Note: Descriptions are shown in the official language in which they were submitted.
Background of the Invention
Fleld of the Invention-
This invention relates to free floating disc
valves; and, in particular, to a positive closure arrangement
for such a valve.
Description of the Prior Art:
A nuclear steam turbine power plant generally
consists of a closed-loop series connection com~risin~ a
steam generator element, a high pressure turbine element,
a moisture separator and reheater element, a low pressure
turbine element and a condenser. Between the steam generator
element and the high pressure turbine there is disposed
a main turbine stop valve and a main turbine~thre~le valve.
These valves control the flow of high pressure, high
temperature motive fluid produced wlthin the steam generator
element into the remai~der of the series connected power
~- plant loop.
-.~ The main stop valve and throttle valve are
- utilized in emergency situations to interdict the flow of
steam into the rest of the power plant system. By rapidly
~ closing the stop and~ ~ valves no further quantity of
.
~ -. - - .: ~ .
. ~ . , - . :
. :
''. ' ~ ' ' ' ' .' '
~03~2~0
motive fluid is permitted to enter the turbine elements
downstream Or the valves. However, steam which has already
passed through the main turbine stop and throttle valves and
expands through the system has the possibility of overspeeding
the turblne elements within the power plant. ~hus, if an
emergency situation, such as a loss of load condition were
to develo~, the main turhine sto~ and throttle valves would
close, but steam trapped in the system must still expand
therethrough into the condenser. The passage of steam
through the low pressure turbine element would, for example,
only exacerbate an overspeed condition and increase the
possibility of turbine failure.
For this purpose, at least one steam pressure
relie~, or dump, valve is disposed between the moisture
separator reheater element and the low pressure turbine.
The dump valve permits venting of steam trapped downstream
of the main turbine stop and throttle valves directly to
the condenser element or into atmosphere.
The dump valve is usually a free floating disc
type valve which is activated by controlling pressures in
a pressure chamber above the disc. When the disc is closed,
a pilot valve completely seals the pressure chamber and per-
mits equalization of pressures above and below the disc.
Decreasing the pressure above the disc, by the expedient
of venting the pressure chamber to atmosphere to the condenser,
permits the high pressure steam on the inlet side of the
valve disc to exert a force tending to raise the valve disc.
Thus, steam passes through the dump valve either to the
condenser or to atmosphere.
3~ It is possible, however, for friction between a seal
-- 2 --
~038Z6V
arran~ement surrounding the valve disc and the interior
portions of the chamber housin~ to prevent the valve disc
from responding to a closlng signal impressed thereon by
suitable governor means. The usual method of` closing dump
valves is to re-isolate the pressure chamber by closing of
the pilot valve and letting the pressures above and below
the valve disc equalize. The weight of the valve, plus any
force unbalance due to a difference in effective areas on
the upper and lower surfaces of the disc, are usually
lQ sufficient to overcome the frictional force generated between
the seals and the valve chamber walls.
-` However, when utilizing a prior art free floating
disc valve in a nuclear steam power plant which generally
operates at lower steam pressures than the conventional
fossil fuel plant, reliance upon the weight of the disc and
the pressure unbalance is not always sufficient to overcome
the frictional force. Thus, the free floating disc within
the dump valve may not predictably re-seat and disruption
- to the entire power plant system will occur. It is therefore
advantageous to provide a positive closure system for a free
floating disc type valve to insure proper seating of the
valve disc when the pressure relief functionhas been performed.
Summary of the Invention
This invention provides a pressure containment
vessel enclosing a volume therein communicating with a
pressure chamber disposed within the valve housing of a
free floating disc type pressure relief valve. The contain-
ment volume allows accumùlation of high pressure fluid
therein when the valve disc is in the closed, or seated
position, and entraps that fluid therein through the use of
-- 3 --
103lSl2:60
suitable control means when the dlsc is opened. To
ensure positive closing of the valve disc, communication ls
reestablished between the pressure chamber and the contain-
ment volume. The introduction of the high pressure fluid
entrapped within the containment volume into the pressure
chamber above the valve disc exerts a sufficient closing
force on the valve disc to ensure proper seating.
It is an ob~ect of this invention to provide a
free floating disc type valve having thereon a closing
arrangement so as to insure positive closure of the valve
disc after performance of the pressure relief function.
It is desirable, and hence a further ob~ect of
this invention, to provide a positive closure system for a
- free floating disc valve so as to eliminate any possibility
of atmopsheric air entering the condenser element of a
steam turbine power plant, which possibility is increased
if the valve disc did not properly seat.
- Brief Description of the Drawings
The invention will be more fully understood from
the following detailed description of the preferred embodi-
ments, taken in connection wlth the accompanying drawings,
in which:
Figure 1 is a diagrammatic view showing the
location of the free floating disc valve embodying the teach-
lngs of this invention in a nuclear steam power plant system;
and
Figure 2 is an elevation view entirely in section
showing a free floating disc valve embodying the teachings of
this invention.
103~3Z60
Description of the Preferred Embodiment
Throughout the following description, similar
reference numerals refer to similar elements in all figures
of the drawings.
Referring first to F'igure 1, a nuclear steam power
- plant 10 disposing a free floating disc type dump valve 12
embodying the teachings of this invention is diagrammatically
shown. The power plant 10 is comprised of a closed-loop
series connection having a steam generator element 14 con-
- 10 nected to a high pressure turbine element 16, a moisture
separator-reheater element 18, a low pressure turbine element
20, and a condenser element 22. The condenser element 22 is
usually maintained at pressures below that of atmosphere.
Intermedlate between the steam generator element
14 and the high pressure element 16 is a main turbine stop
valve 24 and a main turbine control valve 26. The stop valve
24 and the control valve 26 are normally open valves able
to close quickly to interdict any flow of high pressure motive
fluid passing from the steam generator element 14 into the
high pressure turbine element 16 and other elements of the
power plant 10 downstream of the high pressure turbine element
16. If, during an emergency situation, it becomes necessary
to prevent the flow of motive ~luid from entering the closed-
loop series arrangement of the power plant 10, the valves 24
and 26 close in response to a trip signal from a valve con-
trol means (not shown).
However, interdiction of the supply of motive fluid
- into the power plant 10 is not the only requirement that is
necessitated by an emergency condition. For, if steam already
downstream of the stop valve 24 and the throttle valve 26 were
-- 5 --
1~)38~0
permitted to expand through the rest of the system 10,
problems~ such as damage to the low pressure turbine element
20 due to excessive centrifugal force impressed thereon,
could occur.
For this reason, at least one dump valve 12 is
connected in a conduit line 28 between the moisture separator-
reheater element 18 and the low pressure turbine element 20.
The dump valve 12 is connected within the system so that steam
trapped downstream of the main turbine stop valve 24 and
the control valve 26 is permitted an alternate escape route
through the dump valve 12 either to the condenser element
22, indicated by reference arrow 30, or directly to atmosphere,
as indicated by reference numeral 32.
Referring now to Figure 2, the valve 12 is shown
in an elevational view entirely in section and is connected
within the conduit line 28 between the moisture separator-
reheater element 18 and the low pressure turbine element 20
(Figure 1).
The valve 12 is comprised of a body member, or
20 valve housing 34, which has an inlet 36 and outlet 38 disposed
therein. A valve seat 40 is disposed circumferentially about
that portion of the valve housing 34 adjacent the inlet 36.
; ~ The outlct 36 is connected either to the dump line 30, which
communicates with the condenser element 22, or is vented
directly to atmosphere, as indicated by reference arrow 32.
A valve disc 42 is reciprocally movable within the
body member 34 away from the valve seat 40 so as to permit
communlcation between the lnlet 36 and the outlet 38. A
valve chamber 44 circumferentially surrounds the valve disc
3~ 42 and communicates both with the inlet 36 and the outlet 38.
_ 6 --
~)3~26V
The interior of the valve housing 34 defines a
pressure chamber 46 disposed above the valve disc 40. The
pressure chamber 46 is connected to a low pressure region,
such as the condenser 22, through a first control valve 48.
As will be made clear from the description herein, the
pressure chamber 46 communicates through the first valve 48
with a region having a pressure, at initiation of the dump
valve, that is lower than the lowest pressure which appears
withln the pressure chamber 46. An ob~ect of this invention
is to eliminate the possibility of air entering the condenser
element 22 (Figure 1) if the disc 42 did not properly seat.
Air entering the condenser 22 would produce a rapid rise in
condenser pressure which could damage the low pressure
turbine element 20 (Figure 1). It is understood that the -
pressures utilized within the closure system herein described
may be chosen as being below atmospheric pressure.
A pressure containment vessel 49 encloses a contain~
ment volume 50 communicating with the pressure chamber 46
- through a second control valve 52. The first control valve
48 and the second control valve 52 are alternately operated
-~ by suitable control means (not shown). By this it is meant
that when the first valve 48 is in the open position so as
to permit communication between the pressure chamber 46 and
the low pressure region, the second control valve 52 is Glosed
: so as to isolate the pressure containment volume 50 from
- the pressure chamber 46. However, when the first control
valve 48 is closed so as to isolate the press~re chamber 46
from the low pressure region, the second control valve 52
is open so as to permit communication between the pressure
~0 containment volume 50 and the pressure chamber 46. A drain
J.038260
` 54 is connected to the pressure containment volume 50. The
drain 54 is di.sposed so as to provide a path for any conden-
sate which may develop within the containment volume 50.
The valve disc 42 has an opening 56 extending
through the valve disc 42 throu~h which the pressure chamber
46 above the valve disc 42 communicates with the region
beneath the valve disc 42 ad~acent the valve inlet 36.
O-ring seals 60 are disposed circumferentially about the
interior of the valve housing 34 and prevent leakage from
; lO the region ad~acent the valve inlet 36 into the pressure
chamber 46 past the valve disc 42. A drain 58 provides a
- path for relief of any condensate which develops within the
pressure chamber 46. It is desirable to have such a conden-
sate drain disposed inde~endent of communication opening 56.
In operation, the free floating disc valve 12 is
normally closed. When closed, steam passes within the conduit
28 from the mcisture separator-reheater element 18 into the
low pressure turbine element 20. If an emergency should
develop, the valves 24 and 26 interdict the flow of high pres-
~ 20 sure steam from the steam generator element 14 into the rest
- of the nuclear steam turbine power plant lO. However, steam
trapped downstream of the valves 24 and 26 would cause an ~ ;
overspeed condition if it were permitted to expand there- :
through Therefore, the dump valve 12 is opened to permit
~ venting of the steam trapped within the power plant system
downstre2m of the stop valve 24 and throttle valve 26.
When the valve disc 42 is closed, the first control
valve 48 is closed and the second control valve 52 is opened.
Thus, when the valve disc 42 is seated, the pressure chamber
30 46 is isolated from the low pressure region (not shown) and
-- 8 --
1038Z60
the pressure containment volume 50 communicates with the
pressure chamber 46. High pressure fluid in the region
beneath the valve disc 4~ ad~acent the valve inlet 36 enters
the isolated pressure chamber 46 through openings 56 and
58, Over a period of time, the pressure within the pressure
chamber 46 above the valve disc 42 approximately equals the
pressure beneath the valve disc 42 in the region adJacent
the inlet 36. Since the force unbalance above and below the
valve disc 42 is approximately zero, the weight of the valve
........... 10 disc 42 maintains that disc in a seated position against the - :
valve seat 40. Thus, the valve inlet 36 is isolated from
. the valve outlet 38. While the valve disc 42 is closed high ~ -
. pressure ~luid is also accumulated within the pressure con-
tainment volume 50 which communicates with the pressure chamber
46 through the open second control valve 52.
Upon receipt of the emergency trip signal from the
control means (not shown), the settings of the control valves
48 and 52 are alternated. That is, the first control valve 48
is open so as to permit communication between the pressure
20 chamber 46 and the low pressure region (not shown), and the
~; second control valve 52 is closed so as to isolate the
pressure containment volume 50 from the pressure chamber 46,
With the first control valve 48 open, the accumulation of
high pressure fluid above the valve disc 42 within the pres-
sure chamber 46 rapidly vents to the lowpressure region (not
shbwn). With this occurrence, the force exerted by the
high pressure fluid beneath the valve disc 42 adJacent the
inlet 36 results in a net force unbalance acting in a
- direction 62 which moves the valve disc 42 from its seat 40
~ 30 and permits the pressurized fluid near the inlet 36 to enter
_ g _
~38260
the valve chamber 44 and into the valve outlet 38 Thus,
steam trapped downstream of the main turbine stop valve 24
C D nfrD/
and the -th~*tle valve 26 is permitted an alternate escape
route either to the condenser element 22 or to atmosphere,
` as indicated bv reference arrows 30 and 32~ res~ectively.
When the pressure beneath the valve disc 42 is
insufficient to exert a force in direction 62 which maintains
disc 42 away from the seat 40, the valve disc 42 would close.
In the prior art, controlled closure of the valve disc 42
is accomplished by closing the first control valve and letting
pressure within the pressure chamber above the valve disc
equalize with the pressure beneath the valve disc. The
weight of the valve disc itself, plus any pressure force
unbalance due to a difference in effective areas over which
the pressure force o~erates on the top and bottom surfaces of
the disc 42, is sufficient to seat the disc. However, if
friction is generated within the system between the seals
60 and the walls of the housing 34, the combination of the
~` weight of the disc and the pressure force unbalance may not
` 20 be sufficient to insure seating of the valve disc.
This invention provides a positive closure arrange-
ment to insure seating of the valve disc 42 against its
seat 40 after the dump function of the valve 12 has been
accomplished. Utilizing the teachings of this invention,
positive closure of the disc 42 is accomplished as follows.
Upon appropriate signal from the control means (not shown),
the first control valve 48 is closed so as to isolate the
pressure chamber 46 from the low pressure region (not shown).
Alternatively~ upon closure of the first control valve 48,
30 the second control valve 52 opens to permit communication
-- 10 --
1038Z60
between the pressure containment volume 50 and the pressure
chamber 46. Opening o~ the second control valve 52 permits
the entrapped hi~h pressure ~luid within the containment
volume 50 to expand into the pressure chamber 46 above the
valve disc 42. The force exerted by the introduction cr
high pressure fluid which was entraPped within the pressure
containment volume 50 exerts a force on the valve disc 42 ~ .
in a direction 64. The additional downward force exerted on . :
the disc 42 by the high pressure fluid introduced into the ~.
;~ 10 pressure chamber 46 from the pressure containment volume 50
combines with the weight of the disc 42 and any pressure
,- unbalance due to the difference in effective pressure surfaces
above and below the valve disc 42 to insure proper seating
. of the valve disc 42 on its seat 40. Water which may have
condensed from the high pressure fluid entrapped within the
pressure containment volume 50 when such volume is isolated
f from the pressure chamber 46 can be withdrawn therefrom
through the drain 54.
It can thus be appreciated that by provision of a
20 pressure containment volume 50 which alternatively communicates
with the pressure chamber 46 and which permits introduction
of a high pressure fluid into the pressure chamber 46 exerts
a force on the disc 42 which insures positive closure of the
valve dlsc 42 on lts valve seat 40.
