1. INNOVATIVE SHUT-OFF VALVES FOR TURBINES
IN HYDRO POWER PLANTS
O. Schüller
Abstract: TIWAG has developed a series of high-quality spherical
valves for hydro power plants. With the optimal tuning of all the
processes, from the layout and design, the selection of materials and
machining equipment through to the experience gained in the
operation, a remarkable product has been created.
Introductory thoughts to the development of a new product
How can it happen that TIWAG is able to compete for a product like spherical valves
despite the pressure on the prices in the market?
This is only possible if all existing concepts are analysed for their advantages and
disadvantages, however for the realisation a new way has to be chosen, in a creative
process of design. For this a number of inspiring examples can be found in the
history, among them numerous designs done by the manufactures of turbines and
valves.
The support on the way to new solutions can be taken from various tools, e.g. the
value analysis or the guide VDI 2221 “methodology for design and construction of
technical systems and products”. A good description can be found in [1], but the
creative intuition of the engineer cannot be replaced and it is necessary to keep the
general perspective, even if one has to deal with a lot of detailed problems.
The main characteristic features of a successful design are simplicity, robustness,
clear function and a small number of parts that can easily be fabricated.
This background shall be the motive for the design process, considering that one
single perfect solution will not be possible, as it is always necessary to follow the
conditions of existing structures or contracts. To emphasize this, we dare to say that
some 30 years ago for spherical valves a welded construction with a minimum use of
material would have been cheaper than our solution with massive forged rings.
Today we can offer our product for small to medium sized valves because material
costs are low and because only machining has to be done with relative high fees in
our region. The standardised series comprises spherical valves with a nominal
diameter between DN150 and DN1000 and a nominal pressure from PN25 to PN130.

2. Special features of the TIWAG closing valves
Our concept is based on the following standards and solutions:
- a clear concept of design leads to a homogenous line of products
- a small number of parts with clear functionality
- robust and easy-to-service design
- innovative solution for the bearing of the rotating body (registered design 4709)
- simple conditions for manufacturing, no welded parts
- use of forged rings instead of cast parts
- relevant parts made of stainless steel
- compact dimensions
- low stresses and deformations
- high safety for the demanded functions
- low requirements for testing and commissioning
An essential step was the development of the bearing of the rotating body. Usually
large shut-off valves will be designed according to one of the four alternatives for the
bearing of the rotating body in the casing shown in figure 1, with rather high costs for
construction and calculation as well as for manufacturing and mounting.
Var. a) Drehkörper mit angeformten Zapfen, Gehäuse in der Zapfachse geteilt
Var. b) Drehkörper ohne Zapfen, Gehäuse einteilig, Zapfen über innerhalb des
Gehäuses liegende Flanschen an den Drehkörper verschraubt
Var. c) Drehkörper ohne Zapfen, Gehäuse einteilig, Zapfen mit Drehmoment-
übertragenden Stiften oder Vierkanten in den Drehkörper eingesteckt,
Zapfen 1-fach oder 2-fach gelagert
Figure 1: Different
classical solutions for the
journal bearing and the
joint to the rotating body
Var. d) Drehkörper ohne Zapfen, Gehäuse einteilig, Zapfen von außen mit
Dehnschrauben an den Drehkörper verschraubt

3. The alternative d) in figure 1 has the disadvantage that in the highly pre-stressed joint
between rotating body and journal the bending moments from the bearing of the pivot
as well as torque between the rotating body and the servomotor must be transmitted.
Additionally the joint between rotating body and journal bearing also causes a few
problems, among them high tensions with indefinite flow of forces combined with
defects in castings or rust between fitting surfaces. Also these critical areas will not
be accessible for inspections without total dismantling.
TIWAG’s solution is based on:
- elimination of integral cast pivot
- bearing of the journal within the spherical contour of the rotating body
- transmission of torque only in the joint face, no bending moments
This is possible by hollowing
a groove out of the spherical
contour of the rotating body,
where a thick-walled bearing
sleeve is mounted through
an opening in the casing.
The short journal within the
spherical contour allows a
simple undivided casing
(figure 2).
The torque from the rotating
body to the servomotors is
transmitted through friction
via a short trunnion screwed
onto the journal with
antifatigue shafts. Figure 2: Bearing journal within spherical contour
This joint is not subject to bending moments anymore (in contrary to the alternative d)
in figure 1), which are caused by the forces acting on the rotating body and on the
servomotor, as the forces acting on the rotating body are transmitted to the journal.
Therefore it is only possible to transmit the resulting forces and moments through
friction with a high safety factor. Accordingly, the manufacturing costs are low as
there is no need for elements with form closure (such as shear bolts) and the
accessibility for inspection is made easy.
Further advantages are a consequence of this detail of design:
The rotating body, the casing and the flanges of the casing can be made of forged
rings instead of casting or a welded construction. This leads to shorter delivery times,
reduced expenses for material testing and commissioning as well as to the absence
of defects of casting, which would have to be repaired during manufacturing.

4. The tolerances between fitting parts have been analysed thoroughly. As there are
only a few parts, it was not necessary to choose tight tolerances. This guarantees
efficient manufacturing and a short time for mounting and adjustment.
All parts exposed to relative movement or with a greater number of bores and fitting
surfaces, which cannot be protected against corrosion but with expensive stainless
steel plating, are made of stainless steel as a whole.
All the externally mounted elements such as the support of the valve or the fixing of
the servomotor are screwed down on the casing, again without the need for welding.
The use of simple and basic elements such as rings and plates requires relative thick
walls for the fulfilment of their function and not as a necessity due to strength or
deformation. Therefore the calculations of resistance can be reduced to simple and
elementary approaches. In general, FE-calculations will not be necessary. However
an analysis of stress and deformation might be useful for the bearing sleeve.
With the absence of welding constructions and the consequent small number of
elements for each spherical valve the set-up times for the machining are reduced as
it is not necessary to mount the components on the machine tool repeatedly. Also
there is no need for intermediate testing or repair of faults with subsequent heat-
treatment.
Consequently, even for a low piece number, the manufacturing costs could be
reduced to a great extent and a saleable price can be realised despite the rather high
personnel costs in our region.
Figure 3: CAD-presentation of a
spherical valve DN750
The detailed construction work
is done with CAD (figure 3) allowing an economic adaptation to new dimensions.
The development of the production series is based on a unique design concept within
a certain range of nominal diameter and pressure: So the variations have only to
follow geometric and functional similarities and the time for design and construction

5. could be significantly reduced.
Value analysis
A value analysis is the finding of the balance between cost and benefit and has been
done to determine the best solution for the design of the shut-off valves.
One of the results that we found shall be shown with the example of the casing for a
medium-sized spherical valve considering the manufacturing of a small piece
number. We compared two different alternatives under the assumption of unique
labour costs for both of them.
The first alternative is a casing made of forged elements, as we chose it for our
design. The second alternative would be a welded casing.
construction with welded
component of the casing
forged rings construction
number of forged rings 1 2
number of cylindrical shells 0 1
number of conical shells 0 1
number of forged elements for the hub 0 2
number of flanges 0 3
length of the welding seam 0,0 22 x DN
relative total weight 1,0 0,8
comparison of the costs
process of manufacturing construction with welded
forged rings construction
design, construction,
1 1,80
calculation and documentation
material 1 0,86
manufacturing and testing 1 2,35
total of manufacturing costs 1 1,85
The cost intensive processes for the manufacturing of small shut-off valves with a
diameter up to DN800 have been reduced significantly although it is possible to make
adaptations following the demands and profiles of the customer. The largest part
comes from the following processes:
- design, calculation and construction
- set-up times for machining in the shop
- interruption of machining for welding, testing and repair
- large number of components and tough tolerances
- time-consuming mounting in the manufacturers shop
- direct and indirect measures for quality control

6. Special safety aspects for shut-off valves in hydro power plants
The safety for full closure and the consequences for the dimensioning of the
driving mechanism
The shut-down in case of emergency is expected from the shut-off valves in hydro
power plants, which means that they have to close against the nominal flow or even
a multiple of it.
The characteristics regarding flow, hydraulic torque and hydraulic forces have been
taken from the literature [2, 3, 4] and as far as possible verified through measurement
during the commissioning in the plant.
A significant aspect for the dimensioning of the driving mechanism is the friction in
the journal bearing of the rotating body, as the resulting moment acts against the
closing movement.
With the commonly used self-lubricating bearings, which are made of sintered bronze
with fine dispersed graphite, a low friction factor (µ = 0,06 to 0,09) can be reached
when the components are new, well adapted and, above all, if they run in pure and
clean water.
As soon as the water is spoiled with sand and similar elements or when deposits can
accumulate between the journal and the bearing material, the friction factors can
double their value. This is true for all bearings where such accumulations of deposits
are to be expected during the operating time.
This is the reason why the safety for full closure should be guaranteed with a friction
factor of at least µ = 0,2 at nominal pressure or µ = 0,25 at the net head belonging to
the design flow for shut-down.
This situation is well-known to the manufacturers of shut-off valves for hydro power
plants. Nevertheless sometimes standard valves, which are normally used in the oil
and gas industry or in the supply of drinking water, are installed to reduce the
investment costs. These valves are frequently not dimensioned according to the
above written principles and will lead to problems for the operator of the plant within a
couple of years.
Some cases of failure with valves that will not close totally after they are exposed to
the water in power plants for some time or where blockage or deformation of the
driving mechanism is encountered, confirm the benefits of this strict demand. Hints
for a too weak dimensioning of the driving mechanism for valves used in the
chemical industry can be found in [5], although there no problems with sandy water
are to be expected.
Another aspect of the dimensioning of the driving mechanism is the demand that in
case of blocking of the rotating body during opening or closing (e.g. through clamping
of solid parts coming with the water) no parts shall be damaged due to the full
strengths resulting from the pressure in the servomotor.

7. If the friction factor of the journal bearing is set to µ = 0,2 instead of µ = 0,1 then a
larger servomotor is needed to guarantee full closure and, as a consequence, the
strengths in case of blocking of the rotating body will also be larger.
The example of a spherical valve DN750 and PN50 closed with water from the
penstock and opened with oil from an aggregate shall demonstrate that the torque
over the trunnion in the case that the rotating body is blocked will be five times higher
than in the case of an emergency shut-down.
spherical valve DN750, PN50, closed with water and opened with oil:
relative torque and safety factors in the driving components of the rotating body
safety factor with different coefficients
torque related to the of friction in the joints of the driving mechanism
case of operation emergency shut-down at
nominal flow steel/steel steel/steel with corund
μ = 0,2 μ = 0,4
emergency shut-down
1,0 5,0 10,0
at nominal flow
emergency shut-down
2,5 2,0 4,0
at double nominal flow
blocking of the rotating
body with full pressure in 5,0 1,0 2,0
the servomotor
For our design of shut-off valves, the friction joint between trunnion of the rotating
body, journal and lever of the servomotor is dimensioned for such high torque in the
case that the rotating body is blocked.
The necessary pre-stressing is reached with three anti-fatigue shafts for the larger
valves and with one such shaft for the very small ones. Assuming a friction coefficient
of µ = 0,2 between steel faces we demand a safety factor of 1,0 in case of blocking of
the rotating body. Corundum between the joint faces is used as an additional element
of safety. As a consequence in case of an emergency shut-down at nominal flow the
safety factor will be about 10,0.
Joint between the rotating body and the journal
In order to avoid hydrogen induced strain-crack-corrosion?? in the anti-fatigue shafts
even after a long operating time, the 0,2 %-yield stress (Rp0,2) is restricted to a value
between 640 and 750 N/mm2. The pre-stressing of the shafts is chosen as 0,7 * Rp0,2,
which is rather a low value. The shafts are sealed against the entrance of water [6].
As we have shown in the above described example with the safety for torque, the
joint would even be safe in case of a failure of two of the three shafts at emergency
shut-down. Consequently it would also be possible to change one of the three shafts
during normal operation or to remove it for crack testing.

8. Safety against cracks in the journal bearing
The length of the journal bearings is only 0,3 * diameter, therefore the bending strain
is lower than in the usual bearings which are longer. As a consequence and due to
the high-quality forged material, cracks that have very often been encountered on
cast rotating bodies can almost be excluded.
As stainless steel is used for the rotating body and the journal, there is no need for
stainless steel plating or stainless coating in the areas of bearing and sealing. The
experience shows that the transition from this plating or coating to the non stainless
base material is very often the origin of cracks due to contact corrosion or high
residual stresses combined with a corrosive medium. These cracks might grow under
normal operating conditions, due to stress corrosion cracking (with closed rotating
body and water pressure acting on it from one side) or corrosion fatigue (frequent
changing from the closed position to the opening position).
The diagram in figure 4 shows that the cracks or failures in cast steel with stainless
plating that have already a length where they are expected to grow due to stress
corrosion cracking can hardly be detected with MT, whereas the allowable length of
cracks in forged steel is many times higher.
For our design the upper limit for the nominal bending stress in the journal of the
rotating body is approximately 120 N/mm2.
stress concentration factor α k = 1,8
30
limit for recoginition with NDT
25
lenght of failure [mm]
20
forged steel 13/4
15
Figure 4:
10 critical
length of
cast stell 13/4 with residual stresses due to welding cracks or
5 failures
depending
on the
0 nominal
stress in the
70 80 90 100 110 120 130 140 150
journal
nominal stress in the journal [N/mm²]
Another advantage of the journal bearing within the spherical contour of the rotating
body is the reduction of the moments in the rotating body resulting from the bearing
forces and thus lower deformation and bending than in the case of the further journal
bearing of conventional designs.

9. Range of use and production series
Three basic types of shut-off valves have been developed according to the demands
of the market. All of which can be equipped with different solutions for the driving of
the rotating body and for the support on the foundation.
range of
basic serie principle of sealing pressure range
diameter
centric bearing of the rotating 25 bar 150 mm
high pressure
body, sealing ring made of to to
spherical valve
bronze with sliding coating 100 bar 400 mm
double eccentric bearing of the 25 bar 400 mm
low pressure
rotating ring; sealing ring made to to
spherical valve
of elastomer 65 bar 1000 mm
sliding ring operated with 25 bar 400 mm
spherical valve
pressure water to 130 bar to 1000 mm
In the appendix, the different ranges of use are shown in diagrams and there are also
pictures of some of the shut-off valves that have already been delivered.
Examples for the installation of the valves
Many old hydro power plants are equipped with shut-off valves of the type sluice
valve or spherical valve, which are not suitable for an emergency shut-down. These
valves very often have reached the end of their operating period due to corrosion or
wear and the resulting fatigue or because their function is not appropriate anymore.
The old valves shall then be replaced by emergency shut-off valves in the course of
measures for upgrading or modernisation. Of course these valves will also be
needed for new hydro power plants.
The spherical valves designed by TIWAG can even be used to replace sluice-valves
because our design distinguishes itself for its short length. As an example it will be
possible to replace the standard length F5 for a sluice-valve PN25 according to
DIN 3202 with our spherical valve up to the nominal diameter DN600 (figure 5).
The length of the TIWAG-valves grows only a little with the increase of nominal
pressure in contrary to conventional valves. Therefore in plants with high pressure
there will be an additional space between the new valve and the remaining turbine
connection, which can be used for a dismantling pipe. For small installations there is
enough space to insert a fitting flange, which will be needed for the compensation of
movements encountered during the past years of operation.

10. Figure 5: replacement
of a sluice-valve DN400
The overhanging closing weights or servomotors are also kept very tight to allow
the replacement of existing sluice-valves. The arrangement of the driving
mechanism can be varied within certain limits to allow further saving of space or
to improve the access for mounting or inspection.
Bibliography:
[1] Konstruieren neuartiger Produkte
W. Richter, Konstruktion 47 (1995)
[2] Versuche bei hohen natürlichen Gefällen zur Beurteilung des Verhaltens bei
Rohrbruch und Freilauf
J. Osterwalder, Escher Wyss Mitteilungen
[3] Investigating the characteristics of shutoff valves by model tests
F. Strohmer, Water Power & Dam Construction July 1977
[4] Experimentelle Untersuchungen der Kräfte und Momente auf das System
Drosselklappe-Rohrleitung in Wasserkraftanlagen
H. Grein, Dissertation Darmstadt 1977
[5] Anwendererfahrungen bei der Auswahl von Stellgeräten für den Bereich der
chemischen Industrie
K. Meffle, Technische Mitteilungen 1984, Heft 2
[6] Untersuchungen zur wasserstoffinduzierten Rissbildung bei hochfesten
Schrauben aus Vergütungsstählen
K.H. Kloos u.a., VDI – Z 1985, Heft 19
Autor
Ing. Oswin Schüller
TIWAG - Tiroler Wasserkraft AG
A – 6010 Innsbruck; E-Mail: oswin.schueller@tiwag.at

11. Range of use and production series
Three basic types of shut-off valves have been developed according to the demands
of the market. All of which can be equipped with different solutions for the driving of
the rotating body and for the support on the foundation.
range of
basic serie principle of sealing pressure range
diameter
centric bearing of the rotating 25 bar 150 mm
high pressure
body, sealing ring made of to to
spherical valve
bronze with sliding coating 100 bar 400 mm
double eccentric bearing of the 25 bar 400 mm
low pressure
rotating ring; sealing ring made to to
spherical valve
of elastomer 65 bar 1000 mm
sliding ring operated with 25 bar 400 mm
spherical valve
pressure water to 130 bar to 1000 mm
In the appendix, the different ranges of use are shown in diagrams and there are also
pictures of some of the shut-off valves that have already been delivered.
Examples for the installation of the valves
Many old hydro power plants are equipped with shut-off valves of the type sluice
valve or spherical valve, which are not suitable for an emergency shut-down. These
valves very often have reached the end of their operating period due to corrosion or
wear and the resulting fatigue or because their function is not appropriate anymore.
The old valves shall then be replaced by emergency shut-off valves in the course of
measures for upgrading or modernisation. Of course these valves will also be
needed for new hydro power plants.
The spherical valves designed by TIWAG can even be used to replace sluice-valves
because our design distinguishes itself for its short length. As an example it will be
possible to replace the standard length F5 for a sluice-valve PN25 according to
DIN 3202 with our spherical valve up to the nominal diameter DN600 (figure 5).
The length of the TIWAG-valves grows only a little with the increase of nominal
pressure in contrary to conventional valves. Therefore in plants with high pressure
there will be an additional space between the new valve and the remaining turbine
connection, which can be used for a dismantling pipe. For small installations there is
enough space to insert a fitting flange, which will be needed for the compensation of
movements encountered during the past years of operation.