Servo drive for safety and regulating valves

Safety and regulating valves of safety stations meter energy flows in the form of gases, steam or water, in particular in thermal or industrial power plants. In a servo drive for the valves, a drive force for a safety movement of a restrictor body is derived from a working-medium pressure difference acting on the restrictor body. To this end, the spindle drive of the safety valve is constructed in such a way as to be non-self-locking. A rapid-travel mechanism is used instead of a rapid-travel motor. The rapid-travel mechanism is coupled through a non-self-locking gear unit to a planetary gear stage of the servo drive and has a shaft being normally securely braked by a releasable brake device. When the response pressure occurs, the brake device releases the rapid-travel mechanism to perform the safety movement of the restrictor body into its required position by means of the inherent medium. In a positive direction of action, the required position is the open position of the restrictor body, and in a negative direction of action the required position is the closed position.

The invention relates to a servo drive for safety and regulating valves of 
safety stations for metering energy flows in the form of gases, steam or 
water, in particular in thermal or industrial power plants, each safety 
valve having at least one restrictor body being adjustable relative to a 
valve seat and opening or closing a restrictor cross-section through which 
a working medium flows, when a response pressure reaches or exceeds a 
permissible pressure on an inflow or outflow side of the safety valve, the 
servo drive including a spindle drive for the restrictor body, and a 
planetary gear stage coupled to the spindle drive for the superimposable 
introduction of a first drive torque from a regulating drive having a 
regulating motor and of a second drive torque through a rapid-travel 
mechanism to rapidly open or close the valve when the response pressure is 
reached or exceeded. 
In process and power-plant engineering, energy flows of many different 
types have to be reduced or metered. This is done mainly through 
appropriate reducing valves in combination with various servo drives. At 
the same time, all pipeline systems and vessels or components must be 
protected against excessive pressures. Such tasks are mostly undertaken by 
safety valves of the most varied types of construction. 
If the pipeline and vessel systems located upstream of the safety valves in 
the direction of flow are to be protected from excess pressure in such a 
case, the safety valves are referred to as safety valves having a positive 
direction of action. Such safety valves must open reliably at excess 
pressure. If the systems located downstream of the safety valves in the 
direction of flow have to be protected from excess pressure, the safety 
valves are referred to as safety valves having a negative direction of 
action. Such safety valves must close reliably. 
Safety stations or associated safety valves and servo drives are meant to 
undertake both tasks, namely defined reduction or metering of energy flows 
and protection of the plant system from excess pressures. If the safety 
stations concern steam valves in which the steam is also simultaneously 
cooled by a supply of cooling water, the safety stations are referred to 
as steam-converting safety stations. 
Starting from a servo drive of the type defined initially above, which is 
essentially disclosed, for example, by the Siemens advertising publication 
"Hochdruck- und Niederdruck-Umleitstationen fur Kraftwerke mit fossiler 
Feuerung" (High-pressure and low-pressure diverting stations for power 
plants fired by fossil fuels), Order No. A 19 100-E 621-A7-VI, it is an 
object of the invention to provide a servo drive for safety and regulating 
valves, which overcomes the hereinafore-mentioned disadvantages of the 
heretofore-known and devices of this general type and to do so in such a 
way that in principle a safety station having a positive or negative 
direction of action can be realized. In particular, the safety of 
so-called bypass stations is to be increased, the regulating times are to 
be reduced, the connected power of the servo drives is to be reduced and 
finally favorable pricing is also to be achieved without loss of 
functionability. 
With the foregoing and other objects in view there is provided, in 
accordance with the invention, in a safety station having a safety and 
regulating valve for metering energy flows in the form of gases, steam or 
water, in particular in thermal or industrial power plants, the valve 
having an inflow side, an outflow side, a valve seat, and at least one 
restrictor body defining a restrictor cross-section through which a 
working medium flows, the at least one restrictor body being adjustable 
relative to the valve seat for opening or closing the restrictor 
cross-section when a response pressure reaches or exceeds a permissible 
pressure on one of the inflow and outflow sides, a servo drive for the 
valve, comprising a non-self-locking spindle drive for the restrictor 
body, a regulating drive having a regulating motor, a rapid-travel 
mechanism, a planetary gear stage coupled to the spindle drive for 
superimposing an introduction of a first drive torque from the regulating 
drive and a second drive torque through the rapid-travel mechanism for 
rapidly opening or closing the valve when the response pressure is at 
least reached, means for deriving a drive force for a safety movement of 
the restrictor body from a working-medium pressure difference acting on 
the restrictor body, a non-self-locking gear unit coupling the 
rapid-travel mechanism to the planetary gear stage, the non-self-locking 
gear unit having at least one shaft, a releasable brake device normally 
securely braking the at least one shaft, and the brake device releasing 
the rapid-travel mechanism for performing the safety movement of the 
restrictor body into a required position with the inherent medium, when 
the response pressure occurs. 
In accordance with another feature of the invention, the spindle drive for 
the restrictor body has a valve spindle, a spindle nut rotatably mounted 
on the valve spindle, a spindle-nut housing rotatably mounting but axially 
fixing the spindle nut, and an output-shaft journal on the spindle-nut 
housing for converting a rotation of the output-shaft journal through the 
spindle-nut housing and the spindle nut into an axial thrust of the 
spindle and the restrictor body. 
In accordance with a further feature of the invention, there is provided a 
ring gear having an inner periphery and being coupled to the rapid-travel 
mechanism, the planetary gear stage being connected to the output-shaft 
journal, the planetary gear stage including a sun gear having an outer 
periphery and being moved by the regulating drive, and the planetary gear 
stage including planet gears meshing with the outer periphery of the sun 
gear and with the inner periphery of the ring gear. 
In accordance with an added feature of the invention, the non-self-locking 
gear unit coupling the rapid-travel mechanism to the planetary gear stage 
is a non-self-locking worm drive. 
In accordance with an additional feature of the invention, there are 
provided means for remotely actuating a release of a braking engagement of 
the brake device when the response pressure occurs, and a free-wheel 
mechanism coupled to the shaft of the rapid-travel mechanism for 
permitting rotation of the shaft only in a direction of rotation 
corresponding to the safety movement of the restrictor body. 
In accordance with yet another feature of the invention, the at least one 
brake device has a first brake disc sitting securely on and rotating with 
the shaft of the rapid-travel mechanism and a second brake disc being 
axially displaceably but non-rotatably mounted and normally in braking 
engagement with the first brake disc, the second brake disc being mounted 
for movement into and out of braking engagement, and the free-wheel 
mechanism being a directional locking mechanism permitting the shaft to 
rotate only in a direction of rotation corresponding to the safety 
movement of the restrictor body, in a non-securely braked state of the 
shaft. 
In accordance with yet a further feature of the invention, there is 
provided at least one ratchet wheel having a ratchet tooth system, the at 
least one ratchet wheel sitting securely on the shaft of the rapid-travel 
mechanism, the shaft having an axis, and at least one pawl being pivotably 
mounted about a pawl axis parallel to the shaft axis and being 
spring-loaded into engagement with the ratchet tooth system. 
In accordance with yet an added feature of the invention, there is provided 
a pressure-monitoring configuration being connected in a 
pressure-transmitting manner to a working-medium pipeline of the safety 
valve for monitoring an actual pressure and for tripping the brake device 
when the response pressure is reached, the pressure-monitoring 
configuration having pressure monitors for issuing tripping signals, and 
an electromagnet configuration receiving the tripping signals for normally 
holding the brake device for the shaft of the rapid-travel mechanism in 
braking engagement and for lifting the brake device when the 
tripping-signals are received. 
In accordance with yet an additional feature of the invention, the pressure 
monitors are at least two pressure monitors, the electromagnetic 
configuration has at least two brake magnets each being connected 
downstream of a respective one of the pressure monitors, and a common 
transmission member coupling at least two of the brake magnets to the 
second brake disc for controlling the second brake disc by lifting the 
second brake disc when at least one of the brake magnets responds or when 
at least one tripping signal from the pressure monitors is present. 
In accordance with again another feature of the invention, the at least two 
pressure monitors and the at least two brake magnets are disposed in a 
three-channel configuration having one pressure monitor/brake magnet pair 
per channel, the pressure monitor/brake magnet pairs having a one-of-three 
tripping action of the brake magnets by the pressure monitors and a 
one-of-three tripping action of the second brake disc by the brake 
magnets. 
In accordance with again a further feature of the invention, the safety 
valve is an opening valve having a valve opening direction for protection 
against excess pressure in components or pipelines connected to the inflow 
side, and the rapid-travel mechanism has a permitted direction of rotation 
corresponding to the valve opening direction. 
In accordance with again an added feature of the invention, the safety 
valve is a closing valve having a valve closing direction for protection 
against excess pressure in components or pipelines connected to the 
outflow side, and the rapid-travel mechanism has a permitted direction of 
rotation corresponding to the valve closing direction. 
In accordance with again an additional feature of the invention, there are 
provided pressure monitors associated with the inflow side of the safety 
valve for issuing tripping signals, at least one brake magnet connected 
downstream of one of the pressure monitors for locking or releasing the 
rapid-travel mechanism, at least one additional safety leg, a signal line 
connecting the at least one additional safety leg downstream of another of 
the pressure monitors, the non-self-locking spindle drive having a valve 
spindle with a first spindle section connected to the restrictor body and 
a second spindle section flexibly coupled to the first spindle section, 
the additional safety leg having means for displacing the first spindle 
section into an open position relative to the second spindle section, when 
the pressure-monitor tripping signal is present. 
In accordance with still another feature of the invention, there is 
provided a compression-spring configuration coupling the first spindle 
section to the second spindle section, a safety lever linked to an end of 
the first spindle section facing away from the restrictor body, the safety 
lever having at least one free end, a secondary spindle extending 
substantially parallel to the valve spindle, a slot joint linking the 
secondary spindle to the at least one free end of the safety lever, a 
non-self-locking secondary spindle drive for the secondary spindle, the 
non-self-locking secondary spindle drive having a spindle nut, at least 
one first brake disc mounted for rotation with the spindle nut, and 
another brake magnet normally holding the secondary spindle in place on 
the brake disc and releasing the spindle nut for rotation and the 
secondary spindle for axial movement, in the event of a tripping signal 
being supplied from one of the pressure monitors. 
In accordance with still a further feature of the invention, there is 
provided a housing for the secondary spindle drive and the other brake 
magnet, the housing being rigidly coupled to and longitudinally 
displaceably mounted with the second spindle section. 
In accordance with a concomitant feature of the invention, the safety lever 
has a rocker-like two-armed construction, and including another secondary 
spindle, another secondary spindle drive for the other secondary spindle, 
the at least one free end of the safety lever being two free ends, the 
secondary spindles each being linked to a respective one of the free ends 
of the safety lever, a further brake magnet, another housing for the other 
secondary spindle and the further brake magnet, a housing bridge 
interconnecting the housings and the brake magnets, and the housing bridge 
being firmly connected to the second spindle section. 
The advantages achievable with the invention can in particular be seen in 
the fact that a separate rapid-travel motor of, for example, up to 27 kW 
power no longer needs to be used for the servo drive. On the contrary, the 
drive for the valve spindle in the event of safety tripping is actuated by 
the inherent medium. Separate hydraulic drives or pressure-relieved 
actuators, which have constant leakage losses, are also dispensed with. 
Other features which are considered as characteristic for the invention are 
set forth in the appended claims. 
Although the invention is illustrated and described herein as embodied in a 
servo drive for safety and regulating valves, it is nevertheless not 
intended to be limited to the details shown, since various modifications 
and structural changes may be made therein without departing from the 
spirit of the invention and within the scope and range of equivalents of 
the claims. 
The construction and method of operation of the invention, however, 
together with additional objects and advantages thereof will be best 
understood from the following description of specific embodiments when 
read in connection with the accompanying drawings.

The construction and function of three exemplary embodiments are explained 
below in the sequence of FIGS. 1 to 3 and then FIGS. 4 to 6. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the figures of the drawing in detail and first, 
particularly, to FIG. 1 thereof, there is seen a safety station having a 
safety function, which is actuated by an inherent medium, in a positive 
direction of action. Steam flows through an inlet piping connection 2 from 
a working-medium pipeline 2b of a safety valve in a valve opening 
direction indicated by flow arrows fl, against a restrictor body 3 (in 
this case, e.g., a parabolic restrictor body) of the steam valve having a 
housing 1. The steam exerts an axial force on the restrictor body 3, on a 
spindle 4 and on a spindle nut 5. The axial force is in proportion to the 
effective cross-section of the restrictor body and the pressure difference 
between the inlet piping connection 2 and an outlet piping connection 6 
and acts in the opening direction. 
The axial force produced by the inherent medium (steam) is converted into a 
torque in the non-self-locking (in contrast to conventional spindle nuts) 
and rotatably mounted spindle nut 5. The torque is transmitted through a 
spindle-nut housing 7 that is firmly connected to the spindle nut 5, to an 
output-shaft journal 8 of a servo drive. 
The torque passes from the output-shaft journal 8 through a planetary gear 
stage 11 on one hand to a worm stage 9 having a shaft 9a and being 
likewise non-self-locking in contrast to conventional planetary gear units 
and is securely braked by a brake device 10 at pressures below a safety 
pressure, and on the other hand to a self-locking worm stage 12, where it 
is compensated. 
A servo drive motor 13, which also acts on this self-locking worm stage 12 
and in normal operation is controlled by a control system, effects an 
adjustment of the restrictor body 3. 
The function of the worm stage 12, the action of the servo drive or 
regulating motor 13 (also designated as drive or servo motor), the 
torque-dependent control by displacement of the worm and compression of a 
torque spring 14, correspond to previous proven servo-drive technology 
(e.g. Siemens servo drives). 
If the pressure in the inlet piping connection 2 or in the systems located 
in upstream of it increases above a value set at pressure monitors 15 of a 
pressure-monitoring configuration DA, switch contacts 26 open and 
connected brake magnets 16 of a brake-magnet configuration EM become dead 
and fall back into a neutral position. 
A mechanical coupling of the brake magnets 16 to the brake device 10 in 
combination with springs 17, is constructed in such a way that even the 
release of one brake magnet brings about reliable lifting of the brake 
device 10. 
With the lifting of the brake device 10, the non-self-locking worm stage 9 
is released. 
The axial thrust produced by the inherent medium (steam) and acting through 
the restrictor body 3 and the valve spindle 4 is converted into a torque 
in the non-self-locking spindle nut 5 and sets the spindle nut 5, the 
spindle-nut housing 7, the output-shaft journal 8, the planetary gear 
stage 11 and the non-self-locking worm stage 9 into rotary motion. As a 
result, the restrictor body 3 and the valve spindle 4 move upwards in 
accordance with the thread pitch in the spindle nut 5. As long as at least 
one of the switch contacts at the pressure monitors 15 remains open, the 
valve is opened up to the open end position. In the event of premature 
pressure reduction and the closing of the contacts at the pressure 
monitors 15 associated therewith, the opening action (safety stroke) 
actuated by the inherent medium is ended by the braking of the 
non-self-locking worm stage 9 through the brake device 10. 
It is also possible, through the use of a manual key 18, to carry out 
specific partial-stroke or full-stroke tests below the response pressure 
of the pressure monitors 15. 
The opening action (safety stroke) actuated by the inherent medium can be 
effected from the closed end position and from any intermediate position. 
If the supply voltage at the pressure monitors 15 fails, a release of the 
opening action (safety stroke) actuated by the inherent medium is likewise 
effected. 
The opening action (safety stroke) actuated by the inherent medium is also 
effected when the servo drive or regulating motor 13 is simultaneously 
actuated in the closing direction, if contacts of the pressure monitors 15 
are open. Compensation is effected in this case through the planetary gear 
stage 11. 
If the servo drive or regulating motor 13 is simultaneously actuated in the 
opening direction (safety direction) when the safety stroke is tripped, 
this regulating movement is additionally superimposed on the opening 
action actuated by the inherent medium. This is effected by a pawl 19 of a 
directional locking or free-wheel mechanism RG which engages into a 
toothed ratchet wheel or locking wheel 10a' of the brake device 10 and 
releases this locking wheel 10a' only in the direction of rotation 
produced by the opening action (safety stroke) actuated by the inherent 
medium. The ratchet wheel 10a' is connected to a first brake disc 10a in 
such a way as to be fixed in terms of rotation. The first brake disc 10a 
sits securely on and rotates with the shaft 9a of the non-self-locking 
gear unit 9, and a second brake disc 10b is axially displaceably but 
non-rotatably mounted and normally in braking engagement with the first 
brake disc 10a. The second brake disc 10b is mounted for movement into and 
out of braking engagement. A common transmission member 21 couples at 
least two of the brake magnets 16 to the second brake disc 10b for 
controlling the second brake disc 10b by lifting the second brake disc 10b 
when at least one of the brake magnets responds or when at least one 
tripping signal from the pressure monitors 15 is present. 
With regard to FIG. 1, it should also be added that in this figure an 
auxiliary closing spring 27, which is designated as a helical compression 
spring, is inserted between a cover 28 of the spindle 4 and a retaining 
body 29 fixed to the housing. The spring 27 has the task of preventing 
fluttering of the restrictor body 3 at small differential pressures 
between the inlet piping connection 2 and the outlet piping connection 6. 
In FIG. 2, the reference numerals are 2 and 6 are reversed as compared to 
FIG. 1, so that the same reference numeral identifies an element which 
functions in the same way. FIG. 2 illustrates the function of the safety 
station having a safety function, which is actuated by the inherent medium 
in a negative direction. Steam flows from above through the inlet piping 
connection 2 and through the restrictor body 3 (in this case, e.g. a 
perforated restrictor body) to the steam valve having the housing 1. 
The steam exerts an axial force on the restrictor body 3, the spindle 4 and 
the spindle nut 5. The axial force is in proportion to the effective 
cross-section of the restrictor body and the pressure difference between 
the inlet piping connection 2 and the outlet piping connection 6 and acts 
in the closing direction. As is shown by flow arrows f2, the steam forces 
act in the closing direction of the restrictor body 3. The safety movement 
of the restrictor body 3 also takes place in this direction so that the 
free-wheel rotation of the directional locking mechanism RG now takes 
place in the clockwise direction f4 (in the example according to FIG. 1 
the free-wheel rotation takes place in the counter-clockwise direction 
f3). Otherwise, the servo drive according to FIG. 2 is constructed like 
that according to FIG. 1, and therefore the same parts are provided with 
the same reference numerals and the functional sequence is analogous. 
If the pressure in the outlet piping connection 6 or in the systems located 
downstream of it increases above the value set at the pressure monitors 
15, switch contacts 26 open and the connected brake magnets 16 become dead 
and fall back into their neutral position. 
The mechanical coupling of the brake magnets 16 to the brake device 10 in 
combination with the springs 17 is constructed in such a way that even the 
release of one magnet brings about reliable lifting of the brake device 
10. 
With the lifting of the brake device 10, the non-self-locking worm stage 9 
is released. 
The axial thrust which is produced by the inherent medium (steam) and which 
acts through the restrictor body 3 and the valve spindle 4, is converted 
into a torque in the non-self-locking spindle nut 5 and sets the spindle 
nut 5, the spindle-nut housing 7, the output-shaft journal 8, the 
planetary gear stage 11 and the non-self-locking worm stage 9 into rotary 
motion. As a result, the restrictor body 3 and the valve spindle 4 move 
downwards in accordance with the thread pitch in the spindle nut 5. As 
long as at least one of the switch contacts at the pressure monitors 15 
remains open, the valve is closed up to the closed end position. 
In the event of premature pressure reduction and the closing of the 
contacts at the pressure monitors 15 associated therewith, the closing 
action (safety stroke) actuated by the inherent medium is ended by the 
braking of the non-self-locking worm stage 9 through the brake device 10. 
It is also possible, through the manual key 18, to carry out specific 
partial-stroke or full-stroke tests below the response pressure of the 
pressure monitors 15. 
The closing action (safety stroke) actuated by the inherent medium can be 
effected from the open end position and from any intermediate position. 
If the supply voltage at the pressure monitors 15 fails, a release of the 
closing action (safety stroke) actuated by the inherent medium is likewise 
effected. 
The closing action (safety stroke) actuated by the inherent medium is also 
effected when the servo drive or regulating motor 13 is simultaneously 
actuated in the open direction, if the contacts of the pressure monitors 
15 are open. Compensation is effected in this case through the planetary 
gear stage 11. 
If the servo drive or regulating motor 13 is simultaneously actuated in the 
closed direction (safety direction) when the safety stroke is tripped, 
this regulating movement is additionally superimposed on the closing 
action actuated by the inherent medium. This is effected by a pawl 19a 
which engages into the toothed ratchet wheel or locking wheel 10a' of the 
brake device 10 and releases this locking wheel 10a' only in the direction 
of rotation produced by the closing action (safety stroke) actuated by the 
inherent medium. In the safety function in the negative direction, this 
direction of rotation is opposite to that in the safety function in the 
positive direction. 
The exemplary embodiment according to FIG. 3 likewise relates to a safety 
station which is suitable for reducing and metering energy flows (gases, 
water) in process engineering and at the same time for reliably protecting 
the plant systems from excess pressure, and in fact with a safety function 
that is actuated by an inherent medium in the opening direction. 
The safety station is essentially formed of an operating leg and two 
additional safety legs. Tripping of the safety stroke can be effected both 
through the operating leg and through each individual safety leg. The 
operating leg is formed of a motor-driven servo drive, a non-self-locking 
spindle nut and the regulating member having the restrictor body. 
The two additional safety legs, which are independent of one another, are 
disposed between the spindle nut and the regulating member of the 
operating leg. They are formed of non-self-locking gear stages which can 
be securely braked. In the securely braked state, the safety legs form a 
rigid connection between the spindle nut and the regulating member of the 
operating leg. The safety stroke is actuated by the inherent medium in 
accordance with the direction of flow towards the restrictor body in the 
regulating member. 
The motor-driven servo drive is a modification of the proven Siemens 
double-motor drive with a planetary gear unit. The previous engagement 
point of a rapid-travel motor, which is a self-locking worm stage, is 
replaced by a non-self-locking worm stage having an electromagnetic brake 
device on the worm shaft. During normal operation, this non-self-locking 
worm stage remains securely braked. When the safety function responds, the 
brake device lifts and releases the worm stage for the operating-leg 
safety stroke that is actuated by the inherent medium. 
The torque required to perform the safety stroke through the operating leg 
is applied to the motor-driven servo drive by the inherent medium through 
the restrictor body, the valve spindle, the spindle linkage, the securely 
braked safety legs and the non-self-locking spindle nut. 
The safety stroke is performed through the safety legs by lifting the 
associated brake devices at the spindle nuts of the non-self-locking 
thread stages of the safety legs. The spindle shafts, which are fixed in 
such a way as to be locked against rotation, are pressed into the nuts by 
the force of the inherent medium and, when the brake is lifted, they set 
the nuts in rotary motion and thereby enable the regulating member to be 
opened reliably. In the process, both safety legs work completely 
independently of one another. The lifting of the brake device on one 
safety leg is already sufficient to reliably open the regulating member. 
An operating leg BS is essentially formed of a motor-driven servo drive, a 
non-self-locking spindle nut 5 and the regulating member 1, 3. 
Two safety legs SSt 1, SSt 2 are respectively formed of securely brakeable, 
non-self-locking worm stages 20a, 23; 20b, 23, which are coupled through a 
suitable spindle linkage 4a, 4b and are disposed beteween the spindle nut 
5 and the regulating member 1, 3. A spring element 22 is inserted along 
the longitudinal axis of the spindle 4, between a safety lever 4a and a 
housing bridge 4b of the spindle linkage. 
Steam flows through the inlet piping connection 2 against the restrictor 
body 3 (in this case, e.g., a parabolic restrictor body) of the steam 
valve having the housing 1. The steam 
exerts an axial force on the restrictor body 3, the spindle 4, the spindle 
linkage in the form of the safety lever 4a and the housing bridge 4b, 
safety spindles 20a and 20b and the spindle nut 5. The axial force is in 
proportion to the effective cross section of the restrictor body and the 
pressure difference between the inlet piping connection 2 and the outlet 
piping connection 6 and acts in the opening direction. 
The axial force produced by the inherent medium (steam) is converted into a 
torque in the non-self-locking and rotatably mounted spindle nut 5, and 
further explanations relative to the first exemplary embodiment according 
to FIG. 1 in the second, third, fourth, fifth and sixth paragraphs of the 
Description of the Preferred Embodiments, apply to this exemplary 
embodiment. 
With the lifting of the brake device, the non-self-locking worm stage 9 is 
released. 
The axial thrust being produced by the inherent medium (steam) and acting 
through the restrictor body 3, the valve spindle 4 and the spindle linkage 
4a and 4b having the safety spindles 20a and 20b, is converted into a 
torque in the non-self-locking spindle nut 5 and sets the spindle nut 5, 
the spindle-nut housing 7, the output-shaft journal 8, the 
non-self-locking worm stage 9 and the planetary stage II into rotary 
motion. As a result, the restrictor body 3, the valve spindle 4 and the 
spindle linkage 4a and 4b having the safety spindles 20a and 20b move 
upwards in accordance with the thread pitch in the spindle nut 5. The 
valve is opened up to the open end position if the switch contact of a 
pressure monitor 15a remains open long enough. 
In the event of a premature pressure reduction and the closing of the 
pressure-monitor contact 15a associated therewith, the opening action of 
the operating leg BS (safety stroke) actuated by the inherent medium is 
ended by the braking of the non-self-locking worm stage 9 with the brake 
device 10. 
It is also possible, through a manual key 18a, to carry out specific 
partial-stroke or full-stroke tests below the response pressure of the 
pressure monitor 15a. 
The opening action (safety stroke) of the operating leg BS being actuated 
by the inherent medium can be effected from the closed end position and 
from any intermediate position. 
If the supply voltage at the pressure monitor 15a fails, a release of the 
opening action (safety stroke) actuated by the inherent medium is likewise 
effected through the operating leg BS. 
The opening action (safety stroke) of the operating leg BS, which is 
actuated by the inherent medium, is also effected when the servo drive or 
regulating motor 13 is simultaneously actuated in the closing direction, 
if the pressure-monitor contact 15a is open. Compensation is effected in 
this case through the planetary gear stage 11. 
If the servo drive or regulating motor 13 is simultaneously actuated in the 
opening direction (safety direction) when the safety stroke of the 
operating leg is tripped, this regulating movement is additionally 
superimposed on the opening action actuated by the inherent medium. This 
is effected by the pawl 19 of the directional locking mechanism RG which 
engages into the toothed ratchet wheel or locking wheel 10a' of the brake 
device 10 and releases this locking wheel 10a' only in the direction of 
rotation produced by the opening action (safety stroke) actuated by the 
inherent medium. The same action can also be achieved with a free-wheel 
(instead of the pawl 19 and the locking wheel 10a'). 
In addition to the operating leg BS, the two independent safety legs SSt 1, 
SSt 2 are connected. The safety legs SSt 1, SSt 2 are essentially formed 
of the non-self-locking safety spindles 20a and 20b having associated 
brake magnets 16b and 16c. 
In the normal operating state, the safety spindles 20a, 20b are in the 
extended state (in accordance with the position shown). At the same time, 
the two safety spindles are securely braked by associated safety-spindle 
nuts 23 and the respective brake magnets 16b and 16c. Consequently, there 
is a rigid connection between the parts 4a and 4b of the spindle linkage 
and thus also between first and second spindle sections 4.1, 4.2. However, 
if the brake magnets 16b or 16c become dead through the response of 
pressure monitors 15b or 15c, the rigid connection between the spindle 
linkage parts 4a and 4b is neutralized. The force of the inherent medium 
then acts through the first spindle section 4.1 and pushes the tiltably 
mounted spindle linkage 4a and the safety spindle 20a or 20b upwards 
through the rotating safety-spindle nuts. 
The restrictor body 3 can always reach the open end position as soon as the 
safety stroke is tripped through one leg (operating or safety leg). This 
also applies of course during the simultaneous response of two or three 
legs. 
The safety legs can likewise be tested separately through manual keys 18b 
and 18c as well as the brake magnets 16b and 16c. In this case, testing is 
likewise possible below the safety pressure. 
It will be recognized from FIG. 3 that at least one brake magnet 16a is 
connected downstream of a pressure monitor 15a. The brake magnet 16a locks 
or releases a rapid-travel mechanism SG. The at least one additional 
safety leg SSt 1, which is connected downstream of the further pressure 
monitor 15b over a signal line, has means provided by the elements 16b, 
20a, 4a for displacing the first spindle section 4.1 with the restrictor 
body 3, when a pressure-monitor tripping signal is present. The first 
spindle section 4.1 and the restrictor body 3 are displaced into the open 
position relative to the second spindle section 4.2, which is coupled in a 
flexible manner (by the spring 22) to the first spindle section 4.1 and 
has the non-self-locking spindle drive. As mentioned above, two additional 
safety legs SSt 1, SSt 2 are shown and the first spindle section 4.1 is 
coupled to the second spindle section 4.2 through the spring element or 
compression-spring configuration 22. Linked to the end of the first 
spindle section 4.1 facing away from the restrictor body 3 is the safety 
lever 4a that has at least one free end to which the safety or secondary 
spindle 20a, 20b running essentially parallel to the valve spindle 4 is 
linked through a slot joint. The safety or secondary spindle 20a, 20b has 
a non-self-locking secondary spindle drive with at least one first brake 
disc 24 that is mounted in such a way as to rotate with the spindle nut 
23, and the second brake magnet 16b which normally holds the safety or 
secondary spindle 20a in place on its brake disc 24. In the event of a 
tripping signal being supplied from the associated pressure monitor 15b, 
the brake magnet 16b releases the spindle nut 23 for rotation and the 
safety or secondary spindle 20a for axial movement. A housing 25 of the 
secondary spindle drive and the second brake magnet 16b is rigidly coupled 
to the second spindle section 4.2 and is mounted together with the latter 
in a longitudinally displaceable manner. The second safety leg SSt 2 
corresponds to the first safety leg SSt 1. The safety lever 4a is 
therefore preferably of two-armed construction like a rocker, and one 
respective secondary spindle 20a, 20b having one respective secondary 
spindle drive is linked to each of its two free ends. The housings 25 of 
the two secondary spindle drives and their associated brake magnets 16b, 
16c are connected to one another through a housing bridge 4b, and the 
housing bridge 4b is firmly connected to the second spindle section 4.2 of 
the valve spindle 4. 
Explanation of FIGS. 4 to 6 
A planetary gear stage is generally designated by reference symbol B in 
FIGS. 4 to 6. The planetary gear stage has two planet gears b.sub.1 and 
b.sub.2 which are located diametrically opposite one another and which 
mesh with a sun gear A at their inner peripheries and with an internal 
tooth system of a ring gear C at their outer peripheries. The ring gear C 
belongs to the rapid-travel mechanism SG, i.e., if the latter is released 
by the brake magnets, the output-shaft journal can rotate in an unbraked 
manner through the worm drive 9 shown in FIGS. 1 to 3 and the restrictor 
body 3 moves into its open position (FIG. 1 or 3) or into its closed 
position (FIG. 2). 
The table according to FIG. 6 first of all shows that, during the 
regulating operation, the sun gear A is driven and drives the planetary 
gear stage B with it, whereas the rapid-travel mechanism SG is securely 
braked. In effect, the inner gear rim of the ring gear C represents a 
fixed roller track for the planet gears b.sub.1, b.sub.2. 
If a signal "response pressure reached" is now produced by one of the 
pressure monitors because the pressure P is greater than the response 
pressure PGr, the corresponding brake magnet is lifted, i.e. the 
rapid-travel mechanism SG is released, which is the condition dealt with 
in the right-hand column of the table according to FIG. 6. The planetary 
gear stage driven by the output-shaft journal through the worm drive, 
drives the shaft of the rapid-travel mechanism SG with it, wherein it is 
immaterial whether or not the sun gear A is moved by the regulating 
mechanism. In this operating case (response of the safety mechanism), the 
sun gear A represents a roller track for the planet gears b.sub.1, b.sub.2 
and is either stationary (if no regulating command is present) or moves by 
itself. 
The compression-spring configuration 22 in the example according to FIG. 3 
in particular has the following tasks: 
a) Damping the movement of the restrictor body 3, in particular at high 
steam pressures, so that the restrictor body 3 cannot "strike" the housing 
1. This is of importance at the relatively high steam forces of 10 t to 20 
t; 
b) Displacing the spindle section 4.2 of the operating leg BS into the open 
end position if one or both safety legs SSt 1, SSt 2 should respond before 
the operating leg BS, and 
c) Returning the safety legs SSt 1, SSt 2 into their original position 
shown.