Valve packing leakage monitoring device

A device for monitoring leakage of fluid across a seal in a component connected to a pressurized fluid system. The device includes a housing defining a chamber which includes an inlet for receiving fluid leaking across the seal and an outlet. A plate having an orifice is disposed in the chamber transverse to the longitudinal axis of the chamber and between the inlet and outlet for dividing the chamber into a first chamber volume for receiving fluid through the inlet and a second chamber volume for receiving fluid through the orifice and for discharging the fluid through the outlet. A plug is movably mounted for adjusting the open area in the plane of the orifice in the plate. A positioning arrangement is connected to the plug for positioning the plug to create a predetermined open area in the plane of the orifice for permitting the fluid to exit the first chamber volume through the orifice at the same rate at which it enters the first chamber volume when the rate of fluid entering the first chamber volume is at or below a given rate. The positioning arrangement is further responsive to fluid entering the first chamber volume at a rate greater than the given rate for moving the plug away from the orifice so that the fluid exiting the first chamber volume will continue to equal the rate at which the fluid enters the first chamber volume. A device for detecting the movement of the plug produces an output signal corresponding to the distance moved by the plug.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention concerns a device for monitoring the leakage of fluid from a 
component subjected to a pressurized fluid, and more particularly to a 
device for monitoring fluid leakage through a valve stem seal of a valve 
connected for controlling the flow of fluid in a pressurized fluid system. 
2. Description of the Prior Art 
In a pressurized water system, such as a pressurized water nuclear reactor, 
it is known to provide valves for controlling the flow of water in the 
system with leak-off connections between the primary and secondary valve 
stem packings. Water which leaks through the primary valve stem packing 
collects in a reservoir located between the primary and secondary packings 
of the valve stem and is drained off into a sump. Such drainage prevents a 
buildup of fluid pressure between the packings which could damage the 
secondary packing and result in leakage therethrough. In a pressurized 
water nuclear reactor this is particularly important in order to prevent 
radioactively contaminated water from escaping from an otherwise closed 
fluid system. 
In a pressurized water system containing many valves, each having a 
leak-off connection, it is possible to determine the gross leakage of the 
system by measuring the amount of water flowing into the sump. An 
excessive flow into the sump could indicate that the primary packing on 
one of the valves is severely deteriorated. However, in such a system it 
is not possible to remotely assess the condition of any one valve. It is 
necessary to manually check each valve to determine which one is faulty. 
In a pressurized water reactor system, manual checking can be dangerous, 
because if the leakage through the primary packing becomes too great, the 
capacity of the reservoir between the packings could be exceeded. The 
resulting pressure against the secondary packing could cause contaminated 
water to leak through the secondary packing posing obvious health hazards. 
It would therefore be desirable to be able to remotely assess the condition 
of each valve in the system on a continuing basis in order to prevent 
excessive leakage through the respective primary packings. 
U.S. Pat. No. 3,276,246, issued to Truman et al, discloses a leakage 
detector for an oil wellhead wherein a vessel containing a float switch is 
disposed to collect oil leaking out of the top of the wellhead and 
accumulating between upper and lower packing glands. The float has a 
specific gravity lower than that of oil. As the level of the oil 
collecting in the vessel rises the float also rises. At a certain level 
the float activates a proximity switch which shuts down the wellhead 
motor. The vessel is provided with a weep hole for draining minor 
accumulations of oil and/or lubricant and a drain plug which can be 
manually removed to drain the vessel when significant amounts of oil are 
collected in the vessel. A problem with this device is that an excessive 
oil leak may cause the upper packing gland to fail if for some reason the 
float gets stuck or the motor fails to turn off in time before the vessel 
becomes completely filled with oil causing a back pressure against the 
upper packing gland. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a device for monitoring the 
leakage of fluid through a seal or packing of a component subjected to a 
pressurized fluid while at the same time permitting the leaked fluid to 
drain off without building up a back pressure within the component. 
It is a further object of the invention to provide a device for monitoring 
the leakage of fluid through the primary packing of a valve stem in a 
valve connected to a pressurized fluid system while permitting the leaked 
fluid to drain off without creating an excessive back pressure against the 
secondary packing of the valve stem. 
It is another object of the invention to provide a method for scheduling 
maintenance for the packings of the valve stem in a valve provided with a 
leak-off connection with the use of a device for monitoring leakage 
according to the invention. 
The above and other objects are accomplished according to the invention by 
the provision of a device for detecting leakage of fluid across a seal in 
a component connected to a pressurized fluid system. The device includes a 
housing defining a chamber having a longitudinal axis. The housing 
includes an inlet for receiving fluid leaking across the seal of the 
component and an outlet. A plate having an orifice is disposed in the 
chamber transverse to the longitudinal axis and between the inlet and the 
outlet. The plate divides the chamber into a first chamber volume for 
receiving fluid through the inlet, and a second chamber volume for 
receiving fluid through the orifice and for discharging fluid collected 
therein through the outlet. A plug is movably mounted for adjusting the 
open area in the plane of the orifice of the plate. A positioning means is 
connected to the plug for positioning the plug to create a predetermined 
open area in the plane of the orifice for permitting the fluid to exit the 
first chamber volume through the orifice at the same rate at which it 
enters the first chamber volume through the inlet when the rate of fluid 
entering the first chamber volume is at or below a given rate. The 
positioning means is further responsive to fluid entering the first 
chamber volume at a rate greater than the given rate for moving the plug 
away from the orifice so that the fluid exiting the first chamber volume 
will continue to equal the rate at which the fluid enters the first 
chamber volume. A detecting means is provided for detecting the movement 
of the plug and producing an output signal corresponding to the distance 
moved by the plug and hence to the rate of leakage through the seal. 
In a preferred embodiment of the invention the above-described leakage 
monitoring device is employed in combination with a valve for controlling 
the flow of fluid in a pressurized fluid system, wherein the valve 
includes a valve body and a valve stem axially movable within the valve 
body and having one end subjected to the system pressure. Primary and 
secondary valve packings are axially spaced apart along the valve stem for 
providing a seal to minimize fluid leakage between the valve body and the 
valve stem. The primary packing is disposed between the one end of the 
valve stem subjected to the system pressure and the secondary packing. A 
leak-off connection connects a reservoir provided between the primary and 
secondary packings with the inlet of the leakage monitoring device. 
The invention further provides for an advantageous method of providing 
maintenance to the seal of a component subjected to a pressurized fluid 
with the use of a fluid leakage monitoring device as described above. The 
method includes connecting the inlet of the device for receiving fluid 
which leaks across the seal, connecting the outlet of the device to a 
sump, feeding the output of the detecting means to an indicator to provide 
an indication of the amount of leakage fluid passing through the device to 
the sump, and repairing the seal when the amount of leakage fluid passing 
through the device exceeds a predetermined level.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the FIGURE a valve 1, only part of which is illustrated, 
includes a valve body 3 having a valve stem 5 axially movable 
therethrough. Valve stem 5 has a valve plug 7 which controllably engages a 
valve seat 9 for controlling the flow of system fluid from the valve inlet 
11 to the valve outlet 13. Thus, when valve plug 7 is withdrawn from valve 
seat 9 the fluid flows in the direction of arrows 15. As may be 
appreciated, when the valve is open the interface 17 of valve stem 5 with 
body 3 is subjected to the system pressure. In order to prevent leakage of 
system fluid out of the valve between valve stem 5 and valve body 3 a 
double seal arrangement is provided including a primary packing 19 and a 
secondary packing 21 with a lantern ring 23 disposed therebetween. Lantern 
ring 23 includes inner and outer annular grooves 25 and 27, respectively, 
connected by a bore 29. Grooves 25 and 27 and bore 29 serve as a reservoir 
for collecting system fluid which will, as is inherent with any mechanical 
seal, leak through primary packing 19. A packing flange 30, which may be 
threadably engaged with valve body 3, presses against secondary packing 21 
to hold the seal arrangement in place. 
A bore 31 through valve body 3 opens into outer groove 27 for draining 
fluid collected within the spaces of the lantern ring 23 through a 
leak-off connection 33 which in a conventional arrangement leads directly 
to a sump 35 for receiving the fluid leakage. By continuously draining the 
fluid leaking through primary packing 19 the fluid pressure against 
secondary packing 21 is minimized with the result that secondary packing 
21 presents an effective barrier against further leakage up between the 
valve stem 5 and valve body 3. 
In operation, valve stem 5 will be subjected to several thousand cycles of 
up and down movement which inevitably results in a deterioration of the 
packings. If the leakage through primary packing 19 becomes excessive it 
is possible that the leakage fluid will not drain off quickly enough and 
that a back pressure could develop which could cause leakage through 
secondary packing 21. 
The risk of leakage through secondary packing 21 is reduced according to 
the invention by the provision of a device 37 which monitors the rate at 
which leakage fluid is drained off through leakage connection 33. As shown 
in the FIGURE, device 37 comprises a housing having a main body 39 
threadably engaged with an end piece 41. A set screw 42 is preferably 
employed to secure body 39 and end piece 41 against rotation while in use. 
Body 39 has an inlet opening 43 which is connected to leak-off connection 
33. End piece 41 has an outlet opening 45 which is connected to a pipe 47 
leading to sump 35. 
The two piece housing comprised of body 39 and end piece 41 encloses a 
chamber which is divided by a plate 49 having a central orifice 51 into an 
upper chamber volume 53 and a lower chamber volume 55. A gasket 56 is 
positioned beneath plate 49 and between body 39 and end-piece 41 to 
prevent leakage to the atmosphere and to prevent leakage from upper 
chamber volume 53 into lower chamber volume 55 other than through orifice 
51 as will be explained. 
A floating piston 57 is contained within upper chamber volume 53 and is 
held in a dynamic equilibrium by an upper compression spring 59 which is 
supported by the upper surface 61 of piston 57 and the end surface 63 of 
body 39, and a lower compression spring 65 which is supported by a lower 
surface 67 of piston 57 and a circular shim ring 69 which rests on orifice 
plate 49. Piston 57 thus divides upper chamber volume 53 into a partial 
volume 53a between piston 57 and orifice plate 49 and a partial volume 53b 
between piston 57 and end surface 63 of body 39. A piston seal 70 is 
disposed between piston 57 and the inner surface of body 39 to prevent 
leakage therebetween from partial volume 53a into partial volume 53b. 
A hollow tube 71 passes through and is rigidly connected with piston 57. 
Hollow tube 71 extends downwardly just past orifice 51 and has a shaped 
plug 73 fastened to it just above orifice 51 for adjusting the open area 
in the plane of orifice 51 as will be described below. At the opposite end 
of hollow tube 71 a magnetic end portion 75 is provided for movement in 
and out of a slot 77 enclosed by a hat portion 79 at the upper end of body 
39. A plurality of proximity switches 81, two of which are shown in the 
FIGURE, are axially spaced from one another along the outside of hat 
portion 79 for sequential activation by magnetic end portion 75. A switch 
cover 83 is attached by screws 85 to the upper end of body 39 for 
enclosing and protecting switches 81. Switches 81 have lead wires 87 which 
pass through an opening 88 in switch cover 83 and an electrical conduit 89 
for connection to a display device 90. 
In operation, when valve stem leakage occurs through primary packing 19, 
the leaking fluid accumulates in the spaces of lantern ring 23 and is 
transmitted by leakoff connection 33 through inlet opening 43 into partial 
chamber volume 53a of device 37. As mentioned above due to the mechanical 
nature of the seal provided by primary packing 19, a small or nominal 
amount of leakage is always expected to occur. Accordingly, by appropriate 
selection of springs 59 and 65 and shim ring 69, plug 73 is initially 
positioned relative to orifice 51 so that the opening in the plane of 
orifice 51 permits the flow of liquid from partial chamber volume 53a into 
lower chamber volume 55 to equal the nominal in-flow of leaking fluid into 
partial volume 53a. As long as the rate of fluid entering partial chamber 
volume 53a is equal to the rate of fluid flowing out of this volume 
through orifice 51, the position of piston 57, rod 71 and plug 73 remains 
the same. If, however, the rate of fluid flowing into partial chamber 
volume 53a exceeds the rate at which the fluid exits this partial volume, 
then partial chamber volume 53a fills up with fluid and pushes floating 
piston 57 upward. The upward movement of piston 57 simultaneously causes 
an upward movement of plug 73 which expands the area of the opening in the 
plane of orifice 51. The rate at which the open area in the plane of 
orifice 51 expands can be adjusted by appropriately shaping the surface of 
plug 73 which is adjacent orifice 51. 
As primary packing 19 further deteriorates with use the rate of leakage 
into device 37 will increase pushing piston 57 further up within chamber 
volume 53. Magnetic end portion 75 which moves with piston 57 will 
eventually reach the first proximity switch 81, causing it to close. 
Current flowing through the closed proximity switch is fed to display 
device 90 which activates a display to indicate that the leakage through 
the primary packing of the valve stem has reached a predetermined rate. A 
further increase in the leakage will move magnetic end portion 75 into the 
range of the next sequential proximity switch which is activated to 
indicate that a still higher rate of leakage has been attained. Because 
the proximity switches are placed at sequential lift positions, the 
leakage rates can be closely monitored by observing the display device 90 
which indicates the sequential activation of the proximity switches. 
Display device 90 can be of any suitable design to indicate the individual 
status of switches 81. 
Since the leakage rates correspond to the deterioration of the primary 
packing 19, a service schedule for repairing or repacking the valve stem 
packings 19 and 21 can be implemented by using the device in accordance 
with the invention. 
Hollow tube 71 is provided with radial bleed holes 91 so that in the event 
that piston seals 70 break-down, any leakage into partial chamber volume 
53b is piped out through the radial bleed holes 91 down hollow tube 71 for 
discharge to the sump via outlet opening 45 and pipe 47. Thus, partial 
chamber volume 53b is prevented from being filled with fluid which could 
otherwise render the device inoperative. 
The device in accordance with the invention operates to monitor the rate of 
leakage through the valve stem primary packing while at the same time 
permitting the fluid leakage to pass out of the device at the same rate at 
which it enters the device so that no significant pressure build-up will 
occur in the partial chamber volume 53a which could cause failure of the 
valve stem secondary packing 21. 
Since the device according to the invention indicates the status of valve 
leakage it can be used to provide guidance as to when to schedule 
maintenance of the valve stem packings. 
The display 90 can be provided locally with the device 37 or can be 
provided remotely and connected with a plurality of devices 37 for 
monitoring the leakage rates of a respective plurality of valves. 
It should be appreciated that it is within the scope of the invention that 
other positioning mechanisms, such as a bellows-like device or a 
displaceable diaphragm arrangement, can be used in lieu of the disclosed 
piston arrangement for positioning plug 73. 
It will be understood that the above description of the present invention 
is susceptible to various modifications, changes and adaptations, and the 
same are intended to be comprehended within the meaning and range of 
equivalence of the appended claims.