Minute flow regulating valve

A regulating valve capable of precisely controlling minute amounts of gaseous or liquid fluids following an electronic, pneumatic or manual command wherein the fluid is throttled between parallel surfaces which are part of a replaceable trim insert and which are positioned in respect to each other through the use of hydraulic amplifying means.

More specifically, it is an adaptation of the Laminar Flow Restriction 
principle for use as automatically operated small flow control valves, as 
required by the process control industry and particularly by reduced scale 
pilot plants or laboratories. 
This invention relates to a device capable of restricting the flow of 
liquid or gaseous media by producing a laminar flow pattern, where the 
potential energy of the passing fluid is gradually reduced through viscous 
shear friction along a very narrow opening. The efficiency of such a 
device depends on the ability to offer as much wetted surface to the 
passing fluid as possible without necessitating an increase in flow area. 
This can be better understood by comparing my invention with a piece of 
tubing. The hydraulic diameter governing the Reynolds number and 
consequently the amount of fluid friction created in a typical restriction 
may be written as 
EQU d=4A/U 
where A is a flow area and U is the length of wetted surface surrounding 
the flow area in question. Then for a simple tube or orifice with a=0.785 
the hydralic diameter d=1. Assuming the identical flow area of A=0.785 and 
1 as diameter of the inner flow cavity in my invention, d is then 
calculated to be 0.5 or only half of that of a simple orifice by providing 
two wetted surfaces instead of one. 
Further decrease in d can be obtained by selection of a large internal 
diameter to flow area ratio which is not possible in orifices. Fine 
tapered needle valves have been used to provide laminar flow restrictions 
in the past, where the fluid is forced to pass between the outer wall of a 
tapered needle and the inner wall of a tapered orifice. However, it has 
been found that these valves tend to drift, that is, change their 
effective hydraulic diameter after some time which necessitates quite 
frequent recalibration. The mechanism of this drift is not completely 
understood but may be the result of some very minute changes in the plug 
position due to temperature effects or inherent mechanical stresses. It 
has been observed that very minute side movements of the plug will 
effectively change the hydraulic diameter of the valve and therefore its 
specific fluid resistance. 
Use of two parallel surfaces as described in my previous U.S. Pat. No. 
3,144,879 does indeed solve the problem of not only providing an exact and 
reproducible flow passage but also one that provides an extremely wide 
"Rangeability", i.e. the useful ratio of maximum to minimum mass flow 
range due to the following mathematical relationship. 
If one would designate the distance between the two surfaces controlling 
the amount of fluid resistance as H, and the radial distance the fluid has 
to travel through as L, then the differential pressure necessary to pass a 
given mass flow M is 
EQU .DELTA.p=(kML.nu.)/H.sup.3 
wherein .nu. is the kinematic viscosity of the fluid and k is a dimensional 
constant. Thus adjusting H will change either the mass flow or the 
differential pressure by the third power ensuring a very wide rangeability 
for this device. 
The above equation illustrates a dependency of mass flow to H to the third 
power assuming a consistant pressure drop across the valve. With a typical 
H or gap variation between two controlling surfaces from 0.0001" to 0.01", 
the controlled range of mass flow is equal to 1:100.sup.3 =1:10.sup.6 
which indeed was proved to be correct through flow tests conducted on a 
preferred embodiment of my invention. 
As can be appreciated, the task of adjusting the small gap between the two 
controlling surfaces is of critical importance. Manual adjustment was 
solved in my previous (referenced) invention by utilizing the digressive 
motion of two slightly different pitched screw threads located on a common 
adjusting screw. This solution works fine, where manual adjustment is 
sufficient, but is not suitable if adjustment should be the consequence of 
a variation of an electronic or, preferably, pneumatic signal change from 
a process controlling instrument. 
The present invention has overcome the problem of automatic and of minute 
adjustments of the controlling gap between two throttling surfaces by 
utilization of hydraulic amplifying means which, when interspaced between 
conventional linear motion type pneumatic or hydraulic actuators not only 
reduce motion of these actuators to the small fraction required, but in 
the process also amplify the force output of those conventional actuators 
by typically 30 to 50 times thereby effecting closure of said plates 
against hydrostatic pressure levels exceeding 3000 psi. 
Other noteworthy objects of my invention include the provision of packless 
valve construction, that is, contrary to needle valves, no seals are in 
sliding contact with the outside means of adjustment commonly referred to 
as valve stem and the interior parts subjected to the medium to be 
controlled. Seals in my invention can be static types and therefore are 
not subject to wear regardless of the frequency of adjustment. 
Yet, still another object of my invention is the provision of a laminar 
flow restriction, which is rugged for long service life and which is easy 
and inexpensive to manufacture and which does not require matching of 
parts, hand honing and other special production methods heretofore 
required by present devices performing similar functions. 
A further major improvement over my previous U.S. patent application Ser. 
No. 146,630 and my continuation in part thereof, filed on Jan. 30, 1981 is 
the provision of a novel cage trim insert whereby one single gasket seals 
both high and low pressure portions of this removable trim insert and 
thereby eliminates all sliding seals of my invention Ser. No. 146,630 and 
also avoids accidental opening of my invention valve upon loss of 
hydraulic amplifying fluid, a circumstance not excluded with the design 
featured in my continuation in part filed on Jan. 30, 1981. 
These and other objections and advantages of my invention will best be 
understood from the following detailed description, when considered in 
conjunction with the annexed drawings.

DESCRIPTION 
The subject invention comprises a housing 1 having one inlet port 2 and one 
outlet port 3 respectively. Housing 1 furthermore has a central 
longitudinal bore 4 connected to said inlet port by a fluid egress passage 
5. The upper terminating end of bore 4 is sealed by means of a bonnet 
closure 6, bonnet flange 7 and fastening means 8. A flexible diaphragm 9 
is interspaced between the lower terminating portion of bonnet 6 and a 
removable element 11 engaged within housing bore 4. 
Element 11 has a flat terminating lower portion which is sealed against a 
similarly flat surface constituting the lower terminating end of bore 4, 
by a gasket 17. Bonnet member 6 incorporates a central opening 13 
extending throughout its length and enclosing therein a plunger 18 whose 
upper portion 14 is fastened to a stem extension 15 of a conventional 
sliding stem type actuating device 16. The lower portion of plunger 18 is 
totally immersed in a hydraulic fluid contained within opening 13 and 
enclosed by suitable sealing means 19 retained within the upper portion of 
bonnet 6 by a threaded retainer 20. 
Following a vertically downward movement of actuator stem extension 15, 
some of the volume of hydraulic fluid contained within opening 13 is 
displaced, causing a downward deflection of flexible diaphragm 9 which in 
turn forces a downward movement of a piston 21 slidingly arranged in a 
central bore of the cage-like outer portion 22 of element 11. Cage 22 also 
has a lower central bore 23 which, in the shown preferred configuration, 
has a conical concave shape. Bore 23 engages a similarly cone-shaped valve 
plug 24 whose upper stem-like threaded extension 25 is engaged with piston 
21. Whenever the hydraulic fluid in cavity 13 forces a downward movement 
of a piston 21 and thereby valve plug 24, it has to overcome the 
resistance of a pair of conical spring washers 26 whose spring load 
assures a return of piston 21 and a retraction of valve plug 24 towards 
tight engagement with cage bore 23 and thereby effecting tight valve 
closure. 
The cavity occupied by spring 26 is able to communicate with outlet port 3 
by means of a second fluid egress port 27. When valve plug 24 is extended 
downward, an annular flow passage 28 is formed between the parallel wall 
surfaces of the plug and cage bore profiles. Fluid entering inlet port 2 
will pass through this flow passage or throttling gap into the cavity 
occupied by springs 26 and from there through port 27 into outlet port 3. 
Gasket 17 has an important function in that it seals not only down stream 
pressure which may enter longitudinal bore 4 from port opening 27 but it 
simultaneously prevents higher pressure in fluid egress 5 from leaking 
into port 27 whenever valve plug 24 is in the closed position. This 
eliminates the typical requirement in conventional valves to have two 
separate sealing means, one for the upstream and one for the down stream 
pressure areas. 
It is important to keep the length of the flow passage 28 very long in 
respect to the distance or width between the plug and cage bore. 
The typical maximum width of the gap between surfaces 23 and 24 is 0.005". 
This, combined with a typical radial distance of fluid travel of 0.250" 
makes the fluid mechanically important L/d ratio at least 250:1 which will 
keep most fluid conditions in the Laminar regime which in turn will vary 
the fluid resistance, or amount of fluid being passed under constant 
pressure drop, to the third power of the gap width H, as discussed 
previously. This assures an outstandingly wide range between maximum and 
minimum controlled flow which far exceeds the capabilities of conventional 
throttling valves. 
For example, a typical embodiment of my invention can vary the amount of 
gas flow from less than 1 cc/min. at 100 psi pressure drop to more than 
10,000 cc/min. In contrast, conventional needle type valves heretofore 
used, seldom exceed a flow range of 50:1 ! 
An added benefit from the hydraulic positioning means employed in my 
invention, is the benefit of force amplification. A typical embodiment of 
my invention will have a piston 21 diameter of 1" and a plunger 14 
diameter of 3/16". Under the assumption that actuator 16 can produce a 
force of 100 lbs., a hydraulic fluid pressure of 100.times.0.187.sup.2 
.times.3.14/4=3621 psi can be exerted within opening 13, thereby allowing 
piston 21 to overcome equally high pressure levels of process fluid with 
the valve itself. 
One disadvantage of the shown design is the close proximity of the 
hydraulic fluid in chamber 13 in respect to the process fluid. Any 
temperature change in the process fluid will in turn vary the temperature 
of the hydraulic oil, causing thermal expansion and movement of piston 21 
independently of actuator 16. However, compensation can be achieved by 
selecting the material of plunger 18 having a different coefficient of 
thermal expansion to that of bonnet closure 6. 
While preferred embodiment of my invention has been designed to operate 
primarily in the Laminar flow regime (i.e. at Reynolds numbers generally 
below 2,000) it should be understood, that turbulence may exist around 
entrance and exit ports and may even commence between the parallel 
surfaces themselves given high enough fluid velocities. It is also quite 
obvious to employ other than cone-shaped valve plugs or port openings and 
to replace hydraulic fluid seals with metal bellows to prevent an even so 
slight leak or evaporaton of hydraulic fluid. This, however, is a purely 
economic preference and should not be constructed to be a limitation to 
any of my claims. 
It should also be understood, that replacement of the pneumatic or 
electrical actuator 16 with a suitable handwheel arrangement will render 
my invention capable of manual adjustment and thereby expand the range of 
its useful applications without departure from the scope of the following 
claims.