Controller

An actuator comprises a valve case opened upward, a gas-driven actuator having a fixed portion provided on the valve case and fixed thereto and an operating portion movable upward and downward by a drive gas when the gas flows in or out, a valve stem extending upward from inside the valve case to above the case and having its upper end fixed to the operating portion of the actuator, and a valve element provided on the lower end of the valve stem. A valve case fluid seal bellows and an actuator gas seal bellows are connected between the valve stem and the actuator fixed portion and between the actuator fixed portion and operating portion, respectively. A vacuum is contained in a closed space formed by the valve stem, fluid seal bellows, actuator fixed portion, gas seal bellows and actuator operating portion. The variations in the internal pressure of the closed space due to variations in the ambient temperature are much smaller than the pressure of the drive gas, so that the flow rate of fluid remains unchanged by the variations in the ambient temperature.

BACKGROUND OF THE INVENTION 
The present invention relates to a controller suitable for use at low 
temperatures or high temperatures. 
For example as a controller for use at low temperatures as attached to a 
vacuum tank, heretofore known is an axially elongated valve which 
comprises a valve case to be disposed inside the tank, an actuator to be 
provided outside the tank, and an extension pipe for holding the valve 
case in communication with the actuator. 
This valve has the problem that the extension pipe needs to be given a 
particular length in conformity with the design of piping when the valve 
is to be fabricated, further making the vacuum tank larger in size. 
To overcome this problem, a controller has been proposed which is adapted 
for use with its actuator entirely placed in the vacuum tank. 
The proposed controller comprises a valve case opened upward, a gas-driven 
actuator having a fixed portion provided on the valve case and fixed 
thereto and an operating portion movable upward and downward by a drive 
gas when the gas flows in or out, a valve stem extending upward from 
inside the valve case to above the case and having its upper end fixed to 
the operating portion of the actuator, and a valve element mounted on the 
lower end of the valve stem. The controller has a valve case fluid seal 
bellows extending between and attached to the valve stem and the fixed 
portion of the actuator, and an actuator gas seal bellows extending 
between and attached to the fixed portion and the operating portion of the 
actuator. 
The conventional controller described has a closed space formed by the 
valve stem, fluid seal bellows, actuator fixed portion, gas seal bellows 
and actuator operating portion, and air is confined in this closed space. 
The pressure of the air in the closed space varies with the variation of 
the ambient temperature, consequently moving the valve stem. Use of the 
controller as a flow regulating valve therefore involves the fatal problem 
that the movement of the valve stem varies the flow rate of fluid through 
the valve case. The same problem is encountered also in the case where the 
controller is used at high temperatures. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a controller which is 
operable free of variations in the rate of flow of the fluid passing 
therethrough due to variations in the ambient temperature. 
The present invention provides a controller which comprises a valve case 
opened upward, a gas-driven actuator having a fixed portion provided on 
the valve case and fixed thereto and an operating portion movable upward 
and downward by a drive gas when the gas flows in or out, a valve stem 
extending upward from inside the valve case to above the case and having 
its upper end fixed to the operating portion of the actuator, and a valve 
element provided on the lower end of the valve stem, the controller having 
a valve case fluid seal bellows extending between and attached to the 
valve stem and the fixed portion of the actuator, and an actuator gas seal 
bellows extending between and attached to the fixed portion and the 
operating portion of the actuator to form a closed space by the valve 
stem, the fluid seal bellows, the actuator fixed portion, the gas seal 
bellows and the actuator operating portion, the controller being 
characterized in that the closed space contains a vacuum. Since the closed 
space is vacuum which space is formed by the valve stem, fluid seal 
bellows, actuator fixed portion, gas seal bellows and actuator operating 
portion, the variations in the internal pressure of the closed space due 
to variations in the ambient temperature are much smaller than the 
pressure of the drive gas. For this reason, the flow rate remains 
unchanged by the variations in the ambient temperature. Further with the 
conventional axially elongated valve, the extension pipe increases the 
distance of conduction of heat for thermal insulation, whereas with the 
controller of the invention, thermal insulation is effected by the closed 
vacuum space, which therefore ensures a diminished heat loss during use at 
low or high temperatures. 
The fluid seal bellows and the gas seal bellows are joined respectively to 
the valve stem and the actuator fixed portion, and the actuator fixed 
portion and operating portion preferably by electron beam welding. The 
closed space can be made vacuum by joining the fluid seal bellows and the 
gas seal bellows to the valve stem and the actuator fixed portion, and to 
the actuator fixed portion and operating portion, respectively. The 
controller is therefore easy to make.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of the present invention will be described below with 
reference to the drawing. 
FIG. 1 shows a controller embodying the invention. The controller comprises 
a valve case 1 opened upward, a gas-driven actuator 2 provided on the 
valve case 1, a halve stem 3 extending upward from inside the valve case 1 
to above the case 1 and forcibly movable downward by a drive gas when the 
gas flows into the actuator 2, and a valve element 4 provided at the lower 
end of the valve stem 3. 
The valve case 1 has a valve chamber 5, a fluid inlet channel 6 
communicating with the valve chamber 5 and opened downward, a fluid outlet 
channel 7 communicating with the valve chamber 5 and opened laterally, and 
a valve stem guide bore 8 extending from the top central portion of the 
case to the valve chamber 5. At the location where the fluid inlet channel 
6 joins the valve chamber 5, the inner periphery of the case provides a 
valve seat 9. The valve case 1 is formed with a flange 10 at its upper 
portion. 
The valve stem 3 comprises a large stem portion 11 inside the valve case 1 
and a small stem protion 12 extending upward from the large stem portion 
11. The large stem portion 11 has a frustoconical upper end. A bellows 
retaining annular stepped protion 14 is formed between the frustoconical 
portion 13 and the small stem portion 12. 
The stem guide bore 8 comprises a large bore portion 15 having the same 
diameter as the large stem portion 11 and a small bore portion 16 having a 
larger diameter than the small stem portion 12. In the absence of a flow 
of drive gas into the actuator 2, the frustoconical portion 13 is in 
bearing contact with the lower edge of the small bored portion 16. 
The actuator 2 comprises a casing 17 in the form of a cap, a cylindrical 
fixed portion 18 integral with the flange 10 of the valve case 1 and 
positioned in an inside lower portion of the casing 17, and a disklike 
operating portion 19 secured to the upper end of the valve stem 3 and 
movable by the pressure of the drive gas. The casing 17 has a top wall 20 
formed with an inlet 21 for the drive gas. 
The cylindrical fixed portion 18 comprises a large cylinder part 22 close 
to the flange 10 of the valve case 1, a small cylinder part 23 extending 
upward from the large cylinder part 22, a bellows retaining small ring 24 
fixedly fitted in the upper end of the small cylinder part 23, and a 
bellows retaining large ring 25 fixedly fitted around the large cylinder 
part 22 near its lower end. The large cylinder part 22 and the small 
cylinder part 23 have an inside diameter equal to the diameter of the 
small bore portion 16 of the stem guide bore 8. The inside diameter of the 
small ring 24 is equal to the diameter of the small stem portion 12 of the 
valve stem 3. A lower spring retaining part 26 is formed between the large 
cylinder part 22 and the small cylinder part 23. 
The outside diameter of the disklike operating portion 19 is equal to the 
outside diameter of the large ring 25. The lower surface of the operating 
portion 19 is formed with an upper spring retaining part 27 corresponding 
to the spring retaining part 26 of the fixed portion 18, and a bellows 
retaining part 28 continuous with the part 27 and positioned externally 
thereof. 
A valve case fluid seal bellows 29 having a small diameter extends between, 
and is attached to, the small ring 24 and the annular stepped portion 14 
of the valve stem 3. A drive gas seal bellows 30 having a large diameter 
extends between, and is attached to, the large ring 25 and the bellows 
retaining part 28 of the operating portion 19. Consequently, a closed 
space S is formed by the valve stem 3, fluid seal bellows 29, actuator 
fixed portion 18, gas seal bellows 30 and actuator operating portion 19. A 
coiled compression spring 31 extends between, and is attached to, the 
upper spring retaining part 27 and the lower spring retaining part 28. 
The bellows 29, 30 of small and large diameters are secured in place by 
electron beam welding conducted in a high vacuum of 10.sup.-3 to 10.sup.-4 
torr, whereby the closed space S formed by the actuator 2, valve stem 3, 
bellows 29 and bellows 30 is made to contain a high vacuum of 10.sup.-3 to 
10.sup.-4 after the welding. Thus, the high vacuum can be readily 
realized. 
The electron beam welding for securing the bellows 29, 30 may be low-vacuum 
electron beam welding effected with the valve placed in a vacuum of 
10.sup.-1 to 10.sup.-2 torr. Insofar as the bellows are welded with the 
valve placed in a vacuum, also usable is other method, such as laser beam 
welding performed in a vacuum chamber. 
When the valve is brought out of the vacuum chamber into the atmosphere 
after the welding, the operating portion 19, that is, the valve stem 3, 
comes to rest with a balance established between the force exerted on the 
operating portion 19 by the atmospheric pressure and the elastic force of 
the compression spring 31. In this state, the valve stem 3 is tested for 
stroke characteristics under drive pressure at ordinary temperature. 
With the controller wherein the closed space S contains a vacuum, the 
variations in the internal pressure of the space S due to variations in 
the ambient temperature are much smaller than the pressure of the drive 
gas and therefore will not move the valve stem 3. This prevents leakage of 
the fluid and the variation of the fluid flow rate. Furthermore, the 
result obtained by testing the valve stem 3 for stroke characteristics 
under the drive pressure at ordinary temperature can be used as it is when 
the controller is used at high temperatures or low temperatures. With the 
closed vacuum space S provided between the fluid inside the valve case 1 
and the drive gas, the heat-insulating effect of the vacuum eliminates the 
variations of the drive gas pressure due to variations in the temperature 
of the fluid in the valve case 1. The closed vacuum space S diminishes the 
transfer of heat without using an extension pipe to increase the distance 
of heat conduction for thermal insulation. This serves to reduce the loss 
that heat penetrates into the controller from outside when it is used at 
low temperatures and to reduce the loss that heat escapes to the outside 
when the controller is used at high temperatures. 
Although the foregoing embodiment is a controller of the normally open type 
wherein the fluid channel is closed by the introduction of the drive gas, 
the same advantages as above are available also with the controller of the 
normally closed type wherein the fluid channel is opened by the 
introduction of the drive gas, by evacuating the closed space formed by 
the actuator, valve stem, bellows of small diameter and bellows of large 
diameter.