Note: Descriptions are shown in the official language in which they were submitted.
The invention concerns a combined stop and control
valve for turbine installations, in particular for steam
turblne installationæ, the stop and control valve bodie~ of
which are arranged coaxially to one another ina common hous- -
ing and can be controlled independently of each other.
In present-day power plant installation~ the
control valves in the pipes carrying the working medium
to the turbines, particularly in the case of steam turbines,
are alway~ ~upplemented by fast-acting stop valves so that
at least a high-speed shutdown can be carried out in the
e~ent of a control failure or in response to any other
external influences. The u~ual principle of duplicated ~ ;
safety for the whole power installation is thus maintained.
For a long time, so called interceptor valves have been
fitted in the reheat line of steam turbines with reheater~,
as otherwise the volume of steam present in the reheater
and in the connecting pipe would be sufficient following a
shutdown, even though the high-pressure line was closed, to
accelerate the turbine rotor to an unacceptably high over-
speed which itself would endanger the whole power in~tallation.
Combined stop and control valves are known,Swiss
patent No. 539 805,in which the control valve and the stop
valve are contained in a common valve housing. The body of
the control valve is situated upstream from the body of the
stop valve and has the shape of a bell into the hollow portion
of which the plate-shape stop valve travels during the opening
movement. Here~ the valves are prefer~bly so connected that
in their end positions the two valve bodies are in the same
position relative to one anoiher.
During the course of power plant development, with
large steam volumes it was reasonable to employ this form of
~alve for live steam control valves, as well as for interceptor
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valves. The bell-shaped control valve then serve6 to modify
the performance of the steam turbine in response to load
variations.
It has been found, however, that this form of valve
ha~ a tendency to vibrate when the control valve i8 in the
throttled position. Consequently, damage due to wear and
- cyclic stresses can occur with prolonged part-load operation.
The general ob~ect of the invention is to avoid
the disadvantage stated above. This objective i5 achieved
in that the control valve i~ located down5tream from the
stop valve and opens in the direction of the steam flow, and the
control valve body is in the form of a relieving or servo
pi~ton.
The advantage of the invention is to be seen in '~'i
the fact that with the stop valve ahead of the control valve,
viewed in the flow direction, vibratlon-free location of the
valve body i~ achleved by the full pre6sure difference be-
tween live steam and atmosphere in the open position. Fur-
thermore, in contrast to the combined valve mentioned above,
the stop valve body i8 no longer subJected to the throttled
ma88 flow ~et ~rom the control valve during operation, thus
eliminating a further source of vibration. In the case of
the proposed control valve, the advantage is to be seen in
the fact that the throttled flow moves away from the center ;
and thus an energy concentration in the center in the direc-
tion of the valve movement is completely avoided, greatly
reducing the tendency to vibrate.
In a preferred alternative form of the invention,
in order to relieve the pressure on the valve components,
the stop valve is provided with a pilot valve located at
one end of a valve spindle. Sleeve inserts rigidly ~ixed
to the body of the stop valve can be provided with valve
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seats via which the valve lift is carried out.
It is of particular advantage if the stop valve
body and the cover accommodating it in the open positlon
are provided with an annular flat seat which ensure6 a
well-fitting position of both components when the valve
is open.
According to a pre~erred alternative embodiment,
the working medium can be admitted to both sides of the
control valve. In this case it is recommended that working
medium should be drawn from the upstream side of the control
valve through drilled holes in the valve body.
; Further, it is of benefit to make the piston
surfaces of the control valve of such dimensions that
the forces applied by the working medium exert a clQsing
effect on the control valve. With an arrangement of this
kind a pilot valve is not necessary, and therefore, owing -~-
to the absence of freely moving parts in the steam space,
the valve design ls very simple and hence esAentially less
su6ceptible to defects.
In an alternative form of the invention the control
valve body is provided with a control sy~tem acting sequen-
tially to the pressure of the working medium. In this case
it is recommended that ir the piston spaces are li~X~d to
working-medium system when the control valve opens, the
pressure level of thiæ system should be lower than the
pressure level of the working medium to be controlled by
the control valve.
In addition to the known advantage of the prin-
ciple of anticipatory control, namely of obtaining suffi-
ciently large actuating forces with adequately low inertia,
the particular advantage of this configuration is to be
seen in the fact that the control valve body in the form of
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a servo piæton is controlled by the working medium it~elf.
Because high hydraulic pressures are not needed, savings
are achieved in pump capacity, and in addition the whole
extent of the system is reduced.
Examples of the invention are shown in simplified
form in the drawings, in whi~h: -
Fig. 1 ~hows a section through a combined
stop and control valve, and
Fig. 2 1~ a detall ~ectlon through the ~ame
valve being actuated by a follow-up
plston.
Component~ not essential to the invention, such
as splndle bearings, ~eals, fastenings, means of spindle
ad~ustment, etc., are omitted for the sake of clarity.
As shown in Fig. 1, a common housing 1 contains
the ~top valve 2 and the control valve 3. On the inlet
side of the combined valve a cylindrical steam strainer 4
i6 attached on the one hand to the cover 5 of the stop
valve 2, and on the other to the valve ~eat 6. In the open
posltion lllu~trated, the ~top valve body 7 and the valve
seat 6 form a hydro-dynamlcally favourable, annular lnlet
channel to the control valve 3.
The ætop valve 2 is actuated by way of a spindle 8,
the valve-end of whlch is in the form of a double-seated pilot
valve 9. Fixed to the valve body 7 are two sleeve inserts
lO and 11, each of which has a valve seat 12 or 13, respec-
tively, and radial holes 14 and 15.
With the valve in the open position illustrated,
the valve body 7 and the valve cover 5 form a seal with
respect to the steam space by means of annular flat seat 16
and the seat 12 of the pilot valve 9. The seating 16 also
ensures that the valve body 7 i~ firmly located against
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the cover 5. 1~4S~
To explain the principle of operation, a valve
through which working medium is flowing can be considered
first. The ~ull steam pressure obtaining in the steam
space acts on the body o~ the stop valve 7. The closing
procedure i8 initiated by pushing in the spindle 8. The
pllot valve 9 separates from seat 12 and engages seat 13.
Flowing through hole 17 in cover 5, hole 18 in the valve
body 7, hole 1~ in the sleeve insert 10 and also through
the open valve ~eatlng 12, working medlum passes along the
annular gap 19 between spindle 8 and sleeve insert 11
and through hole 15 in sleeve insert 11 into the equalising ~ .
space 20. The pressure in space 20 on valve body 7 is thus
increased; as the spindle 8 moves in further, the valve body
7 is drawn along by way of the pilot valve 9 resting on
valve seat 13.
If the stop valve 2 is to be opened from the closed
posltlon, this procedure ls initiated by raising the spindle
8. The seat 13 is freed, and worklng medlum flow~ via holes 18,
14, the open seat 13 and hole 21 from the flow approach ~lde
into the space form by the closed stop an~ control valves and
by valve seat 6. Pressure in this space 7 is thus increased
and the body follows further raising o~ spindle 8 by way of
the valve seat 12 engaging pilot valve 9.
The control valve body 22 of the control valve 3
is in the form of a piston, and is rigidly joined to the
actuating spindle 23. The construction requires no pilot
valve and thus, owing to the absence of freely moving parts
in the steam space, is very simple and not susceptible to
defects. Because in operati~n the throttled working medium
flows away from the center, an energy concentration at the
center of the piston in the direction OI the valve travel
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is avoided, greatly lessening the inducement of the control
valve 3 to vibrate.
The spindle 23 slides in a spindle guide 24, and the
valve body-piston 22 which as illustrated has a longitudinally
stepped profile slides in a piston correspondingly stepped guide
25 which forms an operating cylinder for the valve body-piston 22,
the outer contour of which forms an annular diffusor 26 together
with the valve seat 6. The spindle guide 24 and the piston guide
25 are fixed in the housing 1 by way of cover 27. The piston
gpaces 28 and 28a are joined to the flow approach side of the
control valve 3 via holes 29 and the annular gap 30. The piston
surfaces of the valve body 22 are so dimensioned that the sum of
the steam forces acting on the piston act to close the valve.
Since the valve can be kept closed only with presaure in the
piston spaces 28 and 28a, the piston is sealed with piston rings
(not shown). Leakage is kept small in this way' any leakage is
led away to a space having a lower pressure via the annular gap
30 in the piston guide 25 and through hole 31 in the housing 1.
The opening and closing operations of the control valve
3 require no further explanation, as the body of the control valve
22 is raised or lowered, respectively, via the actuating spindle
23.
Fig. 2 shows on a rather larger scale the control valve
3' which, unlike the version of Fig. 1, is provided with steam-
operated pilot control. Wherever components of the arrangement
in Figure 2 coincide with those in Fig. 1, they are identified
by the same reference symbols. If only the function is the
same, but the manner of execution is different, however, the
same reference symbols are distinguished by a prime.
The valve body 22' is a servo piston with steam pres-
sure follow-up control, and is therefore no longer rigidly
connected to the actuating spindle 23~. Piston 22'
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and spindle 23 ' again slide in piston guide 25 and spindle
guide 24', respectively. Inside the piston is a sleeve
insert 32 which, for reasons of clarity, i5 shown as being
in one piece. This sleeve insert 32, which for purpo~es of
assembly can of course be in several parts, is rigidly attached
to the piston and incorporates holes 33 ~oining to annular
space 34. The latter is connected to the flow approach side
of the valve body 22' via the hole 35. The space 36 inside the
piston i6 connected to a steam system ~not shown) of lower
pressure (in the case of reheat turbines, for example, the
outlet of the high-pressure turbine if a hlgh-pressure control
valve is concerned) via the channel 37 and recess 39, both of
which are machined on the valve body, and via space 46, hole 30'
and the recess 40 in the piston gulde 25, and also vla the
hole 31 in housing 1. The sleeveinsert 32 has a recess which
is provlded with two control edges 41, 42. A thickened portion
of the actuating spindle 23 ' engages in this rece6s, the
thickened portions having control edges corresponding to the
control edges 41 and 42.
The actuatlng spindle 23' is provided with a cavity
45 which is permanently in communication with the piston
space 20 and, via space 46 which i8 in the form of a slot, with
the piston space 28a. By way of the control edgeæ 41, 42,
therefore, the piston spaces 28 and 28a can be connected as
desired to the flow approach side of the control val~e 3' or
to the steam system of lower pressure.
The follow-up control system functions in the
following manner:
Witn the control valve body 22' closed, let it be
3 assumed that the actuating spindle 23 ' moves downwards from
the position shown. Control edge 42 closes, control edge 41
opens the connection between the space of lower pressure 36
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and the cavity 45 communicating with the piston spaces 28 and
28a. As a result, high-pressure steam escapes from the piston
spaces 2~ and 28a through the channel system 28a, 46, 28, 45,
s 41, 36, 37, 39, 4r(~ 30', 40, and 31. The pressure in the
piston spaces 28 and 28a falls, and the steam ~orces acting
; on the control valve body 22' from its flow approach side move
the body downwards in the opening directlon. In consequence,
control edge 41 is again closed, the control edge 42 begins to
open untll, via the channel 8y8tem 35, 34, 33, 45, 28, 46 and
28a, a pres8ure is reached in piston spaces 28, 28a which
balances the opening steam forces.
; The hole 30' in the piston guide 25 is pre~erably
made as a throttle; in this way a substantial pressure change
can occur temporarily in space 47 when the piston moves
quickly. The purpose of this measure, and also the config-
uration of space 46, is to have a damping counteraction on
the tendency of the follow-up piston to vibrate.
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