Pressure monitoring device isolator

A pressure monitoring device isolator includes an annular member axially interposable in a pipeline for measuring the pressure of fluid in the pipeline. The annular member has an annular sensing fluid chamber, for a pressure sensing fluid, and an annular seal member separating the annular chamber from a central pipeline fluid passage. An opening in the outer periphery of the annular member is adapted to receive a pressure monitoring device. A sensing fluid passage extends radially inward from the pressure monitoring device opening. The sensing fluid passage is of substantially smaller volume than the sensing fluid chamber and the pressure monitoring device opening. A valve passage extends in from the periphery of the annular member to the annular sensing fluid chamber, meeting the sensing fluid passage at an acute angle. The valve passage has radially outer, middle and inner portions of progressively smaller cross sectional area. The inner portion joins the middle portion at an outward facing valve seat. The sensing fluid passage opens into the outer portion of the valve passage, thus communicating with the sensing fluid chamber via the valve passage. A valve member is threaded into the outer portion of the valve passage and is adapted to seat against the valve seat to interrupt the communication of the sensing fluid passage with the sensing fluid chamber.

FIELD OF THE INVENTION 
This invention relates to an improved pressure monitoring device isolator 
apparatus for use in measuring pipeline pressure of fluids (e.g. liquids) 
and, more particularly, to an improved pressure monitoring device isolator 
apparatus which is adapted to minimize the loss of pressure sensing fluid 
when the pressure monitoring device is removed from the apparatus. 
BACKGROUND OF THE INVENTION 
A prior pressure monitoring device isolator utilizes an intermediary 
sensing fluid (e.g. liquid) isolated from the fluid (e.g. liquid) in a 
pipeline, by a resilient pressure transmitting member. Since this 
isolating sensor does not expose the pressure monitoring device to the 
fluid being measured, it is quite useful when measuring the pressure of 
fluids which can be harmful to pressure monitoring devices. U.S. Pat. No. 
4,218,926 discloses such an isolating pressure sensor. 
Although such a system does isolate the pressure monitoring device from the 
pipeline fluid, it provides no isolation from the sensing fluid. The 
sensing fluid in such systems is housed in an annular chamber, one wall of 
which is a resilient pressure transmitting member. The sensor is attached 
to the pipeline so that the pipeline fluid pressure is exerted on the 
resilient member. However, the sensing fluid chamber within the sensor has 
only a finite volume. Therefore, when a pressure monitoring device is 
removed from the isolating sensor while the sensing fluid is under 
pressure of the pipeline fluid, the pressurized sensing fluid is exposed 
to atmospheric pressure and can spray out from the pressure monitoring 
device port. Sensing fluid, if lost in this manner, must be replaced, 
because without sufficient sensing fluid the isolating sensor is 
inoperable. Such replacement of sensing fluid is a costly inconvenience. 
These considerations are particularly true when the sensing fluid is 
noncompressible fluid such as a liquid. Thus, a device which can isolate 
the pressure monitoring device from the pressure applied to the sensing 
fluid, for the purpose of changing or maintaining the pressure monitoring 
device, is desirable. 
A prior art device disclosed in U.S. Pat. No. 4,082,002 uses a valve stem 
movable in a valve bore to disconnect a pressure monitoring device passage 
from a pipeline. The pressure monitoring device passage is threaded 
partway to receive a pressure monitoring device. However, in contrast to 
the present invention, a plug of grease in the pressure monitoring device 
passage transmits pressure from the pipeline liquid to the pressure 
monitoring device. A grease passage, stoppered at its outer end adjacent 
the pressure monitoring device, acutely angles into the outer portion of 
the pressure monitoring device passage for injection of grease thereinto. 
The pressure monitoring device passage extends generally tangentially, of 
and is spaced radially outboard of the central pipeline liquid passage 
through the device. The valve bore extends from the outer periphery of the 
device radially inward toward the central pipeline liquid passage. The 
pressure monitoring device passage meets the valve bore at a 90.degree. 
angle. The outer ends of the pressure monitoring device passage and valve 
bore are circumferentially remote, lying almost one fourth of the device 
perimeter apart. Substantial open space around the device is thus needed 
for operation of the valve and removal of the pressure monitoring device. 
This is especially a problem in crowded pipeline environments where access 
to the pressure monitoring device isolating apparatus is difficult. 
Also, the pressure monitoring device passage in this prior art device is, 
relative to the present invention, of very great volume, since the length 
of the pressure monitoring device passage is nearly equal to one half the 
diameter of the entire device, and the pressure monitoring device passage 
is everywhere at least approximately onehalf the diameter of the threaded 
pressure monitoring device receiving portion thereof. Thus, even when the 
valve is closed, removal of the pressure monitoring device allows a 
relatively large amount of liquid (or grease) to be lost due to spillage. 
Also, the threaded valve bore of this prior art device is formed directly 
in the housing of the device. The valve stem then threads directly into 
the valve bore. Thus if any thread damage occurs due to use of the valve, 
the entire housing may require replacement. 
Also, to seal against fluid leaks past the valve stem into the outer 
portion of the valve bore, the valve stem is surrounded by and moves 
axially through a packing gland which must be held fixedly in its position 
in the valve bore thereby adding to the complexity of the prior device. 
Accordingly, the objects of this invention include provision of: 
a pressure monitoring device isolator which avoids the limitations of the 
prior art discussed above and which is capable of isolating a pressure 
monitoring device from a supply of pressurized sensing fluid to enable 
removal and replacement of the pressure monitoring device without 
significant loss of sensing fluid; 
a pressure monitoring device isolator as aforesaid that is conveniently 
accessible for pressure monitoring device replacement and valve actuation 
even in crowded pipeline environments; 
a pressure monitoring device isolator, as aforesaid, which minimizes the 
volume of sensing fluid exposed to spillage during pressure monitoring 
device replacement; 
a pressure monitoring device isolator, as aforesaid, having readily 
replaceable valve elements; 
a pressure monitoring device isolator, as aforesaid, that provides a seal 
for the valve member which is both inexpensive and easily accessible and 
maintainable; 
a pressure monitoring device isolator, as aforesaid, that is of simple, 
economical construction. 
Other objects and purposes of the invention will be apparent to persons 
acquainted with apparatus of this general type upon reading the following 
specification and inspecting the accompanying drawings. 
SUMMARY OF THE INVENTION 
The objects and purposes of this invention are met by providing a pressure 
monitoring device isolator which includes an annular member axially 
interposable in a pipeline for measuring the pressure of fluid in the 
pipeline. The annular member has a central passage through which fluid in 
the pipeline passes. An opening in the outer periphery of the annular 
member is adapted to receive a pressure monitoring device. A small volume 
sensing passage extends inward in the annular member from the pressure 
monitoring device opening. A valve passage extends in from the periphery 
of the annular member, meeting the sensing fluid passage at an acute 
angle. The valve passage has a small volume inner portion responsive to 
pipeline pressure and an outward facing valve seat joining the sensing 
passage to the inner portion of the valve passage. A valve member is 
movable into the valve passage to seat against the valve seat and 
therewith to interrupt the application of pipeline pressure to the sensing 
passage.

DETAILED DESCRIPTION 
FIGS. 1 and 2 disclose a conventional pressure monitoring device isolator 
11. The pressure monitoring device isolator 11 comprises an annular member 
13. Annular member 13 contains an annular sensing fluid chamber 15 and a 
sensing fluid passage 17 whose outer end defines a threaded pressure 
monitoring device opening 21 for receiving the input nipple 51 of a 
pressure monitoring device 50. The sensing fluid chamber 15 is bounded by 
a radially inner wall 23 of annular member 13 and a ring 25 of U-shaped 
cross-section, elastomeric material sealed to and spaced radially inward 
from wall 23. 
The pressure of a fluid in pipeline 27 is applied to a sensing fluid 
(usually a liquid) in sensing fluid chamber 15 due to the resiliency of 
ring 25. Annular member 13 is formed by three coaxial ring members 14 
fixed together by circumferentially distributed, axially distributed 
screws 18, which ring members clamp therebetween the axial ends of the 
elastomeric ring 25. The elastomeric ring 25 and ring members 14 define a 
central passage 16 through which pipeline fluid flows. Pressure in the 
pipeline 27, when applied to sensing fluid chamber 15, will force sensing 
fluid therefrom into sensing fluid passage 17 and cause pressure 
monitoring device 50 to read out such pressure. The FIGS. 1 and 2 pressure 
monitoring device isolator is disclosed in U.S. Pat. No. 4,218,926, which 
is assigned to the assignee of the present invention and the disclosure of 
which is incorporated herein by reference. 
Turning now to the present invention (FIGS. 3-5), structural elements 
similar to those in FIGS. 1 and 2 are indicated by the same reference 
numerals with a prime mark (') added. The inventive structure of FIGS. 3-5 
particularly differs from that above described with respect to FIGS. 1 and 
2 as follows. The annular member 13' includes a valve passage 19 which 
extends in from the periphery of the annular member 13' to the sensing 
fluid chamber 15' at an acute angle to the sensing fluid passage 17', so 
as to intersect therewith as hereafter discussed. 
The valve passage 19 has a radially inner portion 29, a middle portion 31 
and an outer portion 35. The inner portion 29 opens into sensing fluid 
chamber 15'. The inner portion 29 joins the middle portion 31 of valve 
passage 19 at an outward facing valve seat 33. The middle portion 31 is 
tapered and expands continuously in diameter from valve seat 33 to the 
outer portion 35. The outer portion 35 of valve passage 19 is 
significantly larger in diameter than the inner portion 29. 
An externally and internally threaded valve bushing 37 is threaded into the 
outer end of the outer portion 35 of valve passage 19 and has an enlarged 
head which seats against the outer periphery of the annular member 13'. A 
valve member 39 has a threaded outer shaft 41 threadedly adjustably 
received in the valve bushing 37. 
The valve member 39 has a radially enlarged head 43 fixed coaxially on the 
inner end of shaft 41 and disposed inward of the inner end of the valve 
bushing 37. The head 43 coaxially opposes and is tapered more sharply than 
the tapered middle portion of the valve passage 19. The outer end of the 
shaft 41 is contoured to receive a tool for threading it axially along the 
valve bushing 37. In the embodiment shown, the outer end 47 of shaft 41 is 
diametrally slotted to receive a screwdriver. The axial distance from the 
inner end of the valve bushing 37 to the valve seat 33 substantially 
exceeds the axial length of the head 43 so that the latter can be either 
spaced from or abut the seat 33. The valve member 39 has an annular groove 
in its head 43 which receives an O-ring 35 to prevent fluid leakage 
outward beyond the head 43 along valve passage 19. Air leakage between the 
threads of the shaft 41 and bushing 37 keeps the air pressure between the 
head 43 and bushing 37 at atmospheric pressure to avoid air leakage inward 
past the O-ring 35. The valve member 39 can be moved along the valve 
passage 19 by applying a screw driver to the slotted outer end 47 of valve 
member 39, in order to seat the head 43 of valve member 39 against valve 
seat 33 and thereby interrupt fluid communication between the inner 
portion 29 and middle portion 31 of valve passage 19 or in order to unseat 
the valve head 43. 
Referring to FIG. 4, the threaded pressure monitoring device opening 21' is 
normally filled by the threaded end 51 of a pressure monitoring device 50. 
The sensing fluid passage 17', extending inward from the pressure 
monitoring device opening 21', is of greatly reduced diameter from opening 
21' and of greatly reduced volume from the fluid passage 17 of prior art 
FIG. 1. In fact, in a pressure monitoring device isolator built according 
to the present invention, the fluid passage 17' had a 0.125 inch diameter, 
and the ratio of volumes of prior art passage 17 to present invention 
passage 17' is approximately 9 to 1. 
The inner end of sensing fluid passage 17' connects, not directly to the 
chamber 15' as in FIG. 1, but rather to the inner end of the outer portion 
35 of the valve passage 19 immediately adjacent middle portion 31. 
Turning now to the operation of the apparatus, when the head 43 of valve 
member 39 is not seated (FIG. 4) on valve seat 33, the sensing fluid 
passage 17' communicates with sensing fluid chamber 15' via the outer 
portion 35, middle portion 31 and inner portion 29 of valve passage 19, 
thus allowing the pressurized sensing fluid from chamber 15' to reach 
threaded pressure monitoring device opening 21' and the pressure 
monitoring device therein. On the other hand, when head 43 is seated (FIG. 
3) on valve seat 33, fluid communication between sensing fluid passage 17' 
and sensing fluid chamber 15' is interrupted. The sensing fluid passage 
17' and threaded pressure monitoring device opening 21' are then isolated 
from the pipeline pressure exerted on sensing fluid chamber 15', and the 
pressure monitoring device 50 can be safely removed from the pressure 
monitoring device opening 21'. 
Since pipeline pressure cannot then drive sensing liquid in the sensing 
fluid chamber 15' out of the pressure monitoring device opening 21', loss 
of sensing liquid (which may be expensive and may be difficult to replace 
in chamber 15' without reducing pipeline pressure) and the danger of 
spurting of sensing liquid out of the pressure monitoring device opening 
21' (which could splash on persons nearby) is avoided. 
Also, due to the small diameter and volume of sensing fluid passage 17', 
only a very small portion of the total sensing liquid in the pressure 
monitoring device isolator 11' could possibly spill due to gravity if the 
isolator is tilted. 
The pressure monitoring device opening 21' and sensing fluid passage 17' 
define a fluid path extending from the periphery of annular member 13' 
radially inward. The valve passage 19 is circumferentially near and 
extends inward from the periphery of annular member 13' to join the 
sensing fluid passage 17' at a small acute angle, typically between about 
30.degree. to 40.degree.. In the embodiment shown, the annular member 13' 
is radially extended, as indicated at 60, in the region of the threaded 
pressure monitoring device opening 21', to allow the threaded pressure 
monitoring device opening 21' and valve passage 19 to fit 
circumferentially loosely between adjacent screws 18'. Referring to FIG. 
5, this circumferential nearness facilitates exchanging pressure 
monitoring devices on the annular member 13'. Both pressure monitoring 
device opening 21' and slotted end 47 of valve member 39 can be easily 
accessed at one circumferentially narrow zone on annular member 13'. 
In summary then, and referring to FIGS. 3 and 4, the valve member 39 can be 
inward threaded by rotating its slotted end 47 to interrupt fluid 
communication between sensing fluid chamber 15' and sensing fluid passage 
17', thereby isolating pressure monitoring device opening 21' from the 
pressure in sensing fluid chamber 15'. A pressure monitoring device can 
then be safely removed for repair or replacement. When the new or repaired 
pressure monitoring device is replaced in pressure monitoring device 
opening 21', the slotted end 47 of valve member 39 can be rotated 
reversely to restore fluid communication between sensing fluid chamber 15' 
and sensing fluid passage 17', thereby re-exposing pressure monitoring 
device opening 21' to pressurized sensing fluid. 
Although a particular preferred embodiment of the invention has been 
disclosed in detail for illustrative purposes, it will be recognized that 
variations or modifications of the disclosed apparatus, including the 
rearrangement of parts, lie within the scope of the present invention.