stem 17 for case of 
failure of packing 9. 
While the invention has been described in light of an illustrated preferred 
embodiment, numerous changes may be made both in the design or in the 
selection of materials without departing from the scope of the following 
claims: