Small volume prover

A small volume prover is disclosed which is compact and capable of obtaining highly reliable measurement, keeping a highly accurate base volume without being affected by temperature and pressure of fluid to be measured. The prover includes a cylindrical outer housing having a fluid inlet and a fluid outlet spaced apart from each other, a cylindrical measuring conduit having both open ends and first and second sets of fluid ports radially made in a wall thereof and coaxially mounted within the outer housing and an annular wall mounted between the outer housing and the measuring conduit at the position between the measuring conduit open end and the first set of ports thereof to form an upstream annular passage and a downstream annular passage. During proving preparation a piston is restrained by a piston actuator provided in the outlet-side end of the outer housing to permit the fluid to pass through the annular passage. At the time of measurement start, the piston is released to run and a valve actuator provided at the inlet side acts as a slide valve to closed the first sets of fluid holes.

BACKGROUND OF THE INVENTION 
The present invention relates to a small volume prover for proving 
accuracies of flow meters, and more particularly to a high precision small 
volume prover capable of proving flow meters without being affected by 
test fluid pressure and temperature. 
Flow meter proving apparatuses are used for conducting periodical and/or 
optional characteristic tests of flow meters newly fabricated to use and 
flow meters currently used in lines so that they can measure flow rate at 
a reliable accuracy without the possible characteristic changes due to the 
influences of extrinsic factors such as temperature and pressure and also 
of intrinsic factors such as wearing of movable parts. The characteristic 
tests are conducted basically by two methods: one is called a calibrating 
system using a stationary proving apparatus to which a flow meter to be 
tested is connected, and the other is called a prover system by which a 
flow meter is proved by being mounted in a fluid system. 
Since the above-mentioned prover method can conduct a characteristic test 
of a flow meter as mounted in a line at any time, it is used mainly for 
testing conjectural type flow meters, e.g. turbine meters. 
Flow meter provers operate on such a common principal that a moving 
displacer such as a piston or ball travels simultaneously with fluid flow 
in a cylindrical conduit having a uniform cross-section and displace a 
known volume of fluid in a predetermined section thereof which is 
determined as the reference volume. In proving a flow meter by a prover, 
the corresponding metered volume simultaneously passes through the flow 
meter and the flow meter's readings, i.e. the whole number of pulses 
generated by the flow meter is counted to determine a K-factor(meter 
factor) representing a number of pulses per unit volume displaced. If 
needs be, a continuous flowrate characteristic curve is plotted on the 
basis of a K-factor calculated for a plurality of flowrate measurements. 
To obtain a high resolution meter factor it is needed to increase a number 
of pulses generated per base volume over a certain number, for example, 
10000 pulses for stationary prover having a large base volume. If the base 
volume is less than the above-mentioned one, the desired number of meter 
pulses can not be generated, but a number of clock pulses(time) generated 
for the period that a displacer such as a piston travels and displaces the 
base volume of fluid and meter pulses(time) generated directly before and 
after said duration can be used for determining therefrom a meter factor. 
Therefore, even in case a smaller number of meter pulses is generated, it 
is possible to use small type provers (hereinafter called small volume 
provers) which are portable. 
The small volume provers are designed basically such that a movable piston 
travels through a certain section of a cylindrical measuring conduit of a 
constant cross-section connected in series with a flow meter to be tested 
and the flow meter reading is compared to the displaced volume of fluid. 
The fluid volume is practically determined from the displacement of the 
piston. In proving, a plurality of test results are averaged and then a 
meter factor(K-factor) is determined on the basis of the average value. 
For this reason, the piston reciprocates in the cylindrical measuring 
conduit by the number of flowrate measurements. 
Having traveled a given distance in the cylindrical measuring conduit and 
completed a proving pass, the piston is returned to its initial position 
by means of a hydraulic or pneumatic actuator driving the piston through a 
piston rod against the fluid stream. In this case, fluid can pass the 
cylindrical measuring conduit or a by-path provided in parallel with the 
measuring conduit. 
In case of the fluid passing through the measuring conduit, the piston to 
be returned by means of the actuator is provided with valve functions for 
closing the port during the proving pass and opening the port during 
returning. This method is, hereinafter, called an internal valve method. 
In case of fluid passing through a by-path, a by-pass valve is provided to 
close and open the by-pass, respectively, during a proving pass and 
returning of the piston. Hereinafter, this method is called an outer valve 
method. 
The Japanese laid open patent publication No. 153063/79 discloses a small 
volume prover of the internal valve type in which a piston (movable 
member) includes a poppet valve which is opened to allow only the fluid to 
pass therethrough while the piston is fixed in a non-measurement state, 
and is closed to force the piston to travel simultaneously with a fluid 
stream during a proving pass. However, the poppet valve is frequently 
operated and, consequently, its seat portion may rapidly wear. In case of 
small volume provers, fluid leakage through the piston assembly may give a 
significant influence to their measurement results and, therefore, the 
reliability of the poppet valve may directly concern the test results. 
The Japanese laid open patent publication No. 173418/85 discloses a compact 
type flow meter prover which is of the external valve type. 
FIG. 1 is a view for explaining a conventional small volume prover which 
includes an inlet pipe 81, an inlet 81a, a housing 82, a by-path 83, a 
by-pass valve 84, an actuator 85, an introducing portion 86, a 
displacer(piston) 87, a shaft 88, a main cylinder 89, a downstream portion 
90, an outlet pipe 91, a spring 92, journal bearings 93, 94, a hydraulic 
cylinder 95, a hydraulic piston 96, detecting rod 97, a detecting unit 98, 
sensors 99, 100, 101, a detecting flag 102, a pilot 103 and a sleeve 
bearing 104. 
The housing 82 is composed of a main cylinder 89 serving as a measuring 
cylinder, an introducing chamber 86 being larger in diameter than the main 
cylinder 89 and a downstream portion 90. 
The introducing chamber 86 includes a hydraulic cylinder 95 therein and 
communicates with an inlet pipe 81 connected to the portion adjacent to 
the cylinder-mounted portion. A by-path of the housing 82 is composed of 
the inlet pipe 81, a by-pass pipe 83 and an outlet pipe 91 and includes a 
by-pass valve 84 therein between its inlet 81a and outlet 91a. A hydraulic 
cylinder 95 and the main cylinder 89 are coaxially arranged and a 
hydraulic piston 96, a shaft 88 and a displacer 87 are connected in series 
with each other to form a single member. The shaft 88 is liquid-tightly 
supported by a journal bearing 93. A spring 92 is provided between the 
journal bearing 93 and the displacer 87. 
The displacer 87 is provided with a detecting rod 97 fixed thereto for 
detecting a travel of the displacer 87. 
As shown in FIG. 1, the displacer 87 currently exists in the introducing 
chamber 86 of a large diameter and a detection flag 102 coexists with a 
sensor 99. With a by-pass valve 84 being closed, the fluid introduced 
through the inlet 81a and the inlet pipe 81 passes through the main 
cylinder 89 and is discharged through an outlet 91a of an outlet pipe 91. 
The displacer 87 rests and is ready to start travelling. 
When a command to start measurement is given, a hydraulic piston 96 starts 
moving toward a downstream portion 90 (to the right) to move the displacer 
87 with the aid of the spring 92. A base volume of fluid displaced from 
the cylinder 89 by the displacer 87 is determined as a travel distance of 
the detection flag between two sensors 100 and 101. The displacer 87 then 
stops when a pilot 103 extending axially from the displacer rests in a 
sleeve bearing 104. In this state, the fluid passes the downstream portion 
90 of a large diameter and exits from the outlet 91a. 
When the by-pass valve 84 is opened by the action of an actuator 85, the 
fluid passes through the by path 83 and is discharged from the outlet 91a. 
In this state the displacer 87 is returned to the shown starting position 
by means of the hydraulic piston 96. 
In the above-described small volume prover of the external valve type, the 
displacer 87 with a seal 87a slidably moves in the main cylinder 89 with 
no fear of fluid leakage that is encountered in any prover of the internal 
valve type having a displacer provided with a poppet valve. However, since 
the main cylinder 89 is a single wall conduit precisely finished to have 
an uniform diameter, it can be deformed by the influence of temperature 
and pressure of the fluid. When fluid temperature is high, the main 
cylinder 89 may have a large difference of temperatures between its outer 
and inner surfaces that is also dependent upon the fluid temperature. 
Therefore, it is not easy to correct a change of volume in the main 
cylinder 89. In addition, a change of the fluid pressure may also change 
the reference volume of the small volume prover. Such a construction that 
the by-path line is externally connected to the main cylinder 89 for 
communication with the introducing chamber 86 and the downstream portion 
90 is connected to the portion 90 makes it difficult to reduce the size of 
the prover. 
SUMMARY OF THE INVENTION 
The present invention, therefore, has as its primary object the provision 
of a small volume prover which is of small size and capable of conducting 
high reliable measurements without suffering affection of the fluid 
temperature and, particularly, the fluid pressure. 
Another object of the present invention is to provide a small volume prover 
which is constructed so that a housing is in the form of a closed 
cylindrical vessel having an inlet and an outlet spaced from each other 
and containing a coaxially placed therein cylindrical measuring conduit 
which is supported on the housing inner wall by means of an annular wall 
to form an annular passage by separating an upstream side and downstream 
side and to allow the introduction of fluid through the inlet from a 
connected thereto flow meter to be proved and further its passing through 
the measuring conduit during a proving pass or through the annular passage 
during the time of non-measurement, thereby keeping a constant temperature 
of the fluid stream and maintaining a constant base volume of the 
measuring conduit by minimizing a differential pressure of fluids in and 
around said measuring conduit. 
Another object of the present invention is to provide a small volume prover 
which comprises a closed cylindrical housing having an inlet adjacent to 
one closed end and an outlet adjacent to the other closed end; a 
cylindrical measuring conduit of a constant inside diameter with an open 
inlet-side end and an outlet-side end coaxially laying on an inner wall 
end of the cylindrical housing and having three rows of radially arranged 
ports, which are provided at a certain axial distance in the wall thereof; 
a sealed annular wall dividing an annular passage formed between the 
housing and the measuring conduit into an open-end side annular space and 
an annular chamber including the inlet-side ports of the measuring 
conduit; a slide valve having a valve rod sealably passing through the 
inlet-side end of the housing, which is slidably movable near the open end 
of the measuring conduit to open and close the inlet side slotted holes; a 
piston having a piston rod sealably passing through the outlet-side end of 
the housing, which is movable in the downstream side from the inlet-side 
ports to displace the base volume of fluid in the section defined between 
a row of the inlet-side ports and a row of the outlet-side ports; a valve 
actuator for driving the slide valve through the valve rod to close the 
inlet-side ports only during a proving pass; a piston actuator which acts 
on the piston rod so as to hold the piston near the position of the 
inlet-side ports for the time of proving preparation, to make the piston 
movable for the time of a proving test and to return the piston to its 
starting position; and a position sensor included in the piston actuator 
for detecting the piston passing the difined section of the measuring 
conduit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 2(a),(b),(c), there are shown, respectively, a general 
view of a small volume prover embodying the present invention, an enlarged 
view of portion B of FIG. 2(a) and an enlarged view of portion C of FIG. 
2(a). In the drawings, there are indicated a cylindrical body 1, an outer 
housing 2, an inlet-side end plate 3, an outlet-side end plate 4, a 
concaved ring portion 4a, an inlet 5, an outlet 6, a cylindrical measuring 
conduit 7, upstream slotted holes 8, downstream slotted holes 9, pressure 
relieving holes 10, an annular wall 11, an annular passage 12, a piston 
13, a piston rod 14, a cushion 15, a piston actuator 16, a cylinder 17, a 
concaved portion 17a, a slide valve 18, an annular groove 18a, a through 
hole 18b, a support column 19, a supporting plate 20, a valve rod 21, a 
driving piston 22, a valve actuator 23, a cylinder 24, pressure supply 
ports 25, 26, 27 a stopper 28, a position sensor 29, markers 30, 31, a 
flexible tube 38, air ports 41a, 41b, and a spring 46. 
In FIG. 2(a), a cylindrical body 1 is a closed cylindrical vessel composed 
of an outer housing 2, an inlet-side end-plate 3 and an outlet-side 
end-plate 4. A fluid inlet 5 and a fluid outlet 6 are provided in the wall 
of the outer housing 2 adjacent to, respectively, the inlet-side end-plate 
3 and the outlet-side end-plate 4 thereof. Coaxially mounted within the 
cylindrical body 1 is a cylindrical measuring conduit 7 having both open 
ends which serves as a vessel of reference volume and, therefore, is 
precisely finished to be of a constant inside diameter over all length. 
The three rows of ports are radially made in the wall of the measuring 
conduit: Upstream ports 8 near the inlet-side open-end, downstream slotted 
holes 9 at the downstream side and pressure relieving ports 10 near the 
opposite end of the conduit. An annular wall (ring) 11 is mounted within 
the measuring conduit 7 which is supported near the upstream open end 
(before the upstream holes) by an affixed thereto annular wall 11 which 
divides the annular passage 12 formed between the cylindrical body 1 and 
the measuring conduit 7 into an upstream section and a downstream section. 
Therefore, the reference volume measuring portion of the measuring conduit 
7, which lies between the upstream ports 8 and the downstream slotted 
holes 9, is free from mechanical and thermal distortion through the 
annular wall 11 and the cylindrical body 1. Consequently, the measuring 
conduit 7 forms a constant and accurate base volume of measuring portion 
being free from external influence. The cylindrical body 1 with the 
integrally mounted therein measuring conduit 7 is hereinafter called the 
"main body" of the small volume prover. 
A piston 13 is slidably mounted within the measuring conduit 7 and is 
provided with piston seal means 13a near its both ends. This piston 13 is 
a movable fluid barrier which, in the operation of the prover, is forced 
by meter fluid pressure to travel downstream to displace the base volume 
fluid in the measuring portion of the conduit. The piston 13 is formed 
integrally with a piston rod 14 and a cushion 15. The piston rod 14 is a 
moving member of a plunger type hydraulic unit provided at the outlet-side 
end-plate 4 and acts as driving part of a piston actuator 16 which has 
functions to hold the piston 13 at rest or to return it to the original 
position by opening or closing a pressure inlet 27 (valve means not 
shown), for example, by leading or discharging pressurized fluid into or 
from a cylinder 17. In the operation of the prover, the piston 13 travels 
downstream (toward the downstream slotted holes 9) in the measuring 
conduit in synchronism with the fluid flow. After the piston 13 passes the 
downstream slotted holes 9, the fluid is immediately discharged through 
the pressure relieving ports 10, and thereby piston 13 smoothly 
decelerates to stop without any abrupt mechanical shock. The ports 10 are 
smaller than the upstream slotted holes 8 and the downstream ports 9. The 
set of the downstream slotted holes 9 and the set of the pressure 
relieving ports 10 are arranged at such a distance therebetween that the 
piston 13 starts covering the pressure relieving ports 10 as soon as the 
piston 13 passed the downstream slotted holes 9. However, since a total 
open area of the pressure relieving ports is constant, the cushion effect 
varies depending on flowrate and the piston 13 may suffer an excessive 
force if no additional means is provided. For this reason, a cushion 
member 15 is provided which eliminates the possibility of applying an 
excessive stress on the piston 13. 
In FIG. 2(c), there are shown a cushion member 15 having a tapered spindle 
end 15a and a concave 17a provided within an internal end plate of a 
cylinder 17. The concave 17a has a constant cross-section substantially 
corresponding to the cross-section of the root of the spindle end 15a. As 
the piston rod 14 approaches to the end plate of the cylinder 17, the 
fluid passage in concave 17a becomes narrower to increase flow resistance 
of the fluid to be discharged through the concave 17a producing the 
cushioning effect to the piston rod 14 which is liquid-tightly supported 
by a journal bearing 4b mounted in the outlet-side end-plate 4 of the 
cylindrical body 1. The journal bearing 4b has an air passage 
communicating with an air port 41b in the outlet-side end-plate 4, thereby 
preventing the measuring fluid from flowing into the cylinder 17 of the 
piston actuator 16. In contrary to the case shown in FIG. 2, it is also 
possible to form a concave 17a in the end face of the cushion member 15 
and attach a tapered spindle 15a to the end plate of the cylinder 17. 
Between the piston actuator 16 and the main body of the small volume prover 
is placed a sensor mounting pipe 17b in the wall of which a position 
sensor 29 is mounted for detecting the location of the piston 13. Since 
the prover main body contains the measuring fluid and the piston actuating 
cylinder 16 produces therein high hydraulic pressure, the position sensor 
29 in the wall of the mounting pipe 17b may be subjected to an abnormal 
high pressure if the fluid leaks therein from either the main body or 
actuating cylinder. The provision of the above-mentioned air port 41b and 
a seal member 39 in the front and the rear, respectively, of the sensor 
mounting pipe 17b prevents the abnormal high pressure leakage therein. The 
position sensor 29 may be of electromagnetic, optical or any other type 
that can accurately detect the travel of the piston 13 for displacing the 
base volume of the measuring fluid. In FIG. 2, two markers 30 and 31 are 
made in the form of ring grooves at specified positions, respectively, of 
the piston rod 14. When the sensor 29 detects each of markers 30 and 31 on 
the piston rod 14, it emitts an electromagnetic signal representing a 
given location of the piston 13. 
In the other hand, in the measuring conduit 7 adjacent to the upstream 
open-end thereof is mounted a slide valve 18 which can slide therealong in 
the axial direction to close the upstream ports 8 in the wall of the 
measuring conduit. The slide valve 18 is connected with a supporting 
column 19, a supporting plate 20 and a valve rod 21 in said turn. The 
valve rod 21 has at its end a driving piston 22 which is drivable to move 
in the axial direction by a valve actuator 23 mounted on the inlet-side 
end 3 of the cylindrical body 1. The stroke of the slide valve 18 is 
limited by stop rings 28 and mounted within a cylinder 24 of the valve 
actuator at the opposite ends respectively. The slide valve 18 is open 
when the piston 22 abuts one of the stop rings 28, and it is closed when 
the piston 22 abuts the other stop ring 28. Provision of an annular groove 
18a in the slide valve 18 allows uniform application of fluid pressure on 
the periphery of the valve body, thereby achieving smooth opening and 
closing operations of the slide valve 18. The valve actuator 23 actuates 
under the pressure of fluid such as hydraulic operating oil to be supplied 
and discharged through pressure ports 25 and 26. The valve rod 21 is 
supported by a liquid-tight journal bearing 3a mounted on the inlet-side 
end-plate 3 of the cylindrical body 1. An air port 41a prevents the 
pressurized actuating fluid from leaking into the prover main body. 
A through hole 18b provided in the annular groove 18a of the slide valve 18 
and a through hole 3b provided in the inlet-side end-plate 3 of the 
cylindrical body 1 are connected by means of a flexible tube 38 to which a 
pressure detecting means (not shown) is attached for detecting a fluid 
leakage through the slide valve 18. Prior to the prover operation, fluid 
leakage through the slide valve 18 is checked by monitoring the pressure 
in the tubing 38 so as to predict the possible measurement error due to 
the fluid leaking into the annular passage 12 through the slide valve 18 
during the proving test with the valve closed. 
A spring 46 is mounted on the valve rod 21 between the journal bearing 3a 
and the supporting plate 20 and acts to apply a force to the slide valve 
18 for compensating for a delay due to an inertia force of the valve 18 
when the valve rod 21 is driven by the valve actuator 23. 
As shown in FIG. 2(a), the piston 13 is now locked by the piston actuator 
16 and, as shown by arrows "Q", measuring fluid entered into the 
cylindrical body 1 through the inlet 5 passes through the slide valve 18 
and the upstream ports 8 and enters into the annular passage 12, bypassing 
the measuring conduit 7, and then the fluid exits from the outlet 6. When 
the slide valve 18 is driven into downstream movement and starts covering 
the upstream ports 8, the fluid flow into the annular passage 12 is 
decreased, thereby increasing the upstream pressure against the piston 13 
in the measuring conduit 7. This is explained as follows. Even when the 
valve actuator 23 actuates in synchronism with releasing the pressure port 
27 of the piston actuator 16, a delay of the piston operation occurs by 
the effect of mass and sliding friction of the piston 13 and flow 
resistance by restriction. This pressure increase induces an excessive 
speed change of movement of the piston 13. 
Referring now to FIG. 2(b), there is shown a detailed view of a mechanism 
for equalizing piston motion according to the present invention. In FIG. 
2(b) there are shown guide hole 13b, pushing member 42, a protrusion 42a, 
a receiving member 43, a flange 43a, a spring 44 and a pressure plate 45. 
The pushing member 42 is mounted integrally within the slide valve 18 and 
has a protrusion 42a projecting coaxially in the downstream direction. The 
guide hole 13b is provided coaxially in the upstream end of the piston 13. 
The receiving member 43 has the flange 43a at its top and is loosely 
inserted in the guide hole 13b and locked to the upstream end of the 
piston 13 by means of the pressure plate 45 and the spring 44 mounted on 
the member between the flange 43a and the pressure plate 45. When no 
measurement is conducted, the piston 13 is positioned with a small spacing 
between the protrusion 42a of the pushing member 42 and the flanged end 
43a of the receiving member 43. When the slide valve 18 is moved to the 
specified position to start closing the upstream ports in the measuring 
conduit, the protrusion 42a of the pushing member 42 abuts the flanged end 
43a of the-receiving member 43. Further movement of the slide valve 18 
starts the piston 13 to move slowly by the action of the spring 44, 
thereby eliminating the above-mentioned pressure rise and achieving that 
the piston 13 moves at a constant speed with the meter fluid flow. 
Referring now to FIGS. 3(a) through 3(g), the operating sequence of the 
small volume prover according to the present invention will be described 
as follows: 
FIG. 3(a) shows the prover when preparation for proving (II) is completed 
(with the piston in starting position); FIG. 3(b) shows the prover when a 
proving pass starts; FIG. 3(c) shows the prover when a proving pass is 
conducted; FIG. 3(d) shows the prover when a proving pass is completed; 
FIG. 3(e) shows the prover when preparation (I) starts (returning the 
slide valve); FIG. 3(f) shows the prover when preparation (I) is finished 
(with the slide valve in the opened position), and FIG. 3(g) shows the 
prover when the preparation (II) began (returning the piston to the 
starting position). While the prover is illustrated, for convenience of 
explanation, as separated into three portions--the valve actuator 23, the 
measuring cylinder 7 and the piston actuator 16, its operating sequence is 
the same as that of the prover shown in FIG. 2. Therefore, the like 
elements are given like reference numbers as shown in FIG. 2. In the 
operating sequence description, pressure ports 25, 26 of a valve actuator 
23 and a pressure port 27 of the piston actuator 16 will be indicated as 
ports A,B and C respectively. In FIGS. 3(b) through 3(g), no reference 
character is given. A flow meter to be proved (not shown) is connected in 
series to a fluid inlet 5. 
(a) Preparation (II) has been completed (the prover is ready to start 
proving). 
Pressurized hydraulic fluid enters the valve actuator 23 through the port A 
while the port B is in an open position. An actuating piston 22 stops at 
the side of the port B and the slide valve 18 opens inlet-side slotted 
holes 8. 
In the above-mentioned condition, pressurized hydraulic fluid is introduced 
into the piston actuator 16 through the port C to lock the actuating 
piston 15. The piston 13 stops at the downstream position adjacent to the 
radial row of the upstream ports 8 in the measuring conduit 7. Fluid from 
the flow meter enters the prover body through the inlet 5 and flows 
through the open end of the measuring conduit 7, the upstream ports 8 and 
an annular passage 12, bypassing the piston 13, and then it exits from an 
outlet 6. The fluid to be measured and the measuring conduit 7 thus have 
the same temperature. Only a small difference of pressures of the fluids 
in and out of the measuring conduit 7 will be produced. 
(b) A proving pass starts. 
Pressurized hydraulic fluid enters the valve actuator 23 through the port B 
while the port A is in an open position. The actuating piston 22 moves in 
the direction indicated by an arrow and the slide valve 18 begins covering 
the inlet-side ports 8 in the measuring conduit 7. At the same time the 
port C of the piston actuator 16 is opened and the slide valve 18 
energizes the piston 46 by the force of a spring 46 so as to compensate 
the delay in its motion due to inertia force, thereby achieving the rapid 
movement of the slide valve 18 and the piston 13-at a constant speed. When 
the slide valve 18 closes the inlet-side ports, flow ceases in the annular 
passage 12 and the entire fluid stream enters the measuring conduit to put 
the piston 13 into a proving pass. 
(c) A proving pass being conducted; 
In the state that pressurized hydraulic fluid enters the slide valve 23 
through the port B while the port A is kept open, the actuator piston 22 
stops at the side of the port A. Accordingly, the slide valve 18 entirely 
closes the inlet-side ports 8 in the measuring conduit 7. 
The piston actuator 16 keeps the port C in open position. Fluid to be 
measured flows only in the measuring conduit 7, causing the piston 13 to 
move downstream and, therefore, the downstream fluid to flow through the 
downstream ports 9 and 10 and exits from the outlet 6. Accordingly, the 
measuring conduit 7 maintains the same conditions on fluid temperature and 
pressure as those of the step (a) "preparation for proving". The measured 
volume of fluid is compared with the base volume of the measuring fluid 
displaced for one proving pass of the piston 13, which is defined by two 
position markers 30 and 31 provided on the piston rod 14. 
(d) A proving pass is finished. 
The valve actuator 23 keeps the ports A and B in the same conditions as 
described above in step (c). 
The fluid stream causes the piston 13 to moves toward the downstream 
end-plate 4, passing through the downstream ports 9. The fluid exits from 
the pressure relieving ports 10 and the actuating piston 15 of the piston 
actuator 16 stops near the port C in the measuring conduit. A proving pass 
is completed. 
(e) Preparation (I) is started (to return the slide valve to the initial 
position). 
Pressurized hydraulic fluid enters the slide actuator 23 through the port A 
while the port B is released. The slide valve 18 begins to move 
compressing the spring 46. The piston actuator 16 remains in the same 
position to that of step (d) "a proving pass is completed". The fluid to 
be measured flows in the measuring conduit 7, passes through the 
downstream ports 9 and exits from the outlet 6. The fluid continues 
flowing in said route until the upstream ports are opened. 
(f) Preparation (I) is finished (with the slide valve being in the opened 
position). 
The pressurized hydraulic fluid enters the valve actuator 23 through the 
port A, keeping the port B in opened position. The slide valve 18 is fully 
opened. The piston actuator 16 is in the same condition as that of step 
(d) "a proving pass is completed". The fluid to be measured is divided 
into two streams: one flows through the measuring conduit 7 and the other 
flows through the annular passage 12. Then both streams join together to 
exit from the outlet 6. 
(g) Preparation (II) begins (returning the piston to the starting 
position). 
The pressurized hydraulic fluid enters the valve actuator 23 through the 
port A, keeping the port B in opened position. The slide valve 18 is fully 
opened. 
The pressurized hydraulic fluid enters the piston actuator 16 through the 
port C, causing the piston 13 to move toward the upstream slotted holes 8 
in the measuring conduit 7. 
The fluid flowing downstream in the measuring conduit 7 is pushed back by 
piston 13 and then passes through the upstream ports 8 to flow downstream 
in the annular passage 12. A part of the fluid flow in the annular passage 
12 enters into the measuring conduit through the downstream slotted holes 
9 and the other part exits from the outlet 6. 
The prover will repeat the above-mentioned steps (a) through (g) of its 
operating sequence. 
While in the above-mentioned sequence the slide valve 18 axially moves to 
close or open the upstream slotted holes 8 in the wall of the measuring 
conduit 7. Such a modification is also effective that the slide valve 18 
turns radially in the measuring conduit to close or open the upstream 
slotted holes 8 in the conduit wall. 
FIGS. 4(a),(b) and (c) are views for explaining another modified slide 
valve for use in the small volume prover according to the present 
invention: FIG. 4(a) is a side view of the slide valve, FIG. 4(b) shows 
the valve in closed position and FIG. 4(c) shows the valve in opened 
position. In the drawings, in which elements similar in function to those 
shown in FIG. 2 are denoted by the same reference numerals, there are 
shown: a rotatable slide valve 32, a flange 32a, a groove 32b, a circular 
port 33, a supporting column 34, a supporting plate 35, an actuating rod 
36, and O-rings 37. 
The rotatable slide valve 32 has an outside diameter substantially 
corresponding to the inside diameter of the measuring conduit 7 and is 
slidable therein. A plurality of ports 33 is provided radially in the wall 
of the rotatable slide valve. Said ports 33 are the same or smaller in 
diameter than the upstream ports 8 in the wall of the measuring conduit 7. 
Both sets of ports 33 and 8 are drilled at the same pich .theta. in the 
respective walls. The flanged end 32a of the rotatable slide valve 32 is 
effective for correctly positioning the valve 32 within the measuring 
conduit 7 in such a way that the ports 33 and the ports 8 correctly meet 
each other in the axial direction. The O-rings 37 are fitted in the 
grooves 32b formed on the periphery of the valve 32 to prevent fluid 
leakage. 
Within the measuring conduit 7 the rotatable slide valve 32 can be 
reversibly turned by an angle .theta./2 in directions indicated with 
arrows w by means of the actuating rod 36 which is connected to the valve 
32 via the supporting plate 35 and the supporting column 34 affixed to the 
valve's flanged end 32a. Turning the valve is conducted by turning the 
actuating rod 36 from a conventional hydraulic motor (not shown) mounted 
on the inlet-side end-plate 3 of the prover body. 
FIGS. 4(b), 4(c) show the rotatable slide valve 32 in cases, respectively, 
of closing and of opening the upstream ports 8 in the wall of the 
measuring conduit 7. The smaller a pitch angle .theta. is, the faster a 
valve can close or open the ports. In case of a large flowrate prover it 
is useful to increase effective opening area by forming axially elongated 
ports 31 and 8. Seal means (not shown) are provided between the valve 32 
and the measuring conduit 7 at both sides of the rows of ports 31 and 8 to 
prevent fluid leakage therethrough. 
In the small volume prover described above with reference to FIG. 2, the 
cylindrical body 1 is a vessel closed with the inlet-side end-plate 3 and 
the outlet-side end-plate 4. Means for mounting the measuring conduit 7 
within the cylindrical body 1 will be described in detail with reference 
to FIG. 4. 
FIG. 5 is a view for explaining another small volume prover embodying the 
present invention, wherein elements similar in function to those shown in 
FIG. 2 are denoted by the same reference numerals. In FIG. 5, there are 
shown: a pressure inlet 1a, a pressure port of an annular passage 1b, an 
inner flange 4a, an outer flange 4b, a flexible tube 47, a through hole 
48, a locking device 49, pressure pipes 50, 51, 52, 53, valves 54, 55, 56, 
a connecting portion 57, a differential pressure generator 58, a piston 
59, a regulating rod 60, pressure ports 61, 62 and a differential pressure 
gauge 63. An outlet-side end 4 is composed of an inner flange 4a and an 
outer flange 4b which are coaxially coupled together at their fitting 
portions 4d and tightly connected with each other with bolts (not shown). 
The inner flange 4a is also securely fitted at its recess on the 
outlet-side end of an outer housing 2. The outer flange 4b has a guide 
ring 4c coaxially formed on its inner end surface, on which an outlet-side 
end of a measuring conduit 7 is fitted. The measuring conduit 7 has a 
plurality of locking holes 7a provided radially in wall near its 
outlet-side end fitted on the guide ring 4c. A plurality of L-shaped 
locking blocks 49 are secured with bolts at their bottom 49a to the inner 
surface of the outer flange 4b in such a way that their L-shaped fingers 
are inserted in the corresponding locking holes 7a in the outlet-side end 
of the measuring conduit 7. The measuring conduit 7 is now mounted 
coaxially within the outer housing 2 by means of inner and outer flanges 
4a and 4b. An annular wall 11 is secured at its outer cylindrical surface 
11a to the outer housing 2 and not secured at its inner cylindrical 
surface 11c to the measuring conduit 7 so as to permit easy insertion of 
the measuring conduit 7 into the outer housing 2. Sealing members 11b such 
as O-rings are mounted in grooves formed on the inner cylindrical surface 
11c of the annular wall 11 near both wall surfaces 11a, respectively, to 
prevent leakage therethrough. 
Any type of small volume provers requires the provision of reliable 
prevention of fluid leakage because its base volume is small and during a 
proving test leaking fluid flows as bypass flow of the base volume, 
causing measuring errors. However, since during the proving run of a small 
volume prover differential pressure may be produced permitting fluid 
leakage, it is essential Go provide the prover with means for checking for 
integrity of its seals so as to assure the reliability of the 
measurements. 
The small volume prover according to the present invention requires 
checking for possible leakage through seals for the slide valve 18, the 
inner cylindrical surface of the annular wall 11, and the internal and the 
external wall surfaces of the measuring conduit 7 on which the piston 13 
slides. According to the present invention, such a method for checking for 
leakage and determining the extent of leakage is adopted in which pressure 
along a sliding surface to be checked is reduced by a certain value, the 
reduced pressure is compared with the standard pressure and a check is 
made whether the reduced pressure is recovered to the standard value (by 
leaking fluid) or not (no leakage). 
A differential pressure generator 58 receives pressurized fluid from the 
portion to be checked and reduces the fluid pressure along the sliding 
surface by a certain value. The generator 58 is composed of a closed type 
pressure reducing chamber 58a and an actuating chamber 58b which includes 
a piston 59 movable in the axial direction under the pressure of fluid 
introduced through pressure inlets 61 or 62; and a plunger 59a connected 
with the piston 59 and capable of liquid-tightly moving in and out of the 
pressure reducing chamber 58a and retarding therefrom. As soon as the 
fluid enters the pressure reducing chamber 58a, the piston 59 actuates to 
retract the plunger 59a, thereby pressure of the fluid in the chamber 58a 
is reduced by the volume of expansion therein. The reduced pressure is 
compared to the standard pressure by the differential pressure gauge 63. 
In case of FIG. 5, the standard pressure is of the fluid which enters the 
prover through the inlet 5 and exits from a pressure port 1a and then is 
supplied through piping 50 to the gauge 63. Pressure adjusting rod 60 has 
a thread and can be screwed into the actuating chamber 58b to restrict the 
stroke length of the piston 59, thereby adjusting the differential 
pressure value in the pressure reducing chamber 58a. After completion of 
adjustment the adjusting rod 60 is locked with a nut 60a. While in case of 
FIG. 5 the plunger 59a is driven by means of a pressure actuator, it is 
also possible to use electrical means such as an electromagnetic device, 
piezoelectric device or the like. 
Portions to be checked for possible leakage are the slide valve 18, the 
annular wall 11 and the piston 13. 
The slide valve 18 is provided with a pressure leading system consisting of 
a flexible tube 38, a through passage 3b and a pressure leading tube 51 
connected to a connection box 57. 
The annular wall 11 includes an inner through passage having an opening at 
the inner cylindrical surface 11c between two seals 11b and 11b and an 
opening at the outer cylindrical surface 11d. This passage mates with a 
pressure port 1b in the wall of the outer housing 2 and a pressure leading 
tube 52 is connected at one end to the port 1b and at the opposite end to 
the connecting box 57. 
The piston 13 includes an internal through passage 13c having an opening at 
the periphery between two seals 13a and an opening at the inside surface, 
which is connected by a flexible tube 47 to a through passage 48 in the 
outer flange 4b. A pressure leading tube 53 is connected at one end to the 
through passage 48 and at the other end to the connecting box 57. 
These pressure leading lines through the connection box 57 terminate at the 
pressure reducing chamber 58a of the differential pressure generator 58. 
The lines 51, 52 and 53 are provided with valves 54, 55 and 56, 
respectively, which makes it possible to selectively connect any of the 
pressure leading lines for checking fluid leakage in the slide valve 18, 
the annular wall 11 or the piston 13. Checking the slide valve 18 for 
leakage is conducted prior to the proving test for the purpose of 
preliminarily determining the possibility of leakage through the slide 
valve. 
The slide valve 18 driven by the actuator 23 is frequently operated to open 
and close the upstream slotted holes 8 in the wall of the measuring 
conduit, causing a sealing member (not shown) to wear and be damaged. Easy 
replacement of the sealing members for the slide valve is, therefore, 
highly required for a long time. The small volume prover according to the 
present invention includes the upstream end plate 3 allowing easily 
removing the slide valve. The mechanism of said end plate will be 
described below. 
FIG. 6 is a view for explaining a further modified small volume prover 
according to the present invention: FIG. 6(a) is a sectional view of a 
concerned portion; FIG. 6(b) is a cross-sectional view taken along line 
B--B in FIG. 6(a); and FIG. 6(c) is a plan view of the portion shown in 
FIG. 6(a). In FIGS. 6(a), 6(b) and 6(c), wherein elements similar in 
function to those shown in FIG. 2 are denoted by the same reference 
numerals; there are shown a frame 64, a platform 64a, rails 64b, a guide 
channel 64c, a wheel 65, a clutch door 66, a movable outerside ring 67, a 
fixed innerside ring 68, a holding frame 69, an axial pin 70, a screw 
shaft 72, a screw bearing 73, a handle 74 and an index 75. 
The body of the small volume prover is mounted on a frame 64 having wheels 
65. Two parallel rails 64b are fixed on the frame 64 in the axial 
direction of a measuring conduit 7 thereon. On the rails 64b are slidably 
mounted guide channels 64c, one on each rail, respectively, which can move 
therealong in the direction X being driven by a screw shaft 72 which is 
rotated by turning a handle 74 removably attached thereto. The guide 
channel 64c bears a holding frame 69 to which a clutch door 66 is 
attached. 
The clutch door 66 is composed of a rotatable outerside ring 67 and a fixed 
innerside ring 68 which is removable from the outerside ring 67. The 
rotatable outerside ring 67 is consisted of a rotatable ring 67a and a 
fixed ring 67b: the fixed ring 67b being coaxially welded to the end plate 
of the outer housing and the rotatable ring 67a is integrally constructed 
with the fixed ring 67b so as to be rotated along line N--N of the 
periphery of the fixed ring 67b. The rotatable ring 67a has therein an 
annular groove 67d having a plurality of fingers formed at equal intervals 
on an outer frame portion thereof, while the fixed inner ring 68 has 
fingers 68a, each being so sized in width to pass between two fingers 67c 
of the annular groove 67d. When the rotatable ring 67a is turned in the 
direction indicated by arrows R by use of the removable handle, its finger 
67c in-phasely engages the finger 68a of the fixed inner ring 68 at the 
position of the annular groove 67d of the rotatable outerside ring 67. In 
this time the fixed innerside ring 68 and the rotatable outerside ring 67 
are liquid-tightly sealed therebetween (not shown). 
In FIG. 6(b), the clutch door is unlocked, wherein the fixed innerside ring 
68 is movable in the direction of arrow X in FIG. 6(a) to be separated 
from the rotatable outerside ring 67. The fixed innerside ring 68 has a 
flange 23a to which is secured an actuator 23 integrally connected with a 
slide valve 18. The screw shaft 72 is rotated until the slide valve 18 is 
separated apart from the rotatable ring 67a and then the slide valve 18 is 
turned by 90.degree. about a shaft pin 71 of a supporting column 70 
provided the holding frame 69 in the direction indicated by arrow Q, 
whereby the valve 18 is placed in the position allowing easier repairing 
of its seals. After any repair work is completed the clutch 66 of the door 
can be locked by reversing the above-mentioned steps. 
As is apparent from the foregoing description, the small volume prover 
according to the present invention has the following features and 
advantages: 
(1) The main body of the small volume prover is a closed cylindrical vessel 
having a fluid inlet and an fluid outlet spaced apart from each other and 
includes a coaxially mounted cylindrical measuring conduit and an annular 
wall dividing annular space formed between the measuring conduit and the 
outer housing into an upstream passage and a downstream passage. A flow 
meter to be proved is connected in series to the fluid inlet of the 
prover. Fluid entering the prover body through the inlet flows through the 
annular passage, when no proving is conducted, and flows within the 
measuring conduit only when proving is conducted, so keeping the measuring 
conduit at a temperature of the measuring fluid. Furthermore, there is 
only a little difference of pressures across the wall of the measuring 
conduit, whereby the measuring conduit may always maintain a constant and 
accurately repeatable standard volume. 
As mentioned above, the measuring conduit is free from pressure influence 
and, therefore, is not required to have a thick wall for protection 
against pressure distortion. It may be a precision cylinder having both 
open ends, which is easily machined at high accuracy of its volume and 
also at low cost. Since a slide valve for achieving preparation and start 
is mounted within the prover body, the necessity of providing a by-pass 
line out of the prover is eliminated, thereby realizing reduction of the 
prover's size. 
(2) The slide valve is designed to be a cylinder having a row of ports 
radially made in its wall, which are the same in form and pitch as those 
made in the wall near the inlet-side end of the measuring conduit. It can 
rotate at a small angle of 1/2 pitch, assuring quick-response valve 
operation. 
(3) At the outlet side of the measuring conduit, behind a set of the 
outlet-side ports, is also provided a set of pressure relieving ports of 
smaller size which, after the piston passing the first set of ports, acts 
to smoothly decelerate said piston to a stop without any undesirable 
shock. 
(4) Provision of a cushion at the end of piston rod assures smooth and 
shock absorbed stopping of the piston, protecting it against any abnormal 
shock and stress. 
(5) Between the piston actuator chamber and the prover body, both of which 
pressurized fluid passes through, is provided a position sensor which 
detects the given locations of the piston with safety and no affection of 
the pressurized fluid. 
(6) Provision is made for compensating the nonuniformity of movement of the 
piston due to a difference of moving speeds of the slide valve and the 
piston for the transitional stage of the slide valve moving to cover the 
inlet-side port of the measuring conduit. Since the compensation for delay 
of the piston movement is achieved in the shortest time, it is possible to 
use a measuring conduit of reduced length, i.e. a small volume prover of 
smaller size. 
(7) The measuring conduit is coaxially secured at one end to an outside 
flange having a guide ring and is open free at the other end, thereby 
eliminating the possibility of being deformed by the action of temperature 
and pressure of fluid. Centering of the conduit is achieved at an inside 
flange, eliminating the possibility of being affected by the external 
force. Using locking means allows easy mounting and centering of the 
measuring conduit within the prover body. 
(8) The inlet-side end of the prover body is formed of a clutch door 
including a rotatable outer ring and a fixed inner ring which can be 
removed with the slide valve, allowing easily conducting of a repair of 
sealing members of the slide valve. 
(9) It is possible to predict leakage through the slide valve by checking 
for leakage prior to a proving run. 
(10) Leakage through the seals of the piston within the measuring conduit 
is easily detected, thereby increasing the reliability of measurement by 
the measuring conduit. 
(11) Overhanging the measuring conduit on the outside flange of the prover 
body causes the necessity of checking for leakage in the annular passage. 
Detecting the leakage through seals in the annular passage is possible. 
(12) Leakage detection can be easily carried out by a simply constructed 
easily operated detection system wherein fluid from a selected portion is 
introduced into a closed pressure reduction chamber and its pressure is 
reduced by changing the inner volume of the reduction chamber by means of 
an actuator-driven plunger.