Pressure gauge for thixotropic liquids

A pressure gauge adapted for use in measuring the pressure of a thixotropic fluid subject to aggregation stagnation in which aggregation of the fluid is prevented by controlling stagnation of a magnetic coating liquid in the vicinity of a pressure sensor, and product quality is improved by removing air mixed into the liquid. An outlet is formed at the vertex of a conical holder. An inlet is formed in the conical surface of the holder at a location offset from the center of the cone defining the holder, which is contained in the outlet. A pressure indicator is mounted in the opening portion in the plane of the cone defining the holder.

BACKGROUND OF THE INVENTION 
The present invention relates to a pressure gauge, and more particularly to 
a pressure gauge adapted for use in measuring the pressure of a 
thixotropic fluid subject to aggregation stagnation, such as a liquid 
(magnetic liquid) in which magnetic material is in solution. 
Many types of pressure gauges are known. In one of the known pressure 
gauges, a diaphragm is provided at the pressure introducing portion of the 
gauge. The amount of deformation of the diaphragm when it is elastically 
deformed by pressure is used for determining the pressure of the gas or 
liquid to be measured. 
An example of a diaphragm-type pressure gauge is illustrated in FIG. 4. In 
this pressure gauge, a T-pipe 11 having an inlet A, an outlet B, and a 
conduit 12 for introducing liquid to a diaphragm acting as a pressure 
sensor 13 of a pressure indicator 2 is inserted into a pressure gauging 
portion of a pipe 14. The pressure indicator 2 is attached to the conduit 
12. Assuming that the fluid flows through the pipe 14 from the left side 
to the right side in the figure, the fluid first flows from the inlet A 
into the T-pipe 11, and is divided into two routes, one destined for the 
conduit 12 with the pressure indicator 2 attached thereto and the other 
destined for the outlet B. 
As a result, the fluid fills the conduit 12 to push the diaphragm of the 
pressure indicator 2, thereby to indicate a pressure. 
The pressure gauging system which introduces the fluid to the pressure 
sensor 13 requires space for introducing the fluid, i.e., the conduit 12 
of the T-pipe in the pressure gauge of FIG. 4. In the vicinity of the 
portion where the conduit branches from the pipe, there is little flow of 
the fluid filling the space due to disturbances caused by the flow of the 
fluid in the pipe. The fluid flow gradually diminishes away from the 
branch portion. Since here is little flow, stagnation occurs in the 
vicinity of the diaphragm. 
This phenomenon becomes remarkable as the viscosity of the fluid flowing 
through the pipe increases, thereby more significantly impeding the fluid 
flow. This phenomenon does not cause much of a problem when the fluid is 
gas, water, or a solution of low concentration. However, magnetic fluids 
containing a mixture of a magnetic substance, chemical destaticizer, 
lubricant, binder and the like have a high viscosity and poor fluidity, 
and hence have a strong tendency to stagnate in the vicinity of the 
diaphragm. The magnetic liquid generally has thixotropic properties. When 
it is flowing, a magnetic liquid retains a sol-like fluidity due to the 
shearing force applied to the fluid due to the flow. However, when such a 
solution stagnates, its consistency becomes gel-like, so that aggregation 
occurs. 
As the aggregation progresses, the diaphragm of the pressure sensor 13 
fails to perform its function. A pressure measured under this condition is 
not correct, so that accurate pressure control in the magnetic material 
coating process is impossible. Further, the aggregated matter retained in 
the stagnation region tends to mix with the magnetic liquid as an 
impurity, so that control of the the magnetic liquid concentration is 
impossible. Moreover, air that has been carried in together with the 
magnetic liquid is left in the stagnation region. A disturbance causes air 
held in the stagnation region to rush into the pipe. The air, together 
with the aggregated matter, is transported to the coating head. The result 
is unwanted streaks, bubbles, and the like in the final product. 
To manufacture another type of product, the magnetic liquid in the pipe 
must be replaced by another magnetic liquid. In this case, a fresh 
magnetic liquid is supplied to the pipe after the inside of the pipe is 
cleansed by feedinq detergent into the pipe. In the cleaning process, the 
cleaning fluid tends to collect in the stagnation region, so that 
insufficient cleaning of the inside of the pipe is obtained. In this 
respect, the cleaning work is inefficient. As described above, in the 
pressure gauge for gauging a pressure by introducing the fluid into a 
pressure sensor of the diaphragm, the conduit 12 forms a stagnation region 
of the fluid. This stagnation region causes the mixing of the aggregation 
and air into the magnetic fluid. Reduction of the volume of the fluid 
introducing portion that defines the stagnation region can be done to 
control the mixing of the aggregation and air into the magnetic fluid. 
A pressure gauge based on the reduction of the volume of the stagnation 
region is disclosed in Japanese Utility Model Laid-Open Publication No. 
Hei. 2-9847, for example. In such a pressure gauge, the fluid path is 
flush with the opening portion where the diaphragm is mounted, and a 
pressure gauge mounting seat is used, omitting the conduit 12. Further, a 
restricting portion is provided which restricts the fluid flow gradually 
from the diaphragm mounting opening portion toward the bottom 
corresponding to the fluid path. Provision of the restricting portion 
succeeds in reducing the volume of the space for introducing the fluid 
present between the diaphragm and the fluid path. 
As regards the mounting seat, the space from the fluid path to the 
diaphragm increases toward the circumferential end of the diaphragm. The 
fluid flows more slowly in this space than in the vicinity of the fluid 
path, and hence the fluid is likely to linger in this space. Accordingly, 
the above pressure gauge also suffers from the above-stated problem. That 
is, the aggregation of the fluid interrupts the normal operation of the 
pressure sensor 13 by the diaphragm, impairing the exact gauging of the 
fluid pressure and precise pressure control in the magnet fluid coating 
process. 
Further, the aggregated matter is mixed into the magnetic liquid as an 
impurity, making it difficult to control the concentration of the magnetic 
liquid. Air is also mixed into the liquid. The air, together with the 
aggregated matter, is transported to the coating head, causing streaks and 
bubbles in the final product, and hence deterioration of the product 
quality. In cleaning the inside of the pipe, the cleaning fluid will not 
flow properly, providing insufficient cleaning. This results in 
inefficient cleaning work. 
In this type of the pressure gauge, a planar diaphragm is mounted in the 
fluid path (normally tubular) even under the possibly reduced volume in 
the pressure measuring location, and an empty space essentially exists 
between the fluid path and the diaphragm. The space provides a stagnation 
region for the fluid. 
SUMMARY OF THE INVENTION 
With the view of solving the problems arising from presence of the 
stagnation region, the present invention has an object the provision of aa 
pressure gauge which eliminates aggregation of fluid in the pressure 
measuring location, and satisfactorily cleans the same location when the 
inside of the pipe is cleansed. 
To achieve the above and other objects of the invention, there is provided 
a pressure gauge in which a pressure sensor is provided in connection with 
a holder having an inlet and an outlet to and from which fluid is let in 
and out, and a pressure indicator is connected to the pressure sensor, 
wherein at least the inner space of the holder is substantially conical, 
the pressure sensor is provided on the base surface of the conical inner 
space, the outlet is formed at the vertex of the cone defining the inner 
space of the holder, and the inlet is disposed close to the base surface 
of the cone so as to create a flow of the fluid in a direction tangent to 
the conical surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of a pressure gauge constructed according to the 
present invention will be described with reference to FIGS. 1 and 2. 
FIG. 1 is a front view, partially in cross section, showing a pressure 
gauge constructed according to a preferred embodiment of the present 
invention, and FIG. 2 is a plan view showing the inside of a hole of the 
pressure gauge as seen from above. 
In a pressure gauge 20, a pressure indicator 2 is mounted on a conical 
holder 1 having a conical inner space formed therein. A pipe 10 with an 
outlet B is connected to the vertex 5 of the holder 1. A inlet A, which is 
equal in diameter to the outlet B, is formed in the conical surface 4 of 
the holder 1. Another pipe 10 extends outward from the inlet A. More 
specifically, as best illustrated in FIG. 2 (plan view of the holder 1), 
the inlet A is formed at a location offset from the center C of the cone 
defining the holder by a predetermined distance d (closer to the base of 
the cone), and the pipe 10 extends tangential to the conical surface 4. 
Accordingly, the fluid fed through the inlet A is substantially parallel 
to a diaphragm 13 mounted on the base of the cone. 
The flange 1a of the holder 1 and the flange 2a of the pressure indicator 2 
are coupled together and firmly held by means of a ferrule 3 applied to 
the coupled flanges, thereby to assemble the pressure gauge 20. 
In the pressure gauge 20 thus constructed, a fluid flows from the inlet A 
into the inner space of the holder 1. In the inner space, the fluid flows 
circularly (in the direction of an arrow X) along the inner side of the 
conical surface 4 to fill the inner space and flow out of the inner space 
through the outlet B. The fluid, when it fills the conical inner space, 
pushes up the diaphragm 13, which acts as the pressure sensor of the 
pressure indicator 2, while at the same time rising toward the vertex 5 to 
flow out of the inner space through the outlet B. 
Within the holder 1, the flow of the fluid flowing along the inner side of 
the conical surface 4 in the circular direction (direction X) and the flow 
of the fluid flowing toward the outlet B (in the direction Y) are combined 
to form a spiral flow (direction XY). The spiral flow flows in the form of 
a spiral stream of fluid as if it were guided by a spiral channel 
continuing from the conical base area (diaphragm side) toward the vertex 
of the cone (outlet B). Accordingly, within the holder 1, the fluid 
supplied from the inlet A spirally flows along the inner side of the 
conical surface 4 toward the vertex, and is let out through the outlet B. 
The inner surface of the conical surface 4 may be subjected to a proper 
surface treatment, such as resin coating, electrolysis polishing or 
buffing, in order to prevent the fluid from attaching to the inner wall of 
the conical surface 4 and to ensure a smooth flow of the spiral fluid 
within the holder 1. 
Thus, within the holder 1 of the pressure gauge 20, the fluid constantly 
flows without any stagnation. Accordingly, a fluid having thixotropic 
properties, such as a magnetic liquid, is not allowed to aggregate. The 
air contained is discharged out of the holder 1 from the outlet B, 
together with the fluid since no stagnation of the fluid occurs. 
In the above-described embodiment, the holder 1 is shaped like a cone. 
However, it may take any shape so long as the shape of the inner space of 
the holder is conical, for example, the shape of the conical surface 4, 
which is curved toward the inner space or outward from the inner space. 
Also, while in this embodiment the flow of the fluid emanating from the 
inlet A is parallel to the pressure sensor 13, it may be slightly slanted 
toward the diaphragm. When the inlet A is located some distance apart from 
the base of the conical inner space, stagnation of fluid present closer to 
the diaphragm can be effectively prevented if the fluid flow is slightly 
slanted toward the diaphragm. 
The pressure indicator 2 of the type in which an operator visually observes 
a pressure reading on a scale is employed in the above-described 
embodiment. If required, the same may be connected to a control system. 
As described above, the pressure gauge of the invention is constructed such 
that the inner space of the holder for measuring a pressure is 
substantially conical, the pressure sensor is provided at the base surface 
of the conical inner space, the outlet is formed at the vertex of the cone 
defining the inner space of the holder, and the inlet is disposed close to 
the base surface of the cone so as to create a flow of the fluid in a 
direction tangent to the conical surface. With such a construction, a 
spiral flow of the fluid flowing along the inner side of the conical 
surface is created, thereby eliminating stagnation of the fluid within the 
inner space. Accordingly, the present invention succeeds in solving 
conventional problems arising from the aggregation resulting from the 
stagnation of the fluid of low viscosity or poor fluidity, inexact gauging 
of pressure, product quality deterioration owing to the mixing of impurity 
and air into the fluid, and insufficient cleaning of the inside of the 
pipe. The present invention thus provides excellent control of a coating 
process using magnetic liquid, and uniform products based on the magnetic 
liquid. 
The effects of the present invention will be more clearly described by 
reference to an example. 
The constituents shown in Table 1 below were put into a ball mill and 
sufficiently mixed and dispersed. Subsequently, 30 parts by weight of 
epoxy resin (epoxy combining weight 500) was added to the mixture. The 
resultant mixture was uniformly mixed and dispersed, thereby obtaining a 
magnetic coating liquid (magnetic dispersion liquid). The thus-obtained 
coating liquid was circulated at the rate of 1000 ml/min in a pipe system 
a shown in FIG. 3. The state of air removal within the holder was visually 
observed. 
In the pipe system of FIG. 3, a magnetic coating liquid is fed from a 
storage tank 8 to a pipe system 10, by a pump 9, and stored in the storage 
tank 8. A pressure gauge 20 including a pressure indicator 2 mounted on a 
holder 1 and an air check device 7 having a glass plate 6 to air check 
instead of a pressure indicator are inserted midway of the pipe system 10. 
TABLE 1 
______________________________________ 
No. Constituent Amount (wt %) 
______________________________________ 
1 .gamma.-Fe.sub.2 powder 300 
(needle particles of 0.5 .mu.m in average 
particle diameter as seen in the 
longer diameter, coercive force of 320 
oersted) 
2 Polyvinyl chloride-acetate (copolymer 
30 
ratio 87:13, polymerization degree 
400) 
3 Conductive carbon 20 
4 Polyamide resin (amide valance 300) 
15 
5 Lecithin 6 
6 Silicon oil (Dimethyl polysiloxane) 
3 
7 Xylol 300 
8 Methylisobutyl ketone 300 
9 n-butanol 100 
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The magnetic coating liquid was circulated in the pipe system 10. After a 
predetermined time, air was introduced into the pipe and the residence 
time of air within the holder 1 was measured. Bubbles disappeared after 
approximately 1.3 seconds on the average. The flow of the magnetic coating 
liquid was rotated. 
For comparison, a glass plate 6 was mounted on the top of the conduit 12 of 
the T-pipe 11 shown in FIG. 4. The state of air discharge was observed 
under the same conditions. Bubbles were left stagnated in the conduit 12 
of the T-pipe 11 after one minute. 
Thus, the example of the invention satisfactorily eliminates stagnation of 
the magnetic coating liquid when comparing with the conventional pressure 
gauge.