Pressure transducer body

A pressure transducer body is described which has a bore running its length and contains (a) a means for receiving a pressure transducer, (b) a fluid reservoir, (c) a stationary elastic plug member having embedded therein a T-shaped rigid pin member, and (d) a chamber for receiving a fluid under pressure. The elements of the transducer body are combined in such a way that pressures of fluids flowing into chamber (d) are accurately measured using conventional pressure transducers even at very high pressures (e.g. 20,000 psi). More importantly, perhaps, the configuration of the transducer body permits accurate pressure measurements on pressurized fluids which are corrosive and/or abrasive. This makes the pressure transducer bodies particularly useful in the oilfield service industries for measuring the pressure of acidizing or hydraulic fracturing fluids used in stimulation.

FIELD OF THE INVENTION 
This invention pertains to a new pressure transducer body, and in 
particular this invention pertains to a novel pressure transducer body 
adapted for use in measuring pressures of corrosive and/or abrasive fluids 
subject to pulsating pressure loadings. 
DESCRIPTION OF THE PRIOR ART 
There are a variety of transducer bodies known in the art. For transducer 
bodies that might be subject to heavy pulsating types of loading, the most 
commonly used device contains a diaphram with a hydraulic liquid 
separating the diaphram and a recording pressure transducer. This type of 
transducer body has problems with rupture of the diaphram due to 
pulsations or loss of hydraulic fluid which allows the diaphram to deform 
excessively. 
Another type of transducer body has been a piston type in which a hydraulic 
liquid is located between the pressure transducer and the piston. Again, 
under operating conditions the heavy pulsating types of loading usually 
causes fluid leak off and permits the piston to "bottom out" against the 
transducer. This results in inaccurate and unreliable readings. 
SUMMARY OF THE INVENTION 
A novel pressure transducer body has now been discovered having 
(a) means for receiving a pressure transducer, 
(b) a fluid reservoir, 
(c) a stationary elastic plug member, and 
(d) a chamber for receiving a fluid under pressure; 
said means for receiving a pressure transducer, (a), being located near the 
first end of said transducer body and in fluid communication with said 
fluid reservoir, 
said fluid reservoir, (b), being defined within said bore and being located 
between said means for receiving a pressure transducer (a), and said 
stationary elastic plug member, 
said stationary elastic plug member, (c), having a first end in fluid 
communication with said fluid reservoir (b), and a second end adjacent to 
said chamber for receiving a fluid under pressure, 
said chamber for receiving a fluid under pressure, (d), being defined 
within said bore, 
said plug member (c) also having a rigid pin member, (p), embedded therein; 
said pin member, (p), being defined by an elongate shaft extending 
partially through said stationary elastic plug (c), and positioned coaxial 
to the bore and having (i) a first end disposed toward said fluid 
reservoir plug (b), and defining a flat or substantially flat face which 
is positioned perpendicular to the bore, and (ii) a second end disposed 
toward said chamber for receiving a fluid under pressure (d), said second 
end having an attached head which is external to said plug member, (c), 
and which has a flat or substantially flat face positioned perpendicular 
to the bore, the flat face of the head having a surface area greater than 
a cross-sectional area of the shaft but less than a cross-sectional area 
of the bore.

DETAILED DESCRIPTION OF THE INVENTION 
The invention is illustrated by reference to FIGS. 1 and 2. It is apparent 
that the external shape of the transducer body can take on whatever 
configuration is convenient to the user. The transducer has a first end 
and a second end in defining a bore running the length from the first end 
to the second end. The bore may be of substantially uniform diameter, or 
it may be of various diameters, as shown in FIGS. 1 and 2. The transducer 
body contains a means for receiving a pressure transducer which is located 
near the first end of the transducer body which is in fluid communication 
with a fluid reservoir (13). In FIG. 1, this is illustrated by items (12) 
and (13). 
The fluid reservoir (13) is defined within the bore and is located between 
(12) and a stationary elastic plug member (14). 
The stationary elastic plug member has a first end in fluid communication 
with the fluid reservoir and it has a second end adjacent to a chamber 
(16) for receiving a fluid under pressure. The chamber for receiving a 
fluid under pressure is defined within the bore. 
The stationary elastic plug member can be prepared using a variety of 
elastomeric materials, but it is preferably made of elastomeric materials 
that are resistant to chemicals, heat and abrasion. For example, the plug 
member can be prepared using a variety of rubbers, such as 
styrene-butadiene rubber, ethylene-propylene terpolymers (EPDM), 
urethanes, nitrile interpolymers, fluorinated aliphatic hydrocarbon 
polymers (e.g. those sold by DuPont under the trade name VIATON), and the 
like. Of these, the fluorinated aliphatic polymers are most preferred. The 
elastic plug member can be prepared external to the transducer body but is 
preferably prepared by curing the elastomeric material in situ. By way of 
illustration, the necessary amounts of uncured VIATON rubber is charged to 
the bore, the rigid pin inserted and held in place while the Viaton rubber 
is cured using appropriate amounts of head and pressure to produce a 
substantially void free elastomeric cured plug. 
The T-shaped rigid pin member (15) is defined by an elongate shaft 
extending substantially through the elastomeric plug member and it is 
positioned coaxial to the bore. The shaft of the pin has a first end 
exposed towards the fluid reservoir and it defines a flat or substantially 
flat face which is positioned perpendicular to the bore. Normally, the 
face of the first end is merely a cross-section of the shaft. The second 
end of the shaft is disposed towards the chamber for receiving fluid under 
pressure. The second end of the shaft has a head attached which is 
external to the elastomeric rubber plug. As shown in FIG. 1, the shaft 
extends into the chamber area and the head of the shaft is located outside 
of the elastomeric plug. The head of the shaft also has a flat or 
substantially flat face which is positioned perpendicular to the bore. The 
flat face of the head has a surface area that is greater than a 
cross-sectional area of the shaft itself but less than a cross-sectional 
area of the bore. The T-shaped pin can of unit construction or assembled 
from multiple parts. Preferably, the pin is of unit construction. Also it 
is preferred that the pin and the attached head each have a circular 
cross-section. Preferrably the elongate shaft of said pin member 
terminates at a point near the first end of said stationary elastic plug 
member. The pins may be manufactured by any suitable process, but 
applicants have found it convenient to merely cut a round rod to length 
and to machine part of it down to form the shaft. For example, when 
preparing a transducer body having a one inch diameter bore, the pin has 
been conveniently prepared by cutting a 3/8 inch rod to a length of 
approximately 13/8 inches and machining it down so it as to leave a head 
having 1/4 inch thickness and a shaft having 11/8 inch length and 1/4 inch 
diameter; this pin, for example is used in a VIATON plug cured in situ 
with a plug length of 13/8-11/2 inches. 
The fluid used in the fluid reservoir can be varied and is noncritical so 
long as it is an essentially noncompressible hydraulic fluid. The fluid of 
course, should completely fill the reservoir without leaving air bubbles 
or other void spaces. The fluid can be either liquid or semi-solid and 
applicants have found it useful to use a high viscosity silicon or 
hydrocarbon grease to fill the fluid reservoir. The fluid in the reservoir 
is of course, in fluid communication with the first end of the elastomeric 
plug member and the transducer. In FIGS. 1 and 2, this fluid communication 
is established by merely having a direct interface between the fluid in 
the reservoir and the plug member and the pressure sensing surface of a 
conventional pressure transducer. This is illustrated in FIG. 2. 
Generally, a fluid retaining means is used to prevent fluid in the 
reservoir from bypassing the body of the transducer. One such fluid 
retaining means is illustrated in FIG. 2 where a shoulder is placed in the 
bore of the transducer body. Other fluid retaining means (e.g. O-rings, 
rubber gaskets, etc). can be used; such means would be readily apparent to 
the skilled artisan. The pressure transducers themselves are likewise a 
commercial commodity and can be varied. Those with a circular 
cross-section and flat recording face are, however, preferred. 
The transducer bodies are normally mounted on a pressure pump or pipeline 
carrying a liquid under pressure. The pressurized liquid flows into the 
cavity (16) and impinges against the T-shaped rigid pin member. This 
causes a deflection of the pin member toward the fluid in the fluid 
reservoir, which in turn transmits the pressure to the pressure 
transducer. Pressure transducer bodies formed according to the present 
invention have been found to be exceedingly reliable and durable and have 
performed with a high degree of accuracy. Attempts to prepare "similar" 
transducer bodies using just a solid elastomeric plug (without the 
T-shaped pin) or using an elastomeric plug having a pin without the head 
attached were substantially less accurate and gave less reproducible 
results.