Liquid flow meter or the like for corrosive liquids under pressure

In a liquid fitting for corrosive liquids under pressure, such as a liquid flow meter having an outer pressure resistant housing in which a measuring chamber housing with a movable measuring element is arranged, the space between the outer housing and the measuring chamber housing is filled with the liquid to be measured with the outer housing provided with a thin walled elastic lining at its inside surfaces forming a hollow wall, and the hollow wall filled with a noncorrosive medium.

BACKGROUND OF THE INVENTION 
The invention relates to liquid fittings for corrosive liquids under 
pressure in general and more particularly to an improved fitting such as a 
liquid flow meter for measuring corrosive liquids under pressure. 
Liquid flow meters for measuring liquids under pressure must be designed so 
that their parts which are important to the measuring process, i.e., in 
particular, the measuring chamber which is machined to close tolerances, 
are either not deformed or only slightly deformed under the pressure of 
the liquid. Otherwise the functioning, or at the every least, the 
measuring accuracy of the equipment would be adversely affected to a large 
extent. 
To satisfy these requirements in known commercially available liquid flow 
meters of the type having a pressure resistant outer housing in which a 
measuring chamber housing with a movable measuring element is arranged, 
and a space filled with the liquid to be measured between the outer and 
the measuring chamber housing, the space between the outer and the 
measuring chamber housing is filled with the liquid to be measured under 
pressure. As a result, the pressure outside and inside the measuring 
chamber housing is practically the same and no mechanical pressure is then 
exerted on the measuring chamber housing, so that there is no adverse 
effect on the measuring accuracy. If chemically corrosive media are to be 
measured with the known liquid flow meters, which is quite often the case, 
then the outer housing must also be made of high quality material because 
of the required corrosion resistance. Since the outer housing must be able 
to withstand the pressure of the liquid to be measured, it must be made 
appropriately strong, which requires a relatively large amount of valuable 
material. 
To reduce the required amount of valuable material needed for the outer 
housing, there have been attempts to provide the outer housing with a 
corrosion resistant plastic lining. However, this presents great 
difficulties, among other things, with respect to dimensional 
compatibility, since accurate fitting of the plastic lining into the outer 
housing is necessary, so that the pressure prevailing within the outer 
housing is transmitted to the outer housing without damaging the plastic 
lining. The range of application for using a plastic lining, furthermore, 
is relatively narrow, for instance, because of the temperatures 
permissible for plastic. 
In another attempt to solve the problem, a liquid flow meter which can be 
manufactured inexpensively even in a design for measuring corrosive 
liquids under pressure, has been proposed. In such device the space 
between the measuring chamber housing and the outer housing is tightly 
separated from the liquid to be measured and is kept in pressure 
equalizing connection with the liquid to be measured by means of at least 
one element which is movable by pressure. 
SUMMARY OF THE INVENTION 
The present invention provides an improved solution to this problem. In 
accordance with the present invention the outer housing is provided with a 
thin walled elastic lining at its inside surfaces, forming a hollow wall, 
and the hollow wall is filled with a noncorrosive medium. 
The advantage of the liquid fitting according to the present invention is 
in particular that only a thin walled lining of high quality, corrosion 
resistant material needs to be fabricated, for which the cost is 
relatively small. A less expensive material can be used for the pressure 
resistant, thick walled outer housing, since the latter is not exposed to 
corrosive media. 
In the liquid fitting according to the present invention, the lining is 
fastened, if a divided outer housing is used, at the parts of the housing 
in the area of the respective mating surfaces forming a tight seal for the 
hollow wall. The hollow wall itself is then filled with the noncorrosive 
medium. 
In order to ensure that the thin walled lining can adapt itself well to the 
pressure changes of the liquid to be measured, the flat surfaces of the 
thin walled lining of the liquid fitting according to the present 
invention are advantageously provided with corrugations to increase their 
elasticity. 
In lieu of such corrugations or possibly, as a supplement thereto, it may 
be advantageous to provide the thin walled lining with bellows, whereby 
the ability of the thin walled lining to "breathe" becomes particularly 
high. 
The thin walled lining in the connection stubs of the liquid fitting 
according to the invention is advantageously of cylindrical shape and is 
firmly attached to the outer housing at the respective outer end of the 
connection stub and resiliently connected to the remaining part of the 
thin walled lining in the interior of the outer housing, so that the 
mobility of the thin walled lining cannot be affected by the lining of the 
connection stubs. This objective can also be reached advantageously by 
making the thin walled lining in the connection stubs as corrugated tubes. 
If corrugated tubes are used, moreover, manufacturing tolerances can be 
equalized better. 
The thin walled lining can be fastened to the outer housing in various 
ways. It is possible, to provide the lining with flanges or extensions at 
suitable points and to attach them therewith firmly to the outer housing 
with the interposition of a gasket. For production reasons, it appears 
particularly advantageous to fasten the thin walled lining tightly to the 
outer housing by welding. 
Particularly if, for instance, poisonous liquids flow through the liquid 
fitting according to the present invention or the liquid flow meter 
according to the invention, it is desirable to monitor whether the thin 
walled lining is still tight everywhere. This can be achieved with 
relatively little effort in an advantageous manner by providing an 
indicator for checking the chemical composition of the noncorrosive medium 
projecting into the medium in the hollow wall.

DETAILED DESCRIPTION OF THE INVENTION 
The liquid flow meter shown in FIG. 1 contains an outer housing 1, which 
consists of an upper part 2 and a lower part 3. The upper part 2 as well 
as the lower part 3 are made with relatively thick walls and consist of a 
relatively low quality but pressure resistant material. The upper part 2 
and the lower part 3 of the outer housing 1 are each provided with flanges 
4 and 5, with which they are clamped together. The lower part 3 contains a 
connection stub 6, through which the liquid to be measured flows in, in 
the direction of the arrow 7; the upper part 2 has a connection stub 8, 
through which the liquid to be measured leaves the liquid flow meter. 
Inside the outer housing 1, a measuring chamber housing 9 is clamped with a 
circular flange 10 disposed between the upper part 2 and the lower part 3. 
Inside the measuring chamber housing 9, a ring piston, for instance, may 
be arranged as a measuring element which, together with the measuring 
chamber housing 9 forms a ring piston meter known per se. The rotary 
motions of the measuring element in the measuring chamber housing 9 are 
transmitted via a drive shaft 11 and a magnetic clutch 12, known per se, 
to the input shaft 13 of a counter mechanism, not shown. 
Within the outer housing 2 a thin walled lining 14 of high quality, 
corrosion resistant material is arranged. The thin walled lining 14 is 
welded to a circular flange part 15 in the upper part 2 of the outer 
housing 1 as well as to the housing 16 of the magnetic clutch 12, care 
being taken that the welds seal the hollow wall 17, formed by the outer 
housing 1 and the thin walled lining 14, from the remaining interior of 
the liquid flow meter. The lining of the connection stub 8 is cylindrical 
and is provided at its outer end 18 with a reinforcing flange 19 for 
welding to a connecting flange 20. Inside the housing 1, the cylindrical 
lining is welded to the thin walled lining 14. 
In the same manner as in the upper part 2, the thin walled lining 14 is 
connected to a circular flange 22 in the lower part 3 by a welded joint 
21. The thin walled lining of the connection stub 6, to show a further 
possibility of a lining of the connection stubs, is formed by a corrugated 
tube 23, which carries a fastening flange 24 at its outer end; the 
corrugated tube 23 is welded to the fastening flange 24, which in turn is 
fastened by a bolted connection to the connecting flange 26 of the 
connection stub 6 with the interposition of a gasket 25. At its other end, 
the corrugated tube 23 is movably supported in the longitudinal direction 
by means of ring parts 28 and 29, between which a seal is provided; this 
does not affect the mobility of the thin walled lining 14. The ring parts 
28 and 29 are connected to the thin walled lining 14 as well as to the 
corrugated tube 23 by welding. 
To increase its elasticity, the thin walled lining 14 is provided with 
corrugations 30 and 31 in the upper part 2 as well as in its lower part 3. 
The noncorrosive medium is filled into the hollow wall 17 between the thin 
walled lining 14 and the outer housing 1 through filling holes 32 in the 
upper part 2 or 33 in the lower part 3, which can be closed off by 
threaded plugs 34 and 35, respectively. Instead of these threaded plugs 34 
and 35, an indicator can be inserted through the holes 33, which checks, 
for instance, via a conductivity measurement of the noncorrosive medium, 
whether the hollow wall is properly sealed against the space through which 
the liquid to be measured flows. Openings 38 and 39, which can be closed 
off by further screws 36 and 37, respectively, serve for proper venting 
when the hollow wall 17 is filled. 
The embodiment depicted in FIG. 2 agrees in substance with that according 
to FIG. 1; it differs from the embodiment of FIG. 1 in that the lining 40 
in the upper part 41 of the housing 42 is provided with a bellows 45 in 
addition to corrugations 43 and 44. The lining in the lower part of the 
housing 42 may be similarly constructed. 
However, it may also be sufficient, as shown by the example of the lining 
14 in the lower part 46 of the housing 42 in FIG. 2, to provide only 
bellows 47 in the lower and upper part instead of corrugations. 
To monitor the lining 40 for a tight seal against the interior of the 
liquid fitting, indicators 50 and 51 are inserted through openings 48 and 
49 in the upper part 41 and the lower part 46 in such a manner that they 
project into the bellows 45 and 47. These indicators monitor the chemical 
composition of the medium in the hollow wall. 
With the present invention, a liquid fitting and in particular, a liquid 
flow meter for measuring liquids under pressure is provided, which is 
distinguished by the small amount of high quality material required and by 
relatively low manufacturing costs.