Ultralow pressure relief valve

An ultralow pressure relief valve (10) is disclosed. Sealing fluid (24) is held in place by capillary forces inside capillary tube (12). When pressure in tube (11) exceeds capillary forces, sealing fluid (24) is forced into reservoir (14), protecting pressure gage (20) from overpressurization.

BACKGROUND OF THE INVENTION 
This invention relates to pressure relief devices and more particularly to 
ultralow pressure relief valves. 
DESCRIPTION OF THE PRIOR ART 
Some manufacturing operations are performed at pressure differentials 
measuring less than one inch H.sub.2 O. The equipment used to monitor such 
small differential pressures has a small range and is easily damaged due 
to overpressurization. Present methods of protecting the sensitive 
measuring devices have several drawbacks. 
One method involves use of low pressure switches and solenoid valves to 
vent air pressure to the atmosphere in the event of overpressurization. A 
disadvantage of this arrangement is that the system is slow and is also 
complex and expensive. This type of arrangement is also itself subject to 
damage from excessive variations in pressure. 
Another method of protecting low pressure instruments has been use of 
manometers. However, this type of device has been used mainly for 
differential pressures in excess of one inch H.sub.2 O and does not 
provide the accuracy necessary for differential pressures less than one 
inch H.sub.2 O. 
It is, therefore, an object of the present invention to provide an ultralow 
pressure relief valve capable of functioning at low differential 
pressures. 
A further object of the present invention is to provide an ultralow 
pressure relief valve that is relatively inexpensive. 
Another object of the present invention is to provide an ultralow pressure 
relief valve that is simple in operation and itself is not subject to 
overpressure damage. 
SUMMARY OF THE INVENTION 
According to the present invention, the foregoing and other objects are 
attained by providing a capillary tube between two pressure regions with a 
sealing fluid that is maintained in the capillary tube by capillary 
attraction and which releases to relieve pressure when the pressure 
between the high pressure region and the low pressure region is sufficient 
to overcome capillary attraction. A reservoir may be provided at the end 
of the capillary tube to collect the sealing fluid, which allows the 
sealing fluid to be drawn back into the capillary tube after the 
overpressure condition has passed. A capillary wire may also be used to 
speed the resealing of the capillary tube after the overpressure condition 
.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring more particularly to the drawings and specifically to FIG. 1, 
there is illustrated a preferred embodiment of the present invention as it 
would be used in an ultralow pressure relief valve, designated generally 
by reference numberal 10. Pressure gage 20 is connected to a pressure 
source, indicated by arrow 22, by connecting tube 11. Ultralow pressure 
relief valve 10 is also connected to tube 11. Ultralow pressure relief 
valve 10 is comprised of capillary tube 12, reservoir 14, capillary wire 
16, and sealing fluid 24. 
Sealing fluid 24 serves as a barrier between pressure 22 and atmospheric 
pressure 13. As long as pressure 22 does not exceed atmospheric pressure 
13 by greater than the force of capillary attraction, sealing fluid 24 
remains in place. If pressure 22 exceeds atmospheric pressure 13 by 
greater than capillary pressure, sealing fluid 24 is forced out of 
capillary tube 12 into reservoir 14. When pressure 22 is reduced to 
atmospheric pressure capillary attraction causes sealing fluid 24 to be 
drawn into capillary tube 12, reforming a seal at the end of capillary 
tube 12. 
Capillary wire 16 causes sealing fluid 24 to form a seal at a faster rate 
than if capillary wire 16 was not present. Capillary wire 16 is mounted to 
wire holder 18, which maintains capillary wire 16 in a fixed relationship 
to capillary tube 12 and reservoir 14. 
In the preferred embodiment of the invention, a capillary tube 12 with 
diameter of 1/8 inch was used. In the preferred embodiment, sealing fluid 
24 is water. Tests of ultralow relief valve 10 indicated the valve 10 
relieved at a pressure of 0.2 inches H.sub.2 O with a volume flow rate of 
0.15 standard cubic feet per minute (scfm). The pressure relief set point 
can be varied within certain ranges by using fluid with different 
viscosity and capillary tubes with different internal diameters. 
FIG. 2 is a schematic view of ultralow pressure relief valve 10 showing the 
relationship between capillary wire 16, capillary tube 12, and sealing 
fluid 24 with the seal intact. 
FIG. 3 is a schematic view of an ultralow pressure relief valve 26 designed 
to relieve an overpressure in either pressure region 30 or pressure region 
28. This type device is useful when it is necessary to maintain two 
pressure areas within a certain differential range. Pressure region 28 and 
pressure region 30 are separated by pressure wall 32. 
FIGS. 4 and 5 show a high volume ultralow pressure relief valve 34. 
Pressure wall 32 separates first pressure region 28 and second pressure 
region 30. Reservoir 38 is integral with pressure wall 32 and contains 
sealing fluid 24 shown in FIG. 5. Capillary fingers 36, mounted on 
pressure wall 32, served to draw capillary fluid 24 up into a sealing 
position to separate first pressure region 28 and second pressure region 
30. When the pressure in either region exceeds the capillary attraction 
force, sealing fluid 24 is forced from between capillary fingers 36 and 
the pressures in first pressure region 28 and second pressure region 30 
are equalized. This arrangement allows a larger volume of air to be 
transferred while still maintaining low differential pressures. 
FIG. 6 is a schematic view of a magnetic ultralow pressure relief valve 44. 
First pressure relief area 28 is separated from second pressure region 30 
by pressure wall 32. Capillary tube 12 connects first pressure region 28 
and second pressure region 30. Sealing fluid 46 is a magnetic type of 
fluid, such as those fluids produced by Ferrofluids Corporation, which is 
maintained in place in capillary tube 12 by capillary attraction and by 
the magnetic field produced by magnet 48. Magnet 48 allows capillary tube 
12 to be larger, and thus relieve larger air volume flow rates, than if 
seal 46 were held in place by capillary attraction only. Also magnet 48 
speeds reformation of the seal, after the pressures have been equalized. 
Magnet 48 may be either a permanent magnet or an electromagnet. If magnet 
48 is an electromagnet, then the magnetic field can be varied rapidly by 
electric signal, allowing the pressure relief points of the ultralow 
pressure relief valve 10 to be changed remotely. 
FIG. 7 is an ultralow pressure relief valve 10 capable of detecting the 
presence or absence of sealing fluid 24. Light source 50 is disposed on 
one side of capillary tube 12 in line with detector 52 so that light from 
light source 50 can be detected by detector 52. In this embodiment 
capillary tube 12 is made of a clear material such as glass or plastic. 
The presence or absence of sealing fluid 24 changes the light transmission 
characteristics between light source 50 and detector 52. The strength of 
the light reaching detector 52 is transmitted by wire 54 to detector 56. 
Detector 56 can be set to alarm or otherwise indicate the presence or 
absence of sealing fluid 24, which would indicate an out of balance 
differential pressure condition. 
It is thus seen that an ultralow pressure relief valve may be constructed 
simply and economically. It is also seen that an ultralow pressure relief 
device may be constructed in such a manner that the device itself is not 
damaged by overpressure conditions.